A description of damage types we see in road pavements and their causes

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References available upon request
Pavement Damage
A nation’s highway system will be required to contain increasing numbers of vehicles and traffic
loading likely to occur within the design life. Accordingly, maintaining, preserving and
rehabilitating highway assets are the steps to follow after construction if sufficient funds are
available.
Assuming proper design and construction practices, the gradual pavement deterioration occurs
due to many factors, including variations in climate, drainage, soil conditions, and truck traffic.
Things get worse and complicated in poor condition but still usable roads. Many highway
engineers believe the maximum design period ranges between 15 and 24 years. Therefore, a
period of 20 years is widely used as a basis for design. Probable changes in the general regional
economy, population, and land development along the highway, make estimating traffic
volumes for a 20-year design period inappropriate for many reconstruction or rehabilitation
projects. These projects may be developed on the basis of a shorter design period (5 to 10
years) because of the uncertainties of predicting traffic and funding constraints; in this
environment poor decisions can be very costly.
Pavement roughness, pavement distress (surface condition), and skid resistance (safety) are
methods for determining roadway condition. Pavement roughness refers to irregularities in the
pavement surface that affect the smoothness or in other words quality of the ride. It is an
important characteristic because it affects not only ride quality but also vehicle delay costs,
maintenance cost, and fuel consumption. Pavement distress refers to the condition of a
pavement surface in terms of general appearance; it can be visually noticed. A flawless
pavement is level and has a continuous and intact surface. In contrast, a distressed pavement
may be fractured, distorted, or disintegrated. Common
distress types include the following:
Alligator Cracking: Series of interconnecting cracks that are
caused by fatigue failure of the pavement surface under
repetitive traffic loadings.
Bleeding: A film of bituminous material on the pavement
surface that becomes viscous when warm. It is caused by
excessive amounts of bituminous material in the asphalt
mix.

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Block Cracking: Interconnected cracks that divide the pavement
into rectangular pieces.
Corrugation: A series of closely-ranged ridges and valleys
occurring at regular intervals.
Depressions: Localized areas that are below surrounding
surface causing a “bowl-like” shape.
Longitudinal and Transverse Cracking: These may be parallel
or orthogonal to the centerline of the pavement.

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Patching, Utility Cuts, and Potholes.
Rutting: A surface depression typically occurring along the
wheel paths of a road.
Raveling: Wearing of the pavement surface caused by aggregate
particles breaking loose and the loss of bituminous material binder.

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The following figure lists the three pavement distress groups, the measure of distress, and the
probable causes.
Excessive loading, water penetration, climate change, bad design of pavement layers, materials
not conforming to standards (composition of the bitumen & grading of aggregate), and
improper compaction are all reasons for pavement collapse.
The elastic and viscoelastic properties of HMA (hot mix asphalt) are affected significantly by
temperature variation. During winter, the HMA becomes rigid and reduces the strains in the
pavement. However, stiffer HMA has less fatigue life, which may neutralize the beneficial effect
of smaller strains. Low temperature can cause asphalt pavements to crack.
Moreover, the precipitation from rain and snow affects the quantity of surface water infiltrating
into the sub grade. If water from rainfalls can be drained out within a short time, its effect can
be minimized, even in regions of high precipitation. As soil moisture increases, the load bearing
capacity decreases urging the soil to heave and swell. The harmful effects of moisture can be
reduced or eliminated by: keeping it from entering the pavement base, removing it before it
has a chance to weaken the pavement or using moisture resistant pavement materials.

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References available upon request
Last but not least, the properties of bitumen and aggregates used are very important to the
performance of the pavements. Often pavement distress, such as stripping and rutting, can be
traced directly to the aggregates used. Aggregates must be tough and abrasion resistant to
prevent crushing, degradation, and disintegration when stockpiled, fed through an asphalt
plant, placed with a paver, compacted with rollers, and subjected to traffic loadings. Rutting,
distortion, and raveling can be traced directly to poor asphalt mixture quality and loss of
bonding between base layer and surface layer. A conventional pavement is layered with better
material on top where stress is high and inferior material at the bottom where stress is low. A
seal or surface coat is used to waterproof the surface; tack coat and prime coat are added to
ensure a bond between the paved surface and the overlaying layer. Fundamental engineering
properties and characteristics of asphalt materials are used extensively in pavement
engineering and highway construction. Lack of such knowledge, will result in premature failure
of the pavement surface and reduction of the ability of the pavement to carry the design traffic
load.
As for the pavement’s safety, it is measured by its skid resistance. Skid or slip resistance data
are collected to monitor and evaluate the effectiveness of a pavement in preventing or
reducing skid-related accidents.
Such data is directly related to
the evaluation of pavement
mixtures and surface types.
The roadway condition,
described above, is expressed
by an index rating between 0
and 5, with 5 being very good
and 0 being impassable. It is
known as the present
serviceability index (PSI), and it
is based on physical
measurements for objective

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References available upon request
means. When a pavement is originally constructed, it is in very good condition with a PSI value
above 4. Then, as the number of traffic loadings increases, the PSI declines to a value of 2 which
is normally the minimum acceptable range. After the pavement section is rehabilitated, the PSI
value increase to 4; as traffic loads increase, the PSI declines again until it reaches 2 and
rehabilitation is again required. The performance of a pavement can be described in terms of
PSI and traffic loading over time, as shown.
When analyzing the graph, it is clear that maintenance is the key for pavement preservation.
Lebanese municipalities should follow an effective maintenance preservation program that
combines many strategies and treatments, away from politics and electoral benefits. Three
types of pavement maintenances can be followed:
€ Preventive Maintenance: Planned strategy of cost-effective intervention to an existing
roadway system and its appendages that preserves the system, retards future
deterioration, and maintains or improves the functional condition of the system.
€ Corrective Maintenance: Performed after a deficiency occurs in the pavement such as
moderate to severe rutting, raveling or extensive cracking. It is also known as “reactive”
maintenance.
€ Emergency Maintenance: Performed during an emergency situation, such as a blowup
or sever pothole that needs repair immediately.
A preventive maintenance procedure has shown often to be six to ten times more cost-
effective than a “do-nothing” strategy. Conservatively, $1.00 spent for preventive maintenance
will provide the same pavement condition that costs $4-5.00 if rehabilitation is needed. By
extending the life of a pavement until it needs rehabilitation, preventive maintenance allows
the municipality to balance its budget for both maintenance and construction. Preventive
maintenance treatments include: crack sealing, armor coating, fog sealing, broom or scrub
seals, and thin overlays.
The benefits of using pavement management systems are: improved performance monitoring,
improved administrative credibility and engineering input in policy decisions. More than ever
before, the need for a rational and objective process to ensure that funds are efficiently used
for pavement improvements should become an agreement point along all parties.