Many causes for potholes

Laurie Powell is only partly right about lack of camber being the cause of potholes (Forum edition 489).

It is easy to see on the Peninsula that there are many roads, with adequate camber, that still have potholes, so lack of camber cannot be a main factor.

On any road, it is the road base that actually carries the traffic load: the bitumen seal is only a coating over the road base, and its main function is to eliminate dust and provide a smooth running surface.

However, where there is no side drainage, run-off forms large pools, regardless of the amount of camber, and water can penetrate into this road base.

If the wrong base has been used, or if the base has not been properly compacted, or if the base drainage is inadequate, the road base can move.

Bitumen has no tensile strength, so any movement in the base will cause cracking, and water will then enter through the cracks, causing more movement and opening up a pothole.

Since the problem is in the base, filling the hole with bitumen can only be a stop-gap measure, but, if there is systematic immediate repair of potholes to a proper standard, unlike the situation in Central Coast, the road can still be maintained economically over an acceptable lifetime.

Of course, poor drainage is not the only reason for deterioration of the surface.

Over time, bitumen can be perished by the sun's rays, particularly in countries with severe climates like Australia's.

Also, the bond can be damaged by impact forces: the rolling motion of tyres, particularly on heavy vehicles, puts a longitudinal stress on the road surfacing, creating a rippled profile that is easily cracked.

Anyone old enough to have driven on unsealed roads will remember the typical corrugated surface caused by this repetitive movement.

It is an interesting fact that lack of a long-life, low-cost, low-maintenance road surface is one of the great engineering failures of our time.

We can put a man on the moon, but we cannot drive to the supermarket on a trouble-free road.

Email, 5 Mar 2020

Bruce Hyland, Woy Woy