ROAD MAINTENANCE PLANNING

Transcription

INDEVELOPMENT:
John van Rijn
INDEVELOPMENT:
Road Maintenance Planning
Any part of this publication may be fully reproduced or translated provided that the source and
author are fully acknowledged.
Edition 2006.
2
INDEVELOPMENT:
Table of Contents:
1
Introduction
4
2
Shoulders
6
3
Storm water drains
7
4
Street markings
7
5
GuardRails
8
6
Barriers
9
7
Traffic Signs
10
8
Traffic lights
10
9
Street lights
10
10
10.1
Pavements
12
Earth and Gravel Roads
14
10.2 Asphalt concrete
10.2.1 Long-term maintenance planning
10.2.2 Short and medium term maintenance planning
10.2.3 Impacts of Repairs
19
21
24
43
10.3 Concrete pavements
10.3.1 Long-Term Maintenance Planning
10.3.2 Middle-Long Term Maintenance Planning
45
51
54
Appendix a: Life expectancy of rehabilitation
56
Appendix B: Thaw-Frost damages
59
Appendix C: Analysing Deflection tests
61
3
INDEVELOPMENT:
1
Road composition
INTRODUCTION
A road is more than just a pavement on top of a base course, it
contains various elements, who all have their specific functions.
Typically a road would contain elements like:
• Drains,
• Streetlights
• Guard rails
• Street markings
• Traffic lights
• Street furniture
• Shoulders
• All sorts of structures like bridges and flyovers
In many countries, the responsibilities to maintain these assets are
shared by several agencies. The traffic police department may be
involved. And often one differentiates between urban, rural and
national road networks.
This report present guidelines for preparing maintenance plans for
open storm water drainage, shoulders, street lights, traffic lights,
guard rails, street markings, street furniture and pavements.
Guidelines for piped drainage and sewer systems and structures are
presented in other documents.
Organisation of road
maintenance
Road maintenance organisations usually work with the following
framework
• Routine maintenance
• Periodic maintenance
• Reconstructions
• Emergency maintenance
Routine maintenance
Routine maintenance are all maintenance activities that have to be
carried out at least once per year, if not more frequent. Such
activities include inspections, cleaning of drains, controlling of
vegetations, filling of potholes and ruts, etc.
Road agencies often receive a fixed budget on basis of an inventory
that quantifies the assets in age; length, area or volume. In most
cases the road maintenance department is free to allocate the
routine budget line as it pleases, provided that it is used for
damages that fit in routine maintenance.
In other countries the routine maintenance program of works and
their budget needs to be approved by senior management.
Undersigned suggests equipping inspectors with sufficient tools,
materials and equipment to carry out patching techniques. However
inspectors may be prohibited to carry out small repair works. When
routine works programs and their budget need prior approval by
senior management, it is unlikely that the inspectors will be granted
enough budgets to carry out repair works while doing their
inspections. Senior management may be concerned about the
consumption of the total budget of the road department for routine
4
INDEVELOPMENT:
maintenance. Routine maintenance budget demands are low in
comparison with any other form of maintenance and new
construction projects.
Emergency maintenance
Emergency repairs are all maintenance activities that have to carried
out immediately to safe lives or prevent disastrous consequences of
damaged infrastructure. Typical examples of such emergencies are
structural damages to flyovers due to accidents. Maintenance
departments need unrestricted access to emergency maintenance
budgets that allow them to carry out repairs that mitigate immediate
dangers. Some senior management may wish to control access to
emergency repairs for works with more long-term focus.
Periodic maintenance &
Reconstruction
All repairs that carried out less frequent are considered periodic
maintenance. Periodic maintenance includes all sorts of repairs
including resurfacing, overlays, and reconstruction of pavement,
base and even subbase course. Periodic maintenance intervals vary
according to the needs and may be irregular. The intervals depend
to a large extend on the quality of the construction. Planners should
play with different periodic maintenance scenarios to obtain the
most cost-effective one. They can choose for more frequent but less
effective but cheap repairs, i.e. five year intervals or to work with
larger intervals choosing rehabilitation techniques that are very
effective but also expensive. The interval sets performance
requirements to the routine maintenance budgets and activities.
Ideally planners would choose the most cost-effective scenario.
5
INDEVELOPMENT:
2
Shoulders and slopes
SHOULDERS
The shoulder has three functions:
• Providing side support to the road pavement
• Providing space to the traffic in case of emergencies
• Draining water from the carriageway to the roadside ditch
The usual defects of shoulders are:
• Obstructions on shoulders
• Shoulder higher than carriageway
• Erosion of shoulder
• Shoulder far lower than carriageway
• Reduced visibility for road users due to high vegetation and
subsequently fire hazards
• Weak surface, it can not be used by Non-motorised transport
Shoulder maintenance
Vegetation on slopes can cause several problems. Overgrown trees
or branches can fall and block the carriageway or block the drains.
Vegetation can reduce the visibility of road users, also through fire.
Other problems related to the slopes are surface water erosion and
earth slips. Both erosion and slips can block the drain system.
Shoulder maintenance activities consist of the following activities.
a) Removing obstacles
b) Reshaping shoulders
c) Adding shoulder materials
d) Vegetation control
Except for vegetation control, these maintenance activities can be
initiated failure based. Vegetation control should be done a number
of times per year. The number of times depend the growth of the
vegetation that hinders visibility of the road users and environmental
considerations. Vegetation control activities should be done
preferable after the rains and in the dry seasons. Erosion prevention
should be done as soon as erosion results in slips or channels.
Erosion prevention interventions are refill of channels, guiding water
through constructed channels, seeding vegetation on the slopes or
stone pitching. It is possible to reduce risk for slips by reducing the
slope angle, clearing slip material or constructing retaining walls.
Bush and vegetation control should at least take place up to 3
meters from the edge of the shoulder. The minimum height of the
vegetation/grasses remains 10 cm. Lower heights risks scalping of
the ground. Young trees should not be allowed to grow in these
areas. Trees close to the roads should be kept free from dead and
sick limbs. The boughs and branches overhanging the pavement
lower than 4.5 meters should be removed. It may also be necessary
to remove the so-called heavy branches (branches growing in the
downward direction). Blading is not a satisfactory method of
vegetation control. Excessive blading can cause undesirable air and
water quality problems.
6
INDEVELOPMENT:
When the soil on the slope or shoulders is higher than the actual
pavement, water will accumulate on the pavement, causing
problems to both the pavement as well as the road users.
Accumulation of silt on the shoulders and slopes can not be
predicted nor is it worthwhile to monitor their progress. Such
problems should simple be taken care off with the routine
maintenance budget.
3
STORM WATER DRAINS
The purpose of the Drainage System is to rapidly collect and conduct
rain and ground water away from the carriageway. Water can cause
widespread damage to the road by weakening the pavement
structure. The drainage system is therefore a very important
component of the road.
An open storm-water drainage system consists of ditches & drains,
culverts, drifts and causeways.
The usual defects of open storm-water drainage systems are difficult
to predict and therefore maintenance is initiated after the failure
occurs. However there are some use-based initiated activities.
Season
Before rains
During the rains
End of rains
4
Activity
¾ Clean culverts and drifts
¾ Clean side and mitre drains
¾ Repair side drain erosion and
scour checks
¾ Inspect and remove obstacles
¾ Clean culvert and drifts
¾ Clean side and mitre drains
¾ Repair side drain erosion and
scour checks
¾ Repair erosion on shoulders, on
back slopes and in drains
¾ Reinstate scour checks
STREET MARKINGS
Markings are usually painted lines and symbols to inform the road
users about alignment of the road and traffic rules. The main defect
is off course when the markings are no longer visible. When normal
road paint is used, lines will deteriorate within one year under any
circumstances. Painted symbols usually last up to 3 years.
Thermoplastic lines usually have longer life span. Depending on the
traffic intensity and the climate it may last between 5 and 7 years.
Thermoplastic is hardly ever used for symbols.
7
INDEVELOPMENT:
5
GUARDRAILS
Guardrails should avoid accidents by preventing vehicles driving off
the pavement and hitting other vehicles or objects. Subsequently
guardrails and barriers are designed in a way that they reduce the
harm for drivers and occupants of the vehicles hitting it. Guardrails
are usually composed of a number of galvanised steel items. The
usual defects of guardrails are corrosion, cracking of the posts and
sinking of the guardrails. The last defect is usually a result of
inadequate foundation. The steel is usually galvanised with a layer of
sink. Recycling and expanding the life of the steel is possible through
re-galvanising the different steel items. The minimum remaining
depth of the sink layer should be at least 12 µm. The thickness of
the plank itself should be at least 2.4 mm and the minimum wall
thickness of the poles should be 3.5 mm.
It is close to impossible to measure the thickness of the sink layer in
a uniform manner. Research in the Netherlands has indicated that
the progression of the corrosion is almost linear and depending on
the distance to industries, sea and the road. The progressions of
corrosion (in µm/year) in the Netherlands are:
Class A; 1.8
Class B: 2.4
Class C: 4.8
The class type was determined with the table below.
Distance to
industry less
than 25 km
Distance to
sea less
than 20 km
X
X
X
X
X
X
X
X
8
Distance to
driving lanes
less than 1.5
m
X
X
X
X
Class
type
A
A
A
A
B
B
B
C
INDEVELOPMENT:
The average life of an undamaged guard rail is about 40 years.
Damage
Gouges and
Dents
Leaning or
Bent Posts
Rusting
surface
Repair
Touch up gouges with zinc paint
Replace guardrail sections
Replace tubular backup sections
Replace posts
10
40
40
40
Life
Years
Years
Years
years
Clean and paint with zinc paint
Clean and metallize
Replace
Touch up gouges with zinc paint
Replace guardrail sections
Replace tubular backup sections
10
40
40
10
40
40
Years
Years
Years
Years
Years
Years
Anchor Bolts
Loose from
Embedment
6
BARRIERS
As reinforced concrete barriers hardly ever decay, with exception of
accidents, their maintenance cycle for long-term maintenance
planning is simple based on replacing them every 30 years.
Problem
Repair
Surface
Scaling/surface
popouts
Clean and seal with Silane
Cracks < 1.5 mm
wide
Cracks > 1.5 mm
wide
Delamination of the
surface
Widespread surface
deterioration
9
Life
10 Years
Clean and seal with
epoxy/urethane
seal with HMWM
15 Years
route out crack and seal with
flexible caulk
Remove unsound concrete;
sawcut around perimeter;
remove and patch with fast
setting patch material
If thin areas (25 mm or less)
patch with trowelable mortar
Sawcut around and remove
unsound areas full-depth and
recast in-kind
Replace entire barrier
10 Years
10 Years
15 years
10 years
30 Years
30 Years
INDEVELOPMENT:
7
TRAFFIC SIGNS
The most important aspect of traffic signs is that they should be
visible under most circumstances. Sometimes traffic signs are
removed illegally or were not placed on the correct position. In these
cases the traffic signs need either to be replaced or its position
corrected. In some countries steel traffic signs are often stolen. If
this is common practice, other materials should be considered for
which is less demand in society. Subsequently traffic signs do get
dirty and require cleansing on regular basis. A good practice would
be to clean all signs, once every three years.
8
TRAFFIC LIGHTS
The common defects on traffic lights are the corrosion and reduction
of the sink layer on the post, drop out of the lights, dirty lenses and
mirrors, loose wires and jamming doors.
To avoid jamming doors, the hinges need to be oiled every three
years. The lenses and mirrors need to be cleaned annually. Because
the yellow lamps are more used than the red and green lights, their
life expectancy is usually a lot shorter. If the electricity supply does
not fluctuate too much, the lamps replacement can be initiated use
based. Basically this means that the green and red lamps are
replaced every three years and the yellow lamp every year.
In the occasion that a failure of the lamp may occur, fast
replacement (preferably within a day) is required to avoid
unnecessary accidents or congestion. Red lights may even have to
be replaced sooner, e.g. 8 hours. Furthermore oil coating of all
moving parts is necessary once in the 3 years.
Repairs for the other defects are usually failure based initiated.
9
STREET LIGHTS
Streetlights are usually approached in the same way as the traffic
lights, with the difference that the reaction time for the replacement
of the lights is far less strict and that the lenses and mirrors are only
cleansed when the lights are replaced. Replacement of the lights
should take place once every three years. It may be necessary to
carry out corrective maintenance when two cascading failing lights
are observed. When such failure is observed close to the three year
replacement interval, planners should opt for advancing the
replacement. Corrective maintenance is needed for failing street
lights at crucial locations, like intersections, refuge islands and traffic
furniture conveying important information to road users.
Furthermore oil coating of all moving parts is necessary once in the
3 years. The thickness of the mast wall can be measured and plotted
against time. Depending on the progression rate and the minimum
acceptable thickness it is possible to predict the end of life of the
10
INDEVELOPMENT:
mast. Most metal masts have a conservation of a sink layer. It is
also possible to measure the thickness of the sink layer. If the sink
coating has still a thickness of 50 micrometer of more, damages can
be mitigated. When the remaining thickness is less, it is no longer
possible to enhance resistance against corrosion or erosion. An
alternative threshold value is 5% of the total surface.
Non-sink coatings are usually visually inspected. When the total
damage per mast is smaller than 5%, the coating can be patched.
When the damages are larger, the coating is usually replaced.
Masts have to be replaced when they are
• Deformed and distract road users
• Contain scuffmarks that are deeper than 10% of the wall
thickness
Masts that permanently skew beyond 2% of their height need
corrective maintenance. When the mast during wind forces 5 or less
skew 5% or more of their length, they may need replacement.
Cracks in welds require immediate attention of a certified welder.
Typically, a street light maintenance unit will inspect and carry out
small repairs to the streetlights every two months.
11
INDEVELOPMENT:
10 PAVEMENTS
Without maintenance even asphalt concrete roads will loose their
original service level in as little as 10-12 years; with gravel roads it
is normally in the order of 6-8 years and for earth surfaced roads as
little as 3-5 years.
Unlike bridges, sewer pipes and many other assets, road pavements,
irrespective their condition, always provide some form of access. The
service level of the pavement deteriorates from the one obtained
directly after construction to eventually a road that only allow slow
access to pedestrians, circlers, four wheel drives, busses and lorries.
These roads may have to be closed for motorised traffic during parts
of the year. Some countries cannot afford the highest service level
and accept that certain minor roads are closed for motorised traffic
during the rainy season. The designs of these roads are already
based on this service level. One example of such an approach is the
green roads approach that is adopted in both Nepal and Bhutan.
Irrespective of the adopted service level, road agencies should
safeguard the right of way for future expansion.
Important quality requirements that determine the service level are:
• Reliability of access
• Comfort and speed
• Road safety
• Vehicle operating costs
• Environmental costs
Reliability of access
Jerry Lebo and Dieter Schelling (Design and Appraisal of Rural
Transport Infrastructure, World Bank Technical Paper No. 496)
differentiate four levels of access from the perspective of service:
• No (motorised) access:
• Partial access: motorised access with interruptions during
substantial periods of the year (the rainy season)
• Basic access: defined as reliable all-season access for the
prevailing means of transport with limited periods of
inaccessibility
• Full access: uninterrupted all-year, high quality access
Speed and comfort of the
road
Infrastructure note RT-2 of the World Bank presents the relationship
between the roughness (IRI) of the road and the maximum speed of
different types of vehicles. It also presents a correlation between
road descriptions and Roughness range (IRI). Transport
Infrastructure Notes are available on-line at:
http://www.worldbank.org/html/fdp/transport/publicat/pub_main.ht
m
The table below presents the values of VROUGH for a series of
roughness levels as estimated by the HDM-4 model based on the
Australia study (McLean, 1991)1
1
Rodrigo S. Archando-Callao; Unpaved roads, Roughness estimation by Subjective Evaluation,
Transport note RT 2 World Bank
12
INDEVELOPMENT:
Objective of pavement
maintenance
Failures
Cars
Busses
106
80
64
53
46
40
35
32
105
78
63
52
45
39
35
31
Maximum speeds (km/hr)
Light
Medium
trucks
heavy trucks
105
94
78
71
63
57
52
47
45
40
39
35
35
31
31
28
Articulated
trucks
84
63
50
42
36
31
28
25
Roughness
(IRI)
6
8
10
12
14
16
18
20
The objective of road maintenance and thus that of pavement
maintenance is the continuation of providing road access with
acceptable service levels. This means that the service levels
determine if the road is still in an acceptable condition.
The failures of the road surfaces can be subdivided in conditions that
affect the functionality, and those that affect the structural capacity.
• Functional failures relate to the operational requirements of
the users of the roads, such as comfort, safety and road user
operation costs and thus depend on the service levels
• The structural failures relate to the technical live of the road
in total and pavement in particular.
Functional and structural conditions of a pavement are closely
related; however they are not thoroughly interdependent. Structural
deterioration may decrease pavements functional condition, e.g.
increasing roughness and noise, and affecting at the same time the
risk of the vehicle and its occupants.
However, some types of structural deterioration can occur and
progress to an advanced state without being perceived by the users
(cracking, for example). It is possible, also, that functional
conditions of the pavement could be reduced (such as loss of skid
resistance) without significant structural changes.
Typical functional damages are:
• Roughness
• Rutting
• Skid and slip resistance
• Hydroplaning
The kind of structural damages depend mainly on the material
composition of the pavement. Typical pavements are made of
gravel, asphalt concrete and concrete. However all these materials
have one damage in common: Potholes. Potholes are not only a
sign of structural damages but eventually will effectively reduce the
width of the pavement and thus reduce the potential traffic flow of
the road.
The so-called threshold values or fatal limits of the road attributes
13
INDEVELOPMENT:
like roughness, rutting and skid resistance vary with the service
levels. In general these values depend on the design speed of the
road. When the design speed is high, road users have to be
protected against accidents due to defaults in the road pavement
and it is therefore important to set higher norms with regard to the
road attributes.
10.1 EARTH AND GRAVEL ROADS
The decay of unpaved roads is dominated by the reaction of the
surfacing material and the roadbed on the combined action of traffic
and environment. The surface is typically 100 to 300 mm thick and
is both the wearing and the base course. The surface is usually a
little porous, although in some cases the permeability may be very
low. The deterioration of the surface depends not only on the traffic
but also on its material properties, rainfall and drainage
characteristics. The bearing capacity of the road depends also
largely on the moisture penetration, that on its turn depend heavily
on surface water runoff and side drainage. The two most common
failures of unpaved surfaces are deformations of the road and
erosions.
Shear strength
Planning regravelling
Rutting
2
When the surfacing layer has inadequate shear strength under the
operative drainage conditions to sustain the stresses applied by
traffic loads, shear failure and deformation occur. The road surface
will be soft and slushy under wet conditions so that, while it may be
possible for a few light vehicles to pass, the road will become
impassable after a relatively small number of vehicle passages.2
Regravelling is necessary when 20 % of the road pavement has a
gravel thickness of 5 cm or less. The value of the average annual
gravel thickness loss is usually constant over time and does
correlate linear with Average Daily Traffic, terrain type (hilly, rolling,
or flat) and mean monthly rainfall. It is possible to monitor the
gravel thickness decay and through extrapolation techniques
determine when regravelling is necessary. Alternatively one may use
the following formulas to estimate the year of regravelling.
Rainfall
(m/month)
Material loss
(mm/year)
C for flat
terrain
0.02
0.1
0.2
= c (0.08 ADT + 12.5)
= c (0.09 ADT + 12.5)
= c (0.1 ADT + 12.5)
1
1
1
C for
rolling
terrain
1.07
1.13
1.19
C for
hilly
terrain
1.25
1.33
1.43
Where ADT= Average Daily traffic
The rutting process cannot be predicted with any use-based model.
Condition-based method can be used. Because rutting is not the
most dominant failure on earth and gravel roads, maintenance is
usually carried out when the failure has occurred.
Prof.dr.ir. A.A.A. Molenaar: Structural Design of Pavements, Part 2 Design of Earth and Gravel Roads
14
INDEVELOPMENT:
Corrugations,
depressions and
potholes
When water accumulates on the surface, vehicle tires stir up the
water causing fine material to pass into suspension and being
pushed and pulled out of location. Eventually potholes may occur.
The World Bank provides guidelines for subjective evaluation of the
road surface. It relates the observed condition to the roughness of
the road (expressed in IRI) which in its turn relate to maximum
speeds. The table below provides a series of descriptors for selected
levels on the roughness scale. The categories used to describe
surface shape in this table are:
• Depressions: Dish-shaped hollows in wheel paths with surfacing
in-place
• Corrugations: Regularly spaced transverse depression usually
across the full lane width and with wavelength in the range of
0.7 to 3 m.
• Potholes: Holes in the surface caused by disintegration and loss
of material, with dimensions of more than 250 mm diameter and
50 mm depth. The pothole size is indicated by the maximum
deviation under a 3m straightedge, e.g., 6-20mm/3m, similar to
a construction tolerance. The frequency is given by:
1. Occasional: 1 to 3 per 50m in either wheel path
2. Moderate: 3 to 5 per 50 m in either wheel path
3. Frequent: more than 5 per 50 m in either wheel path
• Ride: the comfortable ride is relative to a medium-size sedan
car with regular independent shock-absorber suspension.
Traffic speed: This indicates common travelling speeds on dry,
straight roads without traffic congestion, with due consideration of
care for vehicle and comfort of the occupants3
3
Rodrigo S. Archando-Callao; Unpaved roads, Roughness estimation by Subjective Evaluation, Transport note RT 2 World
Bank
15
INDEVELOPMENT:
Roughness range
(IRI)
1.5 to 2.5
Road description
Recently bladed surface of fine gravel or soil
surface with excellent longitudinal and
transverse profile (usually found only in
short lengths).
Ride comfortable up to 80 – 100 km/hr,
aware of gentle undulations or swaying.
Negligible depressions (e.g. < 5 mm/3m)
and no potholes.
Ride comfortable up to 70-80 km/hr, but
aware of sharp movements and some wheel
bounce. Frequent shallow-moderate
depressions or shallow potholes (eg. 6-30
mm/3m with frequency 5-10 per 50 meter).
Moderate corrugation (e.g. 6-20/0.7-1.5 m)
Ride comfortable at 40 to 70 km/hr.
Frequent moderate transverse depressions
(e.g. 20-40mm/3-5m at frequency 10-20 per
50 m) or occasional deep depressions or
potholes (e.g. 40-80mm/3m with frequency
less than 5 per 50 m). Strong corrugations
(e.g.>20 mm/0.7-1.5m).
Ride comfortable at 30-40 km/hr. Frequent
deep transverse depressions and/or potholes
(e.g. 40-80 mm/1.5m at frequency 5-10 per
50m); or occasional very deep depressions
(e.g. 80mm/1-5m with frequency less than 5
per 50m) with other shallow depressions.
Not possible to avoid all the depressions
except the worst.
Ride comfortable at 20-30 km/hr. Speeds
higher that 40-50km/hr would cause
extreme discomfort, and possible damage to
the car. On a good general profile: frequent
deep depressions and/or potholes (e.g. 4080 mm/1.5m at frequency 10-15 per 50m)
and occasional very deep depressions
(e.g.>80 mm/0.6-2m). On a poor general
profile: frequent moderate defects and
depressions (e.g. poor earth surface).
3.5 to 4.5
7.5 to 9.0
11.5 to 13.0
16 to 17.5
20 to 22
The progression of the IRI values can be estimated with models
presented in HDM 3 and 4. Transport No. RT-1 of the World Bank
describes these models in more detail. However it is more practical
to monitor the progression of roughness and to use extrapolation
techniques to estimate when roughness values exceed threshold
values.
Repair
The most important requirement of most gravel and earth roads is
the passability. In these situations the required speed of a sedan car
16
INDEVELOPMENT:
does not have to be higher than 40 km/hr. Grading/blading is often
not the most cost-effective measure. Spot improvements in
combination with pothole filling and rut correction are usually more
cost-effective.
SMDP in collaboration with the Department of Roads in Nepal
developed a set of simple guidelines with regard to maintenance
planning of rural roads and highways. These guidelines are very
useful for budgeting purposes.
Table: Annual maintenance requirements in Nepal
Traffic Volume Earth Road
Gravel Road
20 VPD
• Small rut filling once • Small rut filling once
per year
per year
• Spot Regravelling 8% • Spot
Regravelling
of surface per year
2% of surface per
year
• Routine
maintenance
40 VPD
•
•
•
60 VPD
•
•
•
100 VPD
•
•
•
Small rut filling once
per year
Spot
Regravelling
10% of surface per
year
Routine maintenance
•
per year
Spot regravelling 12%
of surface per year
Routine maintenance
•
per year
Spot regravelling 16%
of surface per year
Routine maintenance
•
17
•
•
•
•
•
•
per year
Spot
Regravelling
4% of surface per
year
Routine
maintenance
per year
Spot
regravelling
6% of surface per
year
Routine
maintenance
per year
Spot
regravelling
10% of surface per
year
Routine
maintenance
INDEVELOPMENT:
Periodic Maintenance rural roads Nepal:
Traffic Volume Earth Road
Gravel Road
20 VPD
Not applicable
• Hilly terrain
5 years
• Flat terrain
6 years
40 VPD
Not applicable
• Hilly terrain
5 years
• Flat terrain
6 years
60 VPD
Not applicable
• Hilly terrain
5 years
• Flat terrain
6 years
100 VPD
Not applicable
• Hilly terrain
5 years
• Flat terrain
6 years
18
regravelling every
regravelling every
regravelling every
regravelling every
regravelling every
regravelling every
regravelling every
regravelling every
INDEVELOPMENT:
10.2 ASPHALT CONCRETE
Besides the earlier mentioned functional damages, the following
structural damages may be encountered on asphalt concrete roads:
• Ravelling
• Cracking
• Shoulder deterioration
• Edge breaks
Basically there are three different forms of cracks:
• Longitudinal: parallel to the centre line
• Transverse: across the cross-section
• Mesh cracks.
The loss of skid and slip resistance may the result of stripping
(fretting), bleeding and glazing.
Bleeding and fatting up
Asphalt concrete roads can become slippery because of bleeding and
fatting up processes. Bleeding is the process where bitumen is
forced to road surface due to traffic pressure. Fatting up results in a
loss of binder on the surface. Usually aggregates become visible.
OECD, PIARC and many other road safety research institutes have
found a strong correlation between poor skid resistance and accident
occurrence. Micro texture appears to be the most important texture
19
INDEVELOPMENT:
Rutting
Wide ruts indicate that
more layers are affected
parameter, but macro texture can also have major influence.
Unfortunately it is not possible to develop either a use-based or a
condition-based model for this problem. The best indication is the
traffic behaviour and number of accidents. Because of difficulties to
predict such failures and its high risks with regard to traffic accidents
many road agencies solve these problems with funds from the road
safety budget.
Rutting is defined as the permanent or unrecoverable trafficassociated deformation within pavement layers which, if channelled
into wheel paths, accumulates over time (Paterson, 1987).
Basically there are two types of rutting processes. The first process
occurs in the whole pavement. The second process only occurs in
the top layer. The latter is usually the case when the levelling and
binder course are very stiff and usually thick. Narrow and heaving
ruts are an indication that the rutting process only took place in the
upper layers. Wide ruts are usually an indication that more layers
are affected.
20
INDEVELOPMENT:
Heaving and narrow ruts
indicate that ruts only
affect the Surface layer.
Deformations in Long Life
Pavements typically occur
in the surface layer and
binder course.
Cracks
Together with rutting, cracks are main indications for structural
problems of the road pavement. However not all cracks are
indications of fatigue. Wide longitudinal cracks can pose treads to
cyclists, as their wheel can get trapped in the crack. But experts are
divided if cracks affect the service level of the pavement of other
road users. Crack may result in potholes, raveling and increase the
roughness of the road but this is certainly not always the case.
There are plenty cracked roads, even with block patterns that do
affect the road users at all.
A single longitudinal wheelpath cracks, wider than 1.5 mm indicates
the onset of structural failure in a thick (>200mm approx) pavement
or cracks in bituminous surface one with a cement bound base.
These cracks’ deterioration is likely to progress into block and mesh
cracks, which indicates the end of the structural life.
Narrow cracks, less than 0.5 mm, are often not related to structural
failure. Wider or medium sized cracks which are not located in the
wheelpath are often indications of joints between layers.
Short transverse cracks are probably caused at the surface and are
not indications of fatigue failures. In general these cracks progress
slowly.
Discontinuity in lower layers may cause long transverse cracks. Long
transverse cracks are also indications of joints of cement bound
layers. The space between transverse cracks may reduce due to
aging and traffic load. Such developments indicate structural
problems in the lower layers of the pavement or cement bound
base.
10.2.1 Long-term maintenance planning
Long-term maintenance plans cover the period beyond five years up
to the foreseen end of the life of the road/pavement. Long-term
21
INDEVELOPMENT:
Use-based pavement
maintenance
maintenance plans are important while analysing life cycle costs of
the road network to determine the needed average annual budget.
Various research results show that it is impossible to forecast actual
maintenance demands solely with use-based models. With exception
of perhaps rafeling of porous asphalt concrete, maintenance of
asphalt pavements will be initiated either failure or condition-based.
However for budgeting purposes, planners need use-based models
that allow them to forecast long-term maintenance demands.
Below you find a description of annual and periodic maintenance of
rural asphalt roads in Nepal.
Annual maintenance (Routine/Recurrent activities)
Traffic Volume
Blacktop Road
20 VPD
• Patching 0.5% surface
40 VPD
60 VPD
100 VPD
Periodic Maintenance:
Traffic Vollume
20 VPD
40 VPD
60 VPD
100 VPD
Routine maintenance of
AC-pavements
per year
per year
per year
per year
Blacktop Road
Resurfacing;
Hilly terrain every 5 years
Flat terrain every 6 years
Resurfacing;
Resurfacing;
Resurfacing;
In the Netherlands annual pavement maintenance or routine
maintenance consists of
• Crack sealing
• Slurry seals
• Surface treatments
• Localised mill and replace
Budgets for routine pavement maintenance are large, in particular
on urban and provincial roads. These budgets are justified by the
fact that when annual maintenance repairs take care of all smaller
and medium sized damages like rafeling, (mesh) cracking and
rutting, these damages will not progress. It is not uncommon that
roads have had minor repairs covering 60% of the surface prior
periodic maintenance.
22
INDEVELOPMENT:
Periodic maintenance either consists of one of the following
activities:
1. Overlays 50 mm
2. Surface treatment
3. Mill and replace 40 mm
4. Modified or Rubberised AC Overlay 70 mm
5. Double Surface Treatment
The first four treatments are considered rehabilitation techniques
and the last treatment considered a periodic repair. A reconstruction
involves at least a complete removal of the pavement.
Reconstructions only occur when the existing pavement was
completely under designed.
The Dutch determine their periodic maintenance intervals on basis of
the following criteria
• Sub-base
• Soil condition
• Road classification on basis of equivalent standard axle loads
Subbase/Base
For long-term maintenance demand forecasting, the following three
asphalt pavement construction are available:
1. Subbase/base course of sand
2. Subbase/base course of dry-bound macadam
3. Subbase/base course of wet-mix macadam
Subgrade Conditions
The model distinguishes the following three soil conditions:
1. Sand
2. Clay
3. Peat
Road classification
The model differentiate between the following three divisions:
Road
classification
RC 1
Percentage of heavy
motorised transport with axle
loads higher than 100 kN
12.5
Number of
equivalent standard
axle loads (ESAL)
6
7
10 <X< 10
Maximum expected
axle load
(kN)
180
RC 2
10
10 <X<10
160
X<10
160
RC 3
5
6
5
5
Source: VBW Asfalt: Kosten van Wegverhardingen, 1989
23
INDEVELOPMENT:
Maintenance cycles for 2x1 lane roads
Subbase/
base
Soil
type
Road
class.
All
types
Sand
RC 1
RC 2
RC 3
Routine
maintenance
budget/invest
ment cost ratio
0.0833
0.0934
0.14
All
types
Clay
RC 1
RC 2
RC 3
0.055
0.05
0.12
Drybound
macad
am
Peat
RC 1
RC 2
RC 3
0.045
0.039
0.082
Year of
periodic
maintenance
Year of
rehab.
1
Type
rehabilitation
Life
rehabil
itation
17 (Double
surface treat.)
17 (Double
surface treat.)
13(Double
surface treat.)
15
16
27
Overlay 60 mm
Overlay 50 mm
Mill and replace
15
15
17
15
13
10
Overlay 60 mm
Overlay 50 mm
Mill and replace
15
13
15
12
11
10
Overlay 60 mm
Overlay 50 mm
Mill and replace
12
11
13
Source: VBW Asfalt: Kosten van Wegverhardingen, 1989
2 x 2 roads
Rehabilitation cycles often involve overlays. The need for
rehabilitation may differ from lane to lane. This is in particular the
case in countries where heavy traffic drives on the outer lane. Traffic
composition and volume may also differ on the different directions.
This means that the need for rehabilitation may vary on different
lanes. As it is not possible to use overlays on separate lanes, one
may have to develop special long-term maintenance plans for 2x2
and roads with more lanes. These long-term plans often involve a
mill and replace treatment on the lanes with heavy traffic during the
first rehabilitation cycle. The other lanes are not treated or only
receive a surface treatment during the first rehabilitation cycle.
The second rehabilitation cycle may involve the whole pavement
width or only specific lanes. When the whole pavement width is
treated an overlay is the common repair. When only specific lanes
are repaired; a mill and replace treatment is common. In this case
the third rehabilitation cycle would involve an overlay of the whole
pavement. These rehabilitation cycles often have durations
somewhere between 10 to 15 years. They even may contain spot
repairs.
10.2.2 Short and medium term maintenance planning
Short term maintenance plans cover the investment plans for next
two fiscal years. Because of budgeting procedures this plan may
have to be prepared one, two or even more years in advance.
Medium long-term maintenance plans covers the period in between
the short and long-term maintenance plans, respectively 2 and 5
years. As indicated earlier, most repairs will have to be activated
failure- or condition based. Condition-based maintenance will be
used when it is possible to assess residual lives of the assets on
basis of inspections or test results.
24
INDEVELOPMENT:
Forecasting rehabilitation
and reconstruction
The fatigue of the asphalt layer is the main criteria for initiating
projects that strengthen the intrinsic stiffness and strength of the
pavement. This is usually done with an overlay possibly in
combination with a partly replacement of the pavement (mill).
Fatigue cracking starts usually at the underside of the pavement or
cement bound base layer and progresses upwards to the surface.
These cracks reduce the “bearing height” of the asphalt pavement.
As a result the deformation due to traffic loads increases.
Reconstruction
Reconstructions only occur when the existing pavement was
completely under designed. For example when the original
designation of the road has changed from a neighbourhood access
road to an arterial. These under designed pavements usually have
untreated base courses. In these situations, deflection tests may
require extreme thick overlays with a life shorter than five years. In
such situations it is probably more cost-effective to apply a
reconstruction.
It is possible to make assessments about the residual life of the
pavement through deflection tests and information about the soil,
height and material characteristics of sub-base, base and pavement
and cumulative axle loads. Estimates of residual life have been
found to be within a range of ±2 years when the pavement structure
is approaching conditions that require repairs. Fatigue failures are
often accompanied with damages like rutting and cracking. When
such damages are near their fatal limits, the residual life estimate on
basis of the deflection tests is probably correct or even too
optimistic. When the road surface is not yet close to the fatal limits
for either rutting or cracking, the residual life estimate is likely to be
too pessimistic.
Core samples
Core samples or trial holes provide information about the current
thickness of each of the bound layers and location of cracks below
the surface. It is also used to collect and analyse binder samples and
for all sorts of tests to establish values about the intrinsic strength.
The indirect tensile test is a common laboratory test used for
determining the indirect tensile stiffness modulus (ITSM) of
bituminous materials. Core samples should be taken on the edge of
the wheel path at 10 meter intervals and where ever problems are
visible. The created holes also allow obtaining information about CBR
values of the base and subbase. Usually in-situ techniques are
applied to obtain these values.
Equipment
Deflectograph and Benkelman Beams are equipment items for
assessment of deflections of the pavement due to an applied load. It
is supposed to reveal the extent of the pavement response to
loading. Measurements should take place in each wheel track.
The deflectograph is criticised because the speed of the test vehicle
does not recreate that of vehicle moving at normal speed. Empirical
researches which help interpret deflection results are of little help for
roads on which little research has been done notwithstanding the
fact that this method may not be used on rigid pavements. The Fall
Weight Deflectometer offers a suitable alternative to the
25
INDEVELOPMENT:
deflectograph where these circumstances pose a problem.
Accompanying computer software allows for analysis of the stress
and strain distributions within the pavement and estimates of
strengths of the pavement layers and subgrade. It is possible to
download free software at
http://www.wsdot.wa.gov/biz/mats/pavement/fwd.htm
While selecting the equipment and related software, engineers
should keep in mind that not all software is suitable for their
particular soil conditions. Certain programs assume minimum CBR
values for the subgrade which may not be realistic.
Total Thickness of
Bituminous Material
(TTBM)
Pavements which have been subjected to various maintenance
treatments throughout their life may contain layers of deteriorated
or non-standard materials sandwiched between intact bituminous
layers. It is therefore necessary to set rules about determining the
Total Thickness of Bituminous Material (TTBM). The different
technologies and respective computer programs may adopt different
definitions concerning TTBM. Engineers should be clear about these
definitions. As general rule of thumb, engineers may start with the
following assumption:
• Bituminous surfacing layers (i.e. those within the top 100mm
of the existing pavement) are included in TTBM regardless of
their condition.
• Bituminous layers which are known to be severely
deteriorated and whose upper surface is at greater than a
100mm depth are not included in TTBM.
• Any intact bituminous material (or deteriorated surfacing
material) that is separated from other intact bituminous
materials by either a severely deteriorated bituminous layer
or any granular layer (either of which must be greater than
25mm thick and have their upper surface at greater than a
100mm depth) is not to be included in TTBM.
Need for smaller periodic
maintenance
The need for periodic maintenance (read rehabilitation) depends on
the conventional theory of pavement deterioration, manifested by
fatigue at the underside of the pavement or structural deformation,
and assumes that deflection increases with time and traffic as the
pavement deteriorates from traffic induced stresses.
However, thick well-constructed fully flexible pavements on strong
base and subbase courses do not deteriorate in this way and can
have very long lives in structural terms. The maintenance demand is
generated because of surface decay, affecting the service levels of
the pavement. The dark-grey area in the graph presented-below
show when fatigue (deflection information) in relation to TTBM is no
longer the dominant factor for initiating periodic maintenance. This
means that it is not necessary to strengthen the pavement structure
of Long Life Pavements.
26
INDEVELOPMENT:
The LLP area indicates that the road has a so-called long-life
pavement, which means that structural failures do not occur and
that pavement failures are only related to its service levels.
The threshold value of the TTBM depends partly on the asphalt
concrete characteristics and partly on the axle loads. TRL report 639
presents threshold values for different materials:
DBM 125; 420 mm
DBM 100; 390 mm
DBM 50; 350 mm
HDM; 320 mm
HDM35; 310 mm
When the road pavement fits in the ULLP area the pavement can be
upgraded to a long-life pavement.
Pitfalls in analysis
Detecting problems in the
subbase and subgrade
When the road condition falls in the white area, engineers have to
make assessments about the residual value of the pavement. The
deflection tests give indications about the conditions of whole
pavement or in the case of FWD of single layers. To find out if the
damages where caused by traffic or others a comparison has to be
made with deflection values of relatively untrafficked road sections.
While analysing the software results, engineers should be aware of
the following pitfalls: During long periods of hot weather, the
moisture content in the subgrade may reduce and as a result of that
show lower deflections, indicating an unrealistic higher strength.
Settlement processes of backfills due to open trenches, e.g. sewer
pipe installations, will be indicated by high deflections, even when
the surface is still in good condition.
Where relatively high deflections are associated with a pavement
whose surface condition is good, the cause may be a deterioration in
subgrade strength brought about by a recent increase in the
moisture content. The increase may be the result of thawing at the
end of a prolonged period of cold weather during which frost has
penetrated deep into the pavement, and possibly also the subgrade.
27
INDEVELOPMENT:
Composite pavements
Deflections on composite pavements with at least one cement bound
layer are usually below 15 mm 10-2. To find cracks two consecutive
deflection surveys need to be carried out. In addition it is necessary
to carry out visual inspections to find cracks in the surface.
When the asphalt pavement is oxidised, it may be bridging and
deflection values are lower than expected. Analysis of core samples
will answer if the pavement has oxidised or not.
10.2.2.1 Surface damages
Longitudinal Deformations
Corrective maintenance
Aquaplaning
Rutting
Longitudinal deformations can be measured using so-called profilers.
The little book of profiling, M.W. Sayers and S. M. Karamihas
presents a good overview on profilers. The most common used
profiler is the International Roughness Index (IRI).
Many road agencies apply threshold values for roads with flexible or
rigid pavements of 3.25 to 3.75 IRI. It may be difficult to predict the
progression of roughness, therefore most planners will carry out
corrective maintenance within 2 years after significant damages
have been observed. It is assumed for budgeting purposes that the
roughness areas expand 5% per year and the depth with 0.17
IRI/year.
Roughness problems in flexible pavements in urban areas frequently
occur on storage lanes in front of traffic lights. Most of the
deformation takes place 60 to 80 mm below the surface. Therefore it
is necessary to strengthen the intrinsic stiffness of the layers at this
depth. The best construction method is to apply open hydrocarbon
concrete (0/22) as the binder course and to apply broken stones
as aggregate in the levelling course.
Cracks due to fatigue often result in roughness problems. If this is
the case, the overlay should be placed in two equally size layers.
The minimum of each layer is 75 mm.
Alternatively the existing rough pavement section may be removed
(mill) prior the overlay procedure. The mill is usually between 30 to
60 mm deep, but may be deeper on sections of urban roads before
traffic lights. Note that this procedure needs additional structural
analysis.
Deformations, rutting, inadequate drainage capacity or low camber
slopes may cause aquaplaning; a serious problem for motorised
traffic. Camber slopes may be reduced due to settlements in the
subgrade. Corrective measures should be taken when aquaplaning is
observed or when camber formation is inadequate. Usually a
threshold value of 1% is used.
Maintenance for rutting can be initiated condition based. The ruts
can be measured with deformation gauge. In that case the
measurements are made on regular intervals, which usually vary
between 25 and 200 meters. The deformation gauge is standardised
and 2 meters long. Besides these manual methods the data can also
be collected with electronic-based automated equipment.
The warning levels and intervention levels of course relate on the
one hand on the function of the road link and on the other hand the
proposed repairs. On motorways with a design speed of 120 km/hr,
the maximum allowable intervention level could be set like an
28
INDEVELOPMENT:
average of 18 mm over a 100 m and 23 mm over a 50-meter
length. Often rut development tends to accelerate during the first
ten/twelve years after which the development seems to be linear. It
is suggested to use a norm value of annual increase of 1.5 mm,
when the deterioration process is progressive.
On urban roads, where the design speed is approximately 50 km/hr,
threshold values may be increased. In the Netherlands, the
threshold value for urban road is 30 mm over a length of 15 meter
within an area of 100 meters.
It is possible to get a rough estimate of the end of life due to rutting
with the following equation:
1.48
S/Sn=[t/T]
Where
S, average rut depth
Sn, norm for rut depth
t, age of pavement since construction or last periodic maintenance
T, Residual life at this moment
Cracking
Condition based model
Cracking usually has two phases, crack initiation and crack
progression. Crack progression is said to occur when 0.5 per cent of
the surface is cracked and seems to depend highly on pavement
age, traffic volume, cumulative axle loads and pavement stiffness.
Cracks can easily be monitored, plotted and its behaviour can be
described with a slightly modified Weibull function being:
Fw(n)= C {1-exp [n/µ)β]}
Fw() = probability that an element has cracked
µ = time parameter at indicating when F equals 0.63
Although the Weibull function is written as a function of the number
of load repetitions, n, it can also be written as a function of time, t.
In that case n is replaced by t. For practical purposes it is proposed
to use C = 0.94 for pavements with an asphalt thickness less or
equal than 80 mm, while it is recommended to use C= 0.79 for all
other cases.
β seems to be dependent on the thickness of the asphalt layer, h
(mm), following
log β= -0.341 + 0.295 log h
Inspection rules
An example
The percentage of cracking deals with the amount of wheel track
cracking. The standard length of each section to be inspected is 100
m. The left and right wheel tracks are treated separately, which
means that in fact a 200 m long wheel track section is considered.
The total length of the area in either wheel tracks that show
longitudinal or mesh/block cracking is then determined, and this
value is divided by 200.
Assume a pavement where the right hand wheel track of a lane
shows cracking over a length of 10 m and the left hand wheel track
shows cracking over the length of 20 m. Then the percentage of
29
INDEVELOPMENT:
Transverse cracks
cracked area is {(10+20/200} 100% = 15%. The thickness of the
asphalt layer is 200 mm, so the correction factor C= 0.79 and β =
2.18. If the inspection was done 8 years after the pavement was
constructed, then µ = 16.37 years. If it is assumed that
maintenance will be applied the amount of cracking equals 25%,
then it can be calculated that this amount of damage will occur at t=
10.57 years.4
Reduction of space between transverse cracks over the years is an
indication of structural problems.
Fall Weight Deflection tests can help identifying cracks and joints
which are located below the surface (see sketch below to identify
cracks). Fall weight deflection tests place sensors on the road
surface on varies distances from the load. These sensors allow for
the identification and analysis of different layers and thus allows for
the identification of cracks and joints.
The table below presents the usual recommended deflection sensor
positions.
4
AAA Molenaar: Performance Models, Maintenance management of infrastructure. 1999, TU Delft
30
INDEVELOPMENT:
Rutting and cracking, in particular mesh-cracking are both the result
of repetitive axle loads. And it is not uncommon to observe mesh
cracks in or near ruts. The Transport and Road Research Laboratory
relates the wheel track rutting with rainfall, traffic, cracking patterns
in the roads, kind of base course and repairs. The table below is a
summary of the table presented in their Overseas road note 1
“Maintenance management for district engineers” 5
5
This document is downloadable from www.transport-links.org
31
INDEVELOPMENT:
Base course
Level of
rutting
Extend of
rutting %
Climate
Type of
cracks
Surface
dressing on
Granular
base
< 10 mm
-
Rainfall>150
0 mm/year
or
Traffic >1000
vpd
Rainfall<
1500 mm/yr
and
Traffic <1000
vpd
All
Wheel track
cracking
Non-wheel
track
cracking
Wheel track
cracking
Non-wheel
track
cracking
Any cracking
Rut cracks
Others
cracks
Any cracking
Asphalt
concrete on
granular
base
Actions
Extend of
cracks (%
of section
length)
<5
>5
<10
>10
Seal cracks
Surface dress
Seal cracks
Surface dress
<10
>10
<20
>20
Seal cracks
Surface dress
Seal cracks
Surface dress
-
Treat cracks
and further
investigation
Patch
Further
investigation
Seal cracks
Surface dress
Further
investigation
10-15 mm
>10
>15 mm
<10
>10
All
< 10 mm
-
Rainfall>150
0 mm/year
or
Traffic >1000
vpd
Rainfall<
1500 mm/yr
and
Traffic <1000
vpd
All
All
Any cracking
<10
10-20
>20
Seal cracks
Surface dress
Further
investigation
Rut cracks
Other cracks
-
All
Any cracks
-
Patch
Patch or
treat cracks
Treat cracks
>10 mm
<5 %
>5 %
Source: TRL: ORN 1; Maintenance management for district engineers
32
<5
5-10
>10
INDEVELOPMENT:
Extend of
cracks (%
of section
length)
<10
>10
Actions
Any cracking
<20
>20
Seal cracks
Surface dress
or seal
cracks
Any cracking
-
Rut cracks
Others
cracks
Any cracks
-
Treat cracks
and further
investigation
Patch
Patch or
treat cracks
Further
investigation
Base course
Level of
rutting
Extend of
rutting %
Climate
Type of
cracks
Asphalt
concrete or
surface
dressing on
stabilised
road base
< 5 mm
-
Any cracking
5-10 mm
>10
Rainfall>
1500
mm/year or
Traffic >1000
vpd
Rainfall<
1500 mm/yr
or
Traffic <1000
vpd
All
>10 mm
<5
All
>5
All
-
Seal cracks
Surface dress
Source: TRL: ORN 1; Maintenance management for district engineers
Ravelling
Ravelling is the loss of aggregate from the surface layer. It indicates
lack of bond between the aggregate and the bituminous binder. It
should be noted that it is not easy to make a good rating of the
amount and severity of ravelling. It is a defect that is difficult to
inspect. Some models for surface treatments, dense asphalt wearing
courses and porous asphalt wearing courses have been developed.
Care should be taken in using these models since data was only
collected during a four-year period. The general form of the model
is:
Ln{R*(100-N)/[(100-R)*N]}=a*(t-T)
Where
R= area exhibiting ravelling as percentage of the total area
N= area expressed as a percentage of the total area at which
maintenance is considered needed
t= age of surface at which R was determined
T= age of surface at which N will be reached
A= parameter describing rate of damage development
The parameter A depends on the amount of traffic.
For dense asphalt concrete surface layers:
A=1.25*10-5 * INT
For porous asphalt concrete surface layers;
A=3.08*10-5 * INT
33
INDEVELOPMENT:
For surface treatments:
A=5.71*10-3 * INT – 5.15*10-2 * INTtruck + 1.43*10-5 *
CUMTRUCK – 1.57*10-5 * CUMINT
Where
INT= traffic intensity (vehicles per day)
INTTRUCK= truck intensity (trucks per day)
CUMTRUCK= cumulative amount of trucks
CUMINT= cumulative amount of traffic 6
It is possible to assume that ravelling of porous asphalt concrete
motorways will take serious forms when it is between 9 and 12
years of age.
The use-based models for the other road surfaces are less reliable
and most road engineers will work with condition based models.
Potholes
According to HDM III potholing occurs typically 2 to 6 years after
wide cracking and 3 to 6 years after ravelling of thin surface
treatments. The exact initiation period depends on the quality of the
base, the thickness of the bituminous layer and the annual number
of axles of all vehicles classes in the analysis year. HDM III also
indicates that potholing cannot take place before the area of wide
cracking exceeds 20 percent or the area of ravelling exceeds 30
percent.
HDM-III defined a period (IPT) between the initiation of either wide
cracking or ravelling and the occurrence of the first pothole. This
period was a function of traffic and thickness of asphalt layers and is
given by:
IPT = max(2 + 0.04 HS - 0.5 YAX, 2)
cemented
IPT = max(6 - YAX, 2)
cemented
Where IPT
if base is
(7.1)
if
base
(7.2)
not
is
is the time to initiation of potholing in
years
is the total thickness of bituminous
surfacing
is annual vehicle axles in millions per
lane per year
HS
YAX
Small potholes pose little risks to road users or the road authority.
But the maintenance department should be concerned about the
progression of the diameter and depth of the potholes. It is easy to
identify locations of new potholes and it is easy to predict its growth
with aid of the following formula:
According to the HDM model, rainfall is only influencing the
progression of the potholes and do not influence their initiation,
6
AAA. Molenaar: Maintenance Management of Infrastructure, TU Delft, 1999
34
INDEVELOPMENT:
which is considered to be caused by traffic, pavement strength and
asphalt surfacing thickness. The annual progression enlargement is
estimated with the following formula:
∆APOTPd = min{APOTa [KBASE YAX (MMP + 0.1)], 10}
Where ∆APOTPd
area
APOTa
YAX
lane
MMP
KBASE
HS
is enlargement of potholes in per cent
is area of potholes at start of year
is annual number of axles in millions per
is
is max(2
is
is
is
mean annual rainfall in m/month
- 0.02 HS, 0.3) for granular base
0.6 for cement-treated base
0.3 for bituminous base
thickness of asphalt surfacing in mm
If the potholes were patched, than the enlargement will always be
zero.
Patching of potholes
The Indian Pavement Performance Study, (CRRI, 1993), developed
models for pothole initiation and progression for three surface types
(premix carpet (PMC), semi dense carpet (SDC) and asphalt
concrete).The CRRI models above yield initiation periods in the
range 0.2 - 1.0 years, considerably shorter than the HDM-III model
predictions.
Note that these rules do not apply on porous asphalt concrete
pavements with accelerating/braking motor vehicles. In which case
potholing develops a lot faster after occurrence of ravelling.
Patching of potholes is often a recurrent activity, which is usually
failure-based initiated. A team will inspect the road surface and
repair all potholes, when they appear to be present. The interval
period influences the progression of the area of potholes. HDM 4
uses a model that estimates that if potholes are effectively patched
within 2 weeks after initiation, only 2 % of the maximum annual
increase in pothole area will appear during the course of the year.
The table below present the relationship between the interval of
pothole patching and the influence on the maximum annual pothole
area increase.
35
INDEVELOPMENT:
Interval of pothole patching
2 weeks
1 month
2 month
3 month
4 month
6 month
12 month
Influence on max. Pothole area
increase (%)
2
6
12
20
28
43
100
Patching of potholes has a negative effect on the roughness of the
road. HDM3 assumes that there is a residual roughness of 10% of the
roughness caused by the potholes.
Edge damages
When the shoulder is not providing enough support to the
pavement, because it is lower than the pavement, edge damages
are likely to develop over a period of time. Edge damages can
therefore easily and cheaply be prevented by improving the quality
of the shoulder, by reducing the edge step, improving the stability
and stiffness of the shoulder and widening the shoulder. This
problem is less common on road with (elevated) side walks.
The following model was proposed to be included in HDM 4 to
estimate the annual loss of edge material.
VEB = Keb a0 PSH AADT2 ESTEP Sa1 (a2 + MMP)
[
PSH = max min ( a 3 − a4 CW,1) , 0
where VEB
]
is the annual loss of edge material in
m3/km
is the proportion of time using shoulder
is the annual average daily traffic
is
the
elevation
difference
from
pavement to shoulder in mm
is the mean rainfall in m/month
is the average traffic speed in km/h
is the edge break progression factor
(default = 1)
are calibration parameters
PSH
AADT
ESTEP
MMP
S
Keb
a0 to a4
36
INDEVELOPMENT:
Default Parameters for the HDM-4 Edge Break Model
Parameter
a0
a1
a2
a3
a4
Base Type
Granular
Cemented
AM
ST
AM
ST
50
75
25
50
-1
-1
-1
-1
0.2
0.2
0.2
0.2
2.65
2.65
2.65
2.65
0.425
0.425
0.425
0.425
Source:
Various road research and development institutes have used earlier
described damage progressions and developed simplified conditionbased models. Every model is a simplification of the reality and
engineers should treat them as guidelines and not as standards.
Furthermore national road research and development institutes
should continuously evaluate and improve the models, through a
process of trials and errors. Below you find a description of the latest
maintenance models in the Netherlands, developed by CROW. 7
Their models classify damages on basis of their size and severity,
see the below table, and allow engineers to make assessments of
the residual life on basis of the damage classification and residual
structural life. They distinguish different fatal limits on basis of the
importance of the road. It is safe to assume that the differences
between fatal limits are associated with the design speed. High
speed road have design speeds of 80 km/hr or more. A typical low
design speed road has a design speed between 30 and 50 km/hr.
Note that Long-Life Pavements are assumed to have a residual
structural life of 20 years and more (x>20 years).
Damage type
Small
Medium
Size
Large
7
Severity
Low
Medium
LS1
MS1
LS2
MS2
LS3
MS3
CROW: Evaluatie Wegbeheer; Aanpassingen Wegbeheersystematiek
37
High
HS1
HS2
HS3
INDEVELOPMENT:
Rafeling Dense Asphalt
concrete
Rafeling dense asphalt
concrete
X < 5%
5%≤x<30%
30%≤x<50%
Size X ≥ 50%
The below-presented tables below present respectively the damage
classifications and residual lives of pavements for damage rafeling.
Action should be taken before high design speed roads reach situation
MS2 and before the situation on low design speed roads develops into
MS3.
Severity
5%≤x<20%
OK
LS1
LS2
LS3
20%≤x<50%
X ≥ 50%
MS1
MS2
MS3
HS1
HS2
HS3
Residual life (years) of high design speed roads with observed damage pattern concerning
rafeling
Duration till
Observed damages
rehabilitation OK
LS 1
LS 2
LS 3
MS 1
MS 2
Years
X ≤3
x> 5
x> 5
2-5
1-4
1-3
1-2
4
x> 5
x> 5
2-6
1-5
1-3
1-2
5
x> 5
x> 5
2-6
2-5
1-3
1-2
6
x> 5
x> 5
3-6
2-6
1-3
1-2
7
x> 5
x> 5
x> 5
2-6
1-3
1-2
8
x> 5
x> 5
x> 5
2-6
2-3
1-2
9
x> 5
x> 5
x> 5
3-6
2-3
1-2
10
x> 5
x> 5
x> 5
3-6
2-3
1-2
11
x> 5
x> 5
x> 5
3-6
2-3
1-2
12
x> 5
x> 5
x> 5
3-6
2-3
1-2
13
x> 5
x> 5
x> 5
3-6
2-4
1-2
14
x> 5
x> 5
x> 5
3-6
2-4
1-2
15
x> 5
x> 5
x> 5
3-6
2-4
1-2
16
x> 5
x> 5
x> 5
3-6
2-4
1-2
17
x> 5
x> 5
x> 5
3-6
2-4
1-2
18
x> 5
x> 5
x> 5
3-6
2-4
1-2
19
x> 5
x> 5
x> 5
x> 5
2-4
1-2
X ≥ 20
x> 5
x> 5
x> 5
x> 5
2-4
1-2
38
INDEVELOPMENT:
Residual life of
Duration to
rehabilitation
Years
X ≤3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
X ≥ 20
low design speed roads with observed damage pattern rafeling:
Observed damages
OK
LS 1
LS 2
LS 3
MS 1
MS 2
MS 3
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
Rutting
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
2-6
2-6
2-6
2-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
2-4
2-5
2-5
2-5
2-6
2-6
3-6
3-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
1-4
1-4
2-4
2-4
2-5
2-5
2-6
2-6
2-6
2-6
3-6
3-6
3-6
3-6
x> 5
x> 5
x> 5
x> 5
1-2
1-2
1-3
1-3
1-4
1-4
1-4
1-4
2-4
2-4
2-4
2-4
2-4
2-4
2-4
2-4
2-4
2-4
The following tables present similar information for the damage rutting.
Threshold value for high design speed roads is before reaching MS2
The fatal limit of a low design speed road is before reaching HS1
Rutting
Size
per
m/100m
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
X< 5 m
5m ≤x< 15 m
15m ≤x< 35m
X ≥ 35 m
Severity
10 mm ≤x<20mm
OK
LS1
LS2
LS3
20mm ≤x< 30 mm
X ≥ 30 mm
MS1
MS2
MS3
HS1
HS2
HS3
39
INDEVELOPMENT:
Residual life (years) of high design speed roads with observed damage pattern rutting
Duration till
Observed damages
rehabilitation OK
LS 1 LS 2
LS 3 MS 1
MS 2
Years
X ≤3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
X ≥ 20
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
4-5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
3-4
4-5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
1-3
1-4
2-4
2-4
2-5
3-5
3-5
3-5
3-6
3-6
3-6
3-6
3-6
3-6
3-6
3-6
3-6
3-6
1-3
1-3
1-4
1-4
1-4
1-4
2-5
2-5
2-6
2-6
2-6
3-6
3-6
3-6
3-6
3-6
3-6
3-6
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
Residual life of low design speed roads with observed damage pattern rutting
Duration to
Observed damages
rehabilitation
OK
LS 1 LS 2 LS 3
MS 1 MS 2
MS 3
HS1
Years
X ≤3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
X ≥ 20
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
4-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
2-5
2-6
3-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
40
2-4
2-5
3-6
3-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
1-2
1-3
1-3
1-4
1-4
1-5
2-5
2-5
2-6
2-6
2-6
3-6
3-6
3-6
3-6
3-6
3-6
3-6
1-2
1-2
1-2
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-3
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
INDEVELOPMENT:
Roughness
Damages with a low severity and up to 15 damages with medium
severity are acceptable. Again it is extremely difficult to predict the
progression of roughness. This means that repairs can only be initiated
when damages occur.
Roughness
X< 3
Size
No. / 3 ≤x< 8
100m 8 ≤x< 15
X ≥ 15 pieces
Cracks
Severity
5 mm ≤x< 15 mm
OK
LS1
LS2
LS3
15 mm ≤x< 30 mm
X ≥ 30 mm
MS1
MS2
MS3
HS1
HS2
HS3
The following tables present respectively the damage classification and
estimates of residue lives of roads encountering fatigue cracks. Action
should be taken prior the condition deteriorates into MS3 for high
design speed roads and HS2 on low design speed roads.
Crack sealing is a typical routine maintenance activity. As a general
rule of the thumb, all cracks wider than 5 mm are to be sealed. Routing
cracks before applying a seal has been found to be beneficial.
Severity
Longitudinal
cracks
Cracks
Size
m/100m
X< 5 m
5m ≤x< 25 m
25m ≤x< 50m
X ≥ 50 m
Ok
LS1
LS2
LS3
Longitudinal cracks in or
near ruts
Cracks with branches
Cracks width 5 to 10 mm
Longitudinal cracks with
height differences larger
than 10 mm
Mesh or block cracks and
cracks with width > 10 mm
MS1
MS2
MS3
HS1
HS2
HS3
41
INDEVELOPMENT:
Residual life of
Duration to
rehabilitation
Years
X ≤3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
X ≥ 20
high design speed roads with observed damage pattern cracking
Observed damages
OK
LS 1 LS 2 LS 3 MS 1 MS 2 MS 3
Residual life of
Duration to
rehabilitation
Years
X ≤3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
X ≥ 20
low design speed roads with observed damage pattern cracking
Observed damages
OK
LS 1 LS 2 LS 3 MS 1 MS 2 MS 3
HS1
HS2
Edge damages
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
x>
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
2-4
3-5
4-6
4-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
3-6
4-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
1-3
2-3
2-4
2-5
3-5
3-6
4-6
4-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
2-4
3-5
4-6
4-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
1-2
1-2
1-3
2-3
2-4
2-4
2-4
3-5
3-5
3-6
3-6
4-6
4-6
x> 5
x> 5
x> 5
x> 5
x> 5
2-3
2-4
3-5
3-6
4-6
4-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
1-2
1-2
1-2
1-2
1-2
1-3
1-3
1-4
1-4
1-4
2-5
2-5
2-5
2-5
2-5
2-6
2-6
2-6
1-2
1-3
2-3
2-4
2-5
3-5
3-5
3-6
4-6
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
x> 5
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-3
1-3
1-3
1-3
1-3
1-3
1-2
1-2
1-2
1-2
1-3
2-3
2-4
2-4
2-4
2-5
3-5
3-5
3-6
3-6
4-6
4-6
4-6
4-6
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-3
1-3
2-3
2-3
2-4
2-4
2-4
2-4
2-4
3-5
3-5
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-2
Edge damages are not considered important damages and its repairs
are usually corrective in nature. Shoulder repairs are usually preventing
edge damages. Therefore it is not necessary to estimate residual lives
on basis of the condition of the pavement. However corrective
42
INDEVELOPMENT:
maintenance is needed when the road condition deteriorates into
MS3 on high design speed roads
HS2 on low design speed roads
Edge damage
X <5 m
5m ≤x< 25 m
25m ≤x< 50m
Size X ≥ 50 m
Initiating Routine
Maintenance
Severity
Only minor
damages e.g.
Longitudinal
cracks
Ok
LS1
LS2
LS3
Cracks with branches
Cracks width 5 to 10 mm
Longitudinal cracks with
height differences larger
than 10 mm
Broken edge
MS1
MS2
MS3
HS1
HS2
HS3
Like larger maintenance works, routine maintenance works are also
initiated on basis of actual damage progression. The table below
presents intervention levels for routine maintenance repairs.
Damage
Raveling
Severity classification
M and H
Intervention level
3% per 100 m
Cracks
M and H
Mesh or block cracks
Any
5meter per 100
meter road length
3%
Roughness
Ruts
H
H
3% per 100 m
1% per 100 m
Repair
Local surface
treatment
Fill
Local surface
treatment
Fill
Fill
10.2.3 Impacts of Repairs
The objective of the repair is to increase the life of the assets. The
effectiveness of the repair depends on various criteria, e.g.:
• Damage
• Original design of the pavement structure
• Material subgrade
• Number of equivalent standard axle loading
With aid of information obtained from deflection tests, core samples
and traffic volumes, engineers can calculate the life of structural
repairs, like overlays. It is equally possible to estimate the thickness
of the overlay on basis of design life. Whereby:
ho = Thickness overlay (mm)
he1= equivalent pavement thickness before
overlay
he2= equivalent thickness after overlay
Ea= modulus of elasticity of overlay
Eo= modulus of elasticity of subgrade
43
INDEVELOPMENT:
The equivalent pavement thickness should not
be mistaken for the actual pavement
thickness. It is merely an indication for the
residue intrinsic strength.
The values of the equivalent pavement
thickness can be estimated with the following
formula. Whereby:
hen= equivalent pavement thickness after
number of equivalent standard axle loadings
heq= equivalent pavement thickness when
number of equivalent standard axle loadings
=0
n= total equivalent standard axle loadings
N= total equivalent standard axle loading at
the end of life
β= 4.3
Repairs with the scale of rehabilitation may also be applied to
mitigate surface damages. Appendix A presents a table to estimate
the life of such rehabilitations.
Most engineers will apply a simplified table for smaller repairs
(repairs that do not improve the structural life of the pavement):
Rafeling
Ruts
Fatigue related cracks
Skid resistance
Roughness
Rut filling
Cold asphalt
concrete
3/5+
3/5+
2/4+
3/5+
3/5+
Mini Surface
treatment
Planer milling
and fill
5/7+
5/7+
5/7+
5/7+
5/7+
3/5+
3/5+
2/4+
3/5+
3/5+
Note that 3/5+ means an increase of life expectancy between 3 to 5 years
A properly maintained road lasts forever. However when
maintenance budgets are structurally insufficient, the following may
happen:
When the road agency does not have enough funds to rehabilitate
the pavement, the pavement will loose its service level. Its life will
end due to fatigue or significant surface damages. This typically
happens when the pavement is 10 to 20 years old.
When the road agency does not have enough funds for routine
maintenance, the need for rehabilitation will move forward. Without
routine maintenance, rehabilitation of the asphalt pavement may
have to take place as soon as 8 to 12 years after construction.
When repairs are delayed but will eventually be carried out, repairs
will be more expensive than originally foreseen. After all the damage
will progress not only at the surface, but below the surface. This
means that stronger repairs are necessary. The next table presents
the progression of repair costs due to delays in the Netherlands.
44
INDEVELOPMENT:
Damages
Mesh Cracks
Ruts
Roughness
Rafeling
Other damages
1
1.10
1.01
1.05
1.02
1.06
Impacts of
2
3
1.22 1.38
1.02 1.04
1.11 1.19
1.04 1.07
1.13 1.22
delay of repairs (extra costs)
4
5
6
7
1.56 1.76 2.00 2.00
1.06 1.08 1.10 1.10
1.28 1.38 1.50 1.50
1.11 1.16 1.22 1.30
1.33 1.46 1.61 1.65
x>7
2.00
1.10
1.50
1.30
1.70
10.3 CONCRETE PAVEMENTS
Jointed plain concrete
pavements
Concrete pavements are classified, according to surface type, in:
Jointed Plain Concrete Pavements, without load transfer dowel bars
(JPCP n/d): these are concrete slabs without any reinforcement. The slabs
are usually not longer than 3 to 6 metres to allow for temperature changes.
Joint Spacing
3 - 6 m
Aggregate
Interlock
Slab
Base
JPCP w/d
Jointed Plain Concrete Pavements with load transfer dowel bars
(JPCP w/d): This structure is very similar the JPCP n/d with exception that
dowel bars are added in the transverse joints to transfer the loads.
Joint Spacing
3 - 6 m
Dowels
Jointed reinforced
concrete pavements
Jointed Reinforced Concrete Pavements (JRCP): The slabs of these
pavements may be as long as 10 or even 20 meters. It is possible to create
these long slabs, because of the reinforcement placed in the slabs. The load
transfer between the slabs is achieved with dowel bars.
10 - 20 m
Slab
Dowels
Base
Welded Wire Fabric
(0,1 - 0,2 %)
Continuously reinforced
concrete pavements
d) Continuously Reinforced Concrete Pavements (CRCP): This kind of
pavement does not require joints because the reinforcement is continued of
the full length.
45
INDEVELOPMENT:
Cracks separation
Slab
Base
Reinforcement Steel
0,6 - 0,8 % Area
The most dominant deterioration defects on concrete roads are:
• Cracks.
• Joint Deterioration.
• Surface Defects.
• Other distresses.
Transverse cracks
Below you find some descriptions and drawings of typical failures of
concrete pavements.
Linear cracks divide the slab into 2 –3 pieces and are caused by repeated
traffic loads, curling, or sub grade heaving. Low severity cracking doesn’t ’t
warrant any repair but sealing, partial or full depth patching or slab
replacement may be needed when the distress becomes more severe.
Distress
width
Distress
width
A
D
C
B
Longitudinal Joint
C
D
Transv.
Joint
C
L
Transv.
Joint
A
B
Traffic
Slab
Shoulder
Longitudinal cracks
Distress
width
Distress
width
A
B
D
C
Longitudinal Joint
Transv.
Joint
A
C
Transv.
Joint
B
D
Slab
Shoulder
46
Traffic
C
L
INDEVELOPMENT:
Corner breaks
Corner Break
Pavements with this distress have a corner of the slab broken in a
triangular piece. No repair is required for low severity corner breaks, but
crack sealing or full-depth patching may be performed for slabs in worse
condition.
Longitudinal Joint
C
L
Transv.
Joint
Transv.
Joint
45º
Mid-half Slab
Traffic
Slab
Shoulder
D-cracks
Durability cracks are a pattern of cracks running parallel and close to a joint
or linear crack. They appear as a series of fine, hairline cracks usually
cracking across the slab corners. This type of crack can eventually lead to
disintegration of the entire slab.
Transv.
Joint
Slab 1
Transv.
Joint
Slab 2
Slab 3
Tight pattern, no
missing material
Well developed, with
material loss
10 m2
Moderated
12 m2
High
Slab 4
3 m2
Low
Well defined,
without
materiall loss
Traffic
Shoulder
Joint seal damage is any condition that enables incompressible material to
accumulate in the joints or allows water infiltration.
Joint deterioration
< 0,6 m
Distress
width
B
A
D
C
Crack
Joint
Transv.
Joint
Transv.
Joint
Transv.
Joint
Low Sev.:
1,8 m
Low Sev.:
2m
High Sev.:
1,5 m
A
Joint
C
D
Moder. Sev.:
2,5 m
Traffic
B
Shoulder
47
INDEVELOPMENT:
Faulting is the vertical movement of abutting slabs at joints or cracks.
Faulting of transverse
joints and cracks
A
B
Longitudinal Joint
Transv.
Joint
Transv.
Joint
A
B
Slab
C
L
Traffic
Shoulder
Buckling/Shattering
Buckling or shattering usually occurs in hot weather, at a transverse crack.
The loss of crack sealant allows rocks and other debris to get lodged in the
crack, and the crack is then not wide enough to permit slab expansion.
During warm temperatures and concrete expansion, the only way for the
slabs to move is upward, and a “blow-out ” occurs.
A
B
Junta Longitudinal
Junta
Transv.
Junta
Transv.
A
Losa
B
C
L
Tránsito
Berma
Lane/Shoulder drop off distress is the difference in elevation between
pavement edge and shoulder caused by settlement of the traffic lane or
shoulder.
48
INDEVELOPMENT:
Lane
Drop-Off
A
B
Shoulder
Longitudinal Joint
C
L
Transv.
Joint
Traffic
A
Slab
Shoulder
B
Other distresses
Polished aggregate occurs when the pavement surface becomes smooth to
the touch, resulting in low skid resistance.
Shrinkage cracks are hairline cracks usually a few feet long and not
extending across slab. They generally occur early in a pavement ’s life, and
do not lead to severe distress. No repair is recommended.
Spalling is the breaking or chipping of the slab at a corner or joint. It is also
the disintegration of the slab edges. These cracks do not extend vertically
through the slab. This distress should be repaired, as loss of the seal at the
concrete joints will lead to water and incompressible materials penetrating
the pavement. That can lead to more severe damages. Depending on
severity, a partial or full depth patch is required.
Pumping is the ejection of water or silt from the slab foundation through
pavement joints or cracks. When pumping occurs, cracks should be sealed
or repaired, and edge drains may be installed to remove water from the
pavement sub grade.
A punch out is a localized area of the slab that has broken into pieces. No
repair is needed for low severity punch-outs, but more severely damaged
pavements may require sealing, full-depth patching or total slab
replacement.
Potholes: A patch is an area where the original pavement has been
removed and replaced by similar or different material. Only there are
considered permanent patches.
49
INDEVELOPMENT:
Longitudinal Joint
C
L
Traffic
1
Shoulder
2
3
1 A single punchout
2 “Y” crack with spalling and/or faulting
3 3 punchouts
Punch outs
Lane to Shoulder Separation: Due to the movement of the shoulder the
width of joint between lane and shoulder increases.
Lane - Shoulder
Separation
A
Lane
B
Shoulder
Longitudinal Joint
Transv.
Joint
C
L
Transv.
Joint
Traffic
A
Slab
Shoulder
B
Lane to Shoulder Separation
Deterioration of Constructive Transverse Joints: A series of very nearby (or
interconnected) transverse cracks located close to a constructive joint.
50
INDEVELOPMENT:
< 0,6 m
B
A
Longitudinal Joint
C
L
Constructive
Transversal Joint
Transv.
Joint
A
B
Traffic
Slab
Shoulder
Deterioration of constructive transverse joints
Surface Defects:
Map Cracking: This distress appears as a network of fine, shallow or hairline
cracks that extend only through the upper surface of the concrete. Map
cracking may lead to surface scaling, which is the progressive disintegration
and loss of the wearing surface.
Pop outs appear as a small piece of pavement that breaks loose from the
surface. They generally occur early in the pavement life and do not result in
severe distress.
10.3.1 Long-Term Maintenance Planning
Like asphalt concrete pavements, maintenance of concrete pavements is
also divided in small annual (routine) and large (periodic) maintenance.
Jointed Plain Concrete Pavements, without load transfer dowel bars (JPCP
n/d) usually requires periodic maintenance every 30 years. Periodic
maintenance intervals on the other types of concrete pavements are usually
around 35 years. However it is not uncommon that road agencies increase
these intervals with another ten years, and accept an increase in their total
maintenance budgets. The following table presents an overview of cost
increases because of delayed periodic maintenance on concrete roads:
Delay
(Years)
3
5
10
Maintenance type
JPCP n/d
Routine
Routine & Periodic
Routine
Routine & Periodic
Routine
Routine & Periodic
111
102
135
107
155
111
Other concrete
pavements
114
102
145
107
170
111
Typical periodic maintenance activities involve overlays with asphalt
concrete, overlays with concrete and complete reconstruction. Routine
maintenance activities includes activities like joint and cracks seals,
51
INDEVELOPMENT:
replacement of slabs, improving skid resistance through milling profile,
edge repairs and shoulder placements. The following table present lifeexpectancies of these repairs:
Repair
Joint and crack seals
Replacement of slabs
Diamond grinding
Milling to reduce roughness
Edge repairs and shoulder placements
AC-Overlay (150-120 mm)
Concrete overlay (200-250 mm)
Reconstruction
Slabs Replacement
Partial Depth Repair
Full Depth Repair
Life expectancy
(years)
4-6
10
20
5-10
5-10
20
30
30
HDM 4 has given a description of these repairs. Volume six, Modelling Road
Deterioration and Works Effects is downloadable from
http://www.htc.co.nz/. The following section is a summary of part C of this
document.
Slabs Replacement (SR) consists basically in the replacement of all the
existing slab, done generally when the slab had already lost its capacity of
operating, (when the slab is quite cracked, for example). It is assumed that
base and sub grade are yet in conditions to sustain traffic charges. It is
applied only in pavements JPCP, with or without dowels.
Partial Depth Repair (PDR) is used to repair the superficial deterioration,
which not interests more than a third of the slab thickness. Usually, it is
employed to repair transverse joints in JPCP pavements; however, it can be
used in any part of the slab where have been presented surface distresses.
Full Depth Repair (FDR) is used to repair cracks and joints deterioration in
JRCP pavements, and consists in the removal and replacement of at least a
portion of the existing slab. The deterioration of joints includes breaks and
spalling of the slab edges either transversely or lengthwise. This activity is
also used to repair defects in pavements type CRCP.
Diamond Grinding
Diamond Grinding (DG) is used to restore and improve ride quality of the
pavement, providing a more uniform surface. This is carried out through
the removal of faultings, curlings and deformations of the slab. Also, it is
used to correct an improper transverse slope and an excessive polishing of
the surface. Grinding, furthermore, increases the superficial friction
through the creation of a rough cord capable of draining superficial water
and reducing the aqua-planning potential. Usually, it is used to correct
faulting in pavements JPCP and JRCP.
Load Transfer
Restoration
Load Transfer Restoration (LTR) is used to increase the efficiency in load
transfer with JPCP pavements, through the placement of load transfer
dowelbars in transverse joints. This restoration increases the load transfer
in the transverse joint.
Shoulders Placement
Shoulders Placement (SP) is the placement of tied concrete shoulders in an
existing concrete pavement. It produces an effect similar to the restoration
of load transfer, in the sense that it reduces critical stresses in the slab
52
INDEVELOPMENT:
edge, and reduces corner deflections. It is accomplished in pavements
JPCP, JRCP and CRCP.
Longitudinal Drainage
Placement
Longitudinal Drainage Placement (LDP) is the placement of longitudinal
drains in the pavement contributes to water evacuation infiltrated in
pavement structure. Due to the fact that most of the surface distresses can
be attributed to the water presence, its removal reduces the opportunities
of distress appearance, thus increasing pavement’s life.
Joints and Cracks Seal
Joints and Cracks Seal (JCS) is used to minimise water and uncompressible
material infiltration within the joints. Minimisation of water quantity, inside
and under pavement structure, reduces softening potential of sub grade,
pumping, and drag of the fine of the base or shoulder.
Overlays of Concrete
To overlay or to reinforce a concrete pavement fulfils mainly two functions.
First, it provides an increase in thickness to the upper layer, increasing the
structural capacity of the pavement; second, it provides a new road
surface, free of defects. Existing condition of the pavement has a great
influence on the design of overlays. Mainly, there exist two types of
concrete overlays applicable to an existing pavement, these are: bonded
and unbonded concrete overlay.
Bonded Overlays
In bonded overlays, there are taken special considerations to assure that
the new concrete layer bonds to the existing concrete. Typically, thickness
less than 100 mm increases the structural capacity of the existing slab,
through the creation of a greater section thickness. This type of overlays is
generally necessary in places where the traffic has increased too much over
the levels waited in the original design. They can be also used to improve
the skid resistance of an existing pavement, or to improve low ride quality
due to surface distresses or polishing due to traffic. Bonded overlays are
only effective when the existing pavement is yet in a good condition. These
bonded overlays must not be put on severely deteriorated pavements,
unless these pavements had been previously repaired, or on pavements
that have presented distresses due to problems of materials.
Surface cleanliness is necessary to assure that both layers are bonded in
adequate form.
Unbonded Overlays
In unbonded overlays construction, it must be assured that the new layer is
not adhered to the existing pavement. This involves the placement of an
intermediate layer, and then the construction of the overlay. Typically these
overlays had a thickness greater than 100 mm. Due to the fact that both
layers operate independently, the overlay behaves as a new pavement on a
rigid base. The separation layer acts as an insulation device, which prevents
that the distresses of the inferior cap will be reflected through the overlay.
This type of overlay is more appropriate when the existing pavement is
severely deteriorated. Since both caps act independently, these overlays
require very few previous repairs in the existing layer, compared with other
alternatives. Only areas where could have been presented instability, lost of
support, and local weaknesses, are necessary to repair. More than this,
due to this individual operation of layers, the unbonded overlays are ideal
candidates for treatment of pavements that had presented problems of
cracking type "D" and "alkali-silica" reaction.
53
INDEVELOPMENT:
An adequate selection of the material of the intermediate layer is critical for
a good evolution of the overlay. That layer must cover the whole surface
and, furthermore, must be capable of isolating the overlay of the
deterioration and movements from the existing pavement. If both layers
would begin to interact between them, deterioration of the inferior layer will
be reflected through the overlay, causing its premature failure.
Reconstruction
Cracks and edges.
Joint repairs
Slab replacements
Corner break repairs
Reconstruction involves the removal of the existing pavement and its
replacement by a new pavement structure. It is a viable when the
pavement’s problems cannot be solved with an overlay. Since
reconstruction consists of the removal of the structure of the existing
pavement, it offers the opportunity to correct sub grade or base
deficiencies, to adjust the geometry, to add drainage devices, etc. These
options are not viable when the pavement is only restored or overlaid.
This means that the first maintenance cycle is usually somewhere in
between 30 to 45 years, depending the accuracy of the timing of the
intervention and concrete type. The succeeding maintenance cycle is
usually either 20 or 30 years.
Repairs of cracks and edges would not be necessary during the first ten
years of the pavement life. After the age of ten years about half percent of
the surface would require repairs. However crack filling is usually initiated
as a recurrent activity than all cracks wider than 3 mm and any other areas
with extensive fine cracking should be repaired before the rainy season.
Budgeting joint repairs during the first ten years of the pavement life
should be limited to one percent annual repair of the total joint length. The
other ninety percent will be replaced in the following ten years (11-20 years
of age). It is recommendable to budget annual replacement or repair of 10
percent of the total length during that period.
Although it is very unlikely that slab replacements will take place during the
first 30 years after construction, is recommendable to budget for such
repairs. A rough figure of annual replacement of 0.03% is usually used.
Corner break repairs are budgeted with the same rules of the thumb as the
slap repairs.
10.3.2 Middle-Long Term Maintenance Planning
Middle-long term maintenance planning of concrete roads mainly relates to
the traffic related road conditions, like roughness and skid resistance. The
same fatal limits apply to all types of paved roads, irrespective its material.
With regard to the structural damages, most road agencies limit themselves
to carrying out small maintenance when needed and prepare rehabilitation
project every 30 or 35 years. This rehabilitation projects is a redesign of the
pavements on basis of observed damages and traffic loads.
Condition based maintenance for structural damages can only be used for
three kinds of failures:
1. Transverse joint faulting (average length/km)
2. Spalling of transverse joints (average length/km)
3. Cracks of slabs (%/km)
With exception of cracks of the slabs, it is not possible to set any intervention
levels. Slabs have to be replaced when 35% of it is cracked.
SHRP-H-349 describes methodologies of condition based maintenance for
54
INDEVELOPMENT:
joint seal repairs. The document can be downloaded from
http://gulliver.trb.org/publications/shrp/SHRP-H-349.pdf
Small maintenance
Small maintenance works are initiated when the following damages are
observed:
• Cracks longer than 5 meters long
• Damages to joints longer than 3% of the respective joint
• Unequal settlement near joints over a length longer than 3% of the
joint.
55
INDEVELOPMENT:
APPENDIX A: LIFE EXPECTANCY OF REHABILITATION
56
Damage
Road
type
Repair
overlay 50 mm
Sub
grade
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
Rafeling
Fatigue
cracks
Rutting/
roughness
Surface
treatment
Sand
Clay
Peat
S
C
P
15
16
17
17
15
9+
11+
14+
15+
16+
12/15+
13/16+
15/20+
15/20+
25
15
16
17
17
15
8+
10+
13+
14+
15+
12/15+
9/13+
11/17+
11/17+
20
15
16
17
17
15
7+
9+
12+
13+
14+
12/15+
7/11+
10/13+
10/13+
17
7
8
10
10
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
7
8
10
10
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
7
8
10
10
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
n/e
Slurry seal &
surface
treatment
S
C
P
7
8
10
10
6+
6+
7+
8+
8+
12
13
12
13
15
7
8
10
10
5+
5+
6+
7+
7+
10
9
10
11
13
7
8
10
10
4+
4+
5+
6+
6+
9
8
9
10
12
Slurry seal &
overlay (70 mm)
Mill & Fill 40 mm
S
C
P
Sand
Clay
Peat
15
16
17
17
15
13+
13+
14+
16+
16+
15
16
20
20
20
15
16
17
17
15
12+
12+
13+
15+
15+
15
13
17
17
18
15
16
17
17
15
11+
11+
12+
13+
14+
12
11
13
13
15
15
16
17
17
15
6+
6+
7+
8+
9+
12/15+
13/16+
15/20+
15/20+
-
15
16
17
17
15
5+
5+
6+
7+
8+
12/15+
9/13+
11/17+
11/17+
-
15
16
17
20
15
4+
4+
5+
6+
7+
12/15+
7/11+
10/13+
10/13+
-
Source: VBW ASFALT: Kosten van Wegverharding
Note: 25 means a new life value of 25 years; 15/20+ means additional life of 15 to 20 years on top of remaining residue life
Road
type
Number equivalent standard
axle loads (100 kN)
1
10
7
180
Percentage of trucks with
higher axle loads than the
standard of 100 kN
12.5
6
10
160
10
5
10
160
10
160
5
2
3
4
5
4
5 x 10
Bicycle lanes
Maximum axle load
(kN)
Source: VBW ASFALT: Kosten van Wegverharding
INDEVELOPMENT:
58
APPENDIX B: THAW-FROST DAMAGES
All road maintenance departments are concerned about the
damages because of freezing of the groundwater and capillary water
under the pavement construction. In theory the materials between
the maximum level of the capillary water and the underside of the
pavement should not be affected by the penetration of frost (frost
free layer). The strength of the (sub)base weakens, because the
thaw water closer to the surface can not penetrate into the soil.
Standard solutions which are both practised in Western Europe and
China limits the percentage of fine materials (D<0.063 mm). Many
agencies classify materials as being frost susceptible if 10 percent or
more passes a No. 200 sieve or 3 percent or more passes a No. 635
sieve. The frost free layer in the Netherlands is 80 centimetres. The
below presented table lists the frost-susceptibility ratings of soils.
Those materials with the F3 and F4 classifications are extremely
frost-susceptible, especially if the ground water table is less than
180 cm below the top of the subgrade. Silty soils are particularly
susceptible and their CBR value may be less than 1 during thawing
periods. The thaw period and resulting degraded soil strength may
last from one to four weeks.
If the soil is dry it cannot "freeze" in the accepted sense although its
temperature may be well below -20°. In addition low permeability of
INDEVELOPMENT:
the soil weakens penetration of rain water into the subgrade may
weaken the whole road construction, even in tropical climates. The
best solution is to control penetration of rain water and ground
water levels inside the sub base. The latter can be achieved by
constructing drainage pipes and camber formations of the subgrade
with levels varying between 5 and 10%. A five percent camber slope
is acceptable when high compaction values can be achieved;
otherwise it is recommendable to work with higher values up to 10%
(no compaction of subgrade).
60
INDEVELOPMENT:
APPENDIX C: ANALYSING DEFLECTION TESTS
Deflections are usually measured in the outside of the wheel path of
all the lanes. The interval of the deflection depends on the length of
the link. Usually the length of the link is divided by a fixed number,
e.g. 21. In practice intervals tend vary from 0.02 to 0.032 km.
Per section, the engineer has to calculate the mean and 80-th
percentile deflection values. However it should be kept in mind that
it is probably cheaper to repair localised failures. This means that
engineers have to divide the road length on different sections on
basis of the deflection values. It is necessary to identify a new road
section, when deflection values are significant different (more than
0.254 mm). This activity is usually done per lane and per driving
direction, because traffic volume and composition can differ
considerably. The easiest way to identify different sections is to plot
the values of the deflection tests per lane on a graph. A new section
should also be identified when
• the pavement thickness changes with more than 30 mm
• Different base materials are applied
• Axle loading is significant different
The 80-th percentile deflection value results in thicker overlay than
mean values. It is possible to calculate the 80-th percentile
deflection value with the following formula:
61
INDEVELOPMENT:
The 80-th percentile value is compared with a tolerable deflection at
the surface (TDS). The TDS value depends on the composition of the
base material and the equivalent standard axle load. Whereby most
methods will differentiate between untreated (aggregate) base and a
treated base (e.g. a Portland cement concrete base). When the
treated base is thin (x< 100 mm) or when still high deflections are
observed, the base may not perform as it is intended and it is better
to assume that the base is not treated.
When the average 80-th percentile value is less than the TDS, the
corrective repair can be limited to a seal coat.
When the D80 is larger than the TDS, a corrective measure is
required that restores the structural capacity and thus the deflection
at the surface.
The required percent reduction in deflection (PRD) can be calculated
with the following equation:
This percentage is multiplied with a material equivalence
to obtain a value for the overlay thickness that reduces
the deflections to a tolerable level. The required overlay
thickness is based on the amount of aggregates in the
asphalt concrete in the overlay material.
One of the requirements to the design of the overlay is to avoid
reflective cracking. Therefore it is suggested to apply the following
rules:
Untreated bases
Treated bases
The thickness of the overlay should have the minimum thickness of
the existing pavement thickness (after milling) up to a maximum of
100 mm.
The minimum overlay thickness on top of an pavement on a treated
base is about 100 mm. If the base is an extremely thick Portland
cement concrete like an overlaid PCC freeway that was not cracked,
the minimum thickness is 135 mm.
These recommendations are for a design life of ten years.
Experience suggests that the thickness should be decreased to 75%
for a five year design life and increase to 125% for a twenty year
design life.
62
INDEVELOPMENT:
More information
Caltrans has published its “Flexible Pavement Rehabilitation Manual”,
which provides a lot of information about deflection tests and
rehabilitation options. This document can be downloaded at the
following website:
http://www.dot.ca.gov/hq/esc/Translab/pubs/RehabManualJune2001.pdf#search='asphalt%20pavement%20manual
Caltrans estimates the TDS values on basis of an equivalent
standard axle load of 80 kN. It uses the following formula to
calculate the Tolerated Deflection at the Surface:
Whereby:
A:
Pavement thickness/depth
(m)
0
0.015
0.03
0.045
0.06
0.075
0.09
0.105
0.120
0.135
0.150 or more
Treated base
A-value
2.804
2.771
2.739
2.708
2.677
2.646
2.615
2.584
2.554
2.524
2.494
2.418
Caltrans uses a gravel material equivalence to estimate the
thickness of the overlay, because it is the gravel that provides the
intrinsic strength and stiffness to the overlay. A gravel equivalence
(GE) is estimated on basis of the needed deflection reduction. This
GE-value has to be divided by a gravel factor (Gf), which expresses
the relative strength of various materials when compared to gravel.
The GE value can be estimated with the following formulas:
Required
deflection
reduction (%)
y<10 %
10≤ y < 20%
20≤ y < 30%
30≤ y < 40%
40≤ y < 50%
y≥50%
Asphalt concrete overlay
X (m)
Asphalt concrete over cushion course
X (m)
X= 0.3 y/333.333
X =0.3 (y-6.25)/125
X=0.3 (y-11.53846)/76.92308
X=0.3(y-16.667)55.556
X=0.3(y-20.46512)/46.51163
X=0.3(y-20.46512)/46.51163
X= 0.3 y/333.333
X =0.3 (y-6.25)/125
X=0.3 (y-11.53846)/76.92308
X=0.3(y-17.36843)/52.63158
X=0.3(y-26.12904)/32.25807
X=0.3(y-28.2353)/29.4117
63
INDEVELOPMENT:
The following table presents commonly used Gf values for
rehabilitation. Note these values are different for new pavements:
Material
Asphalt concrete
Hot recycled asphalt concrete
Cold recycled asphalt concrete
Asphalt concrete below analytical depth
Aggregate base
Aggregate subbase
Native soil
64
Gf-value
1.9
1.9
1.5
1.4
1.1
1.0
0

ROAD MAINTENANCE PLANNING

Transcription

Similar documents

Gilsonite - Chemtron

Sadia Rahman TS Materials, Construction Site

8-Year Premium Driveway Resurfacer

Optical Illusions in 3D Sidewalk

EMECOLE - Anderson Manufacturing

REPORT ON PAVEMENT DESIGN FOR THE SECTION OF ROAD

Maintenance Planning Systems for road, rail and

Contractor: Florence Cement Company Engineer: Anderson

GranQuartz - Ameripolish

Al Azizia Panda United, Distribution Facility