Introduction to Defects of Road
The road network and its’ development are one of the leading economic indicators for any country. A good road network offers better mobility, reduced travel time, lesser accident, lesser vehicle maintenance, lesser traffic congestions, and many other advantages. Further, these advantages are obtained to the fullest when the roads are constructed with best practices. Moreover, regular maintenance (hence lesser defects of road) is another aspect of this scenario.
In contrast, not all roads are perfect for commuting. The defects of the road offer hindrance to smooth travelling experience. Who likes the bumpy ride? No one. Also, poorly-maintained highways increase the travel time and vehicle breakdown on them more often.
The defects of roads increase the roughness index of the road. Based on it, we can divide the road into three categories- good, fair, and poor.
In this article, we shall discuss the defects of roads- for flexible and rigid pavement, how to identify them, and their causes.
Defects of Roads- Flexible Pavement
A flexible pavement has many layers. From bottom to top these layers are subgrade, sub-base, base, and wearing layer. The asphalt concrete is the top layer that renders black colour to the road surface. Flexible pavement has no flexural strength and the load is transferred directly to the earth through the road layers.
1. Alligator Cracking -Defects of Road for Flexible Pavement
It is the other name for map cracking and it is a common defect of flexible pavement. The repeated traffic load leads to structural distress. As a result, cracks occur and get inter-connecting forming a mesh-like shape. The alligator cracks get its’ name due to the similar pattern found on alligator skin.
Alligator cracking is a fatigue type of failure. It occurs under heavy and repeated loads.
2. Rutting -Defects of Road for Flexible Pavement
The repeated application of loads over the same place cause two effects-
- The formation of depression along the direction of traffic. It is known as a rut.
- The wearing of the top layer along the wheel path causes small depression. It is known as a shallow rut.
Rutting shows the material has moved sideways forming a depression.
3. Raveling -Defects of Road for Flexible Pavement
The separation of aggregate from the binder makes the surface rough. First, the fine aggregates separate, and later the bigger aggregates also detach.
Regions with snowfall often face the problem of ravelling. Therefore, it is advisable not to put the asphalt in chilling weather.
4. Potholes -Defects of Road for Flexible Pavement
Potholes are one of the most common defects of roads. It is also a major cause of road accidents, especially for bikers.
Removal of material from the road surface causes potholes. The reason for potholes might be the poor-quality material, heavy traffic, lesser bonding between aggregate and binder, and water. Also, absence or poor prime coat/tack coat between the road layers is one of the major causes of potholes.
5. Slippage Crack
A slippage crack is essentially due to the poor bonding between the road layers. The low-quality binder, poor application of binder, and binder over the dust-laden surface are the prime reasons for slippage cracks.
6. Reflection Crack
Under renovation or repair, an asphalt wearing a coat is laid over the rigid pavement. The rigid pavement has longitudinal and lateral joints at fixed intervals. Sometimes, the cracks along joints appear on the top surface. In other words, the rigid pavement joints reflect in the flexible pavement as cracks. Hence, the name reflection cracking suits it.
The transverse undulations formed at the road surface due to the stopping traffic are known as corrugation. The undulations have regular intervals and cause an unpleasant bumpy ride experience.
The water infiltration causes swelling of the subgrade. Therefore, the road surface experiences a localized swelling on the road further causing cracks if not controlled.
9. Edge Cracking
The cracks occurring within 1-2 feet of the road edge are edge cracks. The most common reasons for edge crack are poor drainage, erosion, heavy traffic, and heavy vegetation.
Defects of Rigid Pavement
A rigid pavement has flexural rigidity in it. In simple words, it distributes the traffic load more evenly on the underlying layer. Cement concrete is the construction material for rigid pavement. Let us go through the defects of rigid pavement.
10. Scaling of Concrete -Defects of Road for Rigid Pavement
The wear-tear of the rigid pavement surface due to heavy traffic is scaling. Another reason for the accelerated scaling of the concrete surface is over-vibration during construction. Due to over-vibration, the cement slurry comes to the surface and sets. Thus, under the heavy traffic, the slurry gets easily abraded leaving the exposed aggregates.
11. Shrinkage Cracks -Defects of Road for Rigid Pavement
Concrete shrinkage cracks occur due to insufficient curing. These are hairline cracks on the surface of the rigid pavement.
The shrinkage cracks have a limited length of up to 2m. They may occur in the longitudinal or transverse direction or both.
12. Warping Cracks -Defects of Road for Rigid Pavement
The concrete slabs experience warping stress at the edges. If necessary reinforcement is absent on the joints, irregular cracks develop on the slab edges.
13. Spalling of Joints -Defects of Road for Rigid Pavement
The cracks occurring along the joint due to excessive compressive stresses are known as spalling of joints. Also, the filler material placement at an angle during the construction causes spalling later on.
Another reason for joint spalling is the infiltration of incompressible material into the joint.
Pumping is the process of subgrade material coming out of joints with water. Under the traffic load, the slab is pushed downwards, and the water oozes out of the joint. Pavements with poor drainage often suffer from pumping.
The prime cause of pumping is the water infiltration into the subgrade. The fine subgrade particles get eroded, leaving a cavity in the subgrade. Also, the concrete surface gets stained due to muddy water.
The faulting is the elevation difference between adjacent concrete slabs. It causes a bumpy ride experience. The prime reason for faulting is the settlement of subgrade. Another reason is the formation of a cavity in the subgrade due to erosion.
Pumping is one more reason for faulting.
16. Corner Break
Corners are the most critical area for a slab as they undergo multiple stress combinations. Pumping erodes the subgrade forming a void beneath the slab. It causes a corner break under the traffic.
17. Punch-Out Defect of Rigid Pavement
A local structural failure of the concrete slab is known as a punch-out defect of rigid pavement. It occurs near the joint. There are many factors involved in a punch-out failure. For example, inadequate slab thickness, poor quality material, and eroded support.
Road Surface Defects
Road surface defects correspond to all the defects that affect the road surface only. The pavement needs to have a smooth surface for a smooth driving experience. At the same time, it should also offer enough friction to the tyres to maintain the grip on the road without skidding or slipping.
The road defects may occur in all types of pavements-flexible and rigid. Some of the examples of road surface defects have already been described above. Let us go through them once more.
- Slippage Crack
- Scaling of Concrete Surface
- Shrinkage Cracks
How to identify road defects?
Road defect identification is important to understand what went wrong. So that in future those mistakes can be avoided. To identify road defects let us classify them into three heads.
- Surface Defects
- Structural Defects
- Defects due to external reasons
Surface defects are mainly due to the exposure of aggregates (scaling), bleeding, ravelling and shrinkage cracks. These defects affect the road surface rendering it rough, thus a lesser pleasant experience. However, their effect is not as serious as other defects.
Structural defects affect the structural integrity of the pavement. The reasons for the same are loose foundations, poor quality of material, heavy loads and excessive traffic. For example, faulting, spalling of joints, corner break, potholes, rut, corrugation are structural defects.
Defects due to external reasons include pumping and other defects that arise due to water infiltration, contaminants etc.
Causes of Road Defects
In broad terms, the roads are damaged mainly due to three reasons- poor design, poor material and heavy traffic. The causes of road defects are as follows.
- Poor material quality.
- Avoidance of good construction techniques and practices.
- Selecting the wrong construction materials as per the road usage, temperature etc.
- Faulty designs.
- Excessive traffic.
- Bad drainage.
- Overloaded vehicles.
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