- Introduction
A highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil subgrade whose primary function is to distribute the applied vehicle loads to the subgrade.
The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance favorable light reacting characteristics, and low noise pollution. The major Flexible pavement failures are fatigue cracking, rutting, and thermal cracking. The fatigue cracking of flexible pavement is due to horizontal tensile strain at the bottom of the asphaltic concrete. The failure criterion relates an allowable number of load repetitions to tensile strain and this relation can be determined in the laboratory fatigue test on asphaltic concrete specimens. Rutting occurs only on flexible pavements as indicated by permanent deformation or rut depth on a long wheel load path. Two design methods have been used to control rutting: one to limit the vertical compressive strain on the top of the subgrade and the other to limit rutting to a tolerable amount(12mm) normally. Thermal cracking includes both low-temperature cracking and thermal fatigue cracking.
- FAILURES
Failure in subgrade
- Inadequate Stability
- Excessive application of stresses
- Plastic deformation
1. Inadequate stability
2. Loss of binding action
3. Loss of bearing course materials
4. Inadequate wearing course
- FAILURES ON HIGHWAY:
1. Alligator cracking:
Alligator cracking forms when the subgrade and asphalt base begins to compress from bearing heavy vehicles. Alligator or cracking is commonly found at intersections where vehicles are stopped for a continuous amount of time. Initial cracks will form and spread through water intrusion and further asphalt base compression.
2. Edge Cracking :
Edge cracking forms along the edge of a road a distypically caused by water damage, sufficient base material, and heavy road usage
3. Block Cracking:
Block cracking is formed by seasonal temperature differences that cause the asphalt to expand and contract. Block cracking will form if an asphalt surface has too rigid of a mix design that does not give the surface room for seasonal density changes.
4. Joint cracking:
Joint cracking forms along asphalt overlay projects where a flexible concrete base is paved over. Over time the concrete sub-base will expand and contract causing cracks to form along the joints of the concrete.
5. Transverse Cracking:
Transverse cracks run across an asphalt roadway and are caused by settling or shifting base material, improper paver operation, and extreme temperature shifts.
6. Linear Cracking:
Linear cracking runs parallel with the roadway and is most commonly caused by pavement fatigue but can also bean is unrelated to weaker points in a parking lot or roadway pavement joints.
7. Potholes:
Potholes are formed through prolonged water intrusion from existing cracks in the surface. If alligator cracks and other asphalt stress cracks are not treated, water will begin to erode the surface all the way down to the sub-base. This will cause large holes to form in the asphalt which will spread and cause damage to vehicles. Once a pothole is formed a patch can be applied to the surface, but because the sub-base has been destroyed the area will continue to become compacted.
8. Depression:
Depression in an asphalt surface is formed by uneven sub-bases or compactions over time. Depressions have a lower elevation than the asphalt surface which will cause the area to hold water for longer. Water build-up can cause further issues like raveling or potholes.
9. Rutting:
- TYPES OF ROADS
- Road Failures: Failure in the subgrade, and sub-base or Base course
- Road development in India
- Road development plans in India
- Pavement in Roads
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