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Highway pavement is an essential component of the overall transportation system providing access to various parts of the world and facilitating the movement of people and goods.
Due to its immense importance, it must be well maintained and timely repaired. Else, several problems may arise, ultimately leading to the failure of the pavement itself.
Pavement failure may occur due to various factors such as excessive vehicular stress, sunlight exposure, water intrusion, unequal expansion and contraction due to seasonal changes, etc.
A. Types of Pavement Failure
Some of the types of pavement failure are:
1. Cracking
Cracking is one of the most common types of pavement failure. The nature of the crack itself is fast spreading.
Cracking is usually caused due to use of improper material mix during construction and settling of the subgrade or base during operation.
Several cracking in the pavement are:
i. Alligator Cracking
Alligator cracking is the cracking that is associated with load and structural distress.
These cracks are extensively found at intersections where the vehicles are stopped for a relatively long period because these cracks start to form when the subgrade and base compress due to the excessive imposed wheel load.
a. Causes of Alligator Cracking in Flexible Pavement
1. Weakness in base, surface or sub-grade
2. Thinning of a surface course or base course
3. Poor Drainage
4. Excessive vehicular loads
5. Vehicle stopped for a relatively long period
b. Repair of Alligator Cracking in Flexible Pavement
a. Determine the primary source of the problem and the best way to repair it.
b. If a problem is seen on the surface course, the crack filler is applied.
b. If failure is due to weakening of the base or sub-base course, cut the affected pavement area into rectangular or square shapes. Then patch it like a pothole.
c. Causes of Alligator Cracking in Rigid Pavement
a. Weakening of base
b. Poor drainage
c. Poor quality material mix or use.
d. Repair of Alligator Cracking in Rigid Pavement
1. Full Depth Patching
It is a widely used method for treating alligator cracks in rigid pavements and restoring the structural stability and rideability of the pavements.
It includes the following series of steps:
a. Defining repair boundaries
The boundary of the area to be repaired must be first defined by surveying the region.
b. Sawing old concrete
Full-depth saw cuts facilitate the separation of damaged concrete from the adjacent concrete with minimal damage.
c. Removing old concrete
Concrete removal can be carried out either by lift out or break up. Lifting sawed concrete is faster, requires less labour, and also doesn’t cause any significant damage to the adjacent layers.
In some cases, lifting concrete can be risky, and in such a situation, the deteriorated concrete is broken into smaller fragments and removed by backhoe or hand tools.
d. Preparing the patch area
After removing old concrete, the area to be patched is prepared. If the area contains water, it must be pumped out and cleaned correctly.
e. Placing and Finishing new concrete
Placing the new concrete is usually done by ready-mix trucks or other mobile batch vehicles. Concrete must be evenly distributed and spread. Using the finishing tools, the placed concrete is finished.
ii. Block Cracking
Block cracking is another cracking seen on highway pavements that form a box-like crack on the surface.
This type of cracking is associated with the unusual expansion and contraction of concrete in rigid pavement and due to improper mixing or ageing of asphalt or poor quality asphalt in flexible pavement.
Block cracking is mainly caused by shrinkage of the asphalt or concrete and daily temperature cycling, and it is not load-associated.
a. Causes
1. Use of improper mix
2. Fine aggregates mixed with low-penetration asphalt
3. Poor asphalt binder
4. Ageing of asphalt
5. Temperature cycling
b. Repair
The quicker this cracking is detected, the easier it becomes to repair.
The sealing method of repair can be used for cracks less than ½ inch or lesser.
In severe cracks, the deteriorated pavement must be removed and replaced by an overlay.
c. Causes
1. Use of improper mix
2. Lack of expansion joints in the pavement
3. Temperature cycling
d. Repair
If the crack is less than 1/2 inch, flexible fillers can be used to fill the cracks.
If the crack is larger than 1/2 inch, the affected section of the road is removed and replaced by an overlay. Sometimes, the joining of the sections with metal plates also can be done if traffic is low.
To eliminate the problem of block cracking, it is better to provide expansion joints at regular intervals.
iii. Linear Cracking
Linear cracking is the common type of crack seen parallel to the roadway.
These are generally associated with fatigue and weak points of the pavement.
It is also known as longitudinal cracking.
a. Causes of Linear Cracking
1. Pavement fatigue
2. Reflective cracking
3. Poor construction of joints
b. Repair of Linear Cracking
It can be repaired by sealing or replacement.
For less severe cracks, sealing of the cracks may be done.
For severe cracks, replacement by an overlay may be carried out.
iv. Edge Cracking
Edge cracking is the type of crack that is usually formed at the edge of highway pavements.
These cracks are typically associated with the ingress of water in underlying layers.
a. Causes of Edge Cracking
a. Lack of support at edges of pavement
b. Poor drainage condition
c. Heavy vegetation
d. Heavy traffic alongside the edge of the pavement
b. Repair of Edge Cracking
The initial step for repairing the edge cracks is removing the vegetation from the edges of the pavement and fixing all the issues of drainage.
Sealing of cracks can be done to prevent further damage.
2. Pot Holes
Potholes are the type of flexible pavement failure that can be seen as small depressions on the surface of the pavement and can penetrate deep up to the base course.
These are generally associated with infiltration and also result from alligator cracks if not treated properly.
Generally, severe alligator cracks that are left untreated create small fragments of pavement and when vehicles ride over them result in the formation of potholes.
a. Causes of Pot Holes
1. Pavement fatigue
2. Untreated alligator cracks
b. Repair of Pot Holes
The potholes can be repaired by patchwork which includes the following steps:
i. Repair For Concrete Roads
a. Defining repair boundaries:
The boundary of the area to be repaired must be first defined by surveying the region.
b. Sawing old concrete:
Using full-depth saw cuts, the damaged area is first isolated from the remaining area.
Full-depth saw cuts facilitate the separation of damaged concrete from the adjacent concrete with minimal damage.
c. Removing old concrete:
The removal of concrete can be carried out either by lift out or by breakup.
Lifting of sawed concrete is faster, requires less labour and also doesn’t cause any significant damage to the adjacent layers.
In some cases, lifting concrete can be risky and in such a situation the deteriorated concrete is broken into smaller fragments and removed by backhoe or hand tools.
d. Preparing the patch area:
After the removal of old concrete, the area to be patched is prepared.
If the area contains water, it must be pumped out and cleaned properly.
e. Placing and Finishing new concrete:
Placing of the new concrete is usually done by ready-mix trucks or other mobile batch vehicles.
Concrete must be evenly distributed and spread.
Using the finishing tools, the placed concrete is finished.
ii. Repair for Flexible Pavements
1. Clean the area along the hole with the broom.
2. Trim it vertically to a regular geometrical shape like a square or rectangle.
3. Level the bottom of the hole and remove loose aggregate and foreign materials.
4. Apply a tack coat on the bottom and sides of the holes.
5. Now, apply the patching layer and compact it properly by taping or rolling.
6. If the depth of the hole is greater than 7.5cm, the Patching layer should be provided in 2 or more layers where each layer should be tamped or rolled properly.
3. Depressions
Depression indicates the area on the surface of pavements that has a slightly lower elevation than the surrounding areas.
They become prominently visible after rainfall due to the accumulation of water.
These are also referred to as birdbaths.
a. Causes of Depression
1. Uneven thickness of subsequent layers
2. Unequal compaction
3. Foundation soil settlement
b. Repair of Depressions
In case of severe depression, the asphalt surface has to be replaced while for smaller depressions patching of the area may be done.
4. Rutting
Rutting is a type of pavement failure that results in the formation of channelized depressions particularly in the wheel track of pavement.
Two types of rutting particularly pavement rutting and subgrade rutting may occur.
With time, the wheel of heavy vehicles starts to compact the asphalt surface thereby forming ruts.
a. Causes of Rutting
1. Lateral movement or consolidation of consecutive layers under traffic load
2. Insufficient layer thickness
3. Lack of compaction
4. Improper mix
4. Moisture infiltration
b. Repair of Rutting
If minor rutting has occurred, the rut can simply be filled and provided with an overlay.
In case of severe rutting, the damaged area must be lifted out and replaced by a new layer.
5. Corrugation & Shoving
Corrugations refer to the distresses that occur at regular intervals in the form of ridges and valleys on the surface of the pavement.
They run along the direction of the pavement itself and are usually less than 5 feet.
Similar distresses that run perpendicular to the traffic are known as shoving.
a. Causes of Corrugation and Shoving
1. Weak granular base
2. Excessive fine aggregate
3. Excessively rounded aggregate
4. Extensively soft asphalt
b. Repair of Corrugation and Shoving
It may be repaired by partial or full-depth patchwork as in the case of alligator cracking.
6. Ravelling
It is the type of pavement failure that occurs due to continuous ingress of water thereby causing degradation of the topmost asphalt layer.
As ravelling progresses, the aggregate particles separate from the surface and leave behind eroded-like patches on the surface of the pavement.
a. Causes of Ravelling
1. Excessively porous asphalt
2. The untimely placing of asphalt
b. Repair of Ravelling
A thin hot-mix overlay may be provided. Sealing of the affected areas may also be effective.
Read Also: Flexible Pavement
