The science behind potholes

Come monsoon, and we seem to encounter and embrace ourselves to manoeuvring the dreaded potholes on our streets. Every year, disgruntled citizens take on the civic authorities for the rise in the number of potholes and the threat it poses to motorists. Worldwide, roads seem to be prone to potholes wherever asphalt is used in their construction.

The nature of asphalt (or bitumen) allows binding that can sustain significant plastic deformations. However, a combination of unscientifically laid roads and their continuous wear can result in potholes.

While making the road, the subsurface has to be sufficiently compacted and the asphalt should then be laid over it. Since water can seep through the asphalt, care should be taken to drain the water on the surface with effective stormwater drains to carry the runoff. If the subsurface is not compacted well and when the water seeps in, it can cause the top surface of the asphalt to yield causing a depression. This can further make the surface uneven.

The continuous movement of automobiles in such conditions can add to the problem. At places where the subsurface is not compacted well, repeated movement, particularly, if breaks are applied, results in a shear force, that further damages the surface, resulting in potholes. This can also happen when the weight of the automobiles plying is greater than the designed limit, as the asphalted surface can yield and result in depressions. A depression, followed by rains and heavy traffic are a deadly combination.

Although it appears there is no respite from potholes, there seems to be some hope. Engineers are exploring water-resistant asphalt. This is also laid out taking care of the gradients to ensure water can run off the roads. Although not foolproof, as it also requires to ensure the subsurface is compacted well, at least the water stagnating can be minimised.

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