Milling

Valmir Bonfim
1st Edition
2010
Copyright © 2008 by autor
All rights reserved. This work may not be reproduced in whole or in part, by photocopy
or other means, without the express permission of the author.
1st Revised and Updated Edition
Published by
Suiang G. Oliveira
Cover and graphic design by
Pedro Penafiel
English Version by
Priscila Podboi Adachi & Patricia Pick
Dados Internacionais de Catalogação na Publicação (CIP)
(Câmara Brasileira do Livro, SP, Brasil)
Bonfim, Valmir
Cold milling of asphalt pavements / Valmir
Bonfim. -- 1. ed. -- São Paulo : Exceção Editorial,
2010.
Título original: Cold milling of asphalt
pavements.
ISBN 978-85-60735-02-0
1. Fresagem 2. Pavimentação - Técnicas
3. Pavimentação alfáltica 4. Pavimentos asfálticos
I. Título.
10-03233 Índices para catálogo sistemático:
1. Fresagem : Pavimentos asfálticos :
Engenharia civil 625.85
2. Pavimentos asfálticos : Fresagem :
Engenharia civil 625.85
CDD-625.85
I dedicate this book
to my parents and brothers,
my wife Mônica and
my son Victor
Presentation
As the population of the world continues to grow, so the demands on the
road infrastructure will continue to increase exponentially. This applies
specifically to mobility of people and products. In developing countries,
the establishment of new road infrastructure is the primary spin-off of
this phenomenon, whilst in developed countries the maintenance of the
existing network at an acceptable functional service level is the priority.
Woven into the primary need for mobility is a matrix of second order
necessities including the consideration of the environment, the social impact
and economic imperatives. Let us for a moment reflect on this “triple bottom
line” in the context of cold milling technology as applied to asphalt.
Firstly, the environment is a key consideration in the investigation,
design and maintenance of road infrastructure, given that a road is born
from natural products and lives intimately within the influences of the
environment. Environmental issues that are impacted on by cold milling
technology and are covered in this book include:
• Efficient removal of old asphalt from an existing pavement to ensure
minimal energy consumption and minimal emissions,
• Maximum reuse of the existing materials at its highest level of
recycling, without wastage, by ensuring that the required grading of
RAP is achieved without excessive oversize or insufficient fines,
• Creating the desired working platform after milling to minimize the
need for new materials and will even allow thin surface treatments
to be used to achieve the desired riding quality and functional
performance, and
• Effective treatment of various forms of distress in an existing
pavement without disturbing sound materials unnecessarily.
The social impact is the second factor for consideration in the triple
bottom line. It currently receives more attention than before, which
highlights a healthy shift in the priorities of decision making. Social
issues that are impacted on by cold milling technology and are covered
in this book include:
• Efficiency of the milling process, to minimize construction time and
disruption to normal traffic activities i.e. delays and road user costs,
• Effective application of technology to allow optimal structural and
functional solutions to be applied for public comfort and safety, and
• Safety of the public throughout the construction and rehabilitation
process through minimization of lane occupancy and unidirectional operation with minimal workers on site.
The factor in the triple bottom line that has been given the highest
priority historically, sometimes at the exclusion of others, is the economic
consideration. In this regard, cold milling of asphalt speaks for itself.
Advances in cold milling technology over the past three decades has
enabled sustainable practices in pavement engineering to become a reality
with economic benefits to all parties involved.
As a consequence of the benefits in all aspects of the triple bottom
line, cold milling technology has expanded significantly and currently
supports recycling of flexible pavement materials. It is impossible to
imagine pavement maintenance and rehabilitation without it. At the same
time, it is important to understand the technology and how it should be
most effectively applied.
Engineer Valmir Bonfim’s book brings academic theory together with
a wealth of practical imperatives at the interface of Civil and Mechanical
Engineering, making his book a “Best practice guideline for cold milling of
asphalt pavements”. The contents of this book are important for Contractors,
Consultants, Designers and Road Authorities alike, in order to enhance
understanding of cold milling and enable optimized execution of this
practice, using the appropriate equipment.
Professor Dr. Kim Jenkins
Stellenbosch University, South Africa
Preface
A pavement is designed and built to provide comfortable, safe and
cost-effective ride quality, which is determined by the quality of its
surface. When the surface layer no longer meets that need, it is time
to intervene and restore it.
In some cases, especially when elevation limitations apply to the
finished pavement or when the old material is recycled, the surface
layer, or part of it, must be removed before the new layer is laid. This
is where the milling technique is used.
Although pavement milling has already become a part of the
Brazilian paving scene, there are still very few professionals who
excel in this technique and even fewer who stand out for their vast
experience.
Valmir Bonfim has worked as an engineer in this area for many
years. He brings together a considerable knowledge of the topic,
obtained through substantial academic study and extensive field
experience.
His CV boasts more than twelve million square meters milled using
several variations of the technique, which confers him the competence
to speak as an authority on the subject.
As of 1995 I had the pleasure of seeing him at the Escola
Politécnica da Universidade de São Paulo as my student. He concluded
his master’s degree brilliantly with the dissertation “Study on the
grading resulting from asphalt pavement milling to be used for inplace cold recycling”.
That dissertation was the groundwork for this book, which has been
very accurately written and contains interesting and timely information
for professionals in the industry, researchers, as well as graduate and
postgraduate students who have interest in the subject.
This is a comprehensive book that will meet the needs of technicians
beginning their careers, as well as experienced professionals – a fact
that is sure to make it a success.
Prof. Dr. Felippe Augusto Aranha Domingues
Escola Politécnica da Universidade de São Paulo
Thanks to
• The Wirtgen Group, especially my friend Andreas Marquardt,
for his trust and encouragement to publish my original book in
English and Spanish;
• Professor Doctor Waheed Uddin from the University of Mississippi
in USA for a thorough review of the English manuscript;
• The companies CIBER – Equipamentos Rodoviários, Iguatemi
Consultoria e Serviços de Engenharia and Fresar Tecnologia
de Pavimentos, which were listed in the previous portuguese
editions;
• Nelson Sampaio Pereira, one of the pioneers in asphalt
pavement milling and recycling equipment in Brazil, who was
responsible for my learning and who encouraged me immensely
professionally;
• Professor Doctor Felippe Augusto Aranha Domingues and
Professor Doctor Liedi Bariani Bernucci, from the Escola
Politécnica da Universidade de São Paulo, and Professor Doctor
Leto Momm, from the Universidade Federal de Santa Catarina,
for their teaching, friendship and fantastic support;
• My friend Engineer Danilo Martinelli Pitta for his immense help,
who spared part of his precious time to conduct the technical
revision of this book;
• The professionals who work in the Brazilian highway industry,
for reading the material so thoroughly and making suggestions
that contributed to making this a richer book, among whom
are Engineers Gualberto Pedrini and Dultevir Guerreiro Vilar
de Melo;
• To all of those who have, directly or indirectly, helped to make
this book a reality;
• God, above all things!
Contents
1. Introduction........................................................................... 17
2. Definition of pavement milling.............................................. 19
3. Types of milling classification................................................. 21
3.1. According to the depth of cut....................................... 21
3.1.1. Surface milling..................................................... 21
3.1.2. Shallow milling.................................................... 22
3.1.3. Deep milling........................................................ 22
3.2. According to the resulting roughness on the
pavement....................................................................... 23
3.2.1. Standard milling.................................................. 23
3.2.2. Fine milling......................................................... 23
3.2.3. Micro milling....................................................... 24
4.
Milling machines.................................................................. 27
4.1. Small milling machines................................................. 27
4.2. Medium milling machines............................................. 29
4.3. Large milling machines................................................. 31
5. Main equipment components............................................... 35
5.1. Milling drum................................................................. 35
5.1.1. Milling drum fixing system.................................. 36
5.1.2. Types of milling drums......................................... 36
5.1.2.1. Fine milling drum.................................. 37
5.1.2.2. Micro milling drum................................ 38
5.1.3. Milling drum widths............................................ 41
5.1.4. Milling drum operating on the pavement............ 44
5.2. Cutting tools................................................................. 45
5.3. Cutting tools holders..................................................... 47
5.4. Scrapers blades.............................................................. 48
5.5. Conveyor belt................................................................ 49
5.6. Speed control system..................................................... 51
5.7. Cut depth control system.............................................. 52
5.8. Equipment support system............................................ 52
5.8.1. Equipment mounted on tires............................... 52
5.8.2. Equipment mounted on tracks............................ 53
6. Complementary equipment for operational support............. 55
6.1. Signalling of the work site............................................. 55
6.2. Water tanker................................................................. 56
6.3. Metal detector............................................................... 56
6.4. Finishing on milled areas.............................................. 57
6.4.1. Using small milling machines.............................. 57
6.4.2. With milling units attached to another type
of equipment....................................................... 58
6.4.3. Using slitting saw and pneumatic breakers.......... 58
6.5. Dump trucks................................................................. 60
6.6. Lane sweeping............................................................... 60
6.6.1. Manual sweeping................................................. 61
6.6.2. Mechanical sweeping.......................................... 61
6.7. Hauling the equipment................................................. 63
7. Applying the milling............................................................. 65
7.1. Types of application....................................................... 65
7.1.1. Milling to correct surface distress......................... 66
7.1.2. Discontinuous milling areas................................. 67
7.1.3. Continuous milling of the entire lane.................. 68
7.2.
7.1.4. Edge-shaped......................................................... 69
7.1.5. Milling to correct pavement inclination.............. 70
7.1.6. Finishing milling.................................................. 70
7.1.7. Rumble strip surface milling................................. 72
Milling for the correction of distresses.......................... 72
7.2.1. Cracking............................................................... 74
7.2.2. Patch deterioration.............................................. 75
7.2.3. Potholes............................................................... 75
7.2.4. Rutting................................................................. 76
7.2.5. Depression........................................................... 76
7.2.6. Shoving................................................................ 76
7.2.7. Polished aggregates............................................... 77
7.2.8. Bleeding / flushing............................................... 78
7.2.9. Surface distresses and defects............................... 78
7.2.10. Pumping............................................................. 78
7.2.11. Asphalt layer overlay.......................................... 79
7.2.12. Lane/shoulder drop-off or heave........................ 79
8. Benefits brought by the milling technique............................ 81
8.1. Maintaining pavement grade........................................ 81
8.2. Maintaining joint leveling............................................. 82
8.3. Correcting shoving........................................................ 83
8.4. Maintaining the appropriate level around
manhole covers............................................................. 83
9.
Problems that may occur due to the use of milling............... 85
9.1. Step on the lane............................................................ 85
9.2. Appearance of potholes................................................ 86
9.3. Displacement of bituminous layer slabs......................... 87
10.Productivity of milling machines.......................................... 89
10.1. Opening considerations................................................ 89
10.2. Productivity examples.................................................. 90
11.Designing pavement reinforcement with view to
milling................................................................................... 95
12.Grading of materials from milling........................................101
12.1. Equipment used.......................................................... 103
12.2. Existing wearing course.............................................. 104
12.3. Samples collection...................................................... 104
12.4. Gradation curves........................................................ 105
12.5. Considerations of the results obtained........................115
13.Parameters for asphalt pavement milling control.................117
13.1. Objective.....................................................................117
13.2. Generalities.................................................................117
13.3. Equipment...................................................................117
13.4. Control of cut depth....................................................118
13.5. Control of milled surface texture................................118
13.6. Storing the milled materials........................................118
13.7. Lane clean up...............................................................119
13.8. Reopening to traffic....................................................119
13.9. Measurement.............................................................. 120
Bibliography..............................................................................121
Figures and illustrations credits................................................ 123
1. Introduction
With the oil crisis of the 70s, the shortage of asphalt materials and
the international economic crisis, road technicians worldwide were
moved to meet with fostering agencies to discuss the idea of recycling
paving material from deteriorated roads. The goal was to find a
method of restoring pavement to satisfactory standards that was both
technically and financially efficient.
Initially, the material was extracted from roads through pavement
scarification and then processed at plants.
This procedure was not suitable for such an application because it
produced very large pieces which had to be broken down again before
they could be used in the recycled mix.
Since scarification is a “pulling” procedure, the entire bituminous
layer is removed which makes it impossible to remove the material to
a pre-specified depth.
The milling machine was conceived during the second half of the
70s, simultaneously in Europe and North America, as a tool that would
enable and ensure pavement planing down to pre-specified depths.
According to Wood[1], some of the companies in the United States,
that developed such machines were Barber-Green, CMI, Barco and
Rancho, as well as foreign companies.
Milling is a relatively new technique for pavement recovery,
maintenance and restoration. It was first employed in 1980 in Brazil,
17
when the American milling machine Roto-Mill PR-525, manufactured
by CMI, was used for the Via Anchieta restoration works, for DERSA
(Desenvolvimento Rodoviário S.A.).
Currently, asphalt pavement milling is frequently used as part of
deteriorated pavement restoration processes. Milling is especially useful
for solving typical urban problems, such as avoiding sidewalks and
stormwater drainage systems from being elevated above reasonable
height levels and alleviating cracking propagation.
18
2. Definition of
pavement milling
The term milling is derived from the technique used to plane down
or cut metals and other materials using a driving gear made up of a
rotating cutter with several, constantly rotating corners or mills.
This technique originated the term “milling machine”, which is
used for milling equipment with a specific structure.
The Departamento Nacional de Estradas de Rodagem, in its Glossary
of Technical Road Terms[2], defines pavement milling as the “cold or hot
removal of asphalt surfaces as part of the asphalt pavement recycling
process”.
Pavement restoration milling led to the original two specific types
of machines and processes: the “cold milling machine”, which planes
down the structure through abrasion; and the hot milling process,
which preheats the structure, softening it and making it easier to
plane down.
Therefore, pavements can be milled at both hot and cold
temperatures.
Cold pavement milling is conducted at room temperature and the
pavement does not need to be preheated. The only heating in the
process, albeit negligible, occurs as a result of the energy released from
the impact of the cutting tools on the pavement during the milling.
In this type of milling, part of the aggregate is broken down at
cutting depth and alters the grading curve of the pavement.
19
Figure 1: Milled plate surface
Figure 2: Milled plate
cross-section
Figures 1 and 2 show a milled surface where broken down aggregate
can be seen at cutting level.
In hot milling, which is used as part of the in-place hot recycling
process, the wearing course is preheated. In this case, however, hot
milling is a scarification, since the structure is heated it offers little
resistance to cutting. In this type of milling, the material grading is not
significantly altered, since the objective here is only to separate it so it
can be mixed in with the new material from the asphalt plant.
This technique can also be used on Portland cement concrete
pavements to remove thin layers, to even out concrete pavements, or
in industrial warehouses for the subsequent laying of a new wearing
course.
Based on the above information, the concept of pavement milling
can be more broadly defined as “the removal or planing down of one
or more pavement layers of a predefined thickness, through a hot or
cold mechanical process used as a means to restore pavements”.
20
3. Types of
milling classification
Many authors disagree when it comes to classifying the types of
milling and their applications. However, pavement milling can be most
simply classified according to the thickness of the cut and the resulting
roughness of the pavement.
3.1. According to the depth of cut
The different types of milling can be classified according to the thickness
of cut, as follows: surface milling, shallow milling, or deep milling.
3.1.1. Surface milling
Surface milling, also known as profiling milling, is used only to
correct flaws on the pavement surface.
Consequently, the subsequent resurfacing of the pavement
becomes unnecessary, given that the texture obtained allows for safe,
although uncomfortable, ride quality, with the exception of specific
areas where the remaining asphalt layer may spall and lead to the
appearance of potholes.
It is important to note that the milling drum in some of the
equipment used to improve tire-pavement adherence can be exchanged
for others with higher cutting tool density, which allows for more
comfortable riding surfaces.
21
The DNER Course RP 9 of Pavement Recycling[3] states that most
milling operations improve the road surface texture (macrotexture) as
well as the exposed aggregate surface texture (microtexture), favoring
greater skid resistance.
Similarly, this technique is also used to treat problems such as
bleeding, flushing, and shoving to improve ride quality.
3.1.2. Shallow milling
Shallow milling normally only reaches the upper layers of the
pavement and in some cases reaches further down into the binder layer.
The average depth of cut is 5 cm in shallow milling jobs.
This procedure is used in surface repairs and to correct functional
defects, mainly on urban roads where the pavement grade must be kept
on the same level as drainage devices and other constructions.
According to the DNER Course of Pavement Recycling, the texture
that results from milling increases the bond or shear resistance between
the old pavement and the new wearing course.
In the last years, considering the restricting monetary aspects especially
in state and federal roads, technicians have used this type of milling to
guarantee the quality of the pavement at satisfactory monetary levels.
3.1.3. Deep milling
The depths of cut in deep milling are quite significant and go
beyond the wearing course layer, reaching the pavement binder, base
and even sub-base layers.
This procedure is normally used in structural operations, to rebuild
the pavement structure or even recycle and incorporate the wearing
course into the base.
In functional operations, especially those concerning safety and
the reestablishment of “ideal” operating conditions of surface drainage
systems, this technique is used to correct the original grade of roads.
22
This procedure is also highly recommended for small repairs and
pothole reconfiguration.
As far as roughness is concerned, any kind of drum can be used
for the three types of milling – surface, shallow, and deep; however,
a standard milling drum should be used in cases where only a new
wearing course layer is to be laid. Other drums which cut higher are
impracticable because of the wearing of tools.
3.2. According to the resulting roughness on the
pavement
The different types of milling can be classified according to the
resulting roughness on the pavement: standard milling, fine milling
and micro milling.
The resulting roughness on the pavement surface will depend on the
type of drum used in the milling, as well as the speed of the operation.
The evolution of milling drums has enabled milling machines to have
a wider use. There are currently a number of different types of drums
available in the market, with smaller spacing between the cutting tools.
Later on, you will be introduced to different types of milling drums
and see examples of how they are used.
3.2.1. Standard milling
Standard milling was the name given to the type of milling achieved
by the original drum contained in milling machines and was the first to be
introduced in the market. The spacing of the cutting tools is 15 mm. This
type of milling is used to plane down a layer previously specified in the project
with a view to the subsequent laying of a new wearing course layer.
3.2.2. Fine milling
Fine milling was introduced later on, as a result of the use of milling
drums with cutting tools spaced at approximately 8 mm, and lead to
23
smaller grooves and less roughness on the pavement, making this new
classification possible.
This technique is frequently used in the profiling of roads, since it
allows users to experience better riding conditions. In some cases, the
application of the new wearing course is not needed.
3.2.3. Micro milling
Micro milling is achieved by using drums with cutting tools spaced
at approximately 2 to 3 mm.
It removes a very thin layer of the wearing course, profiling the
surface lengthwise or removing horizontal signaling strips from the
lane surface to alter the road layout.
Initially, micro milling drums were only available for smaller
machines, such as the W 350 model, manufactured by Wirtgen, and
their cutting tools were smaller in comparison with those used in other
types of milling.
In this type of operation, a new coating layer is completely
unnecessary.
The following illustrations show a comparison between the types
of milling according to the resulting roughness on the lane surface,
i.e., standard milling, fine milling and micro milling.
24
Standard
milling
Fine
milling
Micro milling
Figure 3: A comparison between the different types of milling
according to the resulting roughness on the lane surface
25
4. Milling machines
There are many milling machine manufacturers around the world.
In addition to those mentioned in the introduction, there are also
Bitelli (Caterpillar Group), Bomag, Caterpillar, Ciber, Dynapac,
Ingersoll Rand, Marini, Roadtec, Stravostroj, Sakai, Volvo, Weber
and Wirtgen.
Currently, in Brazil, there are many models and different-sized milling
machines, made by a variety of manufacturers that meet the market’s
needs. Some of them have been locally manufactured in Brazil.
Milling machines can be split by size into small, medium and large.
Some machine models and the name of their manufacturers will
be mentioned as examples; however, not all of them are currently
available in Brazil.
Frequently, the name of the equipment model refers to the width
of the milling drum. Manufacturers refer to the width in centimeters
or millimeters – a convention has not yet been established.
Some of the new models made by Wirtgen that used to refer to the
drum width in millimeters have now adopted centimeters for the new
series, such is the case of the W 1000 F, the new version of which is
called W 100 F.
4.1. Small milling machines
These machines are used for the finishing of some of the many
obstructions found on pavements.
27
The finishing used to be one of the main problems in milling;
now smaller machines have been introduced to facilitate this
operation.
They are used mainly in small operations and for specific tasks,
such as finishing repair and milling around manhole covers. Due to
their small size, these milling machines are much more versatile, even
enabling them to do repairs on curbs.
Even small machines usually have a conveyor belt to simultaneously
load the milled material into dump trucks, with the exception of the
models with 350-mm drums.
Some of the small cold milling machine models include:
•
•
•
•
•
•
•
•
•
BM 500/15 (Bomag)
PL 350 S (Dynapac)
MW 500 (Volvo)
SF 515 (Weber)
W 35 (Wirtgen)
W 35 DC (Wirtgen)
W 50 (Wirtgen)
W 50 DC (Wirtgen)
W 60 (Wirtgen)
The milling width of the drum in the machine shown in Figure 4
is 350 mm and its cutting capacity reaches up to 100 mm in one single
Figure 4: W 35 DC cold
milling machine, on three
wheels, by Wirtgen
28
Figure 5: W 50 cold milling machine, by Wirtgen
pass, while the milling width of the drum in the machine shown in
Figure 5 is 500 mm and its cutting capacity reaches up to 160 mm in
one single pass.
W 35 and W 50 are the new releases by Wirtgen that replaced the
W 350 and W 500 models, respectively.
4.2. Medium milling machines
Medium milling machines are used to mill both small and large
areas.
When milling a large area the productivity of previous models
– such as the 1000 C by Wirtgen – was quite poor and unsuitable
for finishing work. New machines with same-width drums, such as
the W 1000 L, W 1000, W 100, W 1000 F and W 100 F, despite
still not being suitable for finishes, perform well when milling
conditions are good, when interruptions are minimal, and when
used on narrow roads, since they are more versatile and easier
to maneuver.
These also include a conveyor belt that dump the RAP in the
trucks while milling.
29
The following are some of the medium cold milling machine
models:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Volpe SF 100 T4 (Bitelli – Caterpillar Company)
Lince SF 150 (Bitelli – Caterpillar Company)
PM 102 (Caterpillar Company)
PRT-225 (C.M.I.)
PL 1000 RS (Dynapac)
SFS 100 (Stavostroj)
1000 C (Wirtgen)
W 1000 (Wirtgen)
W 1000 L (Wirtgen)
W 1000 F (Wirtgen)
W 100 F (Wirtgen)
W 1200 F (Wirtgen)
W 120 F (Wirtgen)
W 1300 F (Wirtgen)
W 130 F (Wirtgen)
1300 DC (Wirtgen)
1500 DC (Wirtgen)
W 1500 (Wirtgen)
Some of these models above are no longer sold by the manufacturers,
but are still being used.
All the machines shown in Figure 6 have 1000-mm milling width
drums. As for their cutting capacity, the W 1000 can reach 250 mm
in a single pass; the PL 1000 RS model, by Dynapac, 250 mm; the
PRT-225 front loading model, by C.M.I., 200 mm; and the PM 102
front loading model, by Caterpillar, 305 mm in a single pass.
30
a
b
W 1000: cold milling machine,
by Wirtgen
PL 1000 RS: cold milling machine,
by Dynapac
c
d
PRT-225: cold milling machine,
by C.M.I.
PM 102: cold milling machine,
by Caterpillar
Figure 6: Models with 1000-mm milling width drums
4.3. Large milling machines
These are used to mill large areas, since the milling drums are wider
than those in the models mentioned previously.
Large machines are recommended for areas with perfect working
conditions. Ideal conditions being narrow roads and when there is
minimal traffic.
Even though the steering system has evolved, excessive maneuvering
must be avoided, since the equipment size makes it cumbersome and
may harm the productivity and create problems for local traffic.
Next are listed some large cold milling machine models:
• BM 2000/60 (Bomag)
• PM-200 (Caterpillar)
31
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
PM-465 (Caterpillar)
PM-565 (Caterpillar)
PL 2000 S (Dynapac)
MT 2000 (Ingersoll Rand)
MP 2000 (Marini)
RX 45 (Roadtec)
RX 700 (Roadtec)
W 1900 (Wirtgen)
2000 DC (Wirtgen)
W 200 (Wirtgen)
2100 DC (Wirtgen)
W 210 (Wirtgen)
W 2000 (Wirtgen)
W 2100 (Wirtgen)
W 2200 (Wirtgen)
Figure 7 shows similar equipment models, provided with drums
ranging between 1900 and 2000 mm in width. In terms of cutting
capacity, the Caterpillar PM-465 milling machine can reach up
to 305 mm at a single pass; the Marini MP 2000 milling machine
can reach up to 320 mm; the Dynapac PL 2000 S can reach up to
320 mm; and the Wirtgen W 1900, 320 mm.
The W 2200 milling machine, by Wirtgen, with a 2.20-m wide
drum, has an option that enables 4.20 m, and reaches up to 350 mm
in one single pass.
32
b
a
MP 2000: cold milling machine,
by Marini (7.b)
PM-465: cold milling machine,
by Caterpillar (7.a)
d
c
PL 2000 S: cold milling machine,
by Dynapac (7.c)
W 1900: cold milling machine,
by Wirtgen (7.d)
Figure 7: Models with 2000-mm wide milling drums
33
5. Main equipment
components
This chapter presents the main components of the milling equipment,
and describes their functions and their operational significance.
5.1. Milling drum
The milling drum is a rigid cylinder made of special steel, to which
the cutting tools are attached – this varies from manufacturer to
manufacturer.
The cutting system is basically the same for all models. The
equipment is provided with a milling drum that rotates at high speeds
and, once started, begins to remove the pavement.
The milling drums are driven by chains, belts or hydraulic engines,
depending on the model and manufacturer.
On the majority of the drums, the cutting tools are positioned so as
to form a “V” shape, as a result of the design formed by two helicoids
starting from the drum’s middle portion. When combined with the
rotation, the milled material is forced to move to the center of the
milling drum housing, facilitating its discharge to the conveyor belt
during the milling, or it deposits the material between the rear tracks
on the pavement when cold in-place recycling takes place.
Some models, such as the C.M.I. PRT-225, are provided with drums
formed by one single helicoid; this causes the milled material to be
directed sideways and to be discharged to the conveyor belt.
35
5.1.1. Milling drum fixing system
Milling drums can be classified based on the type of connection
of the fixing system:
i) Weld-on system: This is a helical system where the holders
are welded directly to the milling drum. This system was
used in the past, but has become obsolete due to its difficult
maintenance.
ii) Segmented system: This is a helical system formed by segments
screwed directly to the milling drum. Each segment is formed by
a pressed base consistent with the curvature of the drum, and
by the holder system. In spite of the significant evolution when
compared to the weld-on system, the maintenance still requires
welding services when the cutting holder must be replaced
during the milling.
iii)Quick-change toolholder system: The helicoid is formed by
blocks welded to the milling drum, and special holder is mounted
on each block, screwed to the block itself. This type of drum is
quite convenient in the event of drum repair, allowing for the
exchange of the toolholder in a few minutes, with no need for
welding services.
5.1.2. Types of milling drums
Originally, only one type of drum was available for cold milling
machines in terms of the resulting pavement roughness – the standard
milling model.
The milling drum is unquestionably the milling equipment
component that has evolved the most, including the evolution of the
holder connection and exchange systems. The number of drums with
smaller spacing between the cutting tools, results in shallower groove
depths and better road texture.
36
5.1.2.1. Fine milling drum
Fine milling was introduced in order to reduce the roughness of the
pavement, primarily for application in areas where the milled surface
will be exposed to traffic, services on pavement surface leveling, and
improvement of the tire-pavement adherence.
The milling drum is provided with a greater number of cutting
tools, i.e., it is denser.
Figure 8 illustrates two milling drums for standard milling and fine
milling and presents a schematic drawing of the spacing between the
cutting tools – 15 mm and 8 mm, respectively.
Figure 8: Comparison of standard and fine milling drums
When exposed to traffic, fine milling provides greater riding
comfort when compared to standard milling. The use of fine milling
brings additional benefits, such as the reduction of the required material
thickness, when fine graded polymer asphalt concrete is applied.
Wirtgen offers fine milling drums for small, medium and large cold
milling machines.
Additionally, there are fine milling drums offered on the market
with a greater number of cutting tools, including the 6 mm x 2
37
model, by Wirtgen. The 2000-mm wide drum has 672 cutting tools
and can be installed on Wirtgen W1900 and W2000 cold milling
machines.
5.1.2.2. Micro milling drum
In micro milling, the spacing is even smaller compared to fine
milling, and it may reach 2 to 3 millimeters.
There are two types of micro milling drums, with different cutting
tool sizes and, consequently, different toolholder sizes.
Drums for small equipment were initially introduced, with cutting
tools smaller than those used on standard milling drums and fine
milling drums.
Figure 9 shows a drum used specifically for micro milling; and Figure
10 shows a comparison of the cutting tools used for standard milling
and those used for micro milling, for this specific type of drum.
Figure 9: Micro milling drum – smaller
cutting tools than the standard drum
One of the applications of this technique is the removal of old
markings, in order to apply new markings as shown in Figure 11. Small
size equipment is recommended for the alteration of the road layout,
due to its greater versatility.
38
Figure 10: Comparison between
standard milling and micro milling tools
Figure 11: Road layout altered using
micro milling of the wearing course
Among other applications, micro milling is employed for the
correction of the road’s longitudinal grade, with no need for the
application of a new wearing course layer. A micro milling drum was
introduced in Germany for this purpose, and installed on large class
equipment – Wirtgen model W2000, with a 2000-mm wide drum and
1,080 tools, as seen in Figure 12.
On lane segments with no traffic speed control, it is crucial that
the longitudinal grade is within the limits specified in the project. This
type of drum allows for the correction of the grade purely through
39
Figure 12: Special micro milling
drum provided with 1,080 tools
micro milling, and the resulting roughness of the wearing course does
not require the application of any type of overlay material.
Wirtgen has hundreds of milling drum types, and this particular
type was designed for micro milling and allows for the possibility of lane
correction, minimizing the costs for compliance with the standards
required by the jurisdiction, and reducing the time required for solving
the problem and the inconveniences to users.
In comparative terms, a drum used for standard milling has
approximately 180 tools, while the drum of the same width used for
fine milling has 280 tools, depending on the manufacturer.
In Figure 13, part of the pavement traffic marking has not been
milled, and we can see, adjacent to it, that the resulting texture on the
road is practically the same as that of the existing wearing course. In
this case, the longitudinal grade is within the limits established by the
control agency, and conventional milling and subsequent resurfacing
are not required.
40
Figure 13: Micro milling for the correction
of the road’s longitudinal grade
5.1.3. Milling drum widths
The milling drum width is generally linked to the size of the
equipment; however, there are types of equipment that allow for the
change of the drum for models with varying widths, including those
for fine milling.
Some equipment models are assembled in identical chassis, with
models varying based on the width of the milling drum installed and
on the power of the engine.
Milling drums are available in various widths, such as: 350, 500, 600,
900, 1000, 1200, 1300, 1500, 1900, 2000, 2100 mm, among others.
There is equipment, the Wirtgen 1000C cold milling machine, that
allows for the variation of the milling width in multiples of 250 mm;
250, 500, 750 and 1000 mm, as seen in Figures 14 and 15.
41
Figure 14: Milling drum with
segmented system
Figure 15: SF 1000 C model
adapted to mill a 500-mm width
Although various such machines are still in use, this model is no
longer being produced by the manufacturer.
The selected segments are removed and, in order to prevent damage
to the drum during the milling process, the indented segments are
replaced by smooth segments.
The quick change drum shown in Figure 16 is a component of the
Wirtgen 1900 cold milling machine (2000-mm milling width).
Figure 16 also shows the presence of ejectors positioned on the
central portion. The purpose of the ejectors is to help load the milled
material from the drum housing to the conveyor belt.
Figure 16: Quick change
system milling drum
for W1900 cold milling
machine
42
Figure 17:
Drums
available for
the Wirtgen
W1900
model milling
machine
The Wirtgen W1900 model milling machine has a rather interesting
feature that allows it to change the milling drum. This model is
available in the following widths: 600, 900, 1000, 1200, 1900 and 2000
mm for standard milling; and 1000 and 2000 mm for fine milling.
This feature is known as the FCS system, also available in other
models from this manufacturer.
Only two to three hours of mechanical work are required to change
the drum, which makes the equipment much more versatile and allows
for a wider range of applications.
There are also some fittings that can be attached to the milling
equipment, including milling rings, as shown in Figures 18 and 19.
43
Figure 18: Milling ring attached
Figure 19: Milling ring
attached directly to the
milling drum externally
to the equipment
5.1.4. Milling drum operating on the pavement
As shown in Figure 20, the milling drum is operated counter
clockwise.
Figure 20: Milling drum rotation
The operation speed affects the gradation of the material generated
during the milling process, particularly in terms of lumps*, as described
in Chapter 12 of this book.
Lumps: are parts of the pavement composed of one or more aggregates,
surrounded by fine particles and asphalt cement, which are generated during, and
inherent to the milling process.
*
44
5.2. Cutting tools
The cutting tools act directly on the pavement and are responsible
for the cut.
These parts are comprised of a body forged of steel, with a harder
tungsten carbide and cobalt tip.
The cutting tools are provided with a cylindrical ring that surrounds
their base, so that they are maintained inside the holder under pressure,
allowing them to rotate freely during the milling process, in order to
ensure uniform wear.
The applications of cutting tools are not limited to milling
equipment; they can also be used on drills or attached along the blades
of planers, among others.
Figure 21 shows a schematic drawing of the cutting tool used in
cold milling machines.
Figure 21: Cutting tool
dimensions (mm) for
standard milling using cold
milling machines
45
The wear of the cutting tools depends primarily on the type of
application for which they are used and on their quality. However,
other factors may decrease the service life of cutting tools, such as
ambient temperature – the lower the temperature, the greater the
deterioration.
Milling machines are provided with water tanks. The primary
purpose is to spray water on the milling drum. This prevents the
cutting tools from locking, which would cause irregular wear of the
part. Additionally, the water spraying reduces the level of dust generated
during the operation.
The wear of the cutting tools varies according to the intervenient
factors: the hardness and quality of the materials – both aggregates
and bituminous binder, the cut depth, the ambient temperature, and
above all, the level of degradation of the pavement.
According to the Caterpillar Manual[4], cutting tools should be
replaced when:
a) the body of the tool is thin around the end;
b) a flat surface appears on one of the sides of the tool, due to
localized wear, suggesting that the tool is not rotating on its
holder;
c) the tool end breaks;
d) the tool end is no longer capable of cutting.
Figure 22: Identifying cutting tools wear
46
5.3. Cutting tool holders
The holders are attached to the cutting tools. The position and
angle of the holders produce a pavement with rough texture, but flat
and level, with uniform groove distances and depths.
The durability of the holders is directly related to the conditions of
the equipment cutting tools. Cutting tools that have been subject to
severe wear cause the reduction of the equipment efficiency, in addition
to excessive wear of the holders during the services.
Based on what was presented in item 5.1.1, depending on the type
of drum, some holders are welded directly to the milling drum, some
are welded to the segments and screwed to the milling drum. Others
are screwed to parts welded to the milling drum.
Some holders – but not all – are provided with reference guides to
facilitate the welding operations.
However, the holders of the Wirtgen 1000C cold milling machine are
not provided with such guides; in this case, the only point of reference
is their height on the drum. When replacements are necessary, the
welder’s ability determines the precision of the angle.
The holders of the Wirtgen W50 milling machine are provided
with guides that determine the holders’ appropriate height and angle,
thus ensuring a regular surface after the repair.
Figure 23: Cutting tool holder with
reference guide
47
Interferences present on the pavement, such as manhole covers
“covered” by a layer of asphalt, may cause the rupture of the milling
drum’s tools and holders and, depending on the gravity of the problem,
may result in downtime until the damaged parts are replaced.
The system shown in Figure 24 allows for the replacement of the
damaged holder through the simple removal of the screw located on
its lower component, thus avoiding all welding services required for
other types of drums.
Figure 24: Detail of the quick change holder
5.4. Scrapers blades
Scrapers are forged of steel and hard metal, and screwed onto the
scraper plate side-by-side in accordance with the working width of the
milling machine.
Single parts, triple parts and parts of larger widths are available in
stores depending on the manufacturer.
Milling machines are not provided with a system for the suction and
collection of the milled material. As mentioned before, the material
48
Figure 25: Scrapers details in red
is launched onto the conveyor belt whenever a sufficient amount of
material is found in the milling drum housing.
During milling, the scraper plate must be kept closed. The
scraper blades must work on the surface with a certain amount of
pressure, so as to leave the least amount of granular material and
dust on the surface.
Milling with the scraper plate often results in rougher surfaces. A
damaged milling drum can make uneven grooves, however, the scraper
blades minimize the problem.
Damaged scrapers or the lack of some parts may result in an
irregular milling surface. When in good conditions the irregularity
may be caused by the milling drum, with the use of uneven holders
and cutting tools that come from different manufacturers, or still by
natural wearing.
5.5. Conveyor belt
The conveyor belt is the part of the equipment used to raise and
load milled material into dump trucks and simultaneously to the milling
operation for its transportation determined for material deposit.
Almost every type of milling equipment is provided with a
conveyor belt, except for small models where the milled material is
left on the lane.
49
Some types of equipment – normally small and medium class models
– are backloaded, and therefore the trucks must move backwards to
load the milled material.
Large equipment models are generally frontloaded; in such cases,
the dump trucks move ahead of the equipment.
The manufacturers have not defined a criterion for the type
of loading – front or back – based on the size or model of the
equipment.
The general trend is front loading, and some manufacturers have
developed new equipment, similar to the old ones with preference to
front loading.
Following this trend, Wirtgen released front loading W 1000 F
milling machine, a medium size model, as shown in Figure 26.
Figure 26: Wirtgen W 1000 F
frontloaded milling machine
Recently Wirtgen released the front loading models W 100 F,
W 120 F and W 130 F.
Figure 27 shows another medium size model: the W 130 F milling
machine, by Wirtgen.
50
Figure 27: Wirtgen W 130 F
frontloaded milling machine
In practical terms, the rear conveyor belt forces the dump trucks
to steer once the loading is complete if the equipment is working on
a one-way lane and positioned in the flow direction.
In narrow roads of large urban centers a conveyor belt may be
problematic when there is a need for equipment steering, particularly
because of obstacles such as poles and traffic signs positioned too
close to the work area. Fortunately, today some types of equipment are
provided with a folding conveyor belt, which also facilitates equipment
transportation.
5.6. Speed control system
The speed with which the equipment moves is controlled by handoperated levers.
There are two types of speed: the nominal speed and the effective
work speed. The latter is lower and varies with the type of equipment,
the cut depth, the degree of pavement oxidation and degradation
among other factors. As a result, the effective speed can only be
determined through actual field measurements.
51
5.7. Cut depth control system
The milling equipment allows the cutting of the equipment to be
of different thicknesses; equal thicknesses on both sides or distinct
thicknesses on each side of the equipment. The equipment can be
inclined to the right or to the left, as seen in the schematic drawing
of Figure 28.
Figure 28: Milling drum inclinations
The cut depth is checked manually or electronically, depending on
the model, based on the surface elevation of the pavement.
In the manual system, the operator adjusts the cut depth by turning
the levers located on both sides of the equipment and reading the
ruler located on both sides. In the electronic system, the cut depth is
electronically adjusted and the data is conveyed by the optical sensors
directed to the reference surface.
5.8. Equipment support system
The milling equipment is mounted on tracks or massive tires.
5.8.1. Equipment mounted on tires
Most of the small and medium size equipment models are mounted
on tires, generally made from vulcanized elastomer rubber, as illustrated
in Figure 29.
52
Figure 29: Wirtgen W 100 F
cold milling machine – mounted on tires
5.8.2. Equipment mounted on tracks
Large equipment models are generally mounted on tracks which
allow for a better distribution of heavy dead weight loads on the support
surface.
The tracks are coated with polyurethane-type material to prevent
damage or scratches on the surface of the pavement that has been
recently resurfaced.
As illustrated in Figures 29 and 30, some medium equipment models
are available mounted either on tires or tracks.
Figure 30: Wirtgen W 100 F cold milling machine – mounted on tracks
53
54
6. Complementary equipment
for operational support
In this section the main operation support services and the equipment
required for the execution of milling are exposed.
6.1. Signalling of the work site
The execution of milling services requires the signals to alert the
public of work areas, including signs and banners warning about which
services are taking place.
This item is vital to ensure the safety of construction workers and
road users.
During night-time service we recommend the use of sufficient
signs, direction markings and delineators with plenty of reflective
material to promote the safe channelization of vehicles. Under such
conditions, vehicles drivers will have enough time to notice the
obstacles and slow down to the appropriate speed, thus preventing
risks to drivers and workers on-site.
Figure 31: Lane signs for
traffic channelization
55
The devices required to signal the road for vehicle channelization,
in order to prevent traffic from crossing into a lane, will depend on
the type of road and on the lane to be isolated.
When working on a central line in a road with more than two lanes
it is recommended that one of the side lanes be closed, safeguarding
as much as possible the access to the road.
6.2. Water tanker
As described above, water should be sprayed on the milling drum in
order to reduce cutting tools dulling and the amount of dust generated
during the milling activities. For that purpose, a water tanker is required
to supply water.
The machines are provided with tanks of various capacities,
depending on their size and applicability. Some models with greater
tank capacity may not require refilling during an entire work shift.
Other models with smaller capacity tanks require a tank truck for
refilling during the implementation of the services.
6.3. Metal detector
A metal detector is a device used to check for metals located under
the wearing course. The procedure consists of running the detector
over the surface to be milled.
Especially in large urban centers, metals are commonly found under
the asphalt wearing layer, where resurfacing was executed directly on
such elements, including old tram tracks.
Also, it is quite common to find manhole covers under the asphalt
layer in areas that were resurfaced.
The use of metal detectors may prevent equipment damage and
paralization.
56
6.4. Finishing on milled areas
After milling, adequate finishing services must be conducted in the
milled segments, both around manhole covers and adjacent to curbs
or transverse to the cutting direction, for the perfect anchoring of the
new wearing course.
Milling transversally to the direction in which the equipment moves
is necessary both at the beginning and at the end of the milled area,
due to the shape of the drum.
6.4.1. Using small milling machines
In some cases, the productivity is increased when using small
equipment to supplement the work of larger equipment.
This is a common solution for urban pavements with various types
of interferences, such as manhole covers.
While larger equipment mills the continuous surfaces, the smaller
equipment carries out the finishing services around the interferences,
adjacent to concrete curbs, and in areas of difficult access to large
equipment.
Figure 32: Small and large class
cold milling machines working together
57
6.4.2. With milling units attached to another type of equipment
The finishing around the various types of utility interferences can
also be carried out using milling equipment attached to another type
of equipment, as seen in Figure 33.
Bobcat model 863
Case model 1845C
Figure 33: Milling units attached to other equipment
It is important to note that this is not actually a milling machine,
but a hydraulically adapted fitting, and its productivity is much lower
than that of an actual milling machine.
6.4.3. Using slitting saw and pneumatic breakers
When more appropriate equipment is unavailable, it is common
to employ a slitting saw and/or a pneumatic breaker for the finishings
to allow for the perpendicular cutting at the beginning and end
of the milled segments. This ensures a better anchorage of the
asphalt layer.
Figure 34 illustrates the steps required for the finishing services,
using a slitting saw and pneumatic breaker.
58
Figure 34: Finishing procedure at the beginning
and at the end of cutting, to ensure a
better anchorage of the asphalt layer
The procedure illustrated in Figure 35 is also used but only with
the pneumatic breaker for perpendicular cutting.
Figure 35: Finishing using pneumatic breaker
59
6.5. Dump trucks
During the milling, dump trucks are used to transport the milled
material and collect the remaining material left on the road.
The number and type of trucks required should be determined
onsite, based on traffic conditions and the distance of the disposal
area.
In size order, the following is recommended for an average distance
of 10 kilometers (both ways):
• For cold milling 1000: 3 dump trucks (light truck);
• For cold milling 1500: 5 dump trucks (heavy truck);
• For cold milling 2000: 7 dump trucks (heavy truck).
6.6. Lane sweeping
According to Balbo[5], after milling, loose materials (fine particles
or grains) are naturally present on the surface of the pavement. When
the lane is reopened for traffic, this material tends to be lifted by
the movement of the vehicles, creating a dust curtain over the road
surface. This material can also be lifted by horizontal forces between
the vehicles’ tires and the pavement surface and may increase the
braking distance in the case of sudden breaking
That said, after the milling and prior to reopening the milled
lane for traffic, the lane should be swept to remove the loose
materials from the milled surface. This may be done manually or
mechanically.
The material that results from the milling is very rich in binders, as
the mean percentage of emulsion (as weight) incorporated during “in
situ” cold recycling is only around 1.5 to 3.0%. In order to avoid the
aggregation of the milled material on the milled surface, the sweeping
should be carried out concomitantly to the services.
60
6.6.1. Manual sweeping
When milling equipment was introduced in Brazil, lane sweeping
was only done manually and required the work of several men using
brooms, dustbins, and wheelbarrows.
Manual sweeping is not particularly effective, and when used
alone, is unlikely to remove all of the fine material deposited on a
rough surface.
In the areas where the milled lane must be reopened immediately
after a stage of the services is concluded manual sweeping limits the
productivity of the milling equipment because it has to be stopped
early due to the time required to complete the sweeping.
Another disadvantage of manual sweeping is the risk to workers
since services are often carried out while the traffic of vehicles flows
on the adjacent lane.
6.6.2. Mechanical sweeping
Mechanical sweeping has proven more efficient, in terms of the
resulting surface quality by not limiting the productivity of the milling
equipment.
Especially in private roads, mechanical sweeping is preferred because
it provides better results, both in practical and economical terms, but
particularly in consideration of safety aspects and of reopening the
lane for traffic.
Another important factor for the use of mechanical sweeping over
manual sweeping is that mechanical sweeping requires fewer workers
for operation.
There are machines designed specifically for sweeping, such as the
model seen in Figure 36.
61
Figure 36: Sweeping truck
Additionally, there are fittings adapted to other types of equipment, such
as the bobcat, that have been commonly used for this type of service. The
sweeper is attached to the front of the equipment, as seen in Figure 37.
Figure 37: Bobcat with mechanical sweeper
62
When sweeping during resurfacing, either manually or mechanically,
the use of an air compressor is recommended to remove the remaining
fine material from the surface.
6.7. Hauling the equipment
It is unadvisable to move milling machines long distances without
a trailer because it causes considerable wear on the rolling system.
A trailer with a suitable board is recommended to haul these
machines. The ramp should not be steep, especially if the milling
drum is located between the two axles, as it frequently get in the way
of loading the machine onto the trailer. Trailers such as the ones in
Figure 38 are recommended.
a
b
Figure 38: Trailers appropriate for the
transportation of milling equipment
Due to the weight of these machines, the number of necessary axles
must be observed so as not to exceed the tonnage limit.
On highways or, at building sites, it is even possible to build a
structure with local soil or granular material to allow the machine to
be loaded onto the trailer, but in major urban centers that is practically
impossible.
63
7. Applying the milling
The introduction of milling machines was an extremely important
event for pavement restoration in general because of their practicality
and speed. Only places which need repair could be repaired and
restored. Additionally, these machines could:
a) maintain the original lane grade;
b) make repairs without leaving uneven joints when resurfacing
exclusive traffic lanes or applying patches to the pavement;
c) correct and/or change the inclination of lanes in relation to
surface draining systems;
d) maintain leveling around manhole covers, among other
interferences, especially on urban pavements.
In some situations, milling can be the best option for pavements
that have been resurfaced over and over again without prior removal
of the previous wearing course. Furthermore milling can be effective
in relieving weight on bridges and flyovers and reestablishing the
original height inside tunnels, under bridges and flyovers when laying
a new asphalt layer.
7.1. Types of application
Milling has a large number of applications, which despite their
similarities, are used for specific purposes at building sites. In some
cases, the most suitable machines for specific jobs are identified in the
following discussions.
65
7.1.1. Milling to correct surface distress
Milling is used to correct pavement surface distresses and is not
limited to surface milling only, which is used to correct shoving,
bleeding flushing, etc.
In places where bleeding or flushing is observed, surface milling
is used to restore tire-pavement adherence to provide greater comfort
and safety for users.
In places where shoving can be observed, the lane surface is leveled
and areas that need to be repaired are identified with the help of a
ruler that is placed on the pavement. The purpose of this procedure
is to improve riding conditions.
Figure 39: Lane profiling milling
If the drum is in perfect working condition this type of application
makes the resurfacing of the milled surface unnecessary.
Any milling machine can be used for these jobs. The equipment
should be chosen according to availability and the areas to be milled;
however, machines with wider milling drums are recommended to
make the work easier and a fine milling drum minimizes the roughness
on the lane surface.
66
7.1.2. Discontinuous milling areas
The milling of discontinuous areas varies in length and width,
frequently reaching the total width of one or more lanes. In the majority
of jobs, this application is used in the most frequently used lanes.
In cases where the total lane width is not milled, it is advisable to
observe the appearance of lengthwise steps on the pavement while the
resurfacing job is not executed.
Steps resulting from thin cuts can be tolerated for a short period
of time; however, in cases of greater depths, they can place users’ life
at risk, especially those riding motorcycles.
Milling should only be halted when enough areas has been milled
to allow the road to be resurfaced on the same day in order to avoid
steps on the lanes; which may limit the use of milling equipment
productivity.
If the pavement is undergoing deep milling, the area must be isolated
from traffic until the lower (binder) layers have been laid in order to
decrease the height of the step.
Any milling machine can be used in larger areas but small and
medium machines are recommended for smaller repairs because they
are practically and financially more convenient.
Small machines are even suited for minor tasks, such as pothole
covering operations and increasing the productive capacity as opposed
to the reconfiguration conducted with pneumatic breakers.
Figure 40 shows areas of a pavement where interventions were
conducted only at specified locations where the wearing course needed
repairs.
67
Figure 40: Interventions in discontinuous areas
7.1.3. Continuous milling of the entire lane
This technique consists of milling the entire width of the road; the
thickness of the cut is specified in the project.
This procedure is used in places where grading elevations must
be maintained after resurfacing, where there are problems of severe
pavement oxidation or worn surfaces that need to be solved. It is also
used to mitigate pavement crack reflection or spreading effects from
the remaining pavement on to the new asphalt layer, and even to
eliminate other distresses found on the asphalt layer, such as bleeding
flushing and shoving.
Prior to the use of milling machines, resurfacing was done without
prior removal of previous wearing course layers. Milling also enables
the restoration of the original pavement grade and elevations.
Figure 41: Continuous milling of the entire lane
68
Large machines are recommended for these situations as they can
minimize labor time.
7.1.4. Edge-shaped
Edge milling is executed only on the lane edges, by leaning the milling
drum to the desired angle to anchor the new wearing course layer.
It is extremely important to observe the cambering of the existing
pavement before this procedure, because repetitive removal of previous
layers only on the edges of roads cause undesired cambering and
discomfort for users.
According to Bonfim and Domingues[6], there are two cases where
edge milling is unfavorable, as shown in Figure 42.
Figure 42: Inadvisable edge milling situations
Milling width “d” is determined based on the existing cambering
on the road, which in extreme cases, can lead to the milling of the
entire road.
Both Cases “A” and “B” have a critical area due to the cambering
and the narrow milling width “d”. In Case “B”, edge milling was
conducted with a step on both sides.
69
The ideal situation is shown in Figure 43, where the cut ends in
zero on the opposite side of the edge.
Figure 43: Correct edge milling after resurfacing
7.1.5. Milling to correct pavement inclination
This milling application is used to correct and or improve the
existing pavement inclination longitudinally or transversely.
Location and thickness of the cut are usually determined with the
help of a topographic survey of the road.
This application is frequently used in the duplication of roads, where
pavement milling can reduce costs, by making necessary geometric
corrections at the same time.
7.1.6. Finishing milling
This application consists of milling the pavement close to existing
distresses on the pavement surface.
Especially in the case of urban roads, finishing milling complements
the milling done with large machines which generally does not mill
around interferences as shown in Figure 44.
70
Figure 44: Asphalt layer without
milling around manhole covers
Figure 45 shows schematic finishes around various interferences.
Figure 45: Finishing milling
71
7.1.7. Rumble strip surface milling
Rumble strip surface milling discontinuous surface milling, at a
depth of 10 mm, usually conducted along rest areas and shoulders.
The exposed milled surface works as a warning sound when cars
go over the lane’s limit, and offers no safety risks for users.
The easiest way to do the job and not have to worry about distances
between the millings is to replace the back wheels, aligned with the
milling drum, for a set of guide blocks, creating a five side “fake wheel”.
Thus, as the equipment moves forward, the pavement will be milled at
even distances, without the operator having to worry about lifting and
lowering the equipment’s milling drum. Small machines are usually
used for this job, such as the Wirtgen W350.
Figure 46: Rumble strip milling
machine with “fake wheel”
Figure 47: Results of rumble strip
milling on the road
7.2. Milling for the correction of distresses
The assessment of a pavement consists in a set of activities that aim
at describing a pavement’s conditions quantitatively and/or qualitatively
with regard to the level of riding safety and comfort. The functional
aspects of the road as well as its capacity to support the loads imposed
by the traffic must always be considered.
From the user’s point of view, many aspects can indicate point to
the rupturing of a pavement, which is known as a functional rupture.
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Generally speaking, this assessment can be quite subjective because it
considers distresses on the riding surface into account.
Among them we may point as main aspects, the longitudinal
unevenness leading to discomfort, low roughness levels on the surface
leading to a lack of tire-pavement adherence, potholes on the road,
frequent cracking and the erosion of the riding surface, rutting and
severe rippling on the road.
Consequently, a simple visual assessment can reveal the functional
state of a pavement with regard to its “distress morphology”. The
following are exceptions
• Noncompliance with the procedure of standard methodologies
DNER PRO-07/78[7], DNER PRO-08/78[8], DNER ES128/83[9].
• Noncompliance the Instructions for Field Activities published
by DNER[10], which are used at the network level.
Nevertheless, it is very important to identify the probable causes of
the distresses, called genesis, and the factors that led to the increasing
deterioration of the pavement.
Hence, it is possible to choose one among the many rehabilitation
alternatives that will help eliminate or inhibit the propagation of the
distress as a way of extending the service life of the pavement.
Pavement milling is a technically viable solution for many of the
distresses observed on pavements; however, in some cases, it may not
be suited to solve the specific problem, especially bearing in mind the
relative approach to the genesis of the problem, studied by international
road technicians.
Among the many publications on the subject of pavement distress,
we can point out the Distress Identification Manual for the Long-Term
Pavement Performance Studies[11] and MID – Manual de Identificação
de Defeitos de Revestimentos Asfálticos de Pavimentos[12] (Manual for the
Identification of Asphalt Pavement Distress) as beneficial references.
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The MID is a very specific and much recommended manual as
it covers many publications on the subject, in addition to including
illustrations of each type of distress in three different stages of
degradation, i.e. low, medium and high severity.
7.2.1. Cracking
Cracking is the most commonly found distress on asphalt
pavements.
Domingues[12] mentions the following types of cracking: fatigue
cracking, transverse, longitudinal, parabolic, joint reflection and block
cracking.
The first stage of cracking occurs when the pavement fissures. The
cause of the cracking and the way it propagates must be assessed so a
solution can be made on how to fix the problem.
Milling is a suitable solution in cases where cracking propagates
from the top, as it can completely eliminate the problem, as shown
in Figure 48.
Figure 48: Eliminating cracks through milling
Cracking propagates most often from the lower levels up to the
surface. In these cases milling and subsequent resurfacing will not
permanently solve the problem but only delay propagation of cracks.
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Parabolic cracking is of a type of distress that can be permanently
solved by milling, since it is a surface problem caused by the low
resistance of the asphalt mixture or insufficient bond between the
subjacent layers and the pavement asphalt layer.
7.2.2. Patch deterioration
Patch deterioration is a series of damages found in places where
patches have been applied to the pavement. It can be caused by an
insufficient job or even by the over use of patches.
If the distress is technical, construction-based, or if it has been
caused by incorrect use of the material, milling can definitely solve
the problem, because it can remove the damaged layer and allow the
pavement to be reconstituted.
If the problem is structural, one should first determine if milling is
a viable solution. In some cases, a designer can choose to rebuild parts
or the whole pavement.
Recycling of milled material using cement is another option. This
method promotes material consistency and stability, incorporating the
wearing course into the base, which is followed by a new hot layer of
the wearing course.
7.2.3. Potholes
Potholes are localized distresses which usually cover small areas.
Different reasons cause certain wearing course components begin to
break. If an intervention doesn’t take place at this stage, there can be an
increase in the spalling and the consequent appearance of a pothole.
The use of milling machines in such cases, and at the depth needed
to solve the problem, is crucial both in practical and financial terms.
Milling allows the reconfiguration of areas where there are potholes.
Milling additionally provides optimal conditions for reconstructing
and preventing uneven joints.
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7.2.4. Rutting
Rutting is a surface depression in the wheel paths that leads to an
uplift of the asphalt layer.
This distress can be caused by an asphalt mixture which was poorly
designed for local conditions or by a structural deficiency in lower
pavement layers.
In the first case, milling is recommended for the correction of the
distress, as it can completely remove the poorly mixed layer and allow
a new, properly mixed layer to be laid.
In the second case, usually characterized by high severity rutting,
milling can only allow the root cause of the distress to be dealt with. This
is done by removing the thickness necessary to solve the problem.
That means demolishing the whole, or part of the pavement. Later
a financial appraisal is conducted to check the feasibility of using
milling machines.
7.2.5. Depression
Depression, or settling, is the appearance of slightly lower areas on
the pavement resulting from construction distresses or the settlement
of the pavement’s structure in certain places.
Construction depressions on the wearing course layers can be
eliminated by the milling of thin layers followed by resurfacing.
Similar to previous cases, milling can be used to solve problems of
settlement or deformation of the lower layers by removing the necessary
thicknesses so the pavement will be able to bear the loads to which
it is exposed. Such milling may cause breach of the base, subbase or
subgrade layers leading to reconstruction of the pavement.
7.2.6. Shoving
Shoving is a functional distress found on pavement surfaces caused
mainly by the application of a poorly configured asphalt mixture.
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Overlays without the prior removal of the existing layers will only
make the problem more severe.
Some highly fluid mixtures, containing too many binders and
overexposure to high temperatures, are not capable of bearing the
traffic loads, and become deformed. Milling the wearing course is a
suitable technique for such situations, because it allows the thickness
of the problematic pavement to be removed and a new layer to be laid
without changing the grade.
In some low severity distress cases, milling is used only to profile
the wearing course surface with a view to improving traffic conditions
by providing better tire-pavement interaction.
7.2.7. Polished aggregates
Polished aggregates are a functional type of distress, caused by the
wearing of the edges of aggregates exposed on the pavement surface
by traffic. It leads to a lower adherence coefficient and consequently
impairs the adherence between the tire and the pavement.
It is important to point out that polished aggregates can only be
considered as distresses when the adherence coefficient becomes low
enough to reduce skid resistance.
These distresses may occur when the type of aggregate used to make
the asphalt mass is not capable of coping with intense traffic.
Asphalt layer surface milling can be used to create better tirepavement adherence and, as a result, improve skid resistance. However,
in the case of lower quality aggregates, the problem may reoccur after
the pavement has been exposed to traffic for some time.
Micro milling and fine milling are recommended for this type of
operation.
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7.2.8. Bleeding / flushing
Bleeding / flushing is a result of the outcropping of bituminous material
on the pavement surface caused by excessive binder in the mixture, which,
in time, turns into a film that makes the surface smooth.
Bleeding flushing is an irreversible process as there is no way of
removing the excessive binder from the mixture.
The bleeding flushing of the asphalt mass causes tire-pavement
adherence to decrease – a situation that can become worse when the
pavement is wet.
This functional distress can be treated in two ways: surface milling
with no subsequent resurfacing is a temporary solution that improves
tire-pavement adherence; removing the entire wearing course thickness
that contains too much binder and subsequently resurfacing with
appropriate asphalt mass is a permanent solution.
Monitoring has shown that the distress tends to reoccur quickly
with temporary solutions.
7.2.9. Surface distresses and defects
There are many types of structural distresses and defects, which
include raveling, weathering and stripping.
These distresses are characterized by the corrosion of the wearing
course due to the progressive displacement of aggregate particles, the
loss of binders or the loss of adherence between the aggregates and
the asphalt.
Milling can solve the problem based on the solution proposed in the
project, whether superficial or through considerable cut depths.
7.2.10. Pumping
Pumping is a distress caused by traffic loading and is made evident
by the presence of subgrade material on the wearing course surface; this
material reaches the surface through the cracks on the pavement.
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This type of distress frequently occurs when the pavement is cracked
allowing the water infiltration to reach the subgrade, which consists of
a low permeability material, similar to clay. When in the subgrade, this
water drains very slowly and, therefore, remains inside the pavement;
when the tires exerts pressure on the pavement, the water is pumped
up to the surface through the cracks, bringing with it fine subgrade
material particles; consequenctly, the pavement structure collapses
within a short period of time.
Milling and resurfacing will stop large quantities of water from
infiltrating the pavement, but the cracks tend to propagate and the
distress reoccurs within a few months.
The solution consists of the removal of the top layers and the
replacement and stabilization of the subgrade material, followed by
the reconstruction of the remaining pavement layers.
7.2.11. Asphalt layer overlay
Wearing course overlays can be considered a type of distress when
it leads to undesired safety and traffic conditions on the road.
For many years, new layers have been laid on asphalt pavements,
to improve riding safety and comfort conditions, without the removal
of the existing layer. This procedure was used because there were no
suitable machines to remove the material.
Every new resurfacing caused an elevation in the pavement grade,
resulting in several technical and financial problems.
Milling has proven to be very effective in these cases, allowing the
pavement grade to be maintained.
7.2.12. Lane/shoulder drop-off or heave
A lane/shoulder drop-off or heave occurs when asphalt wearing
course layer is overlaid without the use of a suitable machine to
guarantee the original elevation.
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Previously, projects included a difference in elevation between the
shoulder and the lane. This distress can become problematic when
many wearing course layers are overlaid, posing a risk to users.
Apart from that, the increase in the elevation difference between
the shoulder and the lane are usually caused by the settling or the
wearing of the shoulder material.
In his manual, Domingues[12] classifies the drop off between 6 and
12 mm as a low severity distress, between 12 and 15 mm as a medium
severity distress and above 25 mm as a high severity distress.
It is up to the designers to find the most cost-effective solution in
the case of a new lane resurfacing.
If the lane and shoulder have to be resurfaced, milling the edge
of the lane can be a reasonable solution as it eliminates the step and
improves water drainage.
On the other hand, a difference in elevation between the lane and
the shoulder would appear as if only the lane had been resurfaced.
Milling is useful in the both the cases of applying patches and/or
resurfacing the entire lane. Milling in these cases would be a financially
feasible solution for many reasons; one being that it would save the
funds necessary to lay material on the shoulders. This would also
maintain the pavement elevation.
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8. Benefits brought by
the milling technique
T
he use of milling techniques, described above, emphasizes the fact
that milling is highly feasible. However, that does not mean milling
machines must be used in every resurfacing job.
Repeated resurfacing can lead to undesired situations that justify
using milling techniques as a way to solve many problems; that being
the case, these are the technique’s main advantages:
8.1. Maintaining pavement grade
Milling a specific thickness of the wearing course that has been
predefined in a project enables the degraded material to be removed
so new material can be laid without changing the pavement’s elevation
and relatively improving its structure and functionality.
Successive resurfacing without removal of the existing wearing
course can cause aesthetic, functional and safety problems.
Aesthetic problems happen when the elevation of the edge of a lane
is higher than the elevation of the curb.
One of the functional problems that can arise from changes in the
transverse section of the stormwater drainage, is deforming the curb’s
successive wearing course layers, and consequently decreasing their
draining capacity.
Another important functional problem is the decrease of feasible
height under bridges, flyovers, and inside tunnels.
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Changes in the pavement transverse section can also cause safety
problems due to the steep inclination of the lane. Additionally, users
are exposed to accidents resulting from the decrease in curb height,
which is designed to distinguish between the road and the sidewalk.
Figure 49 shows a pavement that was subjected to successive asphalt
resurfacing without the prior removal of the previous wearing course.
In this case the elevation of the lane is approximately 30 cm higher
than the elevation of the curb.
Figure 49: Asphalt wearing course overlay
without prior removal of previous layers
8.2. Maintaining joint leveling
Prior to the introduction of milling machines, it was quite common
to lay a new asphalt layer over an existing one when resurfacing
exclusive lanes or small areas, which caused a difference in elevation
due to uneven joints.
Differences in elevation are an inherent part of the asphalt paving
even though thin asphalt layers are used. Additionally once traffic is
allowed to run freely the material can easily spall in uneven areas.
Even though the thinnest part of the asphalt material is used, the
difference in elevation is an inherent part of the procedure; besides, once
traffic is allowed to run freely, the material easily spalls in certain areas.
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This difference in elevation causes discomfort for users and possible
material deformation and sliding, since the new wearing course layer
cannot be anchored.
Figure 50 shows an illustration of a poorly executed joint job where
the joint is left uneven and with significant spalling.
Figure 50: Patch overlay on
existing pavement
Figure 51: Wearing
course shoving
8.3. Correcting shoving
Shoving causes riding discomfort and, depending on the level of
severity, can pose a risk to users (Figure 51).
In bus lanes, sharp curves, roundabouts and traffic circles, milling
can correct shoving and enable the profiling of the lane.
Therefore, this is a feasible solution for the restoration, maintenance,
and conservation of a pavement.
8.4. Maintaining the appropriate level around
manhole covers
On urban roads there are many interferences from various public
service suppliers causing discontinuity on the pavements.
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These utility structures are located precisely over the many galleries
used for water, electricity, telephone lines, etc., and leave manhole
covers exposed on the pavement.
Resurfacing the road without first milling the pavement causes
a difference in elevation between the new wearing course and
these manhole covers, and makes it necessary for manholes to be
leveled later.
Figure 52: A 10-cm difference in elevation
between the lane and the manhole cover, a
result of two resurfacing processes without prior
removal of the previous wearing course
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9. Problems that may occur
due to the use of milling
Milling can cause pavement problems leading to the stalling of
traffic and repair progress.
Some problems are inherent to the process, such as steps across or
along the adjacent lane. Others however, may be caused by milling
depending on the kind of operation and current condition of the
wearing course.
A project designed by an experienced engineer, geared towards
fully understanding the existing functional and structural state of the
pavement, can minimize some of the executive problems inherent to
the process.
Solutions adopted that were not based on a thorough project can
lead to situations –that generally increase costs of the work or to the
failure of the solution adopted.
9.1. Step on the lane
Step on the lane can be considered the most serious problem
caused by milling if traffic is allowed on the road before resurfacing.
Depending on the depth of cut, it may require that the area be
completely isolated.
There are two types of lane steps: longitudinal and transverse. Both
can be minimized if certain procedures are adopted in areas where
traffic must be allowed on the road before resurfacing.
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The solution for the transverse step is to mill a ramp at the
beginning and the end of the cut and finishing it when resurfacing.
This is usually done with a small milling machine, a slitting saw or a
pneumatic breaker.
The longitudinal step is inherent to the process of milling when
dealing with exclusive driving lanes. For small thicknesses, depending
on the type of road, traffic can be allowed on the road as long as the
lane is duly marked to warn users.
When milling at greater depths, however, that specific segment of
the road must be isolated from traffic.
Some agencies do not allow traffic back on the road before resurfacing
and in such cases the pavement is resurfaced on the same day.
9.2. Appearance of potholes
Milling can cause potholes to appear on the road due to the spalling
of the remaining pavement in places where cutting thicknesses reach
the lower layers, or when the pavement needs to be milled deeper than
the thickness of the wearing course in some areas.
This problem often occurs in places where there is a lot of cracking
on the pavement.
Figure 53: Potholes in milled areas
86
Potholes should be covered with asphalt before traffic is allowed
back on the road in places where spalling was observed. This procedure
stops potholes from propagating, in addition to preventing the
acceleration of the destructive process caused by water infiltration in
the lower pavement layers.
It is important to resurface as soon as the milling is finished to
curtail any setbacks to users, as well as avoid problems caused by the
exposure of the milled surface to stormwater runoff and traffic.
9.3. Displacement of bituminous layer slabs
It is common for bituminous layer slabs to be displaced in milled
areas in cases where almost the whole thickness of the existing
wearing course layer is milled, especially once the traffic is allowed
on the lane.
Figure 54: Slab displacement in milled areas
after the traffic was allowed on the lane
87
When milling, this problem may occur due to the movement of
scrapers located in the lower part of the lid and may continue with
traffic potentially leading to accidents.
Before laying the new wearing course layer, all the debris must be
removed from the lane. Depending on the amount of debris, specific
areas may require new milling, at greater depths.
This problem can be avoided if the pavement’s structure is known
and the milling thickness is defined in the restoration project. As
recommended by Technical Standard DNER PRO-269/94[13], never
leave less than 20 mm of the wearing course, as it will certainly cause
problems.
When this problem occurs it is impossible to maintain the minimum
wearing course thickness. Therefore it is recommended that a new layer
be applied immediately after milling to preserve the whole remaining
structure.
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10. Productivity of
milling machines
10.1. Opening considerations
Milling can be used in numerous situations, be it in large open areas
or places where many obstructions can be found. That being said, we
will present field results with the purpose of illustrating the varying
productivity in different types of jobs.
In terms of the type of work, areas for repair that are continuous
and long will certainly cause milling machines to be more productive,
since they are not subject to as many interferences during the operation.
These are usually operations on expressways and highways.
When milling pavements in urban areas – particularly in major
cities where there is more interference and the time available for work
is very limited – productivity is less than in the previous case.
Some of the factors that can significantly reduce the equipment’s
productivity are listed below:
a) narrow roads;
b) transition zones and crossroads;
c) curbs transverse to the cutting direction;
d) manhole covers;
e) vehicle counting devices;
f) cars parked in areas where the work is being carried out;
g) other types of work under implementation in the same area.
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There are also factors that relate directly to the work in question –
among which are the state of the pavement, the state of the equipment
and weather conditions when the work is being done – which can affect
the productivity as well as the achieved, such as:
a) the cutting thickness;
b) the degree of pavement oxidization;
c) the level of severity of the cracks;
d) the state of the cutting tools;
e) general temperature.
10.2. Productivity examples
With the purpose of establishing parameters to help identify the
type of milling machine required and devise a schedule for a job,
average productivity values based on results achieved in jobs with
similar characteristics is listed below.
This was considered important since the capacity of machines
usually displayed in manufacturers’ catalogues does not take common
problems found on the jobs into account.
The following productivity parameters of a practical nature should
be considered based on average daily 8 hour shifts: time used to mark
the road, equipment downtime for refilling of water and oil, meal times,
and moving between workplaces.
For this the width of the milling drum and the cutting capacity of
the equipment for a single pass will be considered, which is directly
linked to the power of the equipment.
Therefore, these values can be extrapolated to other types of similar
milling equipment that have not been considered here.
Such values may also vary based on the efficiency of the support
team at the time of the implementation of the services.
It is important to note that some clients wanted the milled areas to
be resurfaced on the same day. Therefore, when the milling is linked
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to the resurfacing, the equipment must be stopped in advance in order
to meet this requirement.
The following tables show the three situations most common during
work involving milling thicknesses up to 5 cm.
Milling machines provided with 2-meter wide drums:
TYPE OF SERVICE MILLING MACHINE MODEL
2000 VC
2000 DC
W 1900
Milling of continuous areas, not
associated to the application of a
wearing course
5.000,00 m2
8.000,00 m2
10.000,00 m2
Milling of discontinuous areas, not
associated to the application of a
wearing course
3.500,00 m2
4.000,00 m2
5.000,00 m2
Milling of discontinuous areas,
associated to the application of a
wearing course
1.800,00 m2
2.000,00 m2
3.500,00 m2
Model 2000VC was the first large milling machine introduced in
Brazil, manufactured by CIBER, in the state of Rio Grande do Sul.
There are several 2000VC units still operational in Brazil. Model
2000VC was replaced by model 2000 DC. It is slightly smaller and has
greater cutting capacity. The model currently being manufactured is
the W1900. It is slightly smaller and much more powerful than the
previous versions.
The Caterpillar PM-465 milling machine is a model similar to the
Wirtgen 2000DC that is available in the Brazilian market.
The Caterpillar PM-565 and Wirtgen 2100 DC milling machines,
imported from the U.S. and Germany respectively, are both available
in the Brazilian market. They are equivalent in terms of productivity
and present an approximate 10% higher productivity rate than the
Wirtgen 2000 DC milling machines.
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Milling machines provided with 1-meter wide drums:
TYPE OF SERVICEMILLING MACHINE MODEL
1000 C
W 1000 L
W 1000
Milling of continuous areas, not
associated to the application of a
wearing course
1.800,00 m2
4.000,00 m2
5.000,00 m2
Milling of discontinuous areas, not
associated to the application of a
wearing course
1.500,00 m2
3.000,00 m2
3.500,00 m2
Milling of discontinuous areas,
associated to the application of a
wearing course
1.000,00 m2
2.000,00 m2
2.500,00 m2
A model similar to the Wirtgen 1000C that is available in Brazil
is the Bitelli Volpe SF 100 T4 milling machine.
Based on the presented numbers, we observe that the more modern
and versatile equipment currently available (provided with a 1000mm width drum) has a productivity equivalent to that of the Wirtgen
2000VC model (provided with a 2000-mm drum).
Another important advantage concerns the cut depths that new
equipment models are capable of reaching in a single pass of the
equipment. Model 2000VC can reach up to 15 cm in a single pass;
model W1000L can reach up to 25 cm, and models W1000 and
W1000F can reach up to 30 cm.
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Milling machines provided with 0.50 meter wide drum:
TYPE OF SERVICEMILLING MACHINE MODEL
W 50
Milling of continuous areas, not associated
to the application of a wearing course
1.500,00 m2
Milling of discontinuous areas, not associated
to the application of a wearing course
1.200,00 m2
Milling of discontinuous areas, associated
to the application of a wearing course
900,00 m2
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11. Designing pavement
reinforcement
with view to milling
In Brazil, the great majority of existing roads are built using asphalt
pavement. Among these, special note should be given to those known
as purely flexible (asphalt pavement over layers that have not been
treated with cement). Additionally, in the State of São Paulo, roads
are also constructed using the semi rigid and inverted pavements
(asphalt pavement over systems with one of the subjacent layers
treated with cement).
Flexible and inverted pavements are designed with a pre-established
service life in terms of fatigue of the asphalt materials and the cemented
layer. The initial properties of such materials in terms of plasticity
and elasticity change over time, and they become hard and brittle.
However, some external factors accelerate their deterioration, such
as inadequate drainage (or even non-existent drainage in some cases)
and excessive loading.
The majority of procedures for the structural evaluation of existing
pavements is based on the criterion of deflection reduction, and is
limited to determining the thickness of the reinforcement layer to be
placed over the current surface, in order to restore the riding comfort
and safety.
The milling process, currently used primarily for maintaining the
grade of the pavement, can also be used for the substitution of the
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deteriorated asphalt material to increase service life of the structure
and improve riding comfort.
The majority of current procedures determine the thicknesses of
subsequent overlay to the existing pavements based on models that
consider the deflection reduction, i.e., derived from the relationship
between the allowable deflection (D) and the design deflection (Dc).
If we assume that the inverse of this concept is valid, we can, in
theory, estimate the deflection of the surface of the milled layer (Df ),
as a consequence of the removal of part of the existing wearing course,
with a predetermined cutting thickness (hc).
Based on the admissible deflection (D) and on the deflection
obtained over the milled surface (Df ), we can then determine the
thickness of the reinforcement layer (Href ).
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Where: D = maximum allowable deflection (x10-2 mm)
Dc = characteristic existing deflection (x10-2 mm)
HR = thickness of the reinforcement layer (cm)
Df = deflection after milling (x10-2 mm)
Dc = deflection after milling and reinforcement
layer reconfiguration (x10-2 mm)
Href = thickness of the reinforcement layer (cm)
hc = thickness of cutting (cm)
The Brazilian standard that originally contemplates the use
of recycling is DNER-PRO 269/94 – Projeto e Restauração de
Pavimentos Flexíveis TECNAPAV[13], which can be adapted to
consider milling.
This standard is based on pavement mechanics. It considers the
existence of a univocal relationship between the elastic deformability
represented by the deflection and reduction of the effective module
of the pavement layer represented by the modular relationship. This is
a theoretical-experimental model calibrated from the field conditions
of Brazilian pavements.
For the calculation of the deflection reduction, this procedure also
takes into account the resilient properties of the subgrade, the thickness
of the granular layer (implicitly) and of the effective thickness of the
existing wearing course. The procedure can be summarized by the
application of the equations presented below.
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The equation presented in Standard DNER-PRO 269/94 shows
that the estimated deflection (considering the milling is obtained
after the reconfiguration of the milled thickness (hc) is represented
by the equation for the determination of Dc and takes into account
that it was originally proposed to consider the recycling of asphalt
pavements.
where: heffective = effective thickness of the existing
pavement (cm);
= constants; a function of the resilient
I1, I2
characteristics of the foundation
materials;
= thickness of the existing wearing
he
course (cm);
Meffective = module of the existing wearing course
(kgf/cm²);
Mnew layer = resilient module of the new wearing
course (kgf/cm²);
Np
= number of operations of the standard
axle road (8,2 tf).
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The DNER PRO-269/94 standard subdivides the types of
foundations, as follows:
Tipo I
I1=0 e I2=0
Tipo II I1=1 e I2=0
Tipo III I1=0 e I2=1
For this purpose, the standard includes a table that classifies the
above groups based on the California Bearing Ration (CBR) and on
the percentage of Silt (S), as follows:
CBR (%)
S (%)
35
35 a 65
> 65
10
I
II
III
6 a 9
II
II
III
2 a 5
III
III
III
The percentage of silt is obtained based on the following
equation:
where: P1 = percentage of material with particles
of diameter below 0,005 mm;
P2 = percentage of material with particles
of diameter below 0,075 mm.
In addition to technical standard DNER PRO-269/94, there are
other design models, both in Brazil and abroad, that can be applied to
the use of the milling technique, even though they were not originally
proposed for this particular purpose.
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Among them is the AASHTO-93[14], which considers the
application of the concepts of structural number (SN) and of structural
coefficient (ai). This is a function of the layer modulus value and of
the type of layer material. These parameters should be reassessed
for the loss of structural value due to the milling process.
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12. Grading of
materials from milling
B
ecause of its noble properties, the material generated from the
milling of asphalt pavements can be recycled for paving material.
There are several ways through which to recycle material, including
the combination of rehabilitation options. The constant evolution of
equipment and of plants has increased the number of options in terms
of applicability.
Considering this, Table 1 presents a classification of the most
widespread types of recycling.
One of the major problems encountered during projects of
rehabilitation for recycling concerns the grade change from milling.
This is especially true for those processes carried out with no preheating
of the wearing course that may cause appearance of lumps.
According to the types of recycling in Table 1, lumps do not
constitute a problem for plant recycled mixtures, because lumps of
unwanted size can be removed during an initial sieving stage.
However, for those processes where the materials are mixed in place,
or even for combined processes where part of the material comes from
an asphalt plant, the size of the lumps must be controlled in order to
achieve best results.
101
TABLE 1: TYPES OF RECYCLING
In terms of original geometry
No modifications
With modifications
When the grade elevations
are maintained of the grade
In terms of processing point
In plant
In place
Stationary or moving, hot
or cold
Hot or cold
Mixed
Recycling in place of
the road base and use
of hot recycling, processed
in plant with milled
material
In terms of material milling
Cold
Hot
At ambient
temperature
Pavement is
preheated
In terms of cut depth
Shallow
Deep
Only the wearing course
is cut
Wearing course, base and
even sub-base
In terms of recycled mix
Cold mix
Hot mix
Cold-mixed AC
Asphalt concrete - AC,
hot-mixed open-graded AC
In terms of use of the mix
As recycled base
As binder course
As wearing course
In terms of added materials
Aggregates
Portland Cement and lime
Special emulsion, asphalt cement,
polymers
Asphalt mix
BINDER
Grading correction
Increased structural
capacity
Regeneration
Milled material added
During in-place cold recycling, where the material is simultaneously
milled and recycled, some procedures must be adopted to control the
size of the lumps and ensure that dimensions are acceptable for the
new material grade.
102
The author’s Master Degree dissertation[15] includes a study of the
resulting grade of milled material which was compared with in-place
cold recycling. The study findings are summarized in this section.
This section presents the types of equipment, the type of wearing
course, and the procedures adopted for both sample collection and
tests, in addition to some of the curves obtained in the author’s study.
This allows for future comparisons with other studies.
12.1. Equipment used
The equipment used to mill the pavement was a Wirtgen 2000 VC
milling machine, manufactured in Brazil by CIBER.
Figure 55: Wirtgen 2000 VC cold milling machine
This is large class equipment with a cutting capacity of up to 15 cm
in a single pass, and frontal conveyor belt.
The milling drum is segmented with a cutting width of 2100 mm
and 550-mm diameter – where the segments are positioned. The
diameter formed by the cutting tools is 850 mm. The drum rotation was
measured as 80 rpm. It has 180 cutting tools, of which 18 are located
on the sides for cutting the walls vertically. The remaining 162 cutting
tools act directly on the pavement. The ambient temperature at the
time of milling was approximately 11°C.
The samples analyzed are listed in Table 2, each for cutting
thickness and equipment movement speed.
103
TABLE 2: MATRIX of SAMPLES
CLASSIFICATION OF SAMPLES
Speed = 3 m/min Speed = 6 m/min
Speed = 10 m/min
Thickness = 3 cm
Sample 1
Sample 2
Sample 3
Thickness = 5 cm
Sample 4
Sample 5
Sample 6
Thickness = 8 cm
Sample 7
Sample 8
Sample 9
12.2. Existing wearing course
Figure 56 represents a schematic cross-section of the pavement
milled for the collection of the samples.
Overlay
bituminous layer
Asphalt Concrete
– AC
Thickness = 5 cm
Wearing course of the original
pavement
Asphalt Concrete
– AC
Thickness = 5 cm
Remaining
pavement layers
BINDER etc.
Figure 56: Cross-section of the milled pavement
12.3. Samples collection
The procedure adopted for milling and samples collection is
presented below:
a) position the equipment to commence cutting;
b) set the cutting thickness;
c) start milling; the material is loaded into dump trucks;
d) increase speed;
e) monitor the speed until the sampling speed is reached;
f) maintain constant speed for a certain time, so that all the
material inside the milling drum housing corresponds to the
selected constant speed, which will prevent overloading of the
conveyor belt;
104
g) lift the scraper lid so that the milled material of the sample is
left on the road, start the conveyor belt;
h) repeat steps “d” to “g” until the sampling is complete
corresponding to the third speed and first cutting thickness.
After that, the equipment was once again positioned at the start,
next to the first cutting, and the same procedure was repeated for the
two remaining thicknesses.
At the end, nine piles of milled material were found on the lane,
corresponding to the three thicknesses and three cutting speeds. The
samples were collected from the central portion of each pile which is
the position of the material conveyed to the paver during in-place cold
recycling operations.
The materials were stored in plastic bags to avoid the loss of the fine
material when it was delivered to the Transport Technology Laboratory
of the University of Sao Paulo. Here tests were carried out, and the
grading curves determined. They are presented below.
12.4. Gradation curves
Charts were plotted with three grading curves: one for the original
material prior to milling; one for the milled material without bitumen
extraction; and one for the milled material after bitumen extraction.
Even though the bitumen extraction from the samples using Sox-let[16]
resulted in a slightly higher percentage of fine materials, this difference was
not enough to justify the use of this method, because of the considerable
amount of material to be washed. Therefore, the material was extracted
using a Rotarex[17] taking the care of using two filter papers in order to
minimize the loss of fine materials.
105
Table 3 – Sample 1 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
100
1/2”
12,7
92,7
3/8”
9,52
84,2
Nº 4
4,8
65
Nº 8
2,38
45,8
Nº 10
2
41,1
Nº 30
0,59
23,9
Nº 40
0,42
20,3
Nº 50
0,3
17,6
Nº 80
0,175
13,8
Nº 100
0,148
11,7
Nº 200
0,075
7,3
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
100
100
99,3
100
98
100
86,8
93,4
75
87,2
51,9
67,6
32,3
49,8
29,8
45
13,9
27,6
10
22,5
8,1
18,6
5,4
14,6
4
12,9
0,7
7
Figure 57: Grading curves for sample 1
106
Table 4 – Sample 2 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
100
1/2”
12,7
92,7
3/8”
9,52
84,2
Nº 4
4,8
65
Nº 8
2,38
45,8
Nº 10
2
41,1
Nº 30
0,59
23,9
Nº 40
0,42
20,3
Nº 50
0,3
17,6
Nº 80
0,175
13,8
Nº 100
0,148
11,7
Nº 200
0,075
7,3
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
100
100
99
100
96,7
100
86,1
95
76,8
88,7
56,2
73,1
36,5
54,1
31,4
48,7
13,6
29,2
9,5
24,6
7,2
21,3
4,8
17,3
3,3
14,4
1
8
Figure 58: Grading curves for sample 2
107
Table 5 – Sample 3 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
100
1/2”
12,7
92,7
3/8”
9,52
84,2
Nº 4
4,8
65
Nº 8
2,38
45,8
Nº 10
2
41,1
Nº 30
0,59
23,9
Nº 40
0,42
20,3
Nº 50
0,3
17,6
Nº 80
0,175
13,8
Nº 100
0,148
11,7
Nº 200
0,075
7,3
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
100
100
98,2
100
95,1
100
84,4
95,8
76
93,8
55,1
78,5
35,5
64,5
30,2
53,5
13,4
32,1
9,7
28,3
6,3
23,2
3,3
17,4
2,3
15,4
0,8
9,3
Figure 59: Grading curves for sample 3
108
Table 6 – Sample 4 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
100
1/2”
12,7
92,7
3/8”
9,52
84,2
Nº 4
4,8
65
Nº 8
2,38
45,8
Nº 10
2
41,1
Nº 30
0,59
23,9
Nº 40
0,42
20,3
Nº 50
0,3
17,6
Nº 80
0,175
13,8
Nº 100
0,148
11,7
Nº 200
0,075
7,3
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
100
100
97,7
100
95,1
100
85,6
99,1
76,8
96,6
57,2
81,2
34,7
60,1
30,6
55,1
10,7
32,7
6,3
27,4
4,3
24,3
2,8
17,9
2,2
16,5
1
10,1
Figure 60: Grading curves for sample 4
109
Table 7 – Sample 5 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
100
1/2”
12,7
92,7
3/8”
9,52
84,2
Nº 4
4,8
65
Nº 8
2,38
45,8
Nº 10
2
41,1
Nº 30
0,59
23,9
Nº 40
0,42
20,3
Nº 50
0,3
17,6
Nº 80
0,175
13,8
Nº 100
0,148
11,7
Nº 200
0,075
7,3
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
100
100
98,7
100
94,6
100
84
99,2
76,7
96,2
57,5
82,5
38,4
60,3
29,8
55,5
16,1
33,8
9,2
27,7
5,2
24,8
2,8
20
2,4
18,2
0,9
10
Figure 61: Grading curves for sample 5
110
Table 8 – Sample 6 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
100
1/2”
12,7
92,7
3/8”
9,52
84,2
Nº 4
4,8
65
Nº 8
2,38
45,8
Nº 10
2
41,1
Nº 30
0,59
23,9
Nº 40
0,42
20,3
Nº 50
0,3
17,6
Nº 80
0,175
13,8
Nº 100
0,148
11,7
Nº 200
0,075
7,3
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
100
100
93,6
100
87,3
100
77,2
97,8
69,8
94,7
52,1
79,2
37,9
58,3
29,4
51,9
12,5
31,5
8,3
26,1
6,2
23,5
3,2
18,1
2,7
16,8
1
10
Figure 62: Grading curves for sample 6
111
Table 9 – Sample 7 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
98,8
1/2”
12,7
91
3/8”
9,52
77,9
Nº 4
4,8
54,8
Nº 8
2,38
45,2
Nº 10
2
42,9
Nº 30
0,59
28,6
Nº 40
0,42
23,3
Nº 50
0,3
20
Nº 80
0,175
14,2
Nº 100
0,148
13
Nº 200
0,075
6,9
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
97,8
100
95,2
100
86,1
99,3
67,8
93,7
55,6
85,4
37,1
67,8
25,2
54,1
21,8
50,4
9,9
35,4
8
29,7
6,2
25,7
4,3
16,7
3,3
14
1,3
5,1
Figure 63: Grading curves for sample 7
112
Table 10 – Sample 8 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
98,8
1/2”
12,7
91
3/8”
9,52
77,9
Nº 4
4,8
54,8
Nº 8
2,38
45,2
Nº 10
2
42,9
Nº 30
0,59
28,6
Nº 40
0,42
23,3
Nº 50
0,3
20
Nº 80
0,175
14,2
Nº 100
0,148
13
Nº 200
0,075
6,9
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
94,8
100
87,9
100
82,9
99
71,2
92,8
65,5
85,6
46
69,3
34
57,3
29,7
53,9
22
36,3
11,3
29,9
8,2
25,7
5,3
17,5
4,7
14,3
1,3
7,7
Figure 64: Grading curves for sample 8
113
Table 11 – Sample 9 grading
SIEVES WEIGHT IN %, GOING THROUGH
Discrimination (mm)
Original material 2”
50,8
100
1 ½”
38,1
100
1”
25,4
100
3/4”
19,1
98,8
1/2”
12,7
91
3/8”
9,52
77,9
Nº 4
4,8
54,8
Nº 8
2,38
45,2
Nº 10
2
42,9
Nº 30
0,59
28,6
Nº 40
0,42
23,3
Nº 50
0,3
20
Nº 80
0,175
14,2
Nº 100
0,148
13
Nº 200
0,075
6,9
Milled material, Milled material,
without bitumen with bitumen
extraction extraction
100
100
94,2
100
87,3
100
77,2
98,8
61,4
93,3
51,8
84,7
35,8
65,3
26,1
54,4
23,2
50,9
12,3
38,8
8,7
30,7
7
26,5
4,3
18,2
3,3
16,2
1,1
7,5
Figure 65: Grading curves for sample 9
114
12.5. Considerations of the results obtained
The grading curves are part of the results obtained in the author’s
Master dissertation, and the considerations are presented here.
A comparison among the grading curves obtained and the original
grading curves shows that the milling causes changes in the gradation
curves. The grading curves obtained with bitumen extraction, i.e. after
milling and with no lumps, are “dislocated upward”, which makes the
curve denser or sharper. This occurs because the milling causes the
aggregates to break up at the depth of cut.
The opposite is observed for curves obtained without bitumen
extraction. Despite the fact that part of the aggregates was ruptured,
the material is analyzed as it comes out after the milling. Lumps reduce
the percentage of passing materials for each sieve.
The results of the curves analyzed with lumps, plotted within the
grading stripe, revealed that more often than not such curves exceeded
the lower threshold limits of those stripes on both ends – due to the
absence of fine materials on one side and to the increase in the size of
the lumps on the other. This occurrence is accentuated by the increase
of the milling machine movement speed.
We actually observe a decrease in the amount of fine particles, as the
curve resulting from the samples with lumps is below the original curve.
According to this assessment, the speed of the equipment must be
controlled in order to prevent the development of lumps which are not
desired for the mixture.
The amount of fine materials observed for all grades’ curves,
including the lumps, ranged between 0.7% and 1.3 % passing through
sieve number 200.
The lack of fine materials is one of the reasons why in-place cold
recycling does not result in good cohesion to the mix. For that and
other reasons, the international bibliography recommends a layer of
hot-mixed asphalt be laid over a recycled layer.
115
We observe that the curves are well graded, making it possible to
conduct further studies for the characterization of the mechanical
behavior for use of recycling.
116
13. Parameters for asphalt
pavement milling control
13.1. Objective
To present the conditions for the execution and control of asphalt
pavement cold milling services.
13.2. Generalities
The layer must be removed through cold mechanical milling,
resulting in a surface of rough but uniform texture, i.e., free of different
grooves and other defects, and over which traffic can flow smoothly.
The cold milling process is carried out with no type of material
heating.
13.3. Equipment
The equipment must meet the client’s requirements, and the type
necessary for services within the work’s proposed time schedule.
The requirements of equipment characteristics may include: the
minimum or maximum width of the milling drum, the cutting capacity
in a single pass and the spacing between the cutting tools for normal
milling, fine milling, or micromilling.
Additionally, other characteristics may also be required: the
capacity for the automatic and precise leveling of the cutting to allow
the control and shaping of the cross slope during the operation and
117
the presence of devices that allow for the simultaneous loading of
the milled material into dump trucks; year of fabrication, state of
conservation etc.
13.4. Control of cut depth
The milling thicknesses must comply with the design specifications
and the cut depth control can be checked at the borders, using a meter
or a tapeline, and at the middle, using topographic survey. A line or a
ruler may be used for exclusive lanes.
13.5. Control of milled surface texture
The milled surface’s texture must be rough but uniform, with
no variations between the two passes of the equipment, and for
each application the depth of the grooves must meet the following
standards:
• For standard milling: depth of the grooves 8 mm
• For fine milling:
depth of the grooves 5 mm
• For micro milling:
depth of the grooves 3 mm
The values above refer to milling drums in perfect conditions.
The maintenance of the cutting system – comprised of the tools,
holders and scrapers – must be conducted as often as necessary to
ensure a milled surface of rough and uniform texture.
13.6. Storing the milled materials
The material generated during the milling must be transported
in dump trucks covered with canvas, and deposited in the location
determined by the inspection agency.
118
13.7. Lane clean up
In order to reopen a lane for traffic, or prior to the placement of a
new layer of wearing course, the materials loosened during the process
and found on the milled surface should be cleaned.
It is recommended that the sweeping should be carried out
concomitantly to the milling, in order to facilitate and ensure the
leveling of the cutting between two passes, and to prevent the
aggregation of the material to the milled surface due to work traffic.
The client may select manual or mechanical sweeping:
• Manual sweeping: carried out by workers using brooms, dustpans,
and wheelbarrows. There should be enough workers to prevent
hindering equipment productivity;
• Mechanical sweeping: carried out using adequate sweeping
equipment.
The client may also require, in addition to sweeping, compressed
air jets be used to ensure that loose material is totally removed from
the milled surface before resurfacing.
13.8. Reopening to traffic
After the milling, the lane may be reopened for traffic, as long as
it does not pose risks to users.
Prior to lane reopening, an inspection should assess whether the
road is free of loose materials and/if there were problems caused by the
services, such as slab displacement, development of potholes, etc.
• In the event of slab displacement: all loose material must be
removed;
• In the event of development of potholes: repairs must be carried
out according to appropriate standards.
119
Whenever possible a new layer of wearing course must be laid
prior to reopening the lane to traffic to prevent the weathering of the
remaining structure.
13.9. Measurement
The clients develop a measurement spreadsheet based on their
needs. The measurement spreadsheet may include the unit price for
milling, the costs for equipment, personnel mobilization, lane marking,
and cleanup (sweeping), including the removal of the milled material
and its transportation to its final destination.
Milling services are normally measured in square meters (m²) for an
established cutting thickness and/or cubic meters (m³) for exceeding
thicknesses.
Especially for small areas, the services may also be hired on a global
sum basis.
Finally, the milling equipment may be rented per day or per
month.
120
Bibliography
1. WOOD, J. F. Cold-asphalt recycling equipment. Transportation
Research Record, n.780, p.101-2, 1980.
2. DEPARTAMENTO NACIONAL DE ESTRADAS DE
RODAGEM. Glossário de Termos Técnicos Rodoviários.
Rio de Janeiro, 1997.
3. DEPARTAMENTO NACIONAL DE ESTRADAS DE
RODAGEM. Curso RP 9 – Reciclagem de Pavimentos. Rio
de Janeiro, Diretoria de Desenvolvimento Tecnológico / Divisão
de Capacitação Tecnológica, 1994. v.1-2.
4. MANUAL de recuperação de rodovias. s.l., Caterpillar, 1989.
(Form n.º TPCB8082).
5. BALBO, J. T. Pavimentos asfálticos – patologias e
manutenção. São Paulo, Plêiade, 1997.
6. BONFIM, V.; DOMINGUES, F. A. A. Utilização de fresagem
e reciclagem “in situ” a frio – alternativas na recuperação
de pavimentos asfálticos. In: REUNIÃO ANUAL DE
PAVIMENTAÇÃO, 29., Cuiabá, 1995. Anais. Rio de Janeiro,
ABPv, 1995. v.3, p.602-21.
7. DEPARTAMENTO NACIONAL DE ESTRADAS DE
RODAGEM. Avaliação subjetiva da superfície de pavimentos
– DNER-PRO 07/78. Rio de Janeiro, 1978.
8. DEPARTAMENTO DE ESTRADAS DE RODAGEM.
Avaliação objetiva da superfície de pavimentos flexíveis e
semi-rígidos – DNER-PRO 08/78. Rio de Janeiro, 1978.
121
9. DEPARTAMENTO NACIONAL DE ESTRADAS DE
RODAGEM. Levantamento da condição de superfície de
segmentos-testemunha de rodovias de pavimentos flexíveis
ou semi-rígidos, para gerência de pavimentos a nível de
rede – DNER-ES 128/83. Rio de Janeiro, 1983.
10. DEPARTAMENTO NACIONAL DE ESTRADAS DE
RODAGEM. Instruções para atividades de campo. Rio de
Janeiro, 1994. (item 3 - LVC).
11. DISTRESS Identification Manual for the Long-Term
Pavement Performance Studies. Washington, Strategic
Highway Research Program, 1990. (SHRP-LTPP/FR-90-001).
12. DOMINGUES, F. A. A. MID – Manual para Identificação
de Defeitos de Revestimentos Asfálticos de Pavimentos. São
Paulo, 1993.
13. DEPARTAMENTO DE ESTRADAS DE RODAGEM. Projeto
de Restauração de Pavimentos Flexíveis – TECNAPAV –
DNER-PRO 269/94. Rio de Janeiro, 1994.
14. AMERICAN ASSOCIATION OF STATE HIGHWAY AND
TRANSPORTATION OFFICIALS. AASHTO Guide for
Design of Pavement Structures. Washington, 1993.
15. BONFIM, V. Estudo da granulometria resultante da fresagem
de revestimentos asfálticos com vistas à reciclagem “in situ”
a frio. São Paulo, 1999. p. 179. Dissertação (Mestrado) – Escola
Politécnica, Universidade de São Paulo.
16. DEPARTAMENTO DE ESTRADAS DE RODAGEM.
Determinação da porcentagem de betume em misturas
betuminosas pelo extrator de refluxo – M 146 – 62. São
Paulo, 1962.
17. DEPARTAMENTO NACIONAL DE ESTRADAS DE
RODAGEM. Percentagem de betume em misturas
betuminosas – DNER – ME 53-63. Rio de Janeiro, 1963.
122
FIGURES AND ILLUSTRATIONS CREDITS:
• The photos of figures 1 and 2 were taken by Alex Dias
Carvalho.
• The photo of figure 5 was taken by Ricardo Rodrigues de Souza.
• The photos of figures 4, 11, 16, 18, 19, 23, 25, 27, 30, 32, 38-b,
39, 44, 46 and 47, and the illustrations of figures 8, 17, 21, 24
and 45 were extracted from catalogs and manuals of the Wirtgen
Group.
• The photos of figures 6-b and 7-c were extracted from Dynapac
catalogs.
• The photo of figure 6-c was kindly supplied by engineer
Fernando Márcio Guimarães Sant’Anna, of Fresar Tecnologia
de Pavimentos.
• The photos of figures 6-d and 7-a were extracted from Caterpillar
catalogs.
• The photo of figure 7-b was extracted from a Marini catalog.
• The illustrations of figures 20 and 28 were edited by Pedro
Penafiel from other illustrations extracted from the Caterpillar
course on pavement recycling “Curso RP-9 – Reciclagem de
Pavimentos”.
• The illustration of figure 22 was extracted from the Caterpillar
manual on highway recovery “Manual de recuperação de
rodovias”.
• The photo of figure 29 was kindly supplied by Fernanda
Marcondes Monfrinatti.
• The photo of figure 33-a was extracted from a Bobcat/Comac
catalog.
• The photo of figure 33-b was extracted from a Case catalog.
• The illustrations of figures 41, 42 and 43 were edited by Pedro
Penafiel.
• The photo of figure 51 was taken by Nelson Sampaio Pereira.
• The remaining photos were taken by the author.
123
This work was handset in Goudy
type size 11, printed on 90 g/m² offset
paper, 4 x 4 colors, 14 x 21 format,
by RR Donnelley, in October 2010.