Subbase rutting

Pavement Failure | 6 Types of Pavement Failure

 

Highway pavement is an important component of the overall transportation system providing access to various parts of the world as well as 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. The failure of pavement may occur due to various factors such as excessive vehicular stress, sunlight exposure, water intrusion, unequal expansion and contraction due to seasonal changes etc. Some types of pavement failure are explained below.

 

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. This is because there exist a lot of factors that foster the cracking of pavement. The nature of the crack itself is fast spreading.

Cracking is usually caused due to use of improper mix during construction and settling of the soil. Several cracking may occur in pavements which are explained as follows:

 

i. Alligator Cracking:

Alligator cracking is the type of cracking that is associated with load and structural distresses.

Alligator cracks are extensively found at intersections where the vehicles are stopped for a relatively long period because these cracks start to form when the sub-grade and base compress due to the excessive imposed wheel load.

 

Causes of Alligator Cracking

1. Weakness in base, surface or sub-grade.

2. Thinning of a surface course or base course.

3. Poor Drainage

4. A combination of all of the above

 

Repair of Alligator Cracking

1. Full Depth Patching:

It is a widely used method for treating alligator cracks in pavements and restoring the structural stability and rideability to 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:

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 the 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 of 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. Block Cracking:

Block cracking is another type of 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.

Types of Pavement Failure

Figure: Block Cracks

 

Causes of Block Cracking

1. Use of improper mix

2. Fine aggregates mixed with low penetration asphalt

3. Poor asphalt binder

4. Ageing of asphalt

 

Repair of Block Cracking

Sealing method of repair can be used for cracks less than ½ inch or lesser. Sealing helps to prevent the ingress of moisture to the subgrade.

In case of severe cracks, the deteriorated pavement must be removed and replaced by an overlay.

 

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.

 

Causes of Linear Cracking

1. Pavement fatigue

2. Reflective cracking

3. Poor construction of joints

 

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.

edge cracks

Figure: Edge Cracks

 

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

 

Repair of Edge Cracking

The initial step for repairing the edge cracks is removing the vegetations from the edges of 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 results from alligator crack if not treated properly. Generally, severe alligator cracks that are left untreated create small fragments of pavement and when vehicles ride over them results in the formation of potholes.

Types of Pavement Failure

Figure: Pot Hole

 

Causes of Pot Holes

1. Pavement fatigue

2. Untreated alligator cracks

 

Repair of Pot Holes

The potholes can be repaired by patchwork which includes the following steps:

 

1. 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 the 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 of 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.

 

2. Repair for Flexible Pavement

1. Clean the area along the hole with the broom.

2. Trim it vertically to a regular geometrical shape like square or rectangle.

3. Level the bottom of the hole and remove loose aggregate and foreign materials.

4. Apply tack coat on bottom and sides of holes.

5. Now, apply the patching layer and compact it properly by taping or roller.

6. If the depth of the hole is greater than 7.5cm, 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 have 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 birdbath.

 

Causes of Depressions

1. Uneven thickness of subsequent layers

2. Unequal compaction

3. Foundation soil settlement

 

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 the pavement rutting and subgrade rutting may occur. With time, the wheel of heavy vehicles starts to compact the asphalt surface thereby forming ruts.

Subbase rutting

Figure: Formation of ruts in the pavement

 

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

 

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 valley 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 is known as shoving.

pavement failure

Figure: Corrugation and Shoving

 

Causes of Corrugation and Shoving

1. Weak granular base

2. Excessive fine aggregate

3. Excessively rounded aggregate

4. Extensively soft asphalt

 

Repair of Corrugation and Shoving

It may be repaired by partial or full-depth patchwork as in 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.

pavement failure

Figure: Ravelling in the pavement

 

Causes of Ravelling 

1. Excessively porous asphalt

2. The untimely placing of asphalt

 

Repair of Ravelling 

A thin hot-mix overlay may be provided. Sealing of the affected areas may also be effective.

 

 

Read Also: Flexible Pavement

 

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