Design and Construction of Roller Compacted Concrete Pavements

Transcription

Design and Construction of
Roller Compacted Concrete
Pavements in Quebec
This document is a direct translation of the French document originally
prepared in 2001, as a joint effort by the CAC, ABQ and ACRGTQ. It reflects
the knowledge of the industry at that period of time. An update of the
document will be done in 2006 to incorporate recent changes and
developments in RCC technology.
November 14, 2005
The Roller Compacted Concrete Committee of the Association des constructeurs de routes et
grands travaux du Québec (ACRGTQ), under the supervision of Ronald Blackburn and Philippe
Pinsonneault, recognized the need to synthesize all the current knowledge about the materials,
design, and implementation of roller-compacted concrete (RCC) in Quebec. The Cement
Association of Canada (CAC) and the Association béton Québec (ABQ) approved of the
undertaking and immediately joined in the project. The Centre de recherche interuniversitaire
sur le béton at Université Laval was given the mandate of writing the document. At the request
of CAC, an advisory committee was set up in order to respond to the specific requirements of the
various stakeholders involved in the field of RCC in Quebec. Outstanding cooperation between
the members of the advisory committee made it possible to deliver a document that met the
expectations of the RCC industry in Quebec.
Editors
Pierre Gauthier, P.Eng.
Research Engineer, Centre de recherche sur les infrastructures en béton (CRIB)
Département de génie civil, Université Laval
Jacques Marchand, P.Eng.
Professor, Département de genie civil, Université Laval
Director, Centre de recherche sur les infrastructures en béton (CRIB)
Sponsors
Association des constructeurs de routes et grands travaux du Québec (ACRGTQ)
Association Canadienne du ciment (ACC)
Association béton Québec (ABQ)
Advisory Committee
Ronald Blackburn, P.Eng., Association des constructeurs de routes et grands travaux du Québec
(ACRGTQ)
Alain Desrosiers, T Sc.A., Representative of the Association béton Québec (ABQ)
Émile Hanna, P.Eng., Representative of the Association des ingénieurs-conseils du Québec
(AICQ)
Marc-André Lavigne, Association québécoise du transport et des routes (AQTR)
Claude Lupien, P.Eng., Representative of the Centre d´expertises et de recherche en
infrastructures urbaines (CERIU)
Richard Morin, P.Eng., Laboratoire de la Ville de Montréal
Daniel Vézina, P.Eng., Ministère des Transports
TABLE OF CONTENTS
CHAPTER 1 – INTRODUCTION.............................................................................................................................4
1
PURPOSE AND APPLICATIONS ...........................................................................................................................4
1.1
RCC Definition and Main Characteristics.............................................................................................4
1.2
Background............................................................................................................................................6
1.3
Contents .................................................................................................................................................9
1.4
Flowchart for Producing an RCC Pavement.......................................................................................10
1.5
Standards .............................................................................................................................................11
CHAPTER 2 – MATERIALS...................................................................................................................................12
2
GENERAL .......................................................................................................................................................12
2.1
Binders.................................................................................................................................................12
2.1.1
2.1.2
2.2
2.3
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.4.5
General............................................................................................................................................................ 12
Cement, Blended Cement and SCMs .............................................................................................................. 13
Water ...................................................................................................................................................15
Aggregates ...........................................................................................................................................15
Chemical Admixtures...........................................................................................................................18
General............................................................................................................................................................ 18
Water Reducers ............................................................................................................................................... 18
Set-retarding and Set-accelerating Admixtures ............................................................................................... 19
Air-entraining Admixtures .............................................................................................................................. 19
New Products .................................................................................................................................................. 20
CHAPTER 3 – RCC PROPERTIES........................................................................................................................22
3
GENERAL .......................................................................................................................................................22
3.1
Fresh RCC ...........................................................................................................................................22
3.1.1
3.1.2
3.1.3
3.1.4
3.1.5
3.2
General............................................................................................................................................................ 22
Workability ..................................................................................................................................................... 22
Density ............................................................................................................................................................ 26
Air Content...................................................................................................................................................... 26
Segregation...................................................................................................................................................... 27
Hardened Concrete..............................................................................................................................27
3.2.1
General............................................................................................................................................................ 27
3.2.2
Mechanical Properties ..................................................................................................................................... 28
3.2.2.1
Compressive strength............................................................................................................................ 28
3.2.2.2.
Flexural strength ................................................................................................................................... 30
3.2.2.3
Influence of constituents on compressive and flexural strength............................................................ 31
3.2.2.4
Modulus of elasticity ............................................................................................................................ 37
3.2.2.5
Shrinkage.............................................................................................................................................. 38
3.2.2.6
Fatigue Behavior................................................................................................................................... 38
3.2.3
Durability ........................................................................................................................................................ 39
3.2.3.1
Resistance to internal cracking ............................................................................................................. 40
3.2.3.2
Frost resistance with deicing salts......................................................................................................... 42
3.3
3.3.1
3.3.2
3.3.3
Surface Characteristics........................................................................................................................44
General............................................................................................................................................................ 44
Texture of the Finished Surface ...................................................................................................................... 44
Pavement Roughness ...................................................................................................................................... 45
CHAPTER 4 – RCC MIX DESIGN.........................................................................................................................47
4
GENERAL .......................................................................................................................................................47
4.1
General Principles...............................................................................................................................47
4.2
Mix Design Methods ............................................................................................................................47
4.2.1
Empirical Methods .......................................................................................................................................... 48
4.2.1.1
Design method based on workability limits.......................................................................................... 48
4.2.1.2
Design method based on geotechnical principles ................................................................................. 49
4.2.2
Semi-empirical Method................................................................................................................................... 50
4.2.3
Theoretical Model ........................................................................................................................................... 56
Design and Construction of Roller Compacted Concrete Pavement in Quebec
i
CHAPTER 5 – PAVEMENT DESIGN....................................................................................................................62
5
GENERAL .......................................................................................................................................................62
5.1
General Design Principles...................................................................................................................63
5.2
Fundamentals of Design Methods .......................................................................................................68
5.3
Design Methods ...................................................................................................................................71
5.3.1
Thickness Design for Concrete Highway and Street Pavements Software PCAPAV).................................... 71
5.3.1.1
Design criteria ...................................................................................................................................... 72
5.3.1.2
Design factors....................................................................................................................................... 74
5.3.2
Design Using Concrete Airport Pavement Software ....................................................................................... 77
5.3.2.1
Design factors....................................................................................................................................... 78
5.3.2.2
Factors affecting stress ......................................................................................................................... 80
CHAPTER 6 – CONSTRUCTION OF RCC PAVEMENTS ................................................................................84
6
GENERAL .......................................................................................................................................................84
6.1
Subgrade and Subbase Preparation ....................................................................................................84
6.2
RCC Production...................................................................................................................................85
6.2.1
6.2.2
6.2.3
6.3
6.4
General............................................................................................................................................................ 85
Central Batch Plants........................................................................................................................................ 85
Mobile Central Mixer (Pugmill)...................................................................................................................... 86
Transporting RCC ...............................................................................................................................89
RCC Placement....................................................................................................................................90
6.4.1
General............................................................................................................................................................ 90
6.4.2
Equipment ....................................................................................................................................................... 91
6.4.2.1
Conventional asphalt paver................................................................................................................... 91
6.4.2.2
High-density paver ............................................................................................................................... 93
6.5
6.5.1
6.5.2
Compacting RCC .................................................................................................................................94
General............................................................................................................................................................ 94
Typical Compaction Equipment and Operation Sequencing........................................................................... 95
6.6 Construction Techniques.............................................................................................................................97
6.6.1
Compaction of the First Strip .......................................................................................................................... 97
6.6.2
Rolling a Vertical Fresh Joint.......................................................................................................................... 97
6.6.3
Rolling a Longitudinal Vertical Cold Joint ..................................................................................................... 98
6.6.4
Rolling a Transverse Vertical Cold Joint ...................................................................................................... 100
6.6.5 .............................................................................................................................................................................. 101
Rolling a Vertical Cold Joint for a Two-Lift Pavement ................................................................................................ 101
6.6.6
Horizontal Cold Joint .................................................................................................................................... 101
6.6.7
Crack Control................................................................................................................................................ 101
6.7
6.7.1
6.7.2
6.7.3
6.7.4
6.7.5
6.7.6
Curing................................................................................................................................................102
General.......................................................................................................................................................... 102
Curing Methods............................................................................................................................................. 102
Hot Weather Concreting................................................................................................................................ 103
Cold-Weather Concreting ............................................................................................................................. 103
Surface Protection ......................................................................................................................................... 103
Opening to traffic .......................................................................................................................................... 103
CHAPTER 7 – QUALITY CONTROL .................................................................................................................105
7
GENERAL .....................................................................................................................................................105
7.1
Preliminary Quality Control..............................................................................................................105
7.1.1
7.1.2
7.1.3
7.1.4
7.1.5
7.2
7.3
Materials ....................................................................................................................................................... 105
RCC Mix....................................................................................................................................................... 106
Central Mixer ................................................................................................................................................ 106
Placement Equipment.................................................................................................................................... 107
Placement...................................................................................................................................................... 107
Field Quality Control.........................................................................................................................108
RCC Compliance ...............................................................................................................................110
ii
APPENDIX A RCC SAMPLING PROCEDURE .............................................................................................................. A-1
APPENDIX B PROCEDURE FOR DETERMINING WORKABILITY OF FRESH CONCRETE WITH A VEBE APPARATUS ..B-1
APPENDIX C PROCEDURE FOR DETERMINING THE REFERENCE WET DENSITY OF FRESH CONCRETE WITH THE
MODIFIED PROCTOR TEST........................................................................................................................................ C-1
APPENDIX D PROCEDURE FOR MOLDING RCC TEST SPECIMENS USING A VIBRATING HAMMER FOR COMPRESSIVESTRENGTH TESTING ................................................................................................................................................. D-1
APPENDIX E PROCEDURE FOR MOLDING RCC TEST SPECIMENS USING A VIBRATING HAMMER FOR FLEXURALSTRENGTH TESTING ..................................................................................................................................................E-1
iii
Chapter 1 – Introduction
1
Purpose and Applications
The main purpose of this document is to synthesize current technical knowledge related to the
use of roller-compacted concrete (RCC). It deals with practices recognized by the industry in
Quebec. Also discussed are potential problems and how to avoid them. In this regard, a number
of cautionary statements have been included throughout the document on topics such as the use
of different types of materials used in proportioning RCC mixes, RCC production and its use.
This manual only covers roller-compacted concrete pavements. It does not deal with the
construction of dams or other mass concrete structures due to their technological differences with
respect to materials selection, mix proportioning, properties, and placement.
This manual only covers roller-compacted concrete pavements. It does not deal with
the construction of dams or other mass concrete structures due to their technological
differences with respect to materials selection, mix proportioning, properties, and
placement.
This document is intended for those interested in designing and producing roller-compacted
concrete pavements for industrial, agricultural, and/or urban applications. It has been designed
more specifically for testing laboratories, engineers, owners, contractors, producers / suppliers of
concrete, and technical consultants involved in the concrete industry.
1.1
RCC Definition and Main Characteristics
Roller-compacted concrete is a dry concrete (i.e. mixture of water, cement, aggregate, chemical
admixtures, and cementitious materials if required) requiring external compaction energy for
consolidation. RCC contain more aggregate and less paste, therefore, it is less workable than
conventional concrete. It is placed without reinforcement or forms. RCC is considered a rigid
type pavement and is, therefore, subjected to the same design criteria as any concrete slab.
RCC is a dry concrete (i.e. mixture of water, cement, aggregate, chemical admixtures,
and cementitious materials if required) requiring external compaction energy for
consolidation.
When properly designed, RCC quickly develops high mechanical strength and has good
durability. To illustrate, RCC mixes with a cementing material content of approximately 300
kg/m3 and a water-cementing materials ratio of 0.35 can develop compressive strength of 40
MPa and flexural strength of 5.0 MPa after three days of curing. When subjected to harsh
conditions, these high-performance RCC pavements offer good fatigue behavior, high abrasive
resistance as well as, the ability to withstand high temperatures on its surface. In addition to
their low paste content, which is generally less than 200 L/m3, RCC mixes are also characterized
by their low susceptibility to drying shrinkage cracking. Monitoring the behavior of pavements
built in recent years has revealed an average crack spacing that is generally higher than that
4
normally encountered with conventional concrete. Moreover, observations of in-service RCC
pavements show that when appropriately designed and adequately placed and cured theses
pavements exhibit good durability.
RCC is produced in a central batch plant or in Pugmill mobile mixer. It is transported to the
jobsite in dump trucks. Conventional asphalt paving machines or high-density paving machines
are used for placement, while compaction is achieved with rollers. Unlike conventional concrete
pavement, once consolidated, RCC can bear the weight of vehicular traffic. Figure 1.1 illustrates
the process for producing, unloading, placing, and compacting RCC.
Figure 1.1 - Producing and using RCC (from reference [1.1])
From a materials standpoint, RCC has a lower paste volume thus a more compact granular
skeleton. Mixes are designed to keep the volume of voids to a minimum. Given the low binder
content in RCC, the coarse aggregates are generally coated with a thin layer of paste and in
certain cases many the aggregates are in direct contact with one another.
Figure 1.2 compares RCC to other materials based on water and binder content. As illustrated,
RCC is used as a surface course for industrial and road applications. RCC can also be covered
with a layer of asphalt if required.
5
Plastic
concrete
Binder Content
RCC
Treated
soil
Use as surface course
Compacted
Vibrated
Surface course required
Water Content
Figure 1.2 - Definition of RCC based on binder and water content (from reference [1.2])
The main advantages of using RCC type rigid pavements compared to conventional reinforced
concrete is it’s lower cost due to reduction in binder content and speed of construction. For same
flexural and compressive strengths, RCC pavements contain less cement content than
conventional concrete mixes. Moreover, RCC pavements do not require dowels, tiebars or
formwork, unlike conventional concrete pavements. RCC’s speed of construction considerably
reduces construction costs and operational delays.
RCC pavements are used for a variety of industrial and urban applications such as log storage
and sorting areas, roads for the forestry and mining industries, intermodal container terminals,
bulk storage areas, composting facilities, parking facilities (off-road, military, and passenger
vehicles), municipal streets, and airports.
1.2
Background
RCC was first used in North America in 1942 by the US Army Corps of Engineers. The first
Canadian application dates back to 1976 on Vancouver Island, British Columbia, where it was
used to build a log storage area (52 000 m2, carried out in two phases). The parking facilities at
the Saturn plant in Tennessee stand out as the largest project to date (543 500 m2).
The first RCC project in Quebec was the Robertson Lake Dam. Quebec’s first RCC pavement
goes back to 1987 and 1990, with the construction of test sections at the Lafarge Canada plant in
St-Constant. This extensive study, carried out by the Centre de recherche sur les infrastructures
en béton (CRIB) at Université Laval, focused on freeze-thaw and deicer salt scaling resistance of
RCC pavements. Three 450 m2 individual test sections and an experimental road were built. This
study led to the development of durable RCC mixes, a new mix design methodology and
ultimately to the high-performance RCC concept.
Figure 1.3 illustrates the area (expressed in m2) and volume (expressed in m3) of RCC projects
carried out in Quebec in recent years. The first major project was the 1995 construction of a
6
25 000 m2 (8 750 m3) pavement at Métallurgie Noranda’s Horne Smelter for storing crushed
slag. The 350-mm-thick high-performance RCC pavement had to withstand the high-impact
loading from crushing operations as well as broad thermal gradients. After seven days of curing,
the RCC mix developed an average compressive strength of 55 MPa and an average flexural
strength of 5 MPa.
Area in m2 and volume in m3
160000
140000
120000
100000
Volume
80000
Area
60000
40000
20000
0
1995
1996
1997
1998
1999
Year
Figure 1.3 –RCC pavements in Quebec (from reference [1.3])
Quebec’s largest RCC pavement project is the expansion of the Domtar Paper mill wood lot in
1996, covering 87 000 m2. The slab, measuring 300 mm in thickness, required 26 100 m3 of
RCC. After 7 days of curing, the concrete achieved 50 MPa in compressive strength and 8 MPa
in flexural strength. Figure 1.4 is an aerial photograph of the project while the pavement was
under construction.
7
Figure 1.4 –Aerial photograph of pavement construction at the Domtar Paper mill
(from reference [1.1])
Montréal was the site of Quebec’s first urban use of RCC technology in 1999. The projects
consisted of two RCC road pavements: Chabanel Street (heavy traffic) and Molson Street (light
traffic). Chabanel Street has a 4-lane section (width varying from 7.4 to 11.2 m) 460 m in length,
for a total area of 8 500 m2. The pavement was made with a single 200-mm lift of RCC totaling
1 800 m3. Isolations joints were used at all pavement obstructions and were at an average spacing
of 28m apart. The second project consisted of rehabilitating a section of Molson Street
measuring 120 m in length and 9.3 m in width, for a total area of 1 120 m2 and a total volume of
concrete of 170 m3. The compressive strength of the RCC mixes in these two projects ranged
from 40 to 50 MPa, while the flexural strength ranged between 5 and 6 MPa at 7 days. In both
cases, the RCC was topped with asphalt. The techniques normally used for building industrial
pavements were adapted to the urban setting. These projects enabled the Laboratoire de la Ville
de Montréal to technical specifications (3VM-30) suitable for building pavements and areas for
traffic and storage.
8
1.3
Contents
This manual is divided into seven chapters and five appendices covering test procedures.
Chapter 1 - Introduction provides an overview of the manual, including a definition of rollercompacted concrete and its characteristics as well as a flowchart for producing an RCC
pavement.
Chapter 2 – Materials covers with the materials normally used in RCC mixes and the use of
new products.
Chapter 3 - RCC Properties discusses the various properties of fresh and hardened RCC.
Testing methods for measuring these RCC properties are presented. The influence of materials
on the properties of fresh and hardened RCC are also discussed..
Chapter 4 – RCC Mix Design describes different methods for designing RCC mixes and
provides examples.
Chapter 5 – Pavement Design defines the various design parameters for a rigid RCC pavement
and describes the various design methods.
Chapter 6 – Construction of RCC Pavements describes the various steps in constructing an
RCC pavement, including production, transportation, placing, compaction, construction
techniques, and curing methods.
Chapter 7 – Quality Control identifies the various quality control process which should be
considered before, during, and after construction of the RCC pavement..
9
1.4
Flowchart for Producing an RCC Pavement
Owner
•
Definition of expectations and needs
Characterization of information
related to the site
(Ch. 5)
•
•
•
•
•
•
Site configuration: runoff drainage
Infrastructure type: soil type (presence of organic matter, frost-susceptible soil),
soil bearing capacity (soil geotechnical investigation, if required)
Loading: weight, frequency, tire pressure and/or concentrated load
Type of use: materials storage, chemicals, dumping, erosion
Constraints related to site operations during construction
Life cycle
Pavement design
(Ch. 5)
•
•
Calculate the thickness of the granular sub base
Calculate pavement thickness
RCC technical specifications
•
•
•
•
•
Mix requirements
Production (Ch. 6)
Transportation (Ch. 6)
Placement and compaction (Ch. 6)
Joints (Ch. 6)
RCC mix
•
•
•
•
Mix design (Ch. 4)
Fresh properties: workability and wet density (Appendices B and C)
Producing test specimens (Appendices D and E)
Mechanical strength: flexural and compressive
Test Section
(Ch. 7)
•
Verification of production and placement procedure
Placement
(Ch. 6)
and
Quality control
(Ch. 7)
•
•
•
•
Verification of foundation characteristics: slope, drainage, compaction
Verification of production
Verification of placement: time, thickness, compaction
Curing
⇓
⇓
⇓
•
•
•
•
Curing and protection (Ch. 6)
Quality control (Ch. 7)
Construction tolerances (Ch. 7)
Quality control (Ch. 7)
Figure 1.5 - illustrates the entire process for producing an RCC pavement.
10
1.5
Standards
References in this manual are to the most recent versions of the standards listed below.
CSA International, CAN/CSA A23.1, Concrete Materials and Methods of Concrete
Construction.
CSA International, CAN/CSA A23.2, Methods of Test for Concrete.
American Society for Testing and Materials, ASTM, Section 4 Construction, volume
04.02, Concretes and Aggregates.
Bureau de normalisation du Québec (BNQ), NQ 2621-900, Bétons de masse volumique
normale et constituents.
REFERENCES
[1.1]
Service d’expertise en matériaux (S.E.M.) inc., internal report, multiple pagination.
[1.2]
ANDERSSON, R. “Swedish Experiences with RCC,” Concrete International: Design
and Construction, 1987, vol. 9, no. 2, February, pages 18-24.
[1.3]
GAUTHIER, P., MARCHAND, J., BOISVERT, L., OUELLET, E., and PIGEON, M.,
Conception, formulation, production et mise en œuvre de revêtements en béton compacté
au rouleau, Continuous training GCI-A2455, Centre de recherche interuniversitaire sur le
béton, Département de génie civil, Université Laval, 2000, multiple pagination.
11
Chapter 2 – Materials
2
General
The selection and nature of RCC materials must meet a variety of requirements (mechanical
strength, durability, thermal resistance), depending on the mechanical characteristics required in
the final product. Like conventional concrete, RCC contains cement, water, fine and coarse
aggregates. Mineral admixtures such as silica fume, slag, and/or fly ash, preblended or not with
the cement, can be used to enhance the properties of RCC mixes. Chemical admixtures, such as
water reducers, air-entrainment agents and set retarders, are also common used.
2.1
Binders
2.1.1
General
Most RCC pavements produced in Quebec in recent years have been made with Type 10E-SF
hydraulic cement (Type 10 cement with silica fume). Furthermore, the use of ternary blended
cements (blended cement containing slag, and silica fume: Type 10E-S/SF; blended cement
containing fly ash, and silica fume: Type 10E-F/SF) for producing RCC has increased. Ternary
blended cements are capturing a certain portion of the market for building RCC pavements in
Quebec.
Most RCC pavements produced in Quebec in recent years have been made with Type
10E-SF hydraulic cement (Type 10 cement with silica fume). Furthermore, the use of
ternary blended cements (blended cement containing slag, and silica fume: Type 10ES/SF; blended cement containing fly ash, and silica fume: Type 10E-F/SF) for
producing RCC has increased.
Binder selection and dosage depend, in part, on the mechanical strength required, the rate of
development of mechanical properties, and durability criteria. Generally, RCC mixes for
industrial or municipal pavements are designed and produced with cement contents ranging from
250 to 350 kg/m3, which represents 12% to 16% of the total weight of dry material. Excessive
cement content can induce greater shrinkage cracking and significantly increase production costs
without necessarily enhancing mechanical strength or extending pavement’s service-life. The
cement, blended cement, and SCMs must comply with CSA A5, CSA A362, and CSA A32.5,
respectively.
RCC mixes generally have a cement content that ranges from 250 to 350 kg/m3.
Caution: excessive cement content can induce greater shrinkage cracking and
significantly increase production costs without necessarily enhancing mechanical
strength or extending pavement’s service-life.
12
2.1.2
Cement, Blended Cement and SCMs
All types of cement or blended cement can be used to produce RCC. However, paste
homogeneity problems have been observed in RCC mixes made with Type 30 cement [2.1].
However, paste homogeneity problems have been observed in RCC mixes made with
Type 30 cement.
Using Type 10E-SF cement in RCC mixes improves the microstructure and in turn the
short/long-term mechanical properties. This type of cement also enhances RCC freeze-thaw and
scaling resistance. Silica fume (relative density of 2.20 to 2.25) is comprised of extremely fine
spheres of amorphous silica (0.03 to 1 µm in diameter). The relative density of Type 10 cement
is about 3.15, whereas that of Type 10E-SF is about 2.98, depending on the silica-fume content.
The other types of blended cement are blast-furnace slag cement, fly-ash cement, Type 10E-S/SF
and Type 10E-F/SF ternary blended cements. For example, ternary blended cement was used to
build an RCC pavement at the Lafarge Canada plant in Saint-Constant in 1998. The pavement,
which serves as parking for passenger vehicles, covers approximately 5 000 m2 and is about
150 mm thick. The RCC was made with Type 10E-S/SF ternary blended cement (300 kg/m3)
with a water-cementing materials ratio of 0.36. The average compressive strengths of concrete
specimens tested after 3 and 7 days of curing were 30.6 MPa and 41.0 MPa, respectively, while
the average flexural strength of the RCC specimens were 4.7 MPa and 6.6 MPa. A portion of the
pavement was produced using a similar RCC mix containing blended silica-fume cement. The
compressive strengths for this mixture were 37.0 MPa and 41.6 MPa, while the flexural strengths
were 6.2 MPa and 7.5 MPa after 3 and 7 days of curing, respectively. Observations during
construction indicate that the placement and compacting operations were performed properly.
The pavement had a very close-textured surface. No significant deterioration has been noted
since the structure was put into service.
Supplementary Cementitious materials such as fly ash and slag are normally used as partial
replacement for cement and/or granular material in RCC mixes.
Fly ash is a byproduct of coal-fired power stations. Type F and Type C have been used in RCC
pavements. Since the hydraulic and pozzolanic characteristics of SCMs can vary from one source
to the next, care must be taken in their selection for the production of RCC. Fly-ash relative
density depends on chemical composition and varies from 1.9 to 2.8. The maximum fly-ash
replacement ratio should be limited to 25% of total binder content in order to prevent scaling of
the concrete pavement surface. Figure 2.1 shows a scanning electronic microscope photograph of
fly ash.
13
Figure 2.1 − SEM photograph of fly ash (from reference [2.2])
In addition to the savings from reduced quantity of cement used in RCC mixes, fly ash yields
other benefits to the paving operation. Certain fly ashes enhance fresh RCC consolidation
through an increase in the percentage of fine materials in the mix. Additionally, compaction of
such mixes tends to produce tighter pavement surfaces.
Fly ash also affects certain properties of hardened RCC. It generally reduces short-term
strengths, but enhances long-term mechanical properties. Up to now, few studies have
investigated the effect fly ash may have on RCC durability.
Information concerning the effects of fly ash on the properties of fresh and hardened RCC
deserves careful scrutiny. As mentioned above, the term "fly ash" takes in a broad variety of
products whose chemical reactivity and particle-size distribution may vary widely. As a result,
certain types of fly ash may be more suitable than others for RCC production.
Blast-furnace slag, a by-product of the steel industry, has a relative density between 2.85 and
2.95. Slag source and fineness affect the properties of fresh and hardened RCC and how they
react with given cement (type and source). Figure 2.2 is a scanning electronic microscope
photograph of blast-furnace slag. As shown in the picture slag particles are highly angular
compared to fly ash, which has fairly spherical particles (see Figure 2.1). Slag particles have
hydraulic properties in the presence of calcium and alkalis.
Since the hydraulic and pozzolanic characteristics of SCMs can vary from one source
to the next, care must be taken in their selection for the production of RCC.
14
Figure 2. 2 − SEM micrograph of slag (from reference [2. 3])
2.2
Water
The quality of mixing water for RCC must meet the same standards as conventional concrete
(CAN/CSA-A23.1, Concrete Materials and Methods of Construction). The water content of an
RCC mix ranges between 4.6% and 5.6% (ratio of the total weight of water to the weight of dry
materials). For example, an RCC with a cementing materials content of 300 kg/m3 and watercementing materials (w/cm) ratio of 0.35 requires only 105 L/m3 of water. However, the free
water to be added to the mix can be as little as 60 L/m3, since the aggregates are normally wet
(aggregate water content is greater than absorption). Corrections in mixing water must be made
taking into account aggregate moisture content.
2.3
Aggregates
Fine and coarse aggregates generally account for 75% to 80% of the total volume of an RCC
mix. Aggregates, therefore, play an important role in the properties of both fresh and hardened
RCC. In fresh RCC, the physical properties of aggregates can affect mix workability over time,
depending on their moisture content and absorption characteristics. Segregation during
production and handling of RCC impacts on placement and compaction, as well as, the quality of
the concrete surface. Moreover, the inherent properties of aggregates greatly affect RCC’s
mechanical properties such as compressive and flexural strength, modulus of elasticity, freezethaw durability and scaling resistance.
Aggregates are subject to intense mechanical solicitations during mixing, compaction, and
loading, resulting in fragmentation, abrasion, and even polishing. Aggregates may also be subject
15
to climatic stresses, such as freeze-thaw or wet-dry cycles. Chemical attack (dissolution, sulfate
attack, and alkali-aggregate reaction) can also affect aggregate durability. Since aggregates
influence so many different RCC properties, care must be taken in their selection in order to
yield savings during construction and to safeguard, or even enhance, the structure's design life.
Generally, the aggregate skeleton of RCC mixes is comprised of fine aggregate (5 mm – 80 µm)
and coarse aggregate (20 mm - 5 mm). The nominal maximum size is usually limited to 20 mm
in order to reduce the potential for segregation during production and placement and limiting the
maximum size of aggregate also facilitates placement operations and improves surface texture.
As with conventional concrete, fine aggregates can consist of natural sand, manufactured sand,
or a mixture of both.
Generally, the aggregate skeleton of RCC mixes is comprised of fine aggregate
(5 mm – 80 µm) and coarse aggregate (20 mm - 5 mm).
Coarse aggregates may either be crushed or rounded. Using crushed aggregate reduces the risk of
segregation and increases the quality of the paste-aggregate bond, thereby enhancing the
concrete's mechanical properties. Indeed, RCC mixes designed using the Compressible Packing
Model (formerly called the Solid Suspension Model) have demonstrated that while RCC mixes
made with rounded aggregate yields higher packing density, those containing crushed aggregates
tend to develop higher compressive strength (see Table 2.1) [2.4 - 2.7].
Table 2.1
Compressive Strength of RCC Mixes with a Water-Cementing Material Ratio of
0.35 as a Function of Aggregate Type (from reference [2.4 - 2.7])
Aggregate Type
Crushed aggregate
Rounded aggregate
28-d Compressive Strength
MPa
Type 10E-FS Cement
Type 10 Cement
61.4
54.8
53.6
49.7
The coarse to fine aggregate ratio also plays a role in RCC compressive strength. In fact,
compressive strength decreases as the coarse aggregate content increases (see Figure 2.3). This
tendency can be reduced somewhat by increasing the cement content from 6% to 15% with
respect to the weight of dry materials [2.8].
16
50
Compressive Strength 28 day (MPa)
45
40
35
30
25
20
6 % cement
15
10
9 % cement
12 % cement
5
15 % cement
0
1
1.5
2
2.5
Coarse Aggregate / Fine Aggregate Ratio
Figure 2.3 − Influence of the coarse-fine aggregate ratio on 28-d compressive strength
The different aggregate size distribution used for RCC must comply with CAN/CSA A23.1 or
any other requirements as stated in the specifications.
Other types of granular material may also be used to produce RCC. For example, at the
St-Michel quarry in Montréal the aggregate skeleton of the RCC mix used to build the snow
dumping dock was comprised of natural sand, 20 – 5 mm stone, and manufactured sand. The use
of manufactured sand should be studied beforehand to determine how they affect the concrete's
properties (fresh and hardened) as well as its durability.
The use of manufactured sand should be studied beforehand to determine how they affect
the concrete's properties (fresh and hardened) as well as its durability.
A laboratory tests demonstrated that incorporating manufactured sand as a partial replacement of
fine (5 mm - 80 µm sand) and coarse (20 - 5 mm stone) aggregates in low-cement-content RCC
designed, with the Compressible Packing Model, lowered the packing density of the mix in that
particular case [2.9]. As shown in Figure 2.4, increasing the manufactured sand replacement
percentage in mixes containing 175 and 225 kg/m3 of cement increases the amount of voids, thus
lowering the compactability of the mix. This study suggests that care must be taken when using
granular materials, such as manufactured sand, in RCC mixes.
17
25
30
0.8525
0.8615
0.8575
0.875
Mixes with 175 kg/m3 of cement
Compactness
0.87
Mixes with 225 kg/m3 de cement
0.865
0.86
0.855
0.85
0
5
10
P
15
i
f
20
25
i
30
35
(%)
Figure 2.4 − Variations in RCC mix compactness according to the proportion of stone
screenings (from reference [2.9])
2.4
Chemical Admixtures
2.4.1
General
Most chemical admixtures suitable for conventional concrete can be used to produce RCC.
However, dosages rates for RCC mixes are different than those used in conventional concrete.
The effects of admixtures are reduced because RCCs contain low water content and have shorter
mixing times when mobile pug mills are used. Consequently, admixture dosages must be
increased in order to enhance their effectiveness. The small amount of chloride ions in solution
in chemical admixtures is not a problem since RCC pavements are not reinforced. Care must be
taken since certain admixtures can accelerate or retard set times.
Trial batches should be carried out to determine the optimal dosage of chemical admixtures and
to determine their influence on fresh and hardened RCC properties. Concrete workability should
be measured from the time of initial water – cementing material contact at various intervals (10,
20, 30, and 60 min). Admixture influence on compressive and flexural strength (18hrs, 24 hrs, 7
days and 28 days) also needs to be evaluated.
Admixtures must comply with CAN/CSA A23.1.
2.4.2
Water Reducers
Water reducers are commonly used in RCCs and yield a more homogeneous paste. As a result,
they reduce the amount of water required for a given level of workability. Reducing the watercementing material ratio can generally enhance RCC mechanical properties.
18
Experience has shown that RCCs generally require four times the manufacturer’s minimum
recommended dosage of water reducer than for conventional concretes [2.1]. However, it should
be emphasized that certain water reducers could have a set retarding effect on the mix when used
at high dosages. For example, if the manufacturer’s minimum recommended dosage for
conventional concrete is 100 mL/100 kg of cement, the dosage for RCC would be approximately
400 mL/100 kg of cement. At these dosages, the quantity of admixture per cubic meter is nearly
1000 mL and 1200 mL for cementing material contents of 250 and 300 kg/m3, respectively.
Since water reducers are generally about 50% to 60% water, this quantity must be subtracted
from the total mixing water in order to achieve the targeted w/cm ratio and obtain the desired
workability.
Generally, high-efficiency water reducers or superplasticizers are not commonly used. Their use
can result in RCC mixes that lack the stability needed to support vibratory rollers. Signs of
bleeding have also been observed.
2.4.3
Set-retarding and Set-accelerating Admixtures
Retarders can be used to increase the time for placement. As a result, the normal time specified
between producing the concrete and making fresh horizontal or vertical joints (in the case of a
multi-lift system) can be extended.
Set accelerators are not normally used in RCC pavements unless specified. In most cases, steps
are taken to preserve the workability over time to ensure proper placement and compaction.
2.4.4
Air-entraining Admixtures
It is more difficult to entrain spherical air bubbles in RCC than in conventional concrete. The
reasons for this are as follows:
1) Bubbles can only be formed in a concrete mixture if there is enough mixing water to coat each
bubble with a film of water.
2) Intense mixing action is required since the formation of new surfaces requires an introduction
of energy that is equal to the surface tension of the material multiplied by its area.
Air-entraining admixtures make it easier for bubbles to be formed by reducing the water's surface
tension and stabilizing the air bubbles formed during mixing [2.10].
One approach to entrain air in RCC is to modify the mixing sequence to create spherical air
bubbles in a mix containing the paste and only a portion of the aggregates. Once the air bubbles
have been formed, the rest of the aggregates can be added to the mix. This alternative increases
production costs [2.10]; and cannot be used in Pugmill plants.
Air can be entrained in RCC without modifying the mixing sequence. The mixer's shear energy
must be high enough to create small bubbles. Since it is difficult to adequately mix very stiff
concrete, only certain types of mixers, such as those with twin parallel shafts, can achieve this.
Selecting the proper air-entraining admixture is very important. This is difficult because airentraining admixture's performance cannot be predicted from its chemical composition. The only
19
way to determine air-entraining admixture effectiveness is by laboratory and field testing. RCC
mix design plays a major role since, from a theoretical stand point, the layer of paste around the
aggregate particles must be thick enough to allow the formation of a good air-void system.
However, little information is available on this topic. [2.10].
Addition of air-entraining admixtures can improve RCC workability and durability. High
dosages, however, can adversely affect the RCC workability and stability of the RCC for
compaction operations. During compaction, excess air can lead to significant deformation during
roller operation, producing a wavy surface.
As in the case of water-reducing admixtures, the dosage of air-entraining admixtures required by
RCCs is often higher than the manufacturer’s recommended dosage for conventional concretes.
Addition of air-entraining admixtures can improve RCC workability and durability.
2.4.5
New Products
Manufacturers are currently developing and in some cases are already marketing new
generations of admixtures, such as water reducers that are better suited to dry-concrete
technology. Research is also ongoing to develop more effective air-entraining admixture for
RCC mixes.
REFERENCES
[2.1]
GAUTHIER, P., MARCHAND, J., BOISVERT, L., OUELLET, E., and PIGEON, M.,
au rouleau, Continuous training GCI-A2455, Centre de recherche interuniversitaire sur le
[2.2]
MALTAIS, Y., MARCHAND, J., Influence of curing temperature on cement hydration
and mechanical strength development of fly ash mortars, Cement and Concrete Research,
1997, vol. 27, pages 1009-1020.
[2.3]
Centre de recherche interuniversitaire sur le béton, Département de génie civil, Université
Laval, internal report, multiple pagination.
[2.4]
OUELLET, E., Formulation et étude du comportement mécanique des bétons compactés
au rouleau, Master's thesis, Département de génie civil, Université Laval, 1998, 200 p.
[2.5]
SEDRAN, T., DE LARRARD, F., and ANGOT, D., Prévision de la compacité de
mélanges granulaires par le modèle de suspension solide – Partie I : Fondements
théoriques et étalonnage du modèle, Bulletin de liaison des laboratoires des ponts et
chaussées, 1994, vol. 194, pages 59-70.
[2.6]
SEDRAN, T., DE LARRARD, F., and ANGOT, D., Prévision de la compacité de
mélanges granulaires par le modèle de suspension solide – Partie 2 : Validation – Cas
20
des mélanges confinés, Bulletin de liaison des laboratoires des ponts et chaussées, 1994,
vol. 194, pages 71-86.
[2.7]
DE LARRARD, F., Concrete mixture proportioning – A scientific approach, E & FN
SPON, Editors, 1999, multiple pagination.
[2.8]
NANNI, A. “Limestone crusher-run and tailings in compaction concrete for pavement
applications,” ACI Materials Journal, 1988, May-June, pages 158-163.
[2.9]
OUELLET, E., MARCHAND, J., and REID, E., Comportement mécanique et durabilité
au gel de mélanges de béton compacté au rouleau à faible teneur en ciment, Progress in
Concrete, ACI Eastern Ontario and Quebec Chapter, Sherbrooke, Quebec, 1998,
November 24-25, 6 p.
[2.10] PIGEON, M. and MARCHAND, J., “The Frost Resistance of Roller-Compacted
Concrete,” Concrete International, 1996, vol.18, no. 7, July, pages 22-26.
21
Chapter 3 – RCC Properties
3
General
The dry consistency of fresh RCC has distinctly different properties than conventional concrete.
A properly designed RCC mix develops good mechanical properties (modulus of elasticity,
compressive / flexural strength) as well as good freeze-thaw durability using lower cement
contents than conventional concrete.
3.1
Fresh RCC
3.1.1
General
The main properties of fresh RCC are workability, density, segregation, and high sensitivity to
variations in mixing water. Test methods currently used to determine the properties of
conventional concrete do not apply to RCC.
3.1.2 Workability
Workability is an important RCC property which governs the ease of placement and provides an
indication of production consistency. It is defined as an indicator of the effort required to
consolidate fresh concrete. Workability is an indication of the compaction energy needed to
adequately consolidate fresh concrete. The workability of an RCC mix is determined
experimentally by measuring the time required to consolidate a given volume of RCC at a
specified energy level. Slump testing according to CAN/CSA A23.2-5C is not applicable due to
the dry consistency of fresh RCC. Instead, A Vebe apparatus is used to measure RCC
consistency and is described in the following pages.
Workability is an important RCC property which governs the ease of placement and
provides an indication of production consistency.
Paste volume and fluidity directly influence RCC workability. The paste must be able to flow
and fill the voids between the aggregates during compaction. Inadequate workability (too much
or too little) affects the development of mechanical properties, placement operations, and the
quality and durability of the pavement structure.
Inadequate workability (too much or too little) affects the development of mechanical
properties, placement operations, and the quality and durability of the pavement
structure.
RCC with excessively high workability (i.e. wetter mix) is an indication of too much paste or
water in the mix. This can affect the concrete's final properties, as well as, placement operations.
This increase in w/cm ratio reduces mechanical properties and durability. In the field, this
22
excessive fluidity tends to create interstitial pressure in the compacted concrete. During
compaction such pressure will cause excessive deformation which leads to an undulating
finished surface. In an excessively high workability mix the paste can adhere excessively to the
steel drums of the rollers, which can diminish surface quality.
In contrast, excessively low workability (drier mix), occurs when the mixing water content is
inadequate (the paste volume doesn't fill the voids between aggregate particles). As in the
preceding case, dryer mixes will increase the volume of voids during compaction, which will
reduce mechanical properties and pavement durability. Furthermore, low workability generally
increases segregation during production, loading, transportation, and placement, as well as, a
coarser (open) finished surface. Finally, the lack of workability yields a weaker bond between
layers and joints. Slight variations in water dosage of 1 or 2 L/m3 can noticeably affect mix
workability and placement operations.
Slight variations in water dosage of 1 or 2 L/m3 can noticeably affect mix workability
and placement operations.
RCC workability is measured according to ASTM C1170, Procedure A, using a Vebe apparatus,
as illustrated in Figure 3.1. The test consists of vibrating a RCC sample and measuring the time
required to form a ring of mortar around a Plexiglas plate to which a 22.7 kg surcharge is
applied. The Vebe Consistency Time (expressed to the nearest 5 seconds) is the time required for
the voids in the aggregate skeleton to be completely filled with paste. The vibrating table must be
leveled and fastened to a concrete base to prevent the apparatus from moving during the test
(laboratory and field). The procedure for determining RCC workability is provided in Appendix
B.
Figure 3.1 - Vebe apparatus
23
The workability of RCC mixes currently produced and placed in Quebec is determined using a
Vebe apparatus that has a vibrating table with double amplitude of about 1 mm. Nevertheless,
the double amplitude of the vibrating table (0.43 ± 0.08 mm) specified in ASTM C1170
(Procedure A) cannot adequately measure the workability of typical RCC mixes generally
designed for industrial or urban pavements. A vibrating table operating at the amplitude specified
in ASTM C1170 (Procedure A) doesn't appear to provide a level of energy representative of that
generated by the equipment used to place and compact such RCCs.
Field experience has demonstrated that concrete workability must generally fall between 40 and
90 sec (Vebe consistency time) when the RCC is placed. The maximum time for placement from
the initial water-binder contact should also be limited to 60 min. These values appear to provide
for adequate placement and avoid the workability problems described above. The Vebe
apparatus provides a simple, fast test for determining concrete workability. The results from the
Vebe tests can be greatly influenced by the operator, the type of apparatus, and the procedure
followed. Care is needed when performing the test and interpreting the results.
Field experience has demonstrated that concrete workability must generally fall
between 40 and 90 sec (Vebe consistency time) when the RCC is placed. The maximum
time for placement from the initial water-binder contact should also be limited to 60
min.
There is a direct relationship between RCC workability and Vebe time. For example, an RCC
mix is considered to have high workability if the time required to form a ring of mortar measured
10 min after the initial water-binder contact is about 20 sec or less. On the other hand, a RCC
mix has low workability if the time required to form a ring of mortar (Vebe time) 10 min after
the initial water-binder contact is more than 120 sec Vebe time increases from initial waterbinder contact (i.e. workability decreases). Consequently, it is important to check the stability of
the Vebe time of the RCC mix from production to placement at the job site.
Figure 3.2 provides an example of workability over time of RCC mixes designed with cement
contents of 250 and 325 kg/m3 with water-binder ratios of 0.40 and 0.35, respectively, produced
with a maximum coarse aggregate size of 20 mm and a water reducer.
24
VEBE Time (sec)
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
90
100
Time from initial w/c contact (min)
Figure 3.2 - RCC workability over time
Water content, aggregate absorption and types of SCMs used in a RCC mix affect its
workability. The workability of an RCC mix made with aggregates in SSD (saturated surface
dry) condition will decrease slightly over time (i.e. longer Vebe time). On the other hand, when
aggregate surface moisture exceeds SSD, workability will remain more constant over time and in
some cases may even increase slightly.
Figure 3.3 shows the effects of adding fly ash to an RCC mix [3.1]. The presence of many
hollow fly-ash particles (see Figure 2.1 in Chapter 2) could explain the loss of workability in
these mixes. These hollow spheres are being filled with the free water of the mix, thereby
reducing workability.
VEBE time (sec)
120
Without fly ash
With fly ash
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
90
100
Time from initial w/b contact (min)
Figure 3.3 - Workability over time of an RCC mix with and without fly ash
25
Other factors can also influence RCC workability such as environmental conditions (i.e.
temperature, humidity, and wind) and the temperature of mix constituents (i.e. cement, water,
and aggregates).
3.1.3
Density
Measuring the wet density of fresh RCC makes it possible to check production uniformity and
becomes the reference value for assessing the level of compaction of placed concrete. This wet
reference density also enables comparison with the theoretical density derived from lab tests.
Thus, the test method for measuring wet density must be able to provide for adequate RCC
consolidation and be representative of the degree of compaction achieved in-situ. The test
method should also be easy to carry out and be reproducible. A variety of test methods can be
used to determine the wet density of fresh RCC.
The RCC wet density in the laboratory or in the field is determined using the same compaction
energy (hammer weight and free-fall drop) and the same steel mold specified in CAN/BNQ
2501-255, Method C (modified Proctor test). This wet density becomes the RCC reference
density. When using this method special attention needs to be given to the compaction process
since the hammer used for compaction in this test can fracture aggregates and change the
particle-size distribution. In addition, the quality of the struck-off surface must be similar to that
obtained during final compaction in the field. Fines (less than 5 mm) from the RCC mix are often
added when leveling in order to close the surface texture and achieve a representative reference
wet density. The procedure for determining the representative reference wet density is provided
in Appendix C.
Whether in the laboratory or in the field, this reference wet density is used when making
specimens for compressive and flexural strength (see Appendices D and E). This value is then
used when field density measurements are conducted using direct-transmission nuclear density
testing (ASTM C1040). The ratio of the in-place wet density (measured with a nuclear testing
gauge) to the reference wet density (determined from the modified Proctor test) is equal to the
RCC’s degree of compaction.
3.1.4
Air Content
The pressure-type air meter method (CAN/CSA A23.2-4C) is not generally used for RCC.
Unlike conventional concrete, RCC does not have the deformability characteristics required for
this test method, since the close contact between aggregate particles produces a non-plastic
matrix. Comparing the reference wet density determined by the Proctor test to the theoretical
density provides an estimation of the total air volume in RCC.
Only ASTM C457 (air void characterization in hardened concrete) could provide the percentage
of air voids, including spherical bubbles and compaction voids.
26
3.1.5 Segregation
RCC is particularly subject to segregation due to its low paste volume. Segregation is also a
function of particle-size distribution, nominal maximum size of coarse aggregate, and paste
characteristics. Precautions shall be taken since segregation can occur throughout the handling
process. When RCC is first discharged into dump trucks, the free fall distance must be kept to a
minimum and it must also be deposited uniformly along the length of the truck body: One third
of the load in the front, one third in the middle, and one third at the back.
Steps must also be taken when loading RCC into the paver. The hopper should never be allowed
to run empty before the next load of RCC is dumped into it in order to prevent situations where
the spreader auger would not be covered with RCC. A minimum of 100 mm of RCC shall be
maintained in the paver hopper at all times [3.2]. The retractable panels on both sides of the
hopper must remain open and should never be operated for any reason whatsoever since the
larger aggregate particles tend to accumulate on the hopper sides along those panels. Closing the
panels will push particles towards the feed auger, resulting in segregation in the width of RCC
being placed.
RCC is particularly subject to segregation due to its low paste volume.
Despite all the precautions taken, zones of segregation may also appear after placement by the
paver. Steps must be taken prior to compaction operation to correct any segregation problems.
Screened material from fresh RCC (< 5 mm) applied to segregation areas before compaction
operations will improve the situation. Certain areas such as fresh joints and/or cold joints (i.e.
transverse and horizontal) deserve particular attention.
3.2
Hardened Concrete
3.2.1
General
Recently developed mix-design methods make it possible to produce RCC with optimal
compactness. A properly proportioned RCC mix yields a hardened concrete whose properties
exceed that of conventional concrete having same binder content and water-binder ratio.
RCC properties are particularly affected by the degree of compaction.
As with conventional concrete, the properties of hardened RCC depend on the type of binder,
dosage, water-binder ratio, and aggregate characteristics. The degree of compaction is also of
particular importance in this regard. A study carried out on specimens taken from test sections
consolidated to different degrees (90%, 95%, and 98% with respect to the reference wet density
value) showed that a 3% decrease in compaction (i.e. from 98% to 95%) reduces the
compressive strength by nearly 30%, which in turn diminishes the concrete’s durability.
The procedures for making RCC specimens for compressive and flexural strength testing are
completely different from those currently used for conventional concrete. One technique for
making RCC specimens has proven itself in recent years both in the field and laboratory, and has
27
earned the recognition of contractors, consulting engineers, and testing/control laboratories. The
technique provides for RCC cylinders (compressive strength), prisms (flexural strength), and
several other specimen geometries, such as rectangular prisms for scaling resistance testing. It
involves consolidating fresh RCC with an impact hammer with an appropriate compaction head
in steel molds. The procedure for producing RCC specimens for compressive and flexural
strength testing is described in Appendices D and E, respectively. ASTM C1435 presents a
slightly different procedure for producing test cylinders with an impact hammer.
3.2.2
Mechanical Properties
RCC’s mechanical behavior is mainly influenced by its low paste volume. The compact
aggregate skeleton of RCC mixes significantly contributes to RCC’s excellent mechanical
performance in comparison to conventional concrete.
3.2.2.1
Compressive strength
Optimizing the dry constituents in RCC mixes makes it possible to achieve outstanding
compressive-strength values despite low cement content. The reduction in the porosity of the
aggregate skeleton leads to a lower paste requirement (i.e. cement, silica fume, fly ash, slag, etc.)
to bind all the aggregates. As an example, a correctly formulated RCC mix containing 300 kg/m3
of Type 10E-SF cement with a water-binder ratio of 0.35 generally develops a 28-d compressive
strength greater than 60 MPa. Similarly, a mixture made from 245 kg/m3 of Type 10 cement with
a water-binder ratio of 0.45 achieves a compressive strength of about 43 MPa after 28 days of
curing [3.3]. These results draw attention to the importance of adequately proportioning dry
ingredients. In other words, this means optimizing the aggregate skeleton, which also lowers
fabrication costs considerably.
The high compressive strength of RCC mixes formulated using the optimized aggregate skeleton
method can be accounted for by the greater “interlocking effect” of aggregates. Indeed, the close
contact between aggregates inhibits crack propagation. The properties of the cement matrix
could also explain the high compressive strength of these mixes. The low water-binder ratio
results in a low-porosity cement matrix that tends to generate high compressive strength values.
As a result of the high compactness of the aggregate skeleton, an RCC mix requires less binder
compared to that normally used to fabricate a conventional concrete of comparable compressive
strength. As shown in Table 3.1, for compressive strength values of 45 MPA and 60 MPa, the
binder dosage in RCC mixes is respectively 20% and 28% less than for conventional concrete
[3.4].
28
Table 3.1 - Comparison of RCC and Conventional Concrete Mixes (from reference [3.4]
Conventional Concrete2
Binder (kg/m3)
Water-binder ratio
45 MPa1 of compressive strength – Type 10 cement
350
0.40
60 MPa1 of compressive strength – Type 10E-SF cement
420
Binder (kg/m )
Water-binder ratio
0.34
3
RCC3
270
0.40
300
0.35
1
28 days of curing following initial water-binder contact
Air entrained
3
Non air entrained
2
When properly formulated, RCC rapidly develops excellent mechanical properties. Generally,
the very early mechanical strength of RCC mixes is comparable to or exceeds that of highperformance concrete but with a lower cement content. As shown in Figure 3.4, the mixes
identified as T10-0.50-225 and T10E-SF-0.47-225 (cement type – water-binder ratio - cement
content in kg/m3) achieved a compressive strength of about 17 MPa at 24 hours. The mixes
identified as T10E-SF-0.38-250 and T10E-SF-0.34-300 developed compressive strengths of 24
MPa and 34 MPa, respectively, while a high-performance concrete mixture (identified as HPC)
attained a compressive strength of 20 MPa in the same time period. After 7 days of curing, all the
RCC mixes achieved a compressive strength of at least 38 MPa. At this point, the RCC mix
identified as T10E-SF-0.34-300 had achieved a compressive strength of 60 MPa, which meets
the 28-d compressive strength requirement generally stipulated for high-performance concrete
[3.4].
29
Compressive Strength (MPa)
70
60
50
40
30
T10-0,50-225 (44,4 MPa @ 28D)
T10E-SF-0,47-225 (57,2 MPa @ 28D)
T10E-SF-0,38-250 (63,5 MPa @ 28D)
T10E-SF-0,34-300 (60,2 MPa @ 28D)
BHP (74 MPa @ 28D)
20
10
0
1
2
3
4
5
6
7
Age (days)
Figure 3.4 - Evolution of compressive strength of RCC mixes
The compressive strength of RCC specimens is determined according to the requirements of
CAN/CSA A23.3-9C. As mentioned above, the procedure for fabricating RCC specimens for
compressive strength testing is described in Appendix D. Three test cylinders should be
fabricated for each strength test period.
3.2.2.2.
Flexural strength
Flexural strength (modulus of rupture) is one of the key parameters in designing a concrete
pavement - conventional or RCC. The fatigue criteria (i.e. controlling cracking in a slab
subjected to repetitive loading caused by heavy traffic) is influenced by the concrete's flexural
strength.
Flexural strength (modulus of rupture) is one of the key parameters in designing a
concrete pavement - conventional or RCC.
The flexural strength of adequately designed RCC mixes (optimized aggregate skeleton) is
generally higher than that of conventional concrete. This performance relates directly to the
packing density of the mixture in which the aggregate particles are practically touching one
another. The presence of densely packed aggregates impedes crack propagation since more
energy is required for cracking to occur.
Typically, an appropriately formulated RCC mix containing 250 kg/m3 of Type 10E-SF and a
water-binder ratio of 0.40 achieves an average flexural strength between 4.0 MPa to 4.5 MPa
after 3 days of curing, 5.0 MPa after 7 days, and between 5.5 and 6.0 MPa at 28 days. Similarly,
30
an RCC mix with a cement content of 300 kg/m3 (Type 10E-SF) with a water-binder ratio of
0.35 develops an average flexural strength of 4.0 MPa to 4.5 MPa after 3 days of curing, 5.5
MPa to 6.5 MPa at 7 days, and 7.0 MPa at 28 days.
Evaluating the modulus of rupture (flexural strength) of a concrete specimen under loading
conditions consists of measuring the maximum strain at the bottom of the specimen. Modulus of
rupture can be evaluated depending on where the load is applied: cantilever, center point, or third
point. The first two evaluate flexural strength at a single point, whereas the third method
determines the minimum flexural strength located at the middle third of the specimen. Thirdpoint loading is currently used for RCC since the load is applied over a larger area. CAN/CSA
A23.2-8C (beam with third-point loading) describes the test method for determining the modulus
of rupture of concrete specimens. The procedure for preparing specimens for this test is
described in Appendix E. As with compressive strength testing, three specimens should be
fabricated for each test strength test period.
Each specimen must be made with care, especially its middle third. During testing, the maximum
flexural moment is located at the bottom of the specimen in the middle third of the span. Any
defects in workmanship (i.e. compaction or segregation voids) in this section will constitute a
preferential path for crack propagation, resulting in the flexural strength being underestimated.
Flexural strength is commonly estimated from compressive strength with the following equation:
ƒ
r
= 0 .6
ƒ
'
c
[3.3]. This empirical relation, however, does not appear to be suitable for RCC.
Research in recent years has revealed the following empirical relation between RCC compressive
strength and flexural strength at 28 days (Relation (1)) [3.3]:
0.459
(1)
ƒr = ( f 'c)
Where:
ƒr is the RCC flexural strength (in MPa) at 28 days;
ƒ’c is the average compressive strength (in MPa) of the RCC specimens at 28 days.
Similarly, the ratio between a conventional concrete’s modulus of rupture and compressive
strength is generally considered to be on the order of 0.10, as compared with 0.12 to 0.15 in the
case of RCC.
3.2.2.3
Influence of constituents on compressive and flexural strength
This section discusses the influence of certain materials on the compressive and flexural strength
of RCC mixes: ternary blended cement, fly ash, mineral particles smaller than 80 µm (limestone
filler), and stone screenings. The results presented herein were taken from laboratory
experiments and are provided for informational purposes only. Based on current knowledge, the
conclusions drawn from the studies must be considered with care. Additional laboratory research
and experimental field test sections are required before these developing technologies can be
made part of standard practice in Quebec.
31
The results presented herein were taken from laboratory experiments and are provided
for informational purposes only. Based on current knowledge, the conclusions drawn
from the studies must be considered with care. Additional laboratory research and
experimental field test sections are required before these developing technologies can
be made part of standard practice in Quebec.
Influence of ternary blended cement
A laboratory study on the mechanical behavior of low-cement RCC mixes (i.e. binder content
less than 250 kg/m3), carried out by the Centre de recherche sur les infrastructures en béton
(CRIB) at Université Laval, has shown that ternary blended cement can improve the packing
density of the aggregate skeleton in RCC mixes [3.5]. The study consisted in comparing the
mechanical properties of mixes made with Type 10E-S/SF and Type 10E-F/SF ternary blended
cements compared to mixes made with Type 10 cement. The mixes produced in this laboratory
study were designed using the Compressible Packing Model [3.6].
To date, no low-cement RCC pavements (i.e. cement content below 250 kg/m3) have been built
in Quebec. Additional laboratory research and experimental field test sections are required
before these developing technologies can be made part of standard practice in Quebec.
To date, no low-cement RCC pavements (i.e. cement content below 250 kg/m3) have
been built in Quebec. Additional laboratory research and experimental field test
sections are required before these developing technologies can be made part of
standard practice in Quebec.
In this laboratory project [3.5], two RCC mixes were batched with two types of ternary blended
cement: TER-A (Type 10E-S/SF) and TER-B (Type 10E-F/SF), as shown in Table 3.2. In
addition, an RCC was made with Type 10 Portland cement and one with Type 10E-SF Portland
cement, identified as T10 and T10-SF, respectively. All the mixes were made with a waterbinder ratio of 0.62 and batched with limestone filler representing nearly 50% of the cement
weight. The mixes were designed to have an air-void volume of about 2%.
Table 3.2 RCC Mix Compositions (from reference [3.5])
Mix
T10
T10-SF
TER-A
TER-B
Binder
(kg/m3)
175
175
175
175
Limestone
Filler
(kg/m3)
87
87
87
87
Water
(kg/m3)
108
108
108
108
Sand, 0-5
mm (SSD)
(kg/m3)
730
730
730
730
Stone, 5-20
mm (SSD)
(kg/m3)
1350
1350
1350
1350
Water
Reducer
(mL/m3)
1050
1050
1050
1050
The results from compressive-strength testing are provided in Figure 3.5; flexural-strength
results are given in Table 3.3. As shown in Figure 3.5, the concrete made with the ternary
blended cements tends to develop compressive strength slower than the other two mixes made
32
with Type 10 Portland cement and the Type 10E-SF cement. However, TER-A (Type 10E-S/SF)
and Type 10E-SF 28-d compressive strengths are higher than that achieved by the mixes
containing Type 10 cement. After 7 days of curing, the concretes made with ternary blended
cements developed slightly less flexural strength than those produced with the Type 10 and Type
10E-SF cements, whereas their 28-d values are comparable.
60
T10
T10-SF
TER-A
TER-B
50
40
30
20
10
0
0
7
14
21
28
35
Age (days)
Figure 3.5 − Development of compressive strength of RCC mixes made with different
types of cement (from reference [3.5])
Table 3.3 Flexural Strength of RCC Mixes Made with Different Types of Cement
Age (days)
7
28
T10
4.5
4.8
Flexural Strength
(MPa)
Mixes
T10-SF
TER-A
5.0
3.6
5.5
5.0
TER-B
3.9
4.6
33
Influence of fly ash
A study was carried out on the effects of high fly-ash content (level of cement replacement in
excess of 40%) on the mechanical strength of RCC mixes [3.7]. Compressive-strength and
flexural-strength test results for the different fly-ash contents are presented in Figures 3.6 and
3.7, respectively. The mixes are identified in these figures according to cement content and flyash content expressed in kg/m3. As the figures show, the mechanical strength of the RCC mixes
decreases as the fly-ash content increases. Despite their low early strength, these fly-ash RCCs
developed almost equivalent or in some cases higher long-term strength than Mix 300-0 (without
fly ash) as a result of hydration. After 91 days of curing, the compressive strength of Mix 210135 is nearly 35% higher than that of the RCC mix without fly ash (Figure 3.6). As indicated in
Figure 3.7, the 91-d flexural strength of all the fly-ash RCC mixes is higher than the mix without
fly ash.
70
300(T10)-0(FA) [kg/m3]
60
210(T10)-135(FA) [kg/m3]
50
190(T10)-165(FA) [kg/m3]
40
170(T10)-195(FA) [kg/m3]
30
150(T10)-225(FA) [kg/m3]
20
130(T10)-255(FA) [kg/m3]
10
110(T10)-285(FA) [kg/m3]
0
3
7
28
91
Age (days)
Figure 3.6 − Influence of fly-ash content on RCC compressive strength
34
Flexural Strength (MPa)
10
9
8
7
6
5
4
3
2
1
0
300(T10)-0(FA) [kg/m3]
210(T10)-135(FA) [kg/m3]
190(T10)-165(FA) [kg/m3]
170(T10)-195(FA) [kg/m3]
150(T10)-225(FA) [kg/m3]
130(T10)-255(FA) [kg/m3]
110(T10)-285(FA) [kg/m3]
3
7
28
91
Age (days)
Figure 3.7 − Influence of fly-ash content on RCC flexural strength - (from reference [3.7])
Influence of limestone filler and stone screenings
CAN/CSA A23.1 limits the content of particles smaller than 80 µm in conventional concrete. A
laboratory study dealing with the mechanical behavior and freeze-thaw resistance of low-cement
RCC (cement content less than 250 kg/m3) demonstrated that adding about 7% limestone filler
(mineral particles smaller than 80 µm) with respect to the total weight of dry ingredients in lowcement RCC mixes can generally enhance concrete properties. The mixes produced under this
research program were designed using the Compressible Packing Model [3.6].
The study results indicate that limestone filler enhances the mechanical strength of the concretes
tested. This can be directly related to the filler's impact on aggregate compactness and the
concrete's water-binder ratio. The 7% addition of limestone filler per weight of total dry
constituents yielded a 12% reduction in the concrete's porosity. The enhanced compactness in
RCC mixes tends to slightly reduce the water-binder ratio. Consequently, the water-binder ratio
of a mix with a binder content of 225 kg/m3 formulated both with and without limestone filler
decreased from 0.47 to 0.44 and from 0.65 to 0.59 for a mix with a binder content of 175 kg/m3
(Type 10E-SF cement) with no appreciable reduction in workability. Table 3.4 demonstrates the
positive influence of fines on the aggregate skeleton with respect to mechanical properties
(compressive and flexural) in these concretes. The compressive and flexural strengths of mixes
containing limestone filler outperform those without. Moreover, incorporating fines into the
RCC mixes also improves the pavement's surface texture. However, high contents of particles
smaller than 80 µm (that is, over 15%) can significantly reduce RCC scaling resistance [3.8].
35
Table 3.4 Mechanical Properties of RCC Mixes Formulated with and without Limestone Filler
Mix with 175 kg/m3 of Cement
Without Limestone
With Limestone Filler
Filler
Age (days)
1
7
28
10.0
27.6
41.0
Mix with 225 kg/m3 of Cement
Without Limestone
With Limestone Filler
Filler
14.8
34.8
44.9
18.6
37.8
58.2
1
7
28
2.5
4.0
5.3
26.4
49.5
64.1
2.8
4.8
6.0
4.1
5.0
5.7
4.4
5.7
7.0
This laboratory study also demonstrated the impact limestone filler and stone screenings
additions have on flexural strength in low-cement RCC mixes [3.8]. The mixes were designed
using the Compressible Packing Model. Figure 3.8 presents the flexural-strength results for RCC
mixes made with Type 10 portland cement and a Type 10E-SF portland cement with binder
contents varying from 175 to 227 kg/m3. The mixes are identified as follows: quantity of cement
in kg/m3, water-binder ratio, LF for limestone filler, and SS for stone screenings. As shown in
the figure, Mix 176/0.65 developed a flexural strength of 2.5 MPa after 24 hours, whereas Mix
226/0.50/SS attained 4.5 MPa. The minimum 7-d flexural strength was recorded by Mix
176/0.65 (4.0 MPa), whereas the maximum was achieved by 227/0.44/LF (5.7 MPa). The 28-d
flexural strength of this mix was 7.0 MPa.
1 day
7days
7
6
28 days
5
4
3
2
Type 10
226/0,50/CP
177/0,62/CP
225/0,47
176/0.65
227/0.44/FC
179/0.59/FC
175/0.62/FC
225/0.49
0
175/0.62/FC
1
176/0.65
Average Flexural Strength (MPa)
8
Type 10E-SF
Mixes
Figure 3.8 − Flexural strength of different types of RCC mixes (from reference [3.8])
36
3.2.2.4
Modulus of elasticity
The proportionality constant, E, expresses the ratio between the applied strain and strain, which
is the modulus of elasticity or Young's modulus, as shown in Equation 2.
E=
σ
ε
(2)
where:
E is Young's modulus (MPa); σ is stress (MPa); and ε is strain (mm/mm).
This proportionality constant is a measurement of the material's rigidity. In other words, Young’s
modulus represents the material's property to undergo reversible elastic deformation in response
to a stress.
The properties of the two phases in a concrete mix (i.e. hydrated cement paste and the
aggregates) affect the modulus of elasticity. The aggregates in RCC occupy a significant volume
compared with the paste. As a result, the aggregates have more impact than other parameters
such as binder type and the water-binder ratio. Consequently, even if an RCC mix made with
Type 10E-SF cement develops higher compressive strength than a mix made with Type 10
portland cement, their moduli of elasticity will be nearly identical. Figure 3.9 provides modulus
of elasticity values at different ages for RCC mixes made with Type 10 portland cement and
Type 10E-SF cement with water-binder ratios of 0.35, 0.40, and 0.45 [3.3]. As indicated in the
figure, the average modulus of elasticity for the different RCC mixes is about 30 GPa at 28 d.
40
35
Modulus of 30
Elasticity
25
(GPa)
20
15
10
5
7 days
28 days
90 days
0
0.35 - 297 0.40 - 270 0.45 - 244 0.35 - 312 0.40 - 280 0.45 - 244
Type 10E-SF cement
Type 10 cement
Water Binder Ratio
Figure 3.9 − Modulus of elasticity for different RCC mixes - (from reference [3.3])
37
3.2.2.5
Shrinkage
Concrete shrinkage can be defined as decrease in either length or volume of a material resulting
from changes in moisture content, temperature, or chemical changes. Desiccation and hydration
give rise to shrinkage [3.9]. There are four types of shrinkage:
1) Shrinkage with no moisture exchange (self-desiccation i.e. the aggregate skeleton counters
volume loss resulting from continued hydration [3.10]),
a) Thermal phenomena (heat of hydration)
b) Chemical expansion (ettringite)
2) Shrinkage with moisture exchange (i.e. volumetric changes due to loss of moisture via
capillaries and smaller pores),
a) Plastic shrinkage
b) Drying shrinkage
3) Swelling in water,
4) Carbonation shrinkage - resulting from the dissolution of calcium hydroxide (Ca(OH)2) by
carbon dioxide.
The main factors in drying shrinkage are the water-binder ratio and aggregate volume [3.11].
Drying shrinkage increases with water-binder ratio since it determines the amount of unbound
water in the paste that can evaporate, as well as, the rate at which water rises to the surface of the
concrete. The aggregates restrain paste shrinkage and deformation. The degree to which
deformation is restrained depends on aggregate elastic properties. Moreover, in the case of RCC,
the significant volume of aggregates (i.e. compact aggregate skeleton) reduces drying shrinkage
more than lowering the water-binder ratio does. In fact, the greater the volume of aggregate, the
less affect the water-binder ratio has on drying shrinkage.
RCC usually experiences less drying shrinkage than conventional concrete. In fact, the maximum
drying shrinkage in a typical RCC mix (estimated with Bazant’s equation) generally falls
between 400 and 500 µm/m, compared with values for conventional concrete of 700 µm/m or
more. The low cement content of RCC also reduces drying shrinkage.
3.2.2.6
Fatigue Behavior
The repeated load application can cause a material to fail even if the maximum stresses are lower
than the elastic limit of the material. This phenomenon is known as fatigue. A material's fatigue
index is therefore equal to the fraction of the static alternate strength that the material can
withstand repeatedly for a given number of cycles. The fatigue strength of concrete subjected to
flexural loading is a critical parameter, along with erosion strength (pumping effect), governing
the thickness of RCC pavement during the design phase (see Chapter 5).
The experimental study on the fatigue behavior of concrete or RCC test specimens consists in
subjecting the specimens to flexural loading at different strain amplitudes, σa [3.12]. The number
of cycles (N) required to cause specimen failure is therefore measured. Given the nature of the
variability of the materials being subjected to flexural loading, the test is repeated many times at
38
different stress amplitudes σa. The curve
σ = ƒ(N)
σ
= ƒ(N ) , where ƒ(N) is the
MR
modulus of rupture of concrete, is then graphed on a semi logarithmic scale.
a
or
a
In the general equation for concrete fatigue, the stress ratio, S, which is the ratio of the stress
amplitude to the modulus of rupture,σ a
, is related to the number of load cycles, N, resulting
MR
in fatigue failure [3.13]. This dimensionless term S makes it possible to partially eliminate the
influence of the water-binder ratio, aggregate type / size, and cement type / dosage on fatigue
resistance, N. Whöler’s equation, for example, expresses the relationship between the stress ratio
and the number of loading cycles (3).
S = σ a = a − b(log N )
MR
(3)
where:
S:
σa:
MR:
a and b:
N:
Stress ratio
Stress amplitude
Concrete's modulus of rupture
Experimental coefficients that vary according to the load as well as compressive,
tensile, and flexural strength
Number of loading cycles
Many materials, such as steel, have a Whöler curve that achieves a horizontal asymptote as the
number of cycles increases. The asymptote value determines the endurance limit (σd) of the
material. In the case of a material subjected to cyclic loading at stress levels below the endurance
limit, σd, fatigue failure should not theoretically occur [3.12].
Given the recent development of new RCC design methods (see Chapter 4), research on the
fatigue behavior of optimized RCC mixes should be carried out.
3.2.3
Durability
Concrete’s durability is linked to its ability to resist aggressive agents penetration in its porenetwork. Porosity (i.e. total number of pores), as well as, the pore size distribution in the
hydrated cement paste fraction of the material have a strong influence on the durability of
concrete [3.14].
An RCC mix contains less cement paste than conventional concrete. This low paste content has
two major impacts on the material’s internal structure. First of all, paste distribution is less
homogeneous than in conventional concrete due to the difficulty of dispersing mixing water in a
stiff mix. As a result, RCC contains a certain number of compaction voids that can affect its
freeze-thaw resistance. Their irregular shape clearly differentiates these air voids from the
normal spherical kind. Optimizing the aggregate skeleton reduces the number of compaction
39
voids. Moreover, a high number of compaction voids may form an interconnected network that
seriously jeopardizes durability. On the other hand, compaction voids can play a positive role if
they are sufficiently small and well distributed [3.15].
Compaction voids can play a positive role if they are sufficiently small and well
distributed.
Concrete structures such as RCC pavements exposed to winter conditions are generally subject
to two types of damage caused by freeze-thaw cycles: internal cracking and surface scaling.
While they may occur simultaneously, these phenomena are distinct and independent. If the
concrete contains moisture, freeze-thaw cycles can produce internal cracking, which lowers the
dynamic modulus of elasticity and results in expansion. Surface scaling also occurs during
freeze-thaw cycles when the concrete is exposed to moisture and this process worsens in the
presence of deicing salts.[3.16]. RCC mixes must therefore be designed to resist both of these
types of attack caused by freeze-thaw cycles.
3.2.3.1
Resistance to internal cracking
An appropriate air-void system can provide adequate protection against internal cracking in
concrete subjected to freeze-thaw cycles regardless of void shape. In the case of RCC
compaction voids, spacing and size are the important factors. If the compaction voids are well
distributed (exact required spacing is a function of paste homogeneity, porosity, and
permeability) not interconnected, and small enough, the RCC will be frost resistant. In contrast,
if the compaction voids form a connected network, the concrete will have low freeze-thaw
resistance because the voids will become saturated quickly if moisture is available [3.15].
How compaction voids affect RCC freeze-thaw resistance depends on accurately evaluating their
spacing and determining the spacing required for good frost protection [3.15]. The spacing factor
providing good frost protection for conventional concrete is not necessarily suitable for RCC.
How compaction voids affect RCC freeze-thaw resistance depends on accurately
evaluating their spacing and determining the spacing required for good frost
protection.
_
CAN/CSA A23.1 specifies that the average spacing factor, L (half-distance between the walls of
two adjacent bubbles), determined according to ASTM C457, must be less than or equal to
230 µm, with no value greater than 260 µm.
There is currently no accepted method for determining RCC air-void system characteristics,
although a modified version of the procedure in ASTM C457 is often used. It requires, however,
distinguishing between spherical air voids and compaction voids. They must be counted
separately and all voids greater than 1 mm must be inventoried apart as illustrated in Table 3.5,
which provides four examples. The spacing factor values are given for spherical air voids alone
and spherical air voids with compaction voids smaller than 1 mm (those greater than 1 mm do
40
not affect frost resistance). RCC frost resistance must not be based solely on either one of these
spacing factors, since their exact meaning is not clearly understood. Freeze-thaw testing
according to ASTM C666 (procedure A) is always required [3.15].
Table 3.5 Two methods for calculating spacing factor (from reference [3.15])
Data
ST
SP
SB
NB
SVC
NVC
SLV
AB
2942
2967
2961
2917
621
604
585
525
30
48
41
65
92
320
108
187
43
45
48
76
68
96
116
138
58
33
39
82
1,0
1,6
1,4
2,3
Legend:
S: Number of stops
VC: Compaction voids
T: Total
P: Paste
LV: Large air voids (> 1 mm)
Air Content
(%)
AB+VC
2,5
3,1
3,0
4,8
Spacing Factor
(µm)
AT
LB
L B+VC
4,4
4,2
4,3
7,6
530
200
530
380
510
220
390
300
B: Spherical air voids
A laboratory study on the mechanical behavior and freeze-thaw resistance of low-cement RCC
revealed that the addition of an air-entraining admixture (Vinsol resin) produced a network of
spherical microbubbles that were well distributed throughout the matrix [3.8]. Table 3.6 presents
the characteristics of the air-void system determined by a modified version of ASTM C457 for
RCC mixes. Mixes M1 and M2 were produced without an air-entraining admixture. They
contain 176 and 225 kg/m3, respectively, with water-cement ratios of 0.65 and 0.47, respectively.
Two other mixes (M3 and M4) were produced by adding an air-entraining admixture when the
dry ingredients were being mixed. Their cement contents were 221 and 174 kg/m3 and their
water-cement ratios 0.42 and 0.52, respectively. The admixture dosage was 0.4% by cement
weight for Mix M3 and 0.2% for Mix M4. The mixes were designed using the Compressible
Packing Model [3.6].
Table 3.6 Characteristics of the Air-Void System (from reference [3.8])
Mix
M1
M2
M3
M4
Air Content (%)
With Air
Without Air
Voids
Voids
3.7
1.7
5.1
2.6
5.3
2.2
6.9
3.3
Specific Area (mm-1)
With Air
Without Air
Voids
Voids
14.7
19.8
9.9
13.3
16.1
25.4
15.0
21.6
Spacing Factor (µm)
With Air
Without Air
Voids
Voids
211
267
231
333
145
193
103
100
A properly designed RCC mix, compacted to 100% of the reference wet density, will have
adequate frost resistance. Studies have shown that RCC pavements compacted to 97% or less of
the reference wet density were inadequately protected against frost resistance by the compaction
voids created [3.15]. Moreover, optimization of aggregate compactness produces RCC mixes
that resist freeze-thaw cycles whether or not an air-entraining admixture is used. Portland cement
with silica fume also improves RCC frost resistance.
41
A properly designed RCC mix, compacted to 100% of the reference wet density, will
have adequate frost resistance.
Other criteria can provide frost protection as specified in CAN/CSA A23.1, such as minimum
compressive strength and air content of fresh concrete. The durability requirements under
CAN/CSA A23.1 that apply to conventional concrete should be modified for RCC because of its
specific properties and characteristics in the fresh and hardened states.
3.2.3.2
Frost resistance with deicing salts
A concrete that resists internal cracking will not necessarily resist salt scaling because the
mechanisms involved are different. Scaling resistance depends not only on the concrete's overall
quality and properties, but also on the internal structure of the layers just beneath the exposed
surface of the concrete. Scaling resistance also appears to be directly related to surface
permeability, since permeable surfaces seem to reach the critical degree of saturation more
quickly. In certain cases, the skin of good-quality conventional air-entrained concrete was found
to be more porous and therefore more susceptible to scaling. It was recently demonstrated that air
entrainment was not required to provide scaling resistance in conventional concrete when the
water-binder ratio was under a certain level (approximately between 0.25 and 0.35), depending
on binder characteristics [3.16].
Many studies published in recent years tend to confirm that the permeability of surface layers
affects RCC scaling resistance. A series of scaling tests carried out on specimens taken from test
areas indicates that binder type plays a significant role in salt scaling resistance (see Table 3.7).
Mineral admixtures (fine particles), especially silica fume, improve RCC scaling resistance
[3.15]. Furthermore, it appears that fly ash did not contribute to the scaling resistance of these
mixes. It can, therefore, be concluded that particle fineness positively affects cement-paste
microstructure by better distributing the hydrates between the cement grains, which increases
paste homogeneity. This lowers the permeability of the surface layers, which means that they
resist saturation better. It was also observed that the reduced permeability provided adequate
frost protection in non-air-entrained mixes with a water-binder ratio ranging from 0.30 to 0.35.
Surfaces cured with a curing agent yielded higher scaling resistance than those cured with water
or air. The mineral admixtures densified the matrix and reduced the interconnections between
compaction voids, thereby reducing permeability.
42
Table 3.7 Scaling Testing after 50 Freeze-Thaw Cycles
Group
A
B
C
Binder Type and Weight
in kg/m3
WaterBinder Ratio
Type 10 – 300
Type 30 – 300
Type 10E-SF – 300
Type 10 + FA1 – 300 + 60
Type 10E-SF – 300
Type 10 + FA1 – 300 + 60
0.35
0.35
0.35
0.29
0.27
0.22
AirEntrainment
Admixture
3
-
Curing Type
Loss of Mass
(kg/m2)
Curing agent
Curing agent
Curing agent
Curing agent
Air
Air
4.2
6.9
0.1
0.3
1.5
2.7
1
Fly ash
Group B:
Scaling resistance conforming to NQ 2621-900
Groups A and C: Scaling resistance not conforming to NQ 2621-900
Other results from this series of tests demonstrated that reducing the cement content from
300 to 250 kg/m3 in the mixes containing silica fume had no significant effect on scaling
resistance [3.15].
Based on current knowledge, even though the effect that entrained air has on salt scaling
resistance is not clear, a non air-entrained RCC pavement will be frost resistant only if the
following three conditions are met:
♦ Mineral admixtures, such as silica fume, must be used.
♦ The water-binder ratio must be low enough (< 0.40).
♦ The RCC surface must be maintained moist until the curing agent has been properly
applied.
The following conditions must be met in order to ensure frost resistance of a non-airentrained RCC:
♦ Mineral admixtures, such as silica fume, must be used.
♦ The water-binder ratio must be low enough (< 0.40).
♦ The RCC surface must be maintained moist until the curing agent has been
applied in the correct manner.
The test methods generally used to evaluate RCC scaling resistance are ASTM C672 (Scaling
Resistance of Concrete Surfaces Exposed to Deicing Chemicals) and NQ 2621-900
(Détermination de la résistance à l’écaillage du béton soumis à des cycles de gel-dégel en
contact avec des sels déglaçants). Concrete deterioration is evaluated as a function of the mass of
debris per unit of area (expressed in kg/m2) that has detached from the surface as the result of
daily freeze-thaw cycles while in contact with a chloride solution. The normal limit for
conventional concretes is 0.5 kg/m2. Despite the moderate performance of certain mixes in the
laboratory, field observations demonstrate that RCC pavements in service perform quite well.
43
Another evaluation method is an adaptation of NQ 2621-900, in which scaling resistance is
measured by the mass of debris lost from a concrete specimen immersed in saline solution. This
method appears better suited to RCC pavement, whether covered with a layer of asphalt or not,
in simulating salt penetration through cracks.
3.3
Surface Characteristics
3.3.1
General
The surface quality of RCC pavements can be adapted to the various applications targeted. The
surface of a roadway or parking lot for cars will not have the same quality requirements as an
industrial RCC pavement.
3.3.2
Texture of the Finished Surface
Pavement surface texture can be measured by the sand-patch method, which determines the
average depth of the surface macrotexture (ASTM E965). It consists in applying a known
volume of sand (or any other standardized fine material) to the pavement surface and measuring
the total surface covered. The height of the sand corresponds to the ratio of sand volume and
surface. Other methods for measuring surface texture are available, such as laser, texturometer,
and stereoscopy. Figure 3.10 shows an RCC pavement with a closed textured surface, while
Figure 3.11 depicts an area of segregation.
Figure 3.10 - Closed textured surface (from reference [3.17])
44
Figure 3.11 - Open textured surface (from reference [3.17])
The quality of the finished surface depends on a number of factors. Mix characteristics (i.e.
particle-size distribution, paste volume, etc.) affect the texture as do segregation and placement.
3.3.3
Pavement Roughness
Pavement roughness (i.e. riding comfort) has long limited RCC applications for which vehicle
speed is an important factor, such as ports, sorting areas, and intermodal sorting yards. Riding
comfort is estimated from the positive or negative variations of the pavement with respect to a
level surface. Pavement roughness is affected by longitudinal and transversal undulations, as
well as, the length of vertical deformations.
RCC pavement roughness is significantly affected by construction procedures, variations in
degree of compaction, uniformity of placement by the paver, and compaction operations. Very
high-density pavers have significantly improved the uniformity of RCC pavements.
REFERENCES
[3.1]
TREMBLAY, S., MARCHAND, J., BOISVERT, L., PIGEON, M., OUELLET,
E., and MALTAIS, Y. Méthode de formulation de BCR et effets des AEA sur la
maniabilité - Rapport GCS-96-11, Centre de recherche interuniversitaire sur le
[3.2]
Devis technique normalisé pour le béton compacté au rouleau 3VM-30, Ville de
Montréal, Service des travaux publics et de l’environnement, Division de la voirie,
Section du laboratoire, February 2001, 25 p.
[3.3]
OUELLET, E. Formulation et étude du comportement mécanique des bétons
compactés au rouleau, Master’s thesis, Département de génie civil, Université
Laval, 1998, 200 p.
45
[3.4]
GAUTHIER, P., MARCHAND, J., BOISVERT, L., OUELLET, E., and PIGEON,
M. Conception, formulation, production et mise en œuvre de revêtements en béton
compacté au rouleau. Continuing training GCI-A2455, Centre de recherche
interuniversitaire sur le béton, Département de génie civil, Université Laval, 2000,
multiple pagination.
[3.5]
Centre de recherche interuniversitaire sur le béton, Département de génie civil,
Université Laval, internal report, multiple pagination.
[3.6]
SEDRAN, T., De LARRARD, F., and ANGOT, D. “Prévision de la compacité de
théoriques et étalonnage du modèle,” Bulletin de liaison des laboratoires des ponts
et chaussées, 1994, vol. 194, pp. 59-70.
[3.7]
CHENG, C., WEI, S., and HONGGEN, Q. “The Analysis on Strength and Fly Ash
Effect of Roller-Compacted Concrete with High Volume Fly Ash,” Cement and
Concrete Research. 2000, vol. 30, pp. 71-75.
[3.8]
OUELLET, E., MARCHAND, J., REID, E. Comportement mécanique et
durabilité au gel de mélanges de béton compacté au rouleau à faible teneur en
ciment, Progrès dans le domaine du béton, ACI - section du Québec et de l'Est de
l'Ontario, Sherbrooke, Québec, 1998, 24 et 25 novembre, 6 p.
[3.9]
BISSONNETTE, B. Retraits de la pâte de ciment et du béton, Département de
génie civil, Université Laval, Course notes, 2001, multiple pagination.
[3.10] ACKER, P. Retraits et fissuration du béton, Laboratoire Central des Ponts et
Chaussées, 1992, September, 42 p.
[3.11] NEVILLE, A. Properties of Concrete, Fourth edition, John Wiley and Sons Inc.,
New York, USA, 1995, 844 p.
[3.12] DORLOT, J-M., BAÏLON, J-P., and MASOUNAVE, J. Des matériaux, Éditions
de l’École Polytechnique de Montréal, 1986, 467 p.
[3.13] SHI, X. P., FWA, T.F., and TAN, S.A. “Flexural Fatigue Strength of Plain
Concrete,” ACI Materials Journal, 1993, September-October, pp. 435-440.
[3.14] BARON, J., and OLLIVIER, J-P. La durabilité des bétons, Presses de l’École
Nationale des Ponts et Chaussées, Paris, 1992, 453 p.
[3.15] PIGEON, M., and MARCHAND, J. “The Frost Resistance of Roller-Compacted
Concrete, Concrete International,” 1996, vol. 18, no 7, July, pp. 22-26.
[3.16] PIGEON, M. “La durabilité au gel du béton,” RILEM :Matériaux et
Constructions, 1989, vol. 22, pp. 3-14.
[3.17] Service d’expertise en matériaux (S.E.M.) inc., internal report, multiple
pagination.
46
Chapter 4 – RCC Mix Design
4
General
Most of the design methods generally used for conventional concrete cannot be directly applied
to RCC. Methods for designing RCC mixes are given in the document published by American
Concrete Institute Committee 325.10R-95. They have been developed using different approaches
and have been successfully used. For the most part, these design methods have been based on
empirical or semiempirical approaches that require producing a large number of trial batches in
order to achieve a mix with optimal proportions. Moreover, the Laboratoire Central des Ponts et
des Chaussées (LCPC) in France has, in recent years, developed an RCC mix design method that
was adapted by the Centre de recherche sur les infrastructures en béton (CRIB) at Université
Laval. This method rests on a better understanding of the parameters affecting RCC properties in
the fresh and hardened states. In most cases, a single trial batch is needed to determine the
characteristics of the optimum mix.
4.1
General Principles
Regardless of the design method, RCC mixes must generally comply with certain requirements.
For example, the binder content must be optimal in order to achieve the specified mechanical
properties at minimum cost. In addition, the water-binder ratio must be adjusted for optimal
workability in order to achieve optimal in-place density with the roller compactor. Ideally, the
mix water content must be maintained just under the value that would cause the compacting
roller to produce undulations in fresh concrete and just over the threshold at which a dryer mix
would produce increased segregation. Optimal water content depends on aggregates, as well as,
binder type and quantity. Lastly, the proportions of the different aggregate classes must be
determined in order to achieve the require density and to produce a surface with a closed texture.
In summary, the mix design must produce the densest RCC mix possible with maximum
workability [4.1].
The properties of the RCC mix must be determined in the laboratory before work starts,
regardless of the mix design method used. Measuring the properties of fresh (workability,
density) and hardened (compressive and flexural strength) RCC makes it possible to determine
compliance with technical requirements and specifications. Moreover, it is recommended to
measure workability at 10, 20, 30, and 60 min after initial water-binder contact. The test results
will serve as reference values against which field performance can be compared for qualitycontrol purposes.
4.2
Mix Design Methods
The methods for designing RCC can be broken down into three distinct categories: empirical,
semiempirical, and theoretical.
47
4.2.1
Empirical Methods
The first methods used to design RCC mixes relied on empirical procedures, thus requiring that a
certain number of laboratory batches be produced in order to obtain an RCC with the desired
characteristics. In certain cases, more than 25 trial batches were required to achieve this goal. In
addition, batches were often required in the field to adjust mixes workability. While these
methods are easy to use and relatively effective, they lack flexibility and require a great deal of
time and energy [4.1].
The American Concrete Institute's (ACI) Committee 325.10R-95 described the most commonly
used methods for designing RCC mixes. Two of them are:
♦
♦
Designs respecting certain workability limits.
Designs based on geotechnical methods.
4.2.1.1
Design method based on workability limits
ACI's method is suitable for producing RCC mixes targeting a workability limit. The mix
proportions are determined using a three-step procedure [4.1].
Step 1 consists in producing a preliminary series of trial batches of mortar with different watercement ratios and different sand-cement ratios in order to determine the minimum paste volume.
The density of each mix is determined. As shown in Figure 4.1, a given water-cement ratio
corresponds to a sand-cement ratio leading to optimal density. The second step consists in
selecting the water-binder ratio according to the required mechanical properties. The third step is
adjusting the fine and coarse aggregate proportions in order to achieve the desired workability
once the water-binder and sand-binder ratios have been established [4.1].
Figure 4.1- Optimum mortar parameters for RCC (from reference [4.1])
48
4.2.1.2
Design method based on geotechnical principles
This method from ACI Committee 325.10R-95 is derived from a soil compaction procedure
based on the relationship between RCC dry density and water content. It is more appropriate
when small-size aggregates are used along with a high content of cementitious materials [4.1].
Percent Passing (%)
First of all, the proportion of fine aggregate to coarse aggregate is established using the grading
ranges given in Figure 4.2. Then, a series of concrete mixes with different binder contents are
produced. The binder content can vary from between 12% and 14% of the total weight of dry
materials. Mixes with different water contents are produced for each binder content. The optimal
water content must be established using the method described in ASTM C1557 – Method D,
which makes it possible to select the water content that corresponds to the maximum dry density.
Each concrete sample is compacted in a cylindrical mold with a specific compaction effort. The
compacted concrete is weighed and the dry density calculated. The relationship between the dry
density and water content is then plotted. As shown in Figure 4.3, the maximum value on the
curve represents the water content for obtaining the mix with the optimal dry density. Normally,
the wet density varies very little in this portion of the curve, whereas the calculated dry density is
significantly affected. Finally, the mixes with optimal water content are tested for compressive
strength. The mix having the lowest binder content and achieving the required mechanical
properties is selected [4.1].
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
0.1
1
10
100
Sieve Size (mm)
Figure 4.2 − Grading ranges for RCC (from reference [4.1])
49
2600
Wet Density
3
Unit Weight (kg/m )
2550
Dry Density
2500
2450
2400
2350
2300
2250
4
5
6
7
Total Water Content (%)
Figure 4.3 − Typical relationships between density and water content of RCC mixes
The design method closest to the workability limit is the most commonly used of the two
empirical methods cited above. Generally, this method yields good results in the field. In most
cases, it makes it possible to achieve optimized mixes. In contrast, the method based on
geotechnical principles often yields mixes that are far from optimal [4.1]. The grading curves
predefined in order to establish the proportions of coarse and fine aggregates were based on
average values deduced from a large number of measurements carried out on various types of
aggregates. Furthermore, they are not adjusted for formulating mixes comprising aggregates that
are nearly marginal [4.1].
When using either of these two methods, many laboratory batches must be produced in order to
arrive at the optimal mix. To use either method sound experience with RCC is required. In
addition, if a variety of constituents are used (i.e. a number of granular materials), the design
time will be considerable [4.1].
4.2.2
Semi-empirical Method
By definition, a semi-empirical method is based both on experimental data and empirical
formulas. Optimal paste volume is an example of a semi-empirical method. With this method,
RCC mixes are designed based on a ratio of paste volume to air-void volume. This approach
requires that a number of laboratory batches be produced [4.1].
The method is based on the hypothesis that the optimal RCC mix should have just enough paste
to fill the intergranular spaces remaining after the aggregate skeleton has achieved maximum
density after compaction. This design method is also based on a volume approach. If less paste
than the optimal past volume is used, the voids left after compaction will reduce the concrete's
mechanical properties and increase its permeability. On the other hand, excessive paste content
50
will increase the heat of hydration, as well as, constituent costs, without significantly increasing
physical properties or decreasing permeability [4.2].
Three steps are involved in this design method [4.2]:
1. Establish the proportions of the different aggregate grading classes in order to produce a
mix that, after compaction, will have a minimum number of voids and measure the void
volume of the compacted aggregate per cubic meter.
2. Adjust the paste volume in order to achieve the desired workability.
3. Select the water-binder ratio and the cement and pozzolan proportions required to
produce a paste that meets mechanical requirements.
At present, the optimal paste volume method is only applicable to non-air-entrained RCC mixes.
Attempting to design air-entrained RCC with this method is complex because the air-void system
significantly affects concrete workability and mechanical properties [4.2].
Step 1: Select the optimal particle-size distribution and calculate void volume
This step consists in selecting the proportions for the different aggregate grading classes aimed
toward creating an aggregate skeleton with a minimum amount of voids after compaction. The
modified Fuller-Thompson rule (commonly used to design bituminous concrete mixes) can be
used to obtain a grading curve that yields a dense skeleton (1) [4.2]:
0.45
⎛d⎞
p =⎜
⎟
⎝ D⎠
× 100
(1)
Where:
d:
D:
p:
Sieve size (mm)
Aggregate nominal maximum size
Percent passing sieve size d
Figure 4.4 shows typical Fuller-Thompson grading curves for different nominal maximum sizes
of aggregate. These curves generally yield a compact aggregate skeleton when the particles are
natural sand and cubic aggregates. The curves indicate that the aggregate skeleton must contain
between 10% and 15% of fine particles passing the 160-µm sieve. This percentage includes fines
from the aggregates and cementitious materials [4.2].
51
100.0
Percentage Passing (%)
90.0
80.0
Aggregate nominal
maximum size (mm)
2
2
70.0
1
60.0
1
5
50.0
40.0
30.0
20.0
10.0
0.0
0.01
0.1
1
10
100
Sieve Size (mm)
Figure 4.4 −Modified Fuller-Thompson curves for different aggregate sizes
Fuller-Thompson curves only approximate the ideal grading curve since the volume of voids
after compaction depends on aggregate shape, angularity, surface texture, as well as, the
compaction method used. Naturally rounded aggregates (i.e. smooth surface texture) and cubic
aggregates yield a denser skeleton, while highly angular aggregates containing a large portion of
flat and elongated particles yield a more open skeleton. A change in particle shape and surface
texture can significantly influence the degree of compaction of the aggregate skeleton (more than
20%). The compactness of the aggregate skeleton is particularly affected by the shape and
surface texture of fine aggregates (< 5 mm) [4.2].
Once the relative proportions of the coarse and fine aggregates have been established to produce
a particle-size distribution as close as possible to the ideal, the voids in the compacted aggregate
skeleton must be determined (Vvc). This volume (expressed in liters per cubic meter of
compacted aggregate) is obtained by compacting, under a surcharge, a sample of the aggregate
mixture in a cylindrical container attached to a vibrating table (Vebe device or the CAN/BNQ
2501-062 test can be used). The volume of voids after compaction is calculated from the
apparent final volume of the compacted aggregates, the proportion and the dry density of the
solid grains of each type of aggregate involved in the skeleton. This design method generally
yields a high-performance RCC mix with an optimized aggregate skeleton containing void
volumes of less than 180 L/m3 after compaction. Coarse aggregates containing a small
proportion of flat, elongated particles and natural sand comprised of rounded particles could
further reduce the void volume of the aggregate skeleton [4.2].
52
Step 2: Establish the paste volume for a given level of workability
The second step consists in determining the paste volume required to obtain a specific level of
workability [4.2]. The results of many experimental studies have revealed the relationship
between the workability of non-air-entrained RCC and the ratio of paste volume to void volume
after compaction, where:
Vp:
Vvc:
Volume of paste in 1 m3 of RCC (L/m3)
Volume of voids in 1 m3 of compacted aggregate (L/m3)
The volume of paste Vp (2) for non-air-entrained RCC can be expressed as:
Vp = V water + V cement + V mineral admixture
(2)
Figure 3.5 illustrates the experimental relationship between workability and the paste-void ratio.
This relationship remains approximate since the exact relationship is dependent upon the method
used to determine Vvc and paste rheological properties [4.2].
Figure 4.5 can be used to determine the volume of paste (L/m3) needed to achieve the desired
workability. Generally, a paste-void ratio ranging from 1.0 to 1.05 yields workability varying
from 40 to 90 seconds (Vebe test). One or two trial batches are required to determine the exact
paste volume required to achieve the desired workability.
Workability (sec)
100
80
60
40
20
0
0.95
1
1.05
1.1
1.15
Vp/Vvc
Figure 4.5 - Experimental relationships between workability and paste-void ratio for non airentrained RCC (water-binder ratio < 0.50) (from reference [4.2])
53
Step 3: Select the water-binder ratio depending on the required compressive strength
Once the paste volume required to obtain the desired workability has been established, the last
step is to select the water-binder ratio (w/b) to achieve the specified mechanical strength. Figure
4.6 gives the relationships between 28-d compressive strength and water-binder ratio for RCC
mixes containing cementitious admixtures (silica fume and fly ash). The curves in this figure are
based on experimental results from technical reports and various publications [4.2].
The water-binder ratio that yields the desired mechanical properties depends both on binder
physicochemical properties and aggregate properties. Two or three trial batches are nonetheless
required in order to determine the optimal water-binder ratio and to measure the concrete's
flexural strength, which governs rigid pavement design. Durability criteria may also be factors in
selecting the water-binder ratio for certain applications.
Figure 4.6 - Relationship between the water-binder ratio and 28-d compressive strength of
different RCC mixes (non-air-entrained) (from reference [4.2])
As described in reference [4.2] and illustrated in Figure 4.6, compressive strength plays a
determinant role in selecting the water-binder ratio for RCC. On the other hand, flexural strength
is used to calculate the thickness of an RCC pavement. Consequently, experimental curves
illustrating the relationship between the water-binder ratio and flexural strength of the various
RCC mixes should be produced. Compressive strength can also be used to estimate flexural
strength.
54
Example of the optimal paste volume method
The following example illustrates the procedure for calculating optimal paste volume using the
following data [4.2]:
-
Type T10E-SF
Non air-entrained mix
28-d compressive strength of 60 MPa
Nominal maximum aggregate size of 20 mm
Workability of about 20 sec when placing the RCC
The particle-size distribution, which resembles the modified Fuller-Thompson curve in Figure
4.4 for a maximum aggregate size of 20 mm, can be obtained by combining the particle-size
distributions of two coarse aggregates and natural sand. The void volume of the compacted
aggregate skeleton (Vvc) is 190 L/m3.
According to Figure 4.5, the average Vp/Vvc required to obtain 60-sec workability is 1.05. Since
Vvc equals 190 L/m3, Vp is therefore 200 L/m3 (190 L/m3 × 1.05). The approximate water-binder
ratio required to produce a 28-d compressive strength of 60 MPa with Type T10E-SF cement is
about 0.35, as shown in Figure 4.6.
Equations (3) and (4) provide the weight of binder and water per cubic meter:
M
B
=
V
p
w
l
+
b
d
M
W
=
w
×
b
(3)
B
M
B
(4)
Where:
w/b:
Vp:
dB:
MB:
MW:
Paste water-binder ratio
Paste volume (L/m3)
Binder specific gravity
Binder content (kg/m3)
Water requirement (kg/m3)
Therefore, if Vp = 200 L/m3, w/b = 0.35, and dB = 3.05, Equations (3) and (4) yield the following
values:
MB: 295 kg/m3
MW: 103 kg/m3
(97 L/m3)
(103 L/m3)
(200 L/m3)
Trial batch 1: Vebe time = 35 s
Compressive strength= 56 MPa
55
The workability of this first RCC trial batch is low. A little longer Vebe time could be obtained
with the same w/b, but with Vp under 190 L/m3. Equations (3) and (4) yield:
MB: 280 kg/m3
MW: 98 kg/m3
(92 L/m3)
(98 L/m3)
(200 L/m3)
Although the second trial batch has the desired workability, it fails to meet the 28-d compressive
strength of 60 MPa. A third trial batch must be produced with a slightly lower w/b while
maintaining the same paste volume in order to preserve workability. Therefore, if Vp = 190 L/m3
and w/b = 0.35, Equations (3) and (4) yield:
MB: 295 kg/m3
MW: 103 kg/m3
(96 L/m3)
(94 L/m3)
(200 L/m3)
In this example, three or four trial batches were needed to design the mix. An additional trial
batch is required to establish the flexural strength, as previously stated. If the aggregate skeleton
void volume (Vvc) cannot be determined experimentally, a value between 170 L/m3 (for a
compact aggregate skeleton) and 210 L/m3 (for an open aggregate skeleton) can be used.
4.2.3
Theoretical Model
The introduction of theoretical models constitutes one of the major advances in the area of
concrete mix design. These models provide a method for minimizing the porosity (or
maximizing the compactness) of the aggregate skeleton by optimizing the proportions of the
various aggregate grading classes (sand, stone, cement, mineral admixtures). These theoretical
models have the advantage of taking into account the influence multiple factors have on fresh
and hardened concrete. The Compressible Packing Model (formerly known as the Solid
Suspension Model), developed by the Laboratoire Central des Ponts et Chaussés (LCPC) in
France, has been particularly effective in designing concrete mixes with optimal aggregate
compactness [4.3 − 4.5]. This model has been used successfully to design conventional, highperformance, and self-leveling concrete. The Centre de recherche sur les infrastructures at
Université Laval then adapted the model for designing RCC mixes. The method's effectiveness
has been demonstrated in a number of laboratory research investigations and many RCC
pavement construction projects in Eastern Canada and the United States [4.1]. Since the method
is based on mathematical relationships, it is programmable and, in fact, software has been
developed.
The model can design RCC mixes for industrial applications subject to very high mechanical
loading. By optimizing the binder content it can also be used to produce RCC mixes especially
56
adapted to urban, municipal, and agricultural uses, which are generally subject to less loading. .
Its flexibility allows rapid correction of mix proportions when the materials (i.e. cement,
aggregates) delivered to the site vary over time. It also reduces laboratory trial batches to the
minimum. In most cases, a single laboratory batch is required to adjust mix proportions [4.1].
This design method is based on optimizing the packing of different-sized particles, which
directly affects porosity. The method, therefore, makes it possible to combine constituents to
produce a dry mix with optimal compactness for a given workability. It yields outstanding shortand long-term mechanical properties and reduces the binder content, which inhibits shrinkage
cracking. The compactness of the aggregate mix depends on the particle-size distribution,
aggregate shape, and interaction between particles [4.1].
The input data required for each of the constituents (i.e. binder, mineral admixtures, fine and
coarse aggregates) are particle-size distribution, specific gravity, and void index. Any type of
aggregate can be used with this method as long as this information is known. The model
determines the optimal ratio between the fine and coarse aggregates for a given binder content or
water-binder ratio [4.1]).
More specifically, the model makes it possible to evaluate how particles of different diameters di
(d1>d2…>dn) are compacted based on [4.1]:
-
The specific compactness (αi) of each grading class (i.e. compactness of an arrangement
of particles with similar diameters di);
-
The proportion by weight (yi) of each grading class (expressed with respect to the total
volume of solids).
The model is derived from Mooney’s work on the viscosity of concentrated suspensions of solid
particles. It is based on the hypothesis that the relative reference viscosity (ηr*) of a consolidated
particle arrangement is a finite value. The reference viscosity is defined as being the energy
index required to fully consolidate the concrete. The more energy involved in placing the
concrete, the greater the reference viscosity. The reference viscosity for a unimodal arrangement
of particles of diameter di can be calculated with Equation (5), where βi represents the virtual
packing density of a grading class (i) [4.1].
⎛
⎞
⎜
⎟
⎜ 2.5 ⎟
*
η r , j = exp⎜ 1 1 ⎟
⎜
⎟
+
⎜αi β ⎟
i ⎠
⎝
(5)
Theoretically, if spheres having the same dimension (unimodal) were placed one by one, the
compactness would be 0.74 (virtual packing density βi). This, however, is not possible in
practice, which is why βi represents virtual packing density. Furthermore, the maximum
compactness that can actually be achieved with unimodal spheres is 0.64 (actual packing density
αi). Replacing the values for βi and αi in Equation (5) yields a maximum viscosity for a class of
57
spherical particles of 136 000. Based on Equation (5), the tighter the mix, the greater the
viscosity ηr*, since the actual packing density αi tends to approach the virtual packing density βi
[4.1].
In practice, the real compactness for each grading class (i.e. coarse aggregate, fine aggregate and
cementitious materials) can be easily determined experimentally. The compactness of any
grading class can be determined using the Vebe apparatus (measurement of the void index). An
experimental method has also been developed to measure the compactness of materials such as
cement, fly ash, and fillers. It consists of placing a certain quantity of the cementitious material
in a mortar mixer, then adding a certain volume of water. The compactness value (represented by
the volume of water added) is reached when the paste goes from dry to plastic. If the maximum
relative viscosity is supposed to be similar to an arrangement of spherical particles, which is
136 000, Equation (5) can be used to calculate βi for a given grading class [4.1].
Once the values for βi have been determined for each particle class, Equations (6) and (7) yield
the virtual compactness (γ) of an arrangement of grains of n classes:
γ = the minimum value for all γi when γi ≠ 0
(6)
and the value for each γi is determined with the following equation [4.1]:
γi =
βi
i −1 ⎡
⎛
⎛β
n ⎡
1 ⎞⎟⎤
1 − ∑ ⎢1 − β i + bij β i ⎜ 1 −
⎥ y i − ∑ ⎢1 − aij ⎜ i
⎜
⎜βj
β j ⎟⎠⎥⎦
j =1 ⎣
j =i +1 ⎢
⎢
⎝
⎝
⎣
⎞⎤
⎟⎥ yi
⎟⎥
⎠⎦
(7)
As mentioned above, yi in Equation (7) represents the proportion by weight for each particle
class. The values of yi can be determined from particle-size distribution curves for each material.
The grading curves for granular materials are obtained from a conventional sieve analysis. A
laser technique is generally used to determine the particle-size distribution of particles smaller
than 80 µm [4.1].
The model takes into account particle arrangement as well as phenomena related to the loosening
effect and the wall effect in Equation (7). These interactions are accounted for by the parameters
aij and bij. The loosening effect, represented by the term aij, occurs when a particle is not small
enough to fit into a void between larger particles, as shown in Figure 4.7. The wall effect, as
depicted in Figure 4.8, results in a loosening of particle compactness when a particle is in
proximity to a larger one [4.6].
58
Figure 4.7 - Depiction of the loosening effect (from reference [4.6])
Figure 4.8 - Depiction of the wall effect (from reference [4.6])
The interaction coefficients aij and bij can be easily derived from Equations (8) and (9) [4.1]):
a
ij
d
d
=
b
ij
=
d
d
j
(8)
i
i
(9)
j
59
Once the mix’s virtual packing density (γ) is known, the actual packing density can be
determined using Equation (10) [4.1]:
⎛
⎜
n 2 ,5 y
*
i
η r = exp⎜ ∑
⎜ i =1 1 1
−
⎜
⎝ C γi
⎞
⎟
⎟
⎟
⎟
⎠
(10)
The reference viscosity ηr* must be known in order to use Equation (10). It should be
remembered that the reference viscosity depends on the energy needed to adequately consolidate
the material. In the case of conventional concretes, the concept of viscosity may be related, to a
greater or lesser degree, to concrete slump. When conventional concrete is placed by simple
pouring, viscosity is about 460, whereas a conventional concrete placed using vibration has a
viscosity of 2 600. The reference viscosity of an RCC mix with the required workability for
adequate placement must be established based on past experience. The reference viscosity of
RCC mixes for pavements designed with the solid suspension model averages around 3 000 000
[4.1].
The Compressible Packing Model has proven reliable in designing optimum RCC mixes. This
model makes it possible to design mixes having optimal compactness and workability regardless
of type of application. Generally, only a single trial laboratory batch is required [4.1].
The results from many research studies and field use of these mixes have demonstrated the
enormous potential and versatility of this design method [4.1]. The Compressible Packing Model
provides the means for rapidly calculating the optimal proportions for an RCC mix. This is a
significant advantage in the field, where aggregates and cement sources can change quickly.
REFERENCES
[4.1]
MARCHAND, J., GAGNÉ, R., OUELLET, E., and LEPAGE, S. Mixture
Proportioning of Roller Compacted Concrete – A Review, Concrete Technology
Special Publication SP-171-22, 1997, pp. 457-487.
[4.2]
GAGNÉ, R. High-Performance Roller-Compacted Concrete for Pavement Mixture Design, Application and Durability, International Symposium on
Engineering Materials for Sustainable Development, Okayama, Japon, 2000, 2021 novembre, pp. 74-88.
[4.3]
théoriques et étalonnage du modèle,” Bulletin de liaison des laboratoires des ponts
et chaussées, 1994, vol. 194, pp. 59-70.
60
[4.4]
mélanges granulaires par le modèle de suspension solide – Partie 2 : Validation –
Cas des mélanges confinés,” Bulletin de liaison des laboratoires des ponts et
chaussées, 1994, vol. 194, pp. 71-86.
[4.5]
De LARRARD, F. Concrete Mixture Proportioning – A Scientific Approach,
Editor: E & FN SPON, 1999, multiple pagination.
[4.6]
OUELLET, E. Formulation et étude du comportement mécanique des bétons
compactés au rouleau, Master’s thesis, Département de génie civil, Université
Laval, 1998, 200 p.
61
Chapter 5 – Pavement Design
5
General
RCC pavement design methods adhere very closely to those developed for the design of
conventional concrete. Indeed, both materials behave quite similarly from a structural stand
point. The design thickness for pavements made with RCC or conventional concrete must be
able to maintain tensile stress and fatigue damage due to slab loading within acceptable limits
[5.1]. The base or subbase for an RCC pavement must meet the same parameters as for a
pavement made with conventional concrete and comply with the same frost-protection criteria.
The main design objective is to determine the optimal RCC thickness which will be capable of
withstanding expected design loads, while keeping annual costs to a minimum over the pavement
design life.
The design thickness for pavements made with RCC or conventional concrete must be
able to maintain tensile stress and fatigue damage due to slab loading within
acceptable limits.
Like any other type of rigid or flexible pavement, an RCC pavement is an interface material
between loads applied on its surface and the pavement base. The pavement must therefore be
able to distribute loads and transfer stresses that will not produce excessive strains to the
supporting pavement structure. The pavement must also limit, to a degree, differential soil
movement and limit the resultant surface deformations. Lastly, the pavement must maintain its
long-term structural (bearing capacity) and functional (friction and riding comfort) properties.
RCC pavements exhibit high structural capacity as the result of its mechanical properties
(especially flexural strength) and their outstanding durability, enabling them to withstand the
heavy traffic commonly found in industrial and urban applications. The pavement must be able
to withstand punching and shearing forces and be resistant to rutting.
Figure 5.1 illustrates a typical cross-section of an RCC pavement structure. Pavement thickness
is a function of expected loads, RCC modulus of rupture, and soil characteristics. The minimum
thickness of an RCC pavement is generally considered to be 150 mm. The main functions of the
pavement are to distribute loads and to make the structure impermeable. RCC pavement can be
used as the travel surface and is not normally covered with asphalt for industrial applications.
The granular base prevents pumping of the fines and serves as a platform during construction of
the pavement. The total thickness of the roadway, including the subbase, provides frost
protection [5.2]. There must be an adequate thickness of granular material to provide adequate
protection against freeze-thaw effects for the entire road structure. The base consists of wellgraded, compacted aggregate (20 - 0 mm), while the subbase is a clean granular material not
subject to frost.
62
Figure 5.1 - Cross-section of a typical RCC pavement
The purpose of the base, subbase, and subgrade is to provide relatively uniform support rather
than high load-bearing capacity. This can be compromised by soils that are expansive due to
frost action. The pumping of fines at joints can also lead to non-uniform support [5.3].
5.1
General Design Principles
The calculations for determining the thickness of RCC pavements is based on three general
principles:
1) Load characteristics applied to the pavement.
Loading characteristics constitute the database required to design RCC in industrial pavement
or road. For a given load, this database includes the heaviest axle load, load geometry,
pavement bearing stress (tire pressure), traffic frequency, and traffic growth.
2) Soil characteristics (frost resistance, compressibility, expansion, drainage, and combined loadbearing capacity of the soil and granular base)
Soil characteristics is the second point to take into consideration in determining the RCC
pavement thickness. Soil load-bearing capacity plays a determinant role in this regard. A soil's
supporting capability, given by Westergaard’s modulus of subgrade reaction (k value), is
expressed in MPa/m. This modulus corresponds to a load applied to a plate of known size (760
mm in diameter) divided by the deflection in millimeters of the loaded area. Then, using a
system such as the Unified Soil Classification System (ASTM D2487) shown in Table 5.1, the
modulus of subgrade reaction can be determined for a given type of soil [5.4]. Generally, a
value below the modulus of subgrade reaction range identified in the table is chosen for the
pavement design to provide safe thickness design. A geotechnical survey is carried out to
determine the nature of the in-situ soil. Depending on the scope of the project, the survey can
be carried out using trenches or boreholes. If the survey reveals areas of low-bearing capacity,
63
corrective action can be taken. The modulus of subgrade reaction can be determined directly
in-situ.
As shown in Table 5.1, how a soil reacts to frost must also be taken into consideration in order to
prevent frost heave and loss of subgrade bearing capacity during thaws. Frost protection for RCC
pavement must comply with the same requirements as all other roadways as indicated in Normes
– Ouvrages routiers, Tome II – Construction routière du ministère des Transports (Quebec
Department of Transportation standards governing road construction). The use of lateral drains
for road structures is highly recommended in urban and residential areas
How a soil reacts to frost must also be taken into consideration in order to prevent
frost heave and loss of subgrade bearing capacity during thaws.
Table 5.1 - Soil Classification (from reference [5.4])
Description
Subbase
Material
Excellent
Base
Material
Good
Good to
excellent
Potential
Frost
Action
Compressibility
and Expansion
Drainage
Approximate
k value [5.5]
(MPa/m)
None to
very slight
Almost none
Excellent
150 and +
Fair to good
None to
very slight
Almost none
Excellent
90 to 150
Good to
excellent
Good
Fair to good
Very slight
Fair to poor
72 to 180
Poor to not
suitable
Slight to
medium
Slight to
medium
Slight
Poor to
practically
impervious
72 to 150
Good
Poor to not
suitable
Slight to
medium
Slight
Poor to
practically
impervious
72 to 115
GC
Clayey gravels,
gravel-sand-clay
mixtures
Good
Poor
None to
very slight
Almost none
Excellent
72 to 115
SW
Well-graded sands or
gravelly sands, little
or no fines
Fair to good
Poor to not
suitable
None to
very slight
Almost none
Excellent
52 to 80
SP
Poorly graded sands
or gravelly sands,
little or no fines
SM
Silty sands, sand-silt
mixtures
Fair to good
Poor
Medium to
high
Very slight
Fair to poor
52 to 115
GW
GP
GM
Well-graded gravel or
gravel-sand mixtures;
little or no fines
Poorly graded gravels
or gravel-sand
mixtures; little or no
fines
Silty gravels, gravelsand-silt mixtures
When Not Subject to Frost
Action
If LL ≤ 25; PI ≤ 5
If LL > 25; PI > 5
If LL ≤ 25; PI ≤ 5
64
Description
Subbase
Material
Fair
Base
Material
Not suitable
Clayey sands, sandsilt mixtures
Poor to fair
Inorganic silts and
very fine sands, rock
flour, silty or clayey
fine sands or clayey
silts with slight
plasticity
Inorganic clays of
low to medium
plasticity, gravelly
clays, sandy clays,
silty clays, lean clays
Organic silts and
organic silt-clays of
low plasticity
Inorganic silts,
micaceous or
diatomaceous fine
sandy or silty soils,
elastic silts
Inorganic clays of
high plasticity, fat
clays
Organic clays of
medium to high
plasticity, organic
silts
Peat and other highly
organic soils
If LL > 25; PI > 5
SC
ML
CL
OL
MH
CH
OH
PT
When Not Subject to Frost
Action
Potential
Frost
Action
Compressibility
and Expansion
Drainage
Approximate
k value [5.5]
(MPa/m)
Medium to
high
Slight to
medium
Poor to
practically
impervious
52 to 80
Not suitable
Slight to
medium
Slight to
medium
Poor to
practically
impervious
52 to 72
Poor to fair
Not suitable
Medium to
high
Slight to
medium
Fair to poor
38 to 63
Poor to fair
Not suitable
Medium to
high
Medium
Practically
impervious
38 to 63
Poor
Not suitable
Medium to
high
Medium to high
Poor
48 and -
Poor
Not suitable
Medium to
very high
High
Fair to poor
48 and -
Poor
Not suitable
Medium
High
Practically
impervious
38 and -
Poor to very
poor
Not suitable
Medium
High
Practically
impervious
38 and -
Not suitable
Not suitable
Poor
High
Fair to poor
The bearing capacity of a subgrade and base determines the equivalent modulus of subgrade
reaction. Table 5.2 gives the equivalent modulus of reaction of a road structure for different
values of modulus of subgrade reaction and granular base thickness [5.6].
Table 5.2 - Equivalent modulus of reaction (from reference [5.6])
Modulus of Subgrade
Reaction
(MPa/m)
20
40
60
80
Equivalent Modulus of Reaction -(MPa/m)
Thickness of the Granular Base - (mm)
100
150
225
300
23
26
32
38
45
49
57
66
64
66
76
90
87
90
100
117
65
3) RCC's mechanical properties [5.2].
The third and last point to consider in calculating RCC pavement thickness relates to the
material’s mechanical properties. The two mechanical properties that determine a pavement’s
structural behavior are rigidity and modulus of rupture:
a) Rigidity determines the behavior of RCC under load and is expressed by the modulus of
elasticity, E (Young’s modulus). For a given stress, the lower the elastic deformation, the more
rigid the material is. For comparison purposes, the average modulus of elasticity for RCC is
about 30 GPa at 28 days of curing (regardless of temperature), whereas the modulus of asphalt
pavement is about 3.3 GPa at 20°C. Moreover, the modulus of elasticity of asphalt varies with
temperature (2 GPa at 40°C; 20 GPa for temperatures below freezing) [5.2]. RCC, therefore,
exhibits elastic behavior and mechanical properties that are relatively independent of
temperature. Asphalt, on the other hand, has viscoelastic behavior and mechanical properties
that vary with temperature.
Relationship (1) defines pavement stiffness [5.2]:
STIFFNESS = EI
(1)
where:
E = Young’s modulus for the material
I = Pavement’s moment of inertia
The distribution of load depends on pavement rigidity. As shown in Figure 5.2, a rigid RCC
pavement distributes loads over a larger area than a flexible pavement of the same thickness.
Consequently, for an RCC pavement there are less vertical stresses and deflections transferred
to the granular base and subgrade. In the case of a flexible pavement, the base of the load
distribution cone is smaller than for a concrete pavement. As a result, greater strains are
transmitted to the granular base in asphalt pavements. However, even if the stresses and
deflections transmitted to an RCC pavement's base are smaller than those for flexible
pavement, the thickness of the base and subbase are nevertheless often governed by frost
protection consideration
Figure 5.2 - Stress distribution
66
b) Modulus of rupture (flexural strength) this property determines the material's capacity to
withstand forces resulting from loads and plays a determining role in calculating pavement
thickness. As shown in Figure 5.3, the top and bottom of an RCC pavement is subject to
tensile or compressive stresses depending on the location at which loading occurs (slab center,
corner, edge or joint). In RCC the ratio of tensile stress to flexural stress (modulus of rupture)
is more critical than the ratio of compressive stress to compressive strength. The ratio of
modulus of rupture to compressive strength ranges from 0.12 to 0.15. Designing slab
thickness, therefore, depends on the tensile stresses induced by loading and on RCC flexural
strength. As stated in Chapter 3, CSA A23.2-8C is used to determine RCC modulus of rupture.
Designing RCC slab thickness depends on the tensile stresses induced by loading and
on RCC flexural strength.
Figure 5.3 - Slab stress depending on location of application
Stresses can also be generated in an RCC pavement by phenomena such as warping, thermal
bowing, erosion, and thermal expansion of joints.
RCC pavement performance depends to a significant degree on the accuracy of the data used to
calculate pavement thickness.
The calculations for determining the thickness of an RCC pavement are primarily
based on three points:
♦
Loading characteristics
♦
Soil characteristics
♦
RCC mechanical properties
67
5.2
Fundamentals of Design Methods
Rigid pavement design methods are primarily based on Westergaard elastic analysis for the
mechanical response of a rigid pavement on subgrade. Westergaard's approach is built on the
assumption that the subgrade soil does not transfer shear stress [5.7].
The design methods for determining the thickness of concrete pavements are based on
experience or, empirical, mechanistic-empirical, or mechanistic approaches [5.7]. The methods
based on experience are more or less formal and rely on observations on the performance of past
projects. The empirical approach also ties pavement performance to heavy traffic loadings but is
based on statistical equations derived from a large number of observations on controlled test
roads. While these methods, such as that of the American Association of State Highway
Transportation Officials (AASHTO), make it possible to take into account the conditions
investigated, they are difficult to adapt to situations that deviate from those used in developing
the method. Mechanistic-empirical methods are based on calculating the pavement structure’s
theoretical response to loading and associating it with a response calculated from observing the
behavior of test roads. The methods proposed by the Cement Association of Canada (CAC) and
the Portland Cement Association (PCA) fall within this category. Lastly, mechanistic methods
are built on performance models based solely on mechanistic functions.
All structural design software can also perform the calculations more or less accurately. The
difficulty lies with soil reaction modeling. When using software not specifically adapted to
pavement thickness design, the designer must ensure that the soil modeling is adequate. While
software created for rigid pavement design have little problems in this regard, they are unable to
deal with all possible situations. In any event, the prime concern is to accurately determine slab
stresses resulting from loading. The stresses and strains within the pavement and transferred to
the subgrade must be within material tolerances [5.7]. The tendency in Quebec is to use
empirical or mechanistic-empirical methods, both of which are described below.
The principle of the mechanistic approach is to set the RCC pavement thickness from the outset.
Stresses at the top and bottom of the pavement (depending on loading) are then calculated for
every category (i) of axial load [5.8]. The maximum number of repetitions (Ni) for each load
category (pavement fatigue capacity) is determined as a function of the ratio between the
concrete’s (σ) stress and modulus of rupture (MR). The percentage of the pavement fatigue
capacity used by each load category in the design period is equal to the ratio of the number of
expected repetitions (ni) and the maximum allowable number of repetitions (Ni) [5.8].
The cumulative damage caused to the pavement by fatigue, Df, is given by Relationship (2),
where j represents the total number of load categories in the design period [5.8]:
D
j
f
=∑
i =1
n
N
i
(2)
i
The cumulative damage at the end of the design period must be less than or equal to 1. If the sum
of the damage is greater than 1, the process must be repeated with a thicker RCC pavement until
D ≤ 1. Table 5.3 provides a simplified example that illustrates how damage is determined for an
68
RCC pavement that is 240 mm in thickness placed on a soil with a modulus of rupture of 4.5
MPa and a modulus of subgrade reaction of 35 MPa/m [5.2].
Table 5.3 Simplified Example for Determining Pavement Fatigue Damage
Axial Load
Expected
Repetitions
(ni)
6310
14 690
30 130
64 380
106 900
(kN)
160
150
138
128
118
σ/MR
0.62
0.58
0.53
0.51
0.48
Allowed
Repetitions
(Ni)
18 000
57 000
240 000
400 000
Unlimited
Sum
Fatigue
(%)
35.1
25.8
12.6
16.1
0
89.6
RCC modulus of rupture significantly affects pavement fatigue performance. Table 5.4 gives the
pavement fatigue percentage when the RCC modulus of rupture (MR) has been reduced by only
10% (based on the data in Table 5.3). The decreased MR increases σ/MR by a factor of about
10%. As indicated in Table 5.3, the pavement's fatigue is 89.6% but increases to 589% when the
MR value is reduced by only 10% (Table 5.4). This represents a 6-fold increase in pavement
fatigue and a consequent 6-fold reduction in pavement fatigue life. To illustrate, if the design
period is 30 years, a 10% reduction in the modulus of rupture will result in a pavement fatigue
life of only 5 years [5.2].
A decrease in RCC modulus of rupture of about 10% can reduce the estimated
pavement fatigue life by a factor of 6.
Table 5.4 Determining Pavement Damage (example from Table 5.3 continued)
σ/MR
0.69
0.64
0.59
0.57
0.53
Allowed Repetitions
(Ni)
2 500
11 000
42 000
75 000
240 000
Sum
Fatigue
(%)
252
134
72
16.1
45
589
Similarly, a reduction in RCC pavement thickness increases slab stresses, thereby shortening the
life of the pavement [5.2]. This behavior is described by Relationship (3) where the maximum
stress σmax is determined at any point in the section at a distance y from the neutral axis:
69
σ
max
=
My
max
I
=
My
⎛
⎞
⎜ bh ⎟
max
3
(3)
⎜ 12 ⎟
⎝
⎠
where:
M:
ymax:
I:
b:
h:
moment of flexion of the section
distance of the slab top or bottom from the neutral axis
moment of inertia of the section
section width
pavement thickness
When ymax is equal to h/2, Relationship (3) makes it possible to rewrite the maximum stress
equation (4) as:
σ
max
=
6M
bh
2
(4)
Relationship (4) shows that the maximum stress σmax is inversely proportional to the square of
slab thickness. For example, a 5% reduction in slab thickness (which would only be 10 mm for a
200-mm slab) would increase the maximum stress σmax and σ/MR by about 10%. As stated
above, this would reduce the pavement design life by a factor of 6 [5.2]. Therefore, our example
clearly demonstrates that a reduction in RCC modulus of rupture is directly related to shorter
pavement design life.
Slab thickness and modulus of rupture are predominant factors in the design life of
RCC pavements. A 10% reduction in modulus of rupture or a 5% decrease in slab
thickness theoretically reduces the fatigue life of an RCC pavement by a factor of 6.
The empirical approach, on the other hand, uses the concept of level of service instead of stress
and strain. Level of service depends on roughness and cracking. Observations of a great number
of experimental sections have shown that level of service can be correlated to heavy-traffic
loading. With the empirical approach, traffic is quantified by the concept of equivalent single
axle load (ESAL). The reduction of level of service that can be attributed to the passage of any
single axle is equivalent to a certain number of repetitions of the reference axle. Figure 5.4
provides the level of service curve according to the number of ESALs [5.2].
70
Figure 5.4 - Level of service as a function of ESALs - (from reference [5.2])
In Quebec, mechanistic-empirical methods are generally used to determine RCC pavement
thickness. The first method available (Thickness Design for Concrete Highway and Street
Pavements, distributed by the Cement Association of Canada or CAC) provides the means for
determining concrete pavement thickness for streets, roads, and highways that will withstand the
various types of vehicle traffic [5.6]. The other method normally used in Quebec (Structural
Design of Roller-Compacted Concrete for Industrial Pavements, distributed by the Portland
Cement Association or PCA) makes it possible to determine the allowable number of wheel
loads for a given RCC pavement thickness [5.9]. This is derived from the design method entitled
Design of Concrete Airport Pavement, edited by PCA [5.10]. The first method applies
specifically to calculating the thickness of concrete pavements for urban and residential areas for
different axle categories, whereas the second serves to calculate the thickness of industrial
pavements based on specific loading.
PCA-MATS software is a third method distributed by PCA. Developed for apron design, this
method can determine the stresses within the concrete to calculate slab thickness. Empirical
methods such as AASHTO use the same principles as for designing flexible pavements are not
often used in Quebec for designing RCC pavements.
5.3
Design Methods
5.3.1 Thickness Design for Concrete Highway and Street Pavements Software
PCAPAV)
Thickness Design for Concrete Highway and Street Pavements (distributed by the Cement
Association of Canada) is a mechanistic-empirical method for calculating concrete pavement
thickness based on data pertaining to traffic comprised of different types of vehicles [5.6]. It
applies especially to undoweled, non-reinforced concrete slabs (the type corresponding to
RCC pavements) as well as doweled slabs. The design method can be used in three different
ways as illustrated in Figure 5.5.
71
Figure 5.5 – Types of procedures using the CAC method
5.3.1.1
Design criteria
This design method is based on two design criteria: erosion and fatigue analyses. The fatigue
criterion makes it possible to maintain the stresses generated by repeated loading within limits so
that the concrete does not fail from fatigue. This criterion depends on the concrete’s flexural
strength (modulus of rupture). Fatigue analysis is based on the stresses at the slab edge between
transversal joints representing critical loading, as illustrated in Figure 5.6. The stresses generated
in the slab by loading are shown in Figure 5.7. The concept of cumulative damage Df, as defined
by Relationship (2), is used in studying fatigue. Cumulative damage at the end of the design
period must be less than or equal to 1 [5.8].
Figure 5.6 - Critical flexural stress loading (fatigue analysis)
72
Figure 5.7 - Stresses generated in the slab
The second criterion of the Thickness Design for Concrete Highway and Street Pavements
design method is erosion analysis [5.2]. This criterion limits the erosion of materials underlying
the pavement caused by deflections resulting from repeated loading along edges and joints
(pumping). It can also control faulting at joints and deterioration of shoulders. Critical deflection
occurs at the slab corner when the load is applied near the joint as depicted in Figure 5.8.
Figure 5.8 - Loading for critical deflections (erosion analysis)
The cumulative damage equation for erosion analysis De is defined by Relationship (5) where
C = 0.06 for a pavement without shoulders and 0.94 with a shoulder. Cumulative erosion damage
at the end of the design period must be less than or equal to 1 [5.8].
Cn
De = ∑ i
j
i =1
N
(5)
i
This method determines pavement thickness by analyzing both the erosion and fatigue criterion.
The governing criteria depends on traffic type. If the RCC pavement is subject to light traffic
(municipal residential street), fatigue analysis is generally the guiding factor. On other hand,
73
erosion analysis dominates when the traffic is moderate, such as an RCC pavement for an
industrial application or for an urban road.
Aggregate interlock ensures load transfer between pavement joints. Load transfer at joints is
more effective in RCC slabs than conventional concrete without dowels because of RCC’s
aggregate gradation and higher coarse aggregate content [5.11].
5.3.1.2
Design factors
The calculation of the thickness of an RCC pavement with the Thickness Design for Concrete
Highway and Street Pavements design method is governed by four factors: concrete modulus of
rupture, modulus of subgrade reaction (or subgrade-base), loading, and design period [5.6].
1) RCC flexural strength (modulus of rupture) is determined according to CSA A23.2-8C. The
value of the modulus of rupture at 28 days can be used in calculating pavement thickness
[5.6]. On the other hand, it is also important to take into account that pavements are often put
into service very soon after construction, that is, after only several days. The age of the
modulus of rupture for use in calculating pavement thickness must be taken into account in
order to ensure that the RCC’s flexural strength is adequate to withstand initial traffic loads.
2) The modulus of subgrade reaction or the equivalent modulus of reaction (combined subgrade
and subbase) is generally determined from Tables 5.1 and 5.2, respectively. The minimum
design life for an RCC pavement is normally from 20 to 40 years.
3) The number of vehicles and axle loads during the design period are prime parameters in
pavement thickness design. They are estimated from [5.6]:
1.
AADT, which is the 24-hour two-way vehicle count.
2.
AADTT, which is the 24-hour two-way truck count.
3.
Truck axle load
AADT values are taken from current traffic surveys. The AADT design value can be
estimated based on projection factors similar to those given in Table 5.5 [5.6].
74
Table 5.5
Annual Traffic Growth Rate and Corresponding Projection Factors
Annual Traffic Growth Rate
(%)
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Projection Factors for a
Design Life of 20 Years
1.1
1.2
1.2
1.3
1.3
1.4
1.5
1.6
1.6
1.7
1.8
Projection Factors for a
Design Life of 40 Years
1.2
1.3
1.5
1.6
1.8
2.0
2.2
2.4
2.7
2.9
3.2
For a given annual traffic growth rate, the AADT is multiplied by the projection factor
corresponding to the design period in order to obtain the design AADT (average over the design
period). The safety factors (SF) applied to the loads are as follows [5.6]:
1.
1.2 for interprovincial highways or any other project with a high volume of heavy
traffic.
2.
1.1 for roads and residential thoroughfares with a moderate volume of heavy traffic.
3.
1.0 for secondary roads and residential streets with a low volume of heavy traffic.
Figures 5.9 a), b), and c) illustrate RCC pavement thickness design using PCA-PAV software.
The computation was carried out taking into consideration the predetermined axle loads. The
data listed below are used in the example.
1. Modulus of reaction: 30 MPa/m (110 PCI)
2. RCC 7-d modulus of rupture: 5.0 MPa (725 psi)
3. Axle load category: high
4. Average number of trucks per day, ADTT: 100
5. Design period: 50 years
6. Joint load transfer: aggregate interlock (undoweled joints)
7. Safety factor: 1.2
75
Figure 5.9 a) - PCAPAV software
Figure 5.9 b) - PCAPAV software
Figure 5.9 c) - PCAPAV software
As shown in Figure 5.9 c), a pavement thickness of 180 mm (7”) complies with erosion and
fatigue criteria.
76
It should be noted, this design procedure has certain limitations. The minimum and maximum
pavement thicknesses are 100 mm and 350 mm, respectively, and the modulus of subgrade
reaction must fall between 15 and 200 MPa/m [5.11].
5.3.2 Design Using Concrete Airport Pavement Software
This design procedure, distributed by PCA, provides the means for using pavement thickness to
determine the tensile stress at the bottom of the pavement caused by a given interior axle load
[5.10]. The number of allowable repetitions depends on the ratio of the tensile stress to the
concrete’s modulus of rupture, σ/MR. Unlike the preceding method, this procedure only uses the
fatigue criterion in computing pavement thickness. AIRPORT, the computerized version of the
procedure, distributed by PCA, can be used for pavement thickness design. It has been adapted
for determining RCC pavement thickness and is described in an information bulletin entitled
Structural Design of Roller-Compacted Concrete for Industrial Pavements [5.9].
This method consists in computing the stress at the bottom of the pavement under a circular load
with a radius a (mm) [5.8]. This calculation can be stated as Relationship (6):
σ
i
=
⎤
0.316 P ⎡
⎛1⎞
⎢4 log⎜ b ⎟ + 1.069⎥
2
⎦
h ⎣ ⎝ ⎠
(6)
where:
P:
h:
l:
b:
b:
Load (N)
Pavement thickness in mm
Radius of relative stiffness in mm
a if a ≥ 1.724h in mm
2 2
1.6a + h -0.675h if a < 1.724h in mm
The radius of relative stiffness of the pavement and soil is defined by Relationship (7):
⎡ Eh 3
⎤
l=
10 6
×
⎢ 12 ( 1 − v ) k
⎥
⎣
⎦
0.25
2
(7)
where:
E:
v:
k:
RCC modulus of elasticity in GPa
Poisson’s ratio for the RCC (0.15)
Modulus of subgrade reaction in MPa/m
77
In the case of tandem wheel loads, the value of the radius, a, is calculated in mm with
Equation (8):
a=
(
)
(1 / 2 )
P
0.8521P S
+
qπ
π 0.5227 q
(8)
where:
P:
q:
S:
Load (N)
Tire pressure in MPa
Center-to-center tire spacing in mm
5.3.2.1
Design factors
Four factors govern RCC pavement thickness [5.9]:
1. Supporting strength of the subgrade or subbase-subgrade combination (equivalent
modulus of reaction)
2. Flexural strength of RCC
3. Modulus of elasticity of RCC
4. Vehicle characteristics
•
Wheel loads
•
Wheel spacing
•
Tire characteristics (tire pressure)
•
Number of load repetitions expected during the design life of the pavement
As with the preceding method, the equivalent modulus of reaction (subbase-subgrade
combination) is generally determined from Tables 5.1 and 5.2, respectively. RCC flexural
strength or modulus of rupture is established according to CSA A23.2-8C. The value for the
modulus of rupture used in the computations must correspond to the time when the pavement
will be put into service. This generally corresponds to the measurement taken 7 days after initial
water-binder contact. On the other hand, RCC modulus of elasticity has little impact on the
calculation of pavement thickness. The 28-days modulus of elasticity is normally used.
Normally, calculations are carried out with the maximum axle load to ensure proper pavement
thickness. However, the maximum axle load (including vehicle weight) is not necessarily equal
between each axle. For example, in case of a vehicle close to tipping over, the front axle of a
two-axle vehicle is considered to be supporting most of the load. In such cases the actual front
axle load shall be divided by the load contact area for the front wheels. The load contact area (in
mm2) is the area of slab in contact of each tire carrying the maximum wheel load. It may be
estimated by dividing the wheel load in Newtons (N) by the tire inflation pressure (in MPa).
78
Wheel and axle spacings influence the stress transferred to the pavement. If the tire spacing is
less than 3 times the radius of relative stiffness, l (Equation 7), the effect of more than one wheel
load must be considered in computing pavement stress.
The following is an example using AIRPORT design software to calculate the thickness of an
industrial RCC pavement subjected to load cycles by a Volvo 120 wheel loader. The minimum
thickness design was calculated for an unlimited number of cycles. The maximum wheel is
129 700 N. The tire inflation pressure is 0.414 MPa; wheel spacing is 2 060 mm. The RCC has a
modulus of rupture of 5.5 MPa and a modulus of elasticity of 33 GPa. The modulus of subgrade
reaction is 40 MPa/m. Figures 5.10 a), b), and c) are screenshots of the computations using
AIRPORT software. The pavement thickness for this example is 210 mm, which is the minimum
pavement thickness for unlimited load repetitions. Table 5.6 presents the computations for
different pavement thicknesses for the stresses in the pavement bottom, the stress ratio, and the
number of repetitions.
Figure 5.10 a) - AIRPORT design software
Figure 5.10 b) - AIRPORT design software
79
Figure 5.10 c) - AIRPORT design software
Table 5.6 Computation Results for Different Pavement Thicknesses
Pavement Thickness
(mm)
175
200
225
210
Stress at the Bottom
of the Pavement
(MPa)
3.5
2.9
2.5
2.745
Stress to RCC
Modulus of Rupture
Ratio
0.64
0.54
0.45
0.49
Number of
Repetitions
9 437
201 609
Unlimited
Unlimited
As shown in Figure 5.10 a), the number of allowable repetitions was determined using
Calculation Option 1 (Concrete) and not Option 2 (Roller Compacted Concrete). With Option 1,
an unlimited number of repetitions for a given vehicle type is allowable if the stress ratio, that is,
the ratio of the tensile stress in the bottom of the pavement to the concrete’s modulus of rupture
is less than 0.50. This option was selected in this example, because RCC mixes optimized with
the latest design methods deliver outstanding mechanical properties.
Figure 5.10 c) shows an unlimited number of repetitions for the wheel loader when the pavement
thickness is 210 mm. The stress to modulus of rupture ratio is less than 0.50. Moreover, as
shown in Table 5.6, the number of repetitions is about 200 000 for a pavement thickness of
200 mm. The ratio of stress to modulus of rupture is 0.54.
5.3.2.2
Factors affecting stress
For a given loading condition, certain factors influence the stress intensity at the bottom of the
slab: modulus of subgrade reaction, pavement thickness, and RCC modulus of elasticity (see
Figures 5.11, 5.12, and 5.13, respectively). The data from the preceding example have been used
to illustrate how these factors affect stress. The stress calculations were carried out with
Equation (6).
80
As shown in Figure 5.11, for a given pavement thickness, the stress at the bottom of the slab
decreases as the modulus of subgrade reaction increases. Therefore, more forces are transferred
to the base when the modulus of subgrade reaction increases for a given thickness. On the other
hand, the modulus of subgrade reaction has less influence as the pavement thickness increases.
When the modulus of subgrade reaction increases from 20 to 120 MPa/m, stress in a 150-mm
slab drops by nearly 40%, whereas stress in a 300-mm slab decreases only by about 20%.
6.0
h = 150 mm
h = 200 mm
5.0
Stress (MPa)
h = 250 mm
4.0
h = 300 mm
3.0
2.0
1.0
0.0
10
30
50
70
90
110
130
Modulus of Subgrade Reaction (MPa/m)
Figure 5.11 - Influence of modulus of subgrade reaction on stress for different pavement
thicknesses
As shown in figure 5.12, the stress at the bottom of the slab decreases as RCC pavement
thickness increases for moduli of subgrade reaction of 20, 60, and 120 MPa/m. A 25% increase
in pavement thickness (175 to 200 mm) corresponds to a 20% (0.8 MPa) decrease in stress with a
modulus of subgrade reaction of 20 MPa/m, about 18% (0.6 MPa) with a modulus of subgrade
reaction of 60 MPa/m, and about 17% (0.5 MPa) with a modulus of subgrade reaction of
120 MPa/m. Furthermore, it is clear that the effect of the modulus of subgrade reaction on stress
is inversely proportional to pavement thickness. It should also be noted that variations in the
modulus of subgrade reaction of about 10 MPa have very little effect on stress, regardless of
pavement thickness.
81
6.00
k = 20 MPa/m
Stress (MPa)
5.00
k = 60 MPa/m
k = 120 MPa/m
4.00
3.00
2.00
1.00
0.00
125
175
225
Pavement Thickness (mm)
275
325
Figure 5.12 - Influence of pavement thickness on stress for different moduli of subgrade reaction
Unlike modulus of subgrade reaction and pavement thickness, RCC modulus of elasticity has
little influence on stress at the bottom of an RCC slab. Figure 5.13 depicts the relationship
between stress and modulus of elasticity for a 225-mm slab supported by a soil with a modulus
of subgrade reaction of 40 MPa/m. The graph shows that stress increases proportionally with
RCC rigidity (modulus of elasticity). However, the stress increase is only about 4%, while the
modulus of elasticity rises from 28 to 36 GPa.
2.50
k = 40 MPa/m and h = 225 mm
Stress (MPa)
2.48
2.46
2.44
2.42
2.40
2.38
26
28
30
32
34
36
38
Young's Modulus (GPa)
Figure 5.13 - Influence of modulus of elasticity on stress for a modulus of subgrade reaction of
40 MPa/m and slab thickness of 225 mm
82
REFERENCES
[5.1]
ACI COMMITTEE 325.10R-95 “State-of-the-Art Report on Roller-Compacted Concrete
Pavements, Manual of Concrete Practice,” American Concrete Institute, 1995, 32 p.
[5.2]
SAUCIER, F., CORMIER, B., and DUCHESNE, C. Introduction au dimensionnement et
à la construction des chaussées en béton de ciment, Continuing training, Centre de
recherche interuniversitaire sur le béton, Département de génie civil, Université Laval,
1995, multiple pagination.
[5.3]
Cement Association of Canada, Infrastructure et fondations de chaussées en béton, IS
029-02P(F), 1989, 24 p.
[5.4]
TESSIER, G., R. Guide de construction et d’entretien des chaussées, Association
québécoise du transport et des routes, 1990, 394 p.
[5.5]
MIDDLEBROOKS, T. A. and BERTRAM, G. E. Soil Tests for Design of Runway
Pavements, H.R.B. Proceedings of the 22nd Annual Meeting, 1942, vol. 22, p. 152.
[5.6]
Cement Association of Canada, Thickness Design for Concrete Highway and Street
Pavements, Engineering Bulletin, EB209.03P, 48 p.
[5.7]
DORÉ, G. Conception et gestion des chaussées (course notes), Département de génie
civil, Université Laval, 2000, multiple pagination.
[5.8]
HUANG, Y., H. Pavement Analysis and Design, Prentice Hall, 1993, pp. 608-610.
[5.9]
Portland Cement Association, Structural Design of Roller-Compacted Concrete for
Industrial Pavements, IS233.01, 1987, 8 p.
[5.10] PACKARD, R. G. Design of Concrete Airport Pavement, Portland Cement Association,
1973, 61 p.
[5.11] GAUTHIER, P., MARCHAND, J., BOISVERT, L., OUELLET, E., and PIGEON, M.
au rouleau, Continuing training GCI-A2455, Centre de recherche interuniversitaire sur le
83
Chapter 6 – Construction of RCC Pavements
6
General
RCC pavements are usually built with the same equipment used for asphalt pavements, which is,
in most cases, is well suited for the task. High-density compaction equipment is sometimes
required for specific applications.
RCC pavement placement involves a number of steps: preparation of the subgrade and base;
RCC production, transportation, placement and compaction; jointing, and curing. Precautions
must be taken, from production to curing, to avoid (or at least reduce) concrete segregation and
moisture loss.
A paving pattern must be developed before work begins to define the placement sequence
(direction of paving equipment; length and width of lifts), location of construction joints, and
location of the RCC production plant. The plan makes it possible to ensure continuous
placement, meet placement schedules, and minimize cold joints.
6.1
Subgrade and Subbase Preparation
Subgrade and granular subbase preparation for RCC pavements must comply with the same
requirements as pavements made with conventional concrete. The bearing capacity of the
subgrade and subbase must allow for the adequate compaction of every RCC lift placed. Both the
subgrade and granular subbase must have adequate drainage.
The profile of the granular material after grading and compacting operations should not vary
more than 10 mm in 3 meters with respect to final profile. The granular subbase must be
compacted to at least 95% of the optimal Modified Proctor Density as per CAN/BNQ 2501-255.
RCC is highly sensitive to granular subbase moisture content. The bottom part of an RCC
pavement is subjected to the greatest flexural stresses. Excess water contributed by the pavement
foundation will locally increase the water-cement ratio (water-cementing materials ratio),
thereby lowering the RCC’s mechanical strength in this critical area. Consequently, areas of
excess moisture must be excavated and replaced with new granular material. If this cannot be
done, the situation must be controlled with adequate drainage.
Since RCC is highly sensitive to excess moisture from the granular base, areas of
excessive moisture must be excavated and replaced with new granular material. If this
cannot be done, the situation must be controlled with adequate drainage.
The granular subbase should be dampened prior to placement of the RCC pavement.
84
6.2
RCC Production
6.2.1
General
RCC must be mixed with enough energy to effectively distribute the low quantity of mixing
water and cement throughout the mixture in order to achieve a homogeneous and uniform
mixture. The mixing plant must also be reliable to prevent downtime (increased production
costs) and be equipped with an accurate dosage system for the mix constituents. The mixing unit
must have a high production rate to ensure uninterrupted RCC placement [6.1].
Central batch plants or mobile mixers are used to produce RCC.
Stationary central batch plants or mobile mixers are used to produce RCC. Proximity and
availability of production plants, the volume of concrete to be placed, rate of placement and
budget are factors in selecting a central mixer.
6.2.2
Central Batch Plants
Central batch plants for ready-mix conventional concrete are used in Quebec to produce RCC.
In-situ RCC quality depends to the care taken during production, which is why RCC production
must be closely monitored. Dry-batch stationary central mixers (ready mix concrete truck) must
not be used to produce RCC.
Certain aspects of production must be handled carefully in order to ensure that RCC produced in
a central mix plant is homogeneous and uniform. First of all, because of the high mechanical
stresses to which the mixer is subjected, it is recommended to reduce batch volume to about 50%
of the mixer's rated maximum capacity, which will yield greater mixture homogeneity. In
addition, it will reduce the risk of mechanical breakdown and the resulting production downtime.
Furthermore, RCC requires longer mixing time than conventional concrete. Typically RCC
mixed in this method takes an additional 3 min per batch compared to conventional concrete
(double the normal mixing time). This type of mixer generally produces from 35 to 60 m3/h of
RCC. It is strongly recommended to clean the mixer every 100 m3 during production and at the
end of every production day because of build up of material on the mixing paddles. When
loading trucks the height that fresh RCC is allowed to fall should be kept to a minimum in order
to prevent segregation. Table 6.1 compares production of a conventional concrete and RCC
using a 7.6- m3 capacity Besser mixer [6.1].
Table 6.1 - Production of a 7.6-m3 Capacity Besser mixer(from reference [6.1])
Production Type
Conventional concrete
RCC
Volume of Concrete per Batch
(m3)
7.5
4.5
Production Rate
(m3/h)
140
60
85
Choice of the type of RCC production plant is based on a variety of criteria. Besides economic
considerations and equipment availability, RCC transportation time must be carefully evaluated
taking into account traffic and other possible delays to ensure placement schedules can be met.
Stationary central mix plants must comply with CAN/CSA A23.1 and should have a conformity
certificate issued by the Bureau de normalisation du Québec (BNQ) according to the
requirements of NQ 2621-900. This type of mixing process has a high precision for materials
dosage.
6.2.3
Mobile Central Mixer (Pugmill)
Many medium and large-scale RCC projects in Quebec have been carried out in recent years
with mobile central mixers (pugmills). Figure 6.1 shows mixer schematic; Figure 6.2 is a
photograph of a pugmill. This type of mixer is constantly supplied with raw materials for
continuous production and is equipped with a metering system for volumetric and mass
proportioning.
Figure 6.1 - Schematic of a mobile central mixer (pugmill)
86
Figure 6.2 - Photograph of a mobile central mixer (pugmill) - (from reference [6.2])
Aggregates are stockpiled directly at the site. Precautions are taken to prevent segregation. Front
end loaders provide a continuous supply of aggregates to the hoppers, taking care to avoid
contamination. Aggregates are fed by conveyor to the mixer. The cement is measured at the silo
and either fed directly into the mixer or onto the aggregate conveyor before it discharges into the
mixer. The mixing water and admixtures are added to the dry ingredients at the mixer. The
ingredients are mixed with twin high speed parallel shafts as shown in Figure 6.3.
Figure 6.3 - Schematic of Twin High Speed shaft layout (from reference [6.2])
Experience has shown that fresh RCC tends to accumulate between the blades, thereby reducing
mixer efficiency. The mixing shafts should therefore be cleaned at mid day and at the end of the
work day in order to ensure that the mixer produces consistent quality RCC batches and
minimizes segregation. Figure 6.4 shows the mixing shafts before and after cleaning.
87
(a) Before cleaning
(b) After cleaning
Figure 6.4 - Mixing shafts (from reference [6.2])
The fresh RCC is conveyed to a discharge hopper. This hopper should have a minimum capacity
of 1 t (about 0.4 m3) to provide temporary storage of the RCC awaiting loading into dump trucks
[6.1]. The timed discharge of the hopper prevents free fall of RCC thereby reducing segregation.
Field production of RCC with a pugmill offers a number of advantages, such as rapid
mobilization, reduced transportation time for fresh concrete (located on site), high production
(+100 m3/h), and an efficient mixing system. This type of mixer is generally economically
feasible for projects involving at least 500 m3 of RCC.
Improper transportation of pugmill plant usually translates into major damage that is costly in
terms of time and money. When moving these types of plants the weighing equipment installed
on the proportioning and feed systems, such as the load cells, must be protected against shock
because they can significantly affect accuracy. It is strongly recommended to remove load cells
from the proportioning system before transporting the unit. The mixer must be installed on stable
ground to eliminate any risk of the storage silos turning over (such as the cement silo) and to
minimize vibrations that can affect the proportioning system during calibration and production.
The proportioning and feed systems are the mixer’s main components. They must be regularly
supplied with adequate amounts of the various ingredients in order to yield a uniform and
homogeneous final product. The system for each ingredient must be independent and
autonomous. Furthermore, the control panel must provide for accurate and easy proportioning of
cement, water, admixtures, coarse and fine aggregates.
Ingredient proportioning must comply with production tolerances, which can vary from one
organization to the next. For example, the US Army Corps of Engineers, the Canadian Standards
Association (CSA), and the City of Montreal’s standardized technical specifications for rollercompacted concrete all specify different production tolerances. Table 6.2 gives the recommended
production tolerances by mass. ASTM C685 provides production tolerances by volume.
88
Table 6.2 - Recommended Production Tolerances by Mass
Ingredients
Cement
Water
Admixture (individually)
Aggregate (individually)
Tolerances by Mass
(%)
±2
±3
±3
±2
Calibration of the dosage systems must be carried out with a calibration system independent of
the pugmill internal systems and at the production rate the pugmill is expected to operate at.
Calibration must be performed before work starts and whenever the mixer is moved. It should
also be carried out periodically during production and at the end of the production day. The
volume of RCC produced must also be checked by comparing the amount of RCC placed against
the quantity of materials delivered (cement, coarse and fine aggregates).
6.3
Transporting RCC
RCC is transported from the mixing plant to the job site in dump trucks. The truck box must be
clean and dry. The truck must also be equipped with tarps to reduce water evaporation due to
sun and wind. An evaporation retarder can also be sprayed directly onto the RCC in the truck
body. There must be a sufficient number of trucks to ensure continuous feed of RCC to the
paving equipment.
Every precaution must be taken to prevent RCC segregation when loading the trucks. The
concrete must be discharged into the truck uniformly throughout the entire length of the truck
box: one-third at the front, one-third at the center, and one-third at the back. Care should also be
taken to prevent segregation when discharging the RCC into the paver hopper.
For adequate placement, the transportation time from the mixing plant to discharge into the paver
hopper must be kept to a minimum. As shown in Figure 3.3 in Chapter 3, fresh RCC workability
decreases with time (the Vebe time increases). As a result, transportation time is generally kept
to no more than 45 min, measured from the initial water-binder contact to discharge into the
paver hopper. The transportation time should be further reduced if the ambient temperature is
27°C or greater.
Generally, RCC transportation time, from initial water – cement contact to placement,
is limited to 45 min. The transportation time should be further reduced if the ambient
temperature is 27°C or greater.
89
6.4
RCC Placement
6.4.1
General
RCC is normally placed with a conventional asphalt paver or a high-density paver. The paver
must be able to place RCC to at least 80% of the reference wet density across the entire paving
width before rolling operation. Field experience has demonstrated that, depending on the type of
paver, there is a 10% to 25% difference between the thickness of the RCC layer placed by the
paver and its thickness once compacted with a tandem wheel roller with smooth metal drums.
The pavers shall have enough RCC paving capacity to place at least 1.5 times the mixer's
nominal production capacity. Any equipment that is defective or breaks down must be replaced
so as to not slow down placement operations.
Regardless of the equipment used, it must not deconsolidate the granular base or damage an
underlying compacted RCC lift. Care must also be taken to prevent RCC segregation once the
lift has been placed. This means that the paver hopper should never be completely emptied,
neither should the sides of the hopper ever be raised. The RCC must always cover the feed auger
shaft (a 100-mm layer of RCC must be kept in the hopper at all times [6.3]). Fresh RCC
(material passing 5 mm sieve) must be added to any segregation areas and recompacted to
correct surface defects.
RCC placement operations must meet surface uniformity and lift thickness requirements. The
pavers must be equipped with a system to ensure that the pavement is true to grade. String lines
along the sides of the RCC strip can help in maintaining grade. String lines are required on both
sides when placing the first strip, while a single line is required for subsequent strips. Electronic
grade controls are routinely used. The paver must maintain constant speed and minimize stops in
order to prevent undulation of the pavement surface. A constant hopper discharge rate can
eliminate this problem.
Paver speed affects the degree of compaction [6.4]. No reduction in compaction has been
observed at speeds ranging from 2.2 to 3.7 m/min or 0.13 to 0.22 km/h. In contrast, the degree of
compaction of RCC as it comes out of the paver can be reduced by about 8% of the reference
wet density when the paver travels at a speed of about 5.5 m/min (0.33 km/h). The degree of
compaction across the width of the spreader must be at times at least 80% of the reference wet
density before rolling operations.
It is essential that the RCC be placed continuously to avoid horizontal and vertical cold joints
and to promote bonding between adjacent strips and/or lifts. The maximum interval between
placement of two adjacent strips or two successive lifts is 90 min from the initial water-cement
contact. All the surfaces must be maintained continuously moist. This interval should be reduced
if the ambient temperature is 27°C or higher.
The purpose of the interval is to maintain the workability needed for monolithic joints between
strips and lifts. Optimizing strip width and, more importantly, length is the key to maintaining
the interval. Using at least two pavers in staggered formation makes it possible to reduce the
interval between two adjacent strips. In such cases, RCC production must be adequate to supply
90
all the pavers. At all times the entire RCC surface must be maintained moist by fog spraying to
ensure proper bonding.
The maximum interval between placing two adjacent strips or two successive lifts is
90 min from the initial water-cement contact.
All exposed surfaces of the RCC pavement must be kept moist until final curing. Fog spraying
and/or applying an evaporation retarder is an economical and effective technique and won’t wash
fines and paste from the surface. The edges of each lift, as well as, the pavement surface shall be
kept moist until covered with a second lift of RCC or until the curing agent is applied. It is
mandatory to designate a specific work crew at the outset to be responsible for these operations.
The RCC must be kept moist by fog spraying and/or applying an evaporation retarder
until final curing.
Before beginning of work a detailed RCC paving plan must be developed in order to
maximize RCC placement operations. The plan shall be used to check compliance with
placement and compaction intervals. This procedure limits the number of cold joints, which
enhances bonding between adjacent strips. The plan must also include the placement sequence,
which means paver direction and the length and width of strips. If a pugmill plant is used, the
paving plan can be useful in determining its location and the amount of materials needed for the
daily production.
6.4.2
Equipment
6.4.2.1
Conventional asphalt paver
As a general rule, conventional pavers such as the one illustrated in Figure 6.5 can be used to
place RCC. The degree of compaction of RCC after placement by the paver must be at least 80%
of the reference wet density. The use of track-type pavers is highly recommended.
Figure 6.5 - Conventional asphalt paver (from reference [6.2])
91
The width of a conventional asphalt paver's paving table is very important. In the case of pavers
equipped with a vibrating extension, the strip width should be limited to 4.3 m. Non-vibrating
extensions shall be kept retracted at all times due to the high potential for segregation (see Figure
6.6).
With vibrating extension
Without vibrating extension
Figure 6.6 - Conventional asphalt paver with and without vibrating extensions –
As shown in Figure 6.7, a low-compaction asphalt paver used to place RCC leaves significant
segregation and a very open textured surface.
Figure 6.7 - Conventional asphalt paver with low compaction capability - (from reference [6.5])
92
6.4.2.2 High-density paver
High-density pavers (Figures 6.8 and 6.9) with dual tampers and a vibrating system can deliver
greater initial compaction than conventional asphalt pavers; greater compaction capacity also
increases the rate of placement. Allgemeine Baumaschinen-Gesellschaft (ABG), a German firm,
manufactures this type of equipment. Other examples are illustrated in Figure 6.10.
Figure 6.8 - High-density paver (from reference [6.2])
Figure 6.9 - Texture of RCC placed with a high-density paver (from reference [6.2])
93
(a)
(b)
Figure 6.10 - (a) Another type of high-density paver and (b) a high-density paver with built-in
edger (from reference [6.1])
6.5
Compacting RCC
6.5.1
General
The degree of compaction of fresh RCC affects its hardened properties. Flexural strength is
especially affected by compaction which determines its capacity to withstand loading (note:
concrete is stronger in compression than tension). As shown in Figure 6.11, the bottom of the
pavement is subjected to tensile or compressive stress, depending on where the load is applied.
Adequate resistance to tensile stress at the bottom of the pavement (Figure 6.11, a) requires that
the RCC be compacted to 100% of the reference wet density throughout its entire depth which
means all the way to the bottom of the pavement.
Figure 6.11 - Stress distribution in the center of the pavement depending on location of
application
Once placed, the RCC must achieve 100% compaction with respect to the reference wet density.
In practice, in-place density is deemed acceptable if average of all measurements exceed 99%,
94
with no individual measurement less than 98%. Density is determined in place with a nuclear
density gauge.
Compaction operations must begin within a maximum of 10 min after RCC placement. Fresh
RCC must be compacted within a maximum of 60 min from time of mixing in the central plant. .
Compaction operations must begin within a maximum of 10 min from placement.
Fresh RCC must be compacted within a maximum of 60 min from the initial watercement contact.
6.5.2
Typical Compaction Equipment and Operation Sequencing
Vibratory rollers with a total static weight over 9.5 t and equipped with two smooth metal drums
(see Figure 6.12) are used to compact RCC. The drums must have a diameter between 1.3 m to
1.4 m, a minimum width of 1.7 m and be equipped for both static and dynamic operation. They
must also be able to generate a dynamic force of at least 450 N/cm at variable frequencies and
have a minimum amplitude of 0.75 mm. The drum wipers must be properly adjusted to remove
any particles that may adhere to the drum surface, otherwise each drum revolution will damage
the RCC surface. The drums must be kept dry during compaction operations.
There must be enough of these rollers to handle concrete at a minimum of 1.5 times the mixer's
nominal production capacity. Any equipment that is defective or breaks down must be replaced
so as to not slow down operations.
Figure 6.12 - Vibratory roller with two smooth metal drums (from reference [6.5])
A typical compaction sequence must compact the RCC to 100% of the reference wet density
with a minimum number of roller passes. In nearly all projects, the sequence consists in carrying
out the first 2 passes (back and forth) with a roller with two smooth metal drums operating in
static mode, followed by 4 vibratory passes. It must be pointed out that excessive vibratory
rolling can deconsolidate the compacted surface. When making vibratory passes, the vibrators
must be shut down 2 m before the roller is stopped to prevent making a depression in the
pavement. Changes in direction with tandem rollers must be done far away from the paver on
previously compacted fresh RCC as shown in Figure 6.13 [6.6]. In-place density measurements
taken with a nuclear density gauge after a certain number of passes provide the information
needed to determine the optimal compaction rolling pattern.
95
Figure 6.13 - Changing direction when using tandem rollers (from reference [6.6])
Compaction operations must begin near the edges and follow the directions as given in Section
6.6 (Construction Techniques). Sloped surfaces must be compacted starting from the bottom of
the slope. The maximum roller speed must not exceed 2.5 km/h. Roller passes must overlap by
500 mm. Compaction of the adjacent strips must be carried out so as to ensure proper bonding.
Surface finishing (closing voids and cracks) involves a pneumatic-tired roller (1 t per wheel) or a
5 to 10 t tandem roller with smooth metal drums operating in static mode. Combination rollers
(pneumatic tires and smooth metal drums) are also suitable for surface finishing. Portable
compaction equipment can be used to compact RCC locally around manholes and other surfaces.
Past experience with RCC pavement projects makes it possible to judge if the workability is
adequate by observing how the RCC reacts to static passes of the tandem roller with smooth
metal drums. An RCC with the appropriate workability will deform uniformly when the roller
passes over it. When workability is too high the RCC surface will appear shiny and pasty and the
surface will be spongy when the roller passes over it or even due to foot pressure. In contrast,
inadequate workability will produce a dusty surface under roller pressure and the RCC layer will
not depress. As a result, it will be difficult to compact to the full depth of the lift. Minor
adjustments in mixing water can generally correct the problem if the mix is properly designed.
Whenever workability is inadequate, the RCC must be excavated and discarded before placing
and compacting new fresh RCC.
If the pavement design requires two lifts, they should be placed to form a monolithic bond so that
the stresses are transferred to the total pavement thickness and not to two independent sections.
This can be achieved by adhering to placement and compaction schedules and by keeping the
interface surface moist. Both lifts must have the same thickness, with the bond coinciding with
the neutral axis of stresses (see Figure 6.14). As a result, no tensile or compressive stresses will
occur at the bond interface, although shear stress will be at its maximum.
Figure 6.14 - Stress diagram for a two-lift pavement
96
6.6 Construction Techniques
6.6.1
Compaction of the First Strip
As shown in Figure 6.15, the first strip is compacted with two passes with a tandem roller with
smooth metal drums operating in static mode, starting from the outside edge. This will leave the
compacted width 25 to 50 mm lower than the uncompacted RCC [6.1, 6.3]. The next two passes
are made between 300 to 450 mm from the inside edge. This uncompacted strip is used to adjust
the paver height for placing the adjacent strip of RCC. The remainder of the strip is then
compacted with two passes in static mode. Subsequent roller passes are in vibratory mode. All
passes should overlap by 500 mm. The fresh RCC must be compacted within a maximum of 60
min after the initial water-binder contact.
Figure 6.15 - Rolling the first course (from references [6.1 and 6.3])
6.6.2
Rolling a Vertical Fresh Joint
A vertical joint between two strips of RCC can be considered fresh if less than 90 min (measured
from the initial water-binder contact) have elapsed between the placement of one strip and the
batching of the concrete for the adjacent strip course. As shown in Figure 6.16, the first two
roller passes are made in static mode along the inside edge, leaving a strip of uncompacted RCC
300 to 450 mm wide [6.1, 6.3]. Then, the fresh joint is compacted with two passes in static mode,
overlapping the joint by 300 mm. The uncompacted strip is used to adjust the paver height for
placing the adjacent strip of RCC. The remainder of the strip is then compacted with two passes
97
in static mode. Subsequent roller passes are in vibratory mode. The fresh RCC must be
compacted within a maximum of 60 min after the initial water-binder contact.
Figure 6.16 - Rolling a Vertical Fresh Joint (from references [6.1 and 6.3])
6.6.3
Rolling a Longitudinal Vertical Cold Joint
A vertical joint between two strips of RCC can be considered cold if more than 90 min
(measured from the initial water-binder contact) have elapsed between the placement of one strip
and the batching of the concrete for the adjacent strip. As shown in Figure 6.17, the rolling
begins along the outside edge, leaving the compacted width 25 to 50 mm lower than the
uncompacted RCC. Once compaction operations have been completed, the edge is trimmed with
a saw to the full depth of the strip and at least 300 mm from the edge [6.1, 6.3]. Before a new
strip of RCC can be placed, the vertical surface must be cleaned with air or water jets.
Immediately before paving resumes, a binding grout with a water-binder ratio of 0.35 must be
applied to the sawn face. The adjacent course is placed so as to overlap the hardened RCC by
about 75 mm. The excess fresh RCC is pushed back onto the new strip forming a slight hump.
The fresh joint is then rolled longitudinally with two passes in static mode that overlap the fresh
RCC by 300 mm.
98
Figure 6.17 - Rolling a vertical longitudinal cold joint (from references [6.1 and 6.3])
99
6.6.4
Rolling a Transverse Vertical Cold Joint
A transverse vertical joint between two strips of RCC can be considered cold if more than 90
min (measured from the initial water-binder contact) have elapsed between the placement of one
strip and the batching of the concrete for the adjacent strip. As shown in Figure 6.18, the end of
the strip is rolled and a section between 300 to 450 mm in width is removed [6.1, 6.3]. Before a
new strip of RCC can be placed, the vertical surface must be cleaned with air or water jets.
Immediately before paving resumes, a binding grout with a water-binder ratio of 0.35 must be
applied to the sawn face. The adjacent strip is placed so as to overlap the hardened RCC by about
75 mm. The excess fresh RCC is pushed back onto the new strip forming a slight hump. Lastly,
the fresh joint is rolled in static mode perpendicular to the new RCC strip.
Figure 6.18 - Rolling a transverse longitudinal cold joint (from references [6.1 and 6.3])
100
6.6.5
Rolling a Vertical Cold Joint for a Two-Lift Pavement
Figure 6.19 demonstrates the two-lift construction method. The excess RCC from the bottom lift
is removed to produce a vertical face [6.1 and 6.2].
Figure 6.19 - Vertical cold joint for a two-lift pavement (from references [6.1 and 6.3])
6.6.6
Horizontal Cold Joint
A horizontal joint between two lifts of RCC can be considered cold if more than 90 min
(measured from the initial water-binder contact) have elapsed between the placement of one lift
and the batching of the concrete for the next lift. Before the top lift is placed, the horizontal
surface of the bottom lift must be cleaned with air or water jets to remove debris and dust.
Immediately before placing the top lift, a binding grout with a water-binder ratio of 0.35 must be
brushed onto the surface of the horizontal joint [6.1].
6.6.7
Crack Control
In contrast to the usual practice with slabs on grade made with conventional concrete,
contraction joints are not systematically used to control cracking in RCC pavements. In industrial
settings, contraction joints are seldomly used which results in considerable savings in
construction costs. Random crack spacing is generally about 12 to 15 m, and often more.
Aggregate interlock provides load transfer across cracks. Contraction joints are generally used in
urban settings to control cracking.
If contraction joints are used, they must be sawn at least between 12 to 16 h from the initial
water-binder contact to RCC placement. Generally, a 6-mm wide saw cut is adequate; the cut
depth must be between h/4 and h/3, with h being the pavement nominal thickness. The saw
101
pattern should include items such as manhole covers, sewer manholes, and valve heads. Sawing
must begin as soon as the concrete is hard enough to withstand any damage caused by sawing
operations. The length of time, of course, depends on weather conditions. All sawing operations
must be halted if cracking appears ahead of the saw, if raveling of the joint occurs, or if
aggregates are pulled out. Before a sealing product is applied (and backer rod, if needed), the
joints must be cleaned with sand, air, or water jets. The joint geometry and application of joint
sealants must comply with the manufacturer's recommendations.
When an asphalt overlay is used, the joints in the RCC pavement can be filled with cationic
asphalt emulsion having a minimum pH of 4 (see the following section).
Isolation joints between RCC pavements and buildings consist of strips of fiberboard that extend
the full depth of the pavement.
6.7
Curing
6.7.1
General
Curing consists of promoting cement hydration by controlling the concrete’s moisture and
temperature. More specifically, curing consists in keeping the concrete saturated or close to its
saturation point. Adequate protection against moisture loss is important, since it affects the
proper development of mechanical properties. Lower mechanical properties result in decreased
durability and higher permeability. Loss of surface moisture depends on ambient temperature
and humidity as well as wind velocity. The temperature difference between RCC and the
ambient air also plays a role in moisture loss.
6.7.2
Curing Methods
The most commonly used method for curing RCC is the application of a white-pigmented curing
compound. This technique is effective, economical, and fast. The curing compound must comply
with the requirements of ASTM C309-91. It should be sprayed under pressure at a minimum of
twice the dosage recommended by the manufacturer for rough surfaces without exceeding
2.5 m2/L. Two coats must be applied with the second perpendicular to the first. The entire
surface of the RCC must be covered. The first coat must be applied as soon as compaction
operations have been completed. The second coat is applied once the first coat has dried or no
more than 24 h after application of the first coat. A new coat is applied to any areas damaged
during the 7-d curing period.
One curing method used when the RCC pavement has an asphalt overlay is to apply a cationic
asphalt emulsion with a minimum pH of 4. The pavement surface must be moist at the time of
application. The rate of coverage must leave at least 0.3 kg/m2 of residual emulsion. This curing
technique also serves as a bituminous binder for the asphalt overlay. The RCC surface is cleaned
and then the emulsion is applied at a rate of 0.2 kg/m2 prior to putting down the overlay. During
these operations, the control joints must be filled with emulsion.
102
Other curing methods, such as spraying water and moist burlap are not commonly used for RCC
pavements. If water curing is used, it must begin immediately after compaction operations and
continue for a minimum of 7 days.
6.7.3
Hot Weather Concreting
When the ambient temperature is 27°C or greater, or may reach 27°C while the RCC is being
placed, all necessary equipment and material must be available before paving begins in order to
ensure adequate protection against the effects of hot weather. The RCC surface must be kept
moist. The methods for protecting the concrete must comply with the requirements of CAN/CSA
A23.1.
6.7.4
Cold-Weather Concreting
When the ambient temperature is 5°C or less, or may reach 5°C in the 24 h period after RCC
paving, all protective equipment and material must be available before paving begins in order to
ensure adequate protection against the effects of cold weather. The RCC surface must be kept
moist. The methods for protecting the concrete must comply with the requirements of CAN/CSA
A23.1.
6.7.5
Surface Protection
Once finishing has been completed, no equipment, except that required for curing operations,
must be allowed on the RCC paving surface until the end of the curing period.
Should it begin to rain, paving must be halted and compaction completed quickly. Surfaces that
might be washed out or deteriorated by the rain must be covered with plastic sheeting. Coldweather measures are needed if it snows.
6.7.6
Opening to traffic
Opening an RCC pavement to traffic depends on the following factors:
♦ The mechanical properties of the RCC and early development of mechanical strength.
♦ Pavement loading.
♦ Ambient day and night temperature.
103
REFERENCES
[6.1]
GAUTHIER, P., MARCHAND, J., BOISVERT, L., OUELLET, E., and PIGEON, M.
au rouleau, Continuing training GCI-A2455, Centre de recherche interuniversitaire sur le
[6.2]
Service d’expertise en matériaux (S.E.M.) inc., internal report, multiple pagination.
[6.3]
Montréal, Service des travaux publics et de l’environnement, Division de la voirie,
Section du laboratoire, February 2001, 25 p.
[6.4]
NANNI, A., LUDWIG, D., A., SHOENBERGER, J., E. “Physico-mechanical properties
and load transfer efficiency of RCC pavement,” ACI Materials Journal, 1996, July-August,
pp. 356-361.
[6.5]
Centre de recherche interuniversitaire sur le béton, Département de génie civil, Université
Laval, internal report, multiple pagination.
[6.6]
ANDERSSON, R. “Swedish experiences with RCC,” Concrete International: Design and
Construction, 1987, vol. 9, no. 2, February, pp. 18-24.
104
Chapter 7 – Quality Control
7
General
Despite the increased construction of RCC pavements in the last five years in Quebec, Canadian
and Quebec standards bodies such as the Canadian Standards Association and the Bureau de
normalisation du Québec have yet to publish standards governing the testing and control of fresh
and hardened RCC. The test and control methods used are generally based on ASTM standards,
which are not entirely suitable for current practice in Quebec. Moreover, ASTM standards do not
cover all the test and control methods for fresh and hardened RCC performed in the laboratory
and the field.
As in the case of concrete for any structure, RCC quality control begins with determining that
materials conform to requirements before construction and continues during supervision of the
work at the job site.
It is strongly recommended that RCC quality control in the field be handled by
experienced and qualified personnel in RCC technology. The quality control
laboratory shall have all necessary equipment, in sufficient quantity, to adequately test
RCC quality. Moreover, the equipment must be suitable for use on job site.
Holding a preconstruction meeting with all stakeholders before work starts is also
recommended.
7.1
Preliminary Quality Control
Preconstruction quality control includes determining compliance of materials, the RCC mix
design, the mixing equipment, construction equipment, and paving pattern.
7.1.1
Materials
The procedures for sampling and determining compliance of RCC constituents (binder, mixing
water, aggregates, and admixtures) are generally similar to those for conventional concrete. The
materials are sampled before work begins; their compliance with CAN/CSA A23.2 and/or
project specifications must be verified.
Controlling the quality of materials is important, especially when a pug mill is used. The source
and type of constituents (binder, mixing water, coarse aggregate, fine aggregate, and admixtures)
must be verified. Segregation and / or contamination during transit, unloading, storage, and
handling operations must also be avoided.
105
7.1.2 RCC Mix
The proportioning and adjustment of RCC mixes, as presented in Chapter 4, are carried out in
order to meet specifications. One or more trial batches may be made to measure RCC properties
in the fresh (workability and reference wet density) and hardened (flexural and compressive
strength) states.
As stated previously, binder type and dosage must be determined to produce the desired
mechanical properties as economically as possible and to ensure the long-term performance
required for a specific application (durability, surface wear, structural integrity, and so on). In
addition, binder content must be kept as low as possible to minimize cracking. The water-binder
ratio must be adjusted to produce a mix that can be adequately placed and compacted to its
optimum density.
When determining the workability of the RCC mix, the time required for production,
transportation, and placement must be taken into consideration. Ideally, RCC workability should
be from 40 to 90 sec (Vebe time) at time of placement. Lastly, the ratio of fine aggregate to
coarse aggregate must be selected to yield the required density and to produce a closed textured
surface.
7.1.3
Central Mixer
Selection of the type of central mixing plant is a function of technical and economic
considerations, as well as, the distance of the plant to the job site. As discussed in Chapter 6, the
mixing plant must be able to supply sufficient RCC to the pavers to prevent stopping and
starting, which can result in cold joints. A central mixer's RCC production capacity is about half
of its conventional-concrete capacity, due to the high mechanical stresses and risk of segregation.
The mixing plant should be selected according to its capacity to produce the desired volume of a
homogeneous, uniform product. A stationary central mixer is normally used for projects
involving less than 500 m³, while a pug mill is preferred for projects of more than 500 m³. A
stationary central mixing plant can produce between 35 and 65 m³/h of RCC, compared to an
average of between 40 and 100 m³/h for a Pugmill.
Stationary central mixing plants must comply with CAN/CSA A23.1 and should have a
conformity certificate issued by the Bureau de normalisation du Québec (BNQ) as per NQ 2621900 requirements. Pugmill’s compliance and calibration must be checked before work starts and
upon each time equipment is moved. The various weighing systems must comply with the
required tolerances as specified by the job specifications. Weighing systems calibration and
dosage accuracy for each individual constituent (binder, mixing water, aggregates, and
admixtures) shall be carried out at expected operation production rates. Calibration of the
dosage systems must be carried out with a calibration system independent of the pug mill’s
internal systems. Depending on requirements, weighing-system calibration can be verified at
different times during production.
106
Pugmill compliance and calibration must be checked before work starts and upon each
time equipment is moved. Weighing-system calibration can also be verified at different
times during production.
7.1.4
Placement Equipment
The equipment used to transport, handle, place, and compact the concrete must comply with
project specifications. As stated previously, dump truck boxes must be equipped with tarps.
The pavers must be adequate to place and consolidate the RCC to 80% of the reference wet
density. Moreover, they must have an elevation sensing system to keep the lifts true to grade.
Vibratory rollers with a total static weight over 9.5 t and equipped with two smooth metal drums
(see Figure 6.12) are used to compact RCC. The drums must have a diameter between 1.3 m to
1.4 m, a minimum width of 1.7 m and be equipped for both static and dynamic operation. They
must also be able to generate a dynamic force of at least 450 N/cm at variable frequencies and
have minimum amplitude of 0.75 mm. The drum wipers must be properly adjusted to remove
any particles that may adhere to the drum surface, otherwise each drum revolution will damage
the RCC surface. The drums must be kept dry during compaction operations.
Pneumatic-tired roller, tandem roller with smooth metal drums, or a combination roller can be
used as finishing equipment (for closing voids and cracks). Portable compaction equipment are
used to consolidate RCC locally around manhole and sewer rings.
7.1.5
Placement
Placement compliance is best evaluated by requiring the placement of a site trail test section to
verify the following: RCC production uniformity, the contractor’s placement and compaction
method, and his ability to place adjacent strips. The work crew that will be performing the
construction work must carry out the trial test section using the same construction equipment that
will be used for the project. Generally, a site trial test section consists in paving a 150 m² area in
order to accurately assess placement compliance. More specifically, the site trial test section
makes it possible to check:
-
The central mixing plant’s capacity to produce a homogeneous RCC mix and production rate.
-
The quality of placement and compaction operations.
-
The compaction pattern.
-
The placement of adjacent courses and joint quality (fresh and cold).
-
Differences between the laboratory wet density and field values.
-
Optimal water dosage for the required Vebe time.
-
The number of compaction equipment passes to achieve 100% of the reference wet density.
-
Surface quality and uniformity.
107
The trial test section may also include producing transverse and longitudinal cold joints. Mix
workability and density must be measured during the trial site test section. RCC test specimens
must also be produced in order to assess the concrete's mechanical properties.
It is recommended to include the trial site test section in the specifications. The decision to
specify a trial site test section should take into consideration the placement crew's experience, the
equipment used, project scope, the specific placement plan, mobilization-demobilization costs,
and similar factors.
7.2
Field Quality Control
Quality control in the field provides the means for ensuring pavement quality and durability. It
may include the items listed below:
-
Verification of the granular base
-
Sampling of the mix materials
-
Monitoring of RCC production
-
Monitoring of placement
-
Sampling and testing of fresh RCC properties
-
Specimen production (beams and cylinders)
The granular base must be inspected before any RCC is placed. This procedure consists of
making sure that the slopes and elevation of the granular base comply with specification
requirements. The degree of compaction of the granular base must also be checked (it must be
compacted to at least 95% of the optimal Modified Proctor Density as per CAN/BNQ 2501-255).
The profile of the granular base must be as uniform as possible in order to ensure pavement
uniformity. Any variation of more than 10 mm in 3 m with respect to desired profile should be
corrected.
Stockpiled materials must be sampled in order to establish compliance with technical
specifications. Particle sieve analysis is generally carried out every 500 m³ for major projects.
Monitoring RCC production is very important, especially in the case of a Pugmill. Regular flow
readings for each of the components going through the mixing chamber must be taken in order to
ensure that they fall within production tolerances. Readings should be taken every minute during
the first 10 min of production or whenever production resumes, and every 15 min thereafter. The
condition of the mixer must be checked every 400 to 500 m³ of RCC or at the midpoint in the
production day. The uniformity of placed RCC is an effective indicator of the mixer production
efficiency. Generally, the blades must be cleaned at the midpoint and at the end of every
production day. Before starting RCC production, the aggregate moisture content must be
determined in order to adjust the volume of mixing water required. Water-content measurements
must be taken at the start of every production day and at regular intervals during production.
Monitoring RCC placement consists of ensuring that the placement and compaction time limits
are complied with in order to avoid consolidation problems and unplanned cold joints. This must
108
be carried out for the duration of the project. Every load of RCC placed must comply with the
following:
♦ Transportation time must not exceed 45 min, measured from the initial water-binder
contact to placement. The transportation time should be further reduced if the ambient
temperature is 27°C or greater
♦ The maximum interval between placing two adjacent strips or two successive lifts is
90 min from the initial water-binder contact, depending on ambient temperature. This
interval should be reduced if the ambient temperature is 27°C or higher.
♦ Fresh RCC must be compacted within a maximum of 60 min from the initial water-binder
contact and compaction operations must begin within a maximum of 10 min of
placement.
While set-retarding admixtures can be used to increase these times, their effects on fresh and
hardened RCC must be tested prior to use.
Monitoring RCC placement also involves verifying the following:
♦ All exposed surfaces of the RCC pavement must be kept moist by fog spraying and/or
applying an evaporation retarder until the final curing agent is applied. The curing agent
must be applied at the proper rate immediately after compaction operations (see Section
7.6.2 Curing Methods).
♦ The quality of placed and compacted RCC must be controlled as the work progresses.
Similarly, the profile of the compacted surface must be measured using a 3-m
straightedge (see the requirements in Section 7.3 RCC Compliance).
♦ The slope of the pavement given in the specifications must be verified. The minimum
slope to ensure runoff on RCC pavements is about 2%.
♦ The quality of the RCC surface after compaction and curing must comply with
specifications.
The last issue in monitoring RCC placement is checking the wet density after compaction. This
is done using a nuclear denseometer with a single 300-mm probe in direct transmission mode
according to ASTM C1040. The degree of RCC compaction is equal to the ratio of the in-place
RCC determined by the nuclear denseometer to the reference wet density of the sampled material
times 100 (see the requirements in Section 7.3 RCC Compliance). Wet density values should be
used to calculate the ratio instead of dry density in order to minimize the source of errors
(evaluation of the mix’s total water content, including the aggregate moisture content).
Measurements of RCC wet density are taken by inserting the probe to a depth of half of the lift
thickness. The probe should not penetrate the granular base or underlying RCC lift. Staggered
readings must be taken every 10 m for each paver strip, as soon as possible after compaction
operations.
Sampling and measuring fresh properties provides information about the quality and
homogeneity of RCC production. Sampling shall be carried out at the paver discharge, at the
outer edge of the vibrating table. The workability and reference wet density of the initial loads of
109
the fresh RCC are determined (see the procedures in Appendices B and C, respectively) to ensure
that job site production corresponds to laboratory results. After the initial loads, the workability
of the fresh RCC is normally measured after at least 60 min of continuous production. Additional
workability tests can be performed whenever production resumes. RCC wet density is
determined according to the procedure described in Appendix C whenever production resumes
and at least every 225 m³ produced.
RCC specimens for use in determining the concrete’s mechanical properties (flexural and
compressive strength; see the procedures in Appendices D and E, respectively) must be cast for
every 225 m³ produced or at least once each production day. Fresh RCC is sampled if production
has been underway for at least 1 h. The concrete must not be sampled at the start of production,
that is, during the first 40 m³ or when production resumes. Normally, six cylinders (150 mm in
diameter × 300 mm in length or 100 mm in diameter × 200 mm in length) are produced for 7-d
and 28-d compressive strength testing (3 for each age). Flexural testing requires six
100 × 100 × 400 mm prisms (3 for each age). If required, additional specimens may be produced
to measure concrete properties at other ages, such as 24 h and 3 d.
7.3
RCC Compliance
RCC compliance is generally based on the items presented below.
The pavement surface should not have any variations of more than 12 mm measured using a 3-m
straightedge and the pavement surface must not vary more than 12 mm from grade. At least 80%
of the measurements must comply with these requirements [7.1]. The pavement surface must be
smooth and even, free of defects such as surface tearing, polygon-shaped cracking, segregation,
potholes, or areas loosened or deteriorated by placement operations. Construction and cold joints
must not have raveling; the shoulders of contraction joints must not be damaged.
The degree of compaction is deemed compliant if all the measurements of the fresh RCC are
equal to 100% of the reference wet density in accordance with the procedure described in
Appendix C. The degree of compaction is deemed acceptable if the average of all measurements
exceed 99%, with no individual measurement less than 98%. Any section of fresh RCC with a
degree of compaction less than 97% must be compacted again to achieve a value of 98% or
greater. This additional compaction must be completed within the time limits noted in Section
6.5. If the compaction results indicate no increase in the in-place wet density, the reference wet
density of the fresh RCC must be determined again in accordance with the procedure described
in Appendix C. If a comparison of the degree of compaction values to the new reference wet
density shows no difference in the degree of compaction, the section of RCC should be replaced
with fresh RCC and compacted.
When testing flexural strength at a given age, the average of three consecutive tests must be
greater than or equal to the design modulus of rupture, with no result being less than 90% of the
design value [7.1].
110
Thickness of RCC pavement can be established by coring. Thickness is generally deemed to be
compliant if the average length of the cores is greater than or equal to the specified thickness,
and if no individual core has a length less than 95% of the specified thickness.
Another method suggests that pavement thickness can be deemed compliant if the average length
of 5 cores (cores are between 110 to 125mm diameter) drilled to the full depth of the RCC lift for
a given lot is greater than or equal to the required thickness calculated with Relationship (1). A
given lot of RCC is considered 4000 m2. If the pavement area is smaller than 4000 m2 it is
considered a lot.[7.1].
Treq = 0.36D + Ts – 15
where:
Treq:
D:
Ts:
(1)
Required thickness in mm
Difference in mm between the longest and shortest of the 5 cores for the same
batch
Specified thickness in mm
REFERENCES
[7.1]
Montréal, Service des travaux publiques et de l’environnement, Division de la voirie,
Section du laboratoire, February 2001. 25 p.
111
APPENDIX A
RCC Sampling Procedure
A-1
Field of Application
The method deals with the procedure for taking RCC samples delivered or prepared at the site to
make test specimens for laboratory testing and field characterization.
A-2
References and Restrictions
This procedure makes reference to CAN/CSA A23.2-1C and to Appendices C, D, and E herein.
It is very important to note that these appendices (A through E) are adaptations of existing
standards based on laboratory and field experiments in Quebec.
A-3
Equipment
♦
♦
♦
A-4
Sampling RCC
♦
Note:
Sieve conforming to CAN/CGSB-8.2.
Sieve analysis equipment conforming to CSA A23.2-1C.
Small tools such as a scoop and rubber bucket.
Periodically collect 2 samples of fresh concrete (of suitable volume), in accordance with the CSA
A23.2-1C test method. The first is used to determine the reference wet density; the second to
make test specimens and determine workability.
The sampling procedures are currently being studied in a research program.
A-1
APPENDIX B
Procedure for Determining Workability of Fresh Concrete with a Vebe Apparatus
B-1
The method deals with the procedure for determining the workability of fresh RCC with a Vebe
apparatus.
B-2
This procedure makes reference to ASMT C1170-91 and to Appendix A herein.
B-3
Equipment
♦
♦
♦
B-4
RCC Workability
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
Note:
Vebe vibrating table conforming to ASTM C1170-91.
Steel cylindrical molds conforming to ASTM C1170-91.
Small tools such as a scoop and rubber bucket.
The vibrating table must be level and fastened to a concrete base to prevent the apparatus from
moving during the test (laboratory and field).
Attach the mold and dampen the interior with a damp cloth.
Collect a representative sample of fresh RCC (about 13 kg), taking care to avoid segregation.
Place the fresh RCC in the steel mold without causing segregation; strike off the top. Do not
consolidate the concrete.
Attach the mold to the vibrating table.
Dampen the plate and then place it on the concrete using the guide.
Center the plate (which is smaller than the inside diameter of the mold) inside the mold so that a
ring of mortar can form around it.
Attach the rod to the vibrating table.
Put the 22.7-kg surcharge on the plate, making sure that it is properly fastened to prevent its
movement during the test.
Turn on the vibrating table.
Wait 2 or 3 s for the system to stabilize before noting the start time.
When the ring is completely formed, stop the test and determine the elapsed time. This is the
Vebe time of the material from the initial water-binder contact (round off to the nearest 5 s).
Remove the plate and visually determine the percentage of closed surface of the consolidated
RCC.
B-1
APPENDIX C
Procedure for Determining the Reference Wet Density of Fresh Concrete with the
Modified Proctor Test
C-1
The method deals with the procedure for determining the wet density of samples of fresh RCC
prepared in the plant or field. This is the reference value for wet density used when making test
specimens.
C-2
This procedure makes reference to NQ 2501-255 and to Appendix A herein.
Moreover, it is the most important test for smooth field operations and therefore must be
clearly understood.
C-3
Equipment
♦
♦
♦
♦
C-4
Determining the Reference Wet Density
♦
♦
♦
♦
♦
♦
♦
Note:
Steel molds conforming to NQ 2501-255.
Hand-held hammer conforming to NQ 2501-255.
Scales conforming to NQ 2501-255.
Straightedge conforming to NQ 2501-255.
Collect RCC samples (about 10 kg) as described in Appendix A herein; avoid segregation.
Dampen the interior of the mold with a damp cloth.
Weigh the mold and base, without the collar, to the nearest gram.
Fill the mold with 5 layers of about 1.1 kg each.
Compact each layer with 56 hammer blows, ensuring that they are evenly distributed over the
entire surface of the concrete.
Strike off excess after the last layer is placed so that the volume of concrete is the same as the
volume of the mold. If necessary, close the surface with fresh RCC passing through a 5-mm
sieve.
Calculate the wet density of the fresh RCC. The volume of the mold used must be calculated to
± 0.001 L.
C-1
APPENDIX D
Procedure for Molding RCC Test Specimens Using a Vibrating Hammer for
Compressive-Strength Testing
D-1
The method deals with the procedure for molding RCC test specimens using a vibrating hammer for
compressive-strength testing.
D-2
This procedure makes reference to ASTM C1435-99 and to Appendix A herein.
D-3
♦
♦
♦
♦
♦
♦
♦
D-4
♦
♦
♦
♦
♦
♦
♦
D-5
Equipment
Cylindrical steel sleeves conforming to ASTM C1435-99.
Cylindrical plastic molds conforming to CAN/CSA A23.2-3C.
Steel collar conforming to ASTM C1435-99.
Vibrating hammer weighing 10 ± 2 kg conforming to ASTM C1435-99.
Circular metal base with a diameter of 140 ± 3 mm conforming to ASTM C1435-99.
Compaction plate conforming to ASTM C1435-99.
Small tools such as a trowel and scoop.
Molding Specimens for Compressive-Strength Testing
The specimens must be produced within 20 min of collecting the sample.
Calculate the total weight of the RCC needed to mold the test cylinders (152.4 mm in
diameter × 304.8 mm in length) based on the reference wet density determined according to the
procedure described in Appendix C. The volume of the specimens used must be evaluated to
± 0.001 L.
The thin-walled plastic cylinder must be oiled and then inserted into the metal sleeve.
Put three layers of equal weight of concrete into the mold, preventing segregation. Strike off the surface
by hand with cement paste.
Use the vibrating hammer and plate to consolidate each layer of concrete.
Place the collar around the mold before putting the last layer of concrete into the mold.
Store the specimens on a rigid, level surface protected from sunlight, vibration, and other disturbances
in an environment maintained at 20 ± 5°C. The specimens should be removed from the molds 24 ± 4 h
after fabrication and moist-cured at 23 ± 2°C so that they are constantly covered with a thin coating of
moisture until time of testing. The specimens must not be exposed to running water.
Compressive-Strength Testing
Carry out compressive-strength testing in accordance with CAN/CSA A23.2-9C.
Note:
D-1
APPENDIX E
Procedure for Molding RCC Test Specimens Using a Vibrating Hammer for FlexuralStrength Testing
E-1
The method deals with the procedure for molding RCC test specimens using a vibrating hammer for
flexural-strength testing.
E-2
This procedure makes reference to CAN/CSA A23.2-3C.and to Appendix A herein.
It is very important to note that these appendices (A through E) are adaptations of existing standards
based on laboratory and field experiments in Quebec.
E-3
Equipment
♦
♦
♦
♦
♦
Rectangular steel molds with inside measurements of 100 × 100 × 400 mm.
Vibrating hammer weighing 10 ± 2 kg conforming to ASTM C1435-99.
Removable steel collar to contain the last layer of concrete.
Steel compaction plate with a minimum thickness of 15 mm that can fit into the rectangular mold.
Steel finishing plate with a minimum thickness of 15 mm that can fit into the rectangular mold.
E-4
Molding Specimens for Flexural-Strength Testing
♦
♦
The specimens must be produced within 20 min of collecting the sample.
Using the wet density determined in accordance with Appendix C, weigh a quantity of fresh concrete
corresponding to the volume of the test specimen to be produced.
Use a flat shovel to fill the mold to the halfway point, moving the shovel along the rim of the mold to
distribute the concrete evenly and keeping segregation to a minimum. A tamping rod can be used to
spread the concrete evenly within the mold prior to consolidation.
Compact the concrete until the mold is half full. Install the collar. Put in the remaining concrete and
compact it.
Remove the collar, place the steel plate on top of the mold, and complete consolidation by applying the
compactor to the steel plate.
Spray all concrete surfaces with an evaporation retarder. Immediately cover the specimens with a
nonabsorbent, nonreactive plate to help retard evaporation.
Store the specimens on a rigid, level surface protected from sunlight, vibration, and other disturbances
in an environment maintained at 20 ± 5°C. The specimens should be removed from the molds 24 ± 4 h
after fabrication and moist-cured at 23 ± 2°C so that they are constantly covered with a thin coating of
moisture until time of testing. The specimens must not be exposed to running water.
♦
♦
♦
♦
♦
E-5
♦
Flexural-Strength Testing
Carry out the flexural testing in accordance with CSA A23.2-8C.
Note: The sampling procedures are currently being studied in a research program.
E-1

Design and Construction of Roller Compacted Concrete Pavements

Transcription

Similar documents

Meshuga 4 Sushi Encino September 30, 2016

Graphic Identity and Style Guide

Review - Histology and Histopathology

Pentra-Sil 244+ - GLENSIL INDONESIA

pentra-sil® (ih) - Quest Building Products

Glory Hole Spillway Repair - Knowles Industrial Services

Pentra-Sil - Lesa Pentra Floor

Pentra-Sil (NL)

Concrete

View our Company Portfolio