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May 2009
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Why Concrete is Better

Asphalt Roads versus Concrete Roads … what is better long term? There is no easy way to answer this question; it depends on the climate the roads are subjected to, the traffic volumes, the maintenance contracts, etc. But yesterday I had the opportunity to attend a seminar that shifted my preference to concrete roads.

What is diamond grinding?

The seminar I attended yesterday was on diamond grinding; a process where a machine chews up the concrete, creating longitudinal lines in the road leaving the surface smoother and more level. Basically a cylindrical cutting head, with many little diamonds as teeth, is attached to a machine that runs over the driving surface and creates the longitudinal lines in the road. This process is really only meant for concrete roads; the asphalt is too soft and would tear away with a diamond grinding machine.

But diamond grinding doesn’t just improve the drivability of the road, it also enhances the safety. Those longitudinal lines increase the surface friction of the road, which helps with the drainage of water at the tire-pavement surface. It also helps to decrease the noise of a highway; as a concrete highway surface wears it becomes ‘polished’ and quite loud. By restoring some friction with diamond grinding the noise is decreased.

The biggest advantage to diamond grinding is the cost savings. It is significantly cheaper to diamond grind a highway that to put on an asphalt overlay. The asphalt overlay would require bridge clearances to be changed and moving most guide-rail, curb and gutter – all of which adds up to significant costs.

Why aren’t concrete roads used more in Toronto? (and this gets a little technical)

SALT. NaCl. Cl-Chloride is an element that has deleterious effects on concrete. When the chloride penetrates the concrete it attacks the reinforcing steel of the road, significantly decreasing the strength of the concrete. The break down of the concrete is also contributed to the alkali reactions that break down the cement paste and aggregates.

To make it simple think of most freeway/highway bridges. Often you see reinforcing steel that is sticking out from the concrete face. The chlorides have attacked the steel causing to rust other reactions take place and the concrete breaks down and your left with exposed, rusted steel. But on a road this is so much worse, because the heavy trucks and cars breakdown the weakened concrete even further.

That’s why we have asphalt coverings on our concrete roads, to protect the concrete from the salt.

Concrete takes top prize

In the end I think concrete is a better solution to roads. This diamond grinding process can be done three or four times significantly increasing the life of the road. Plus when they do the diamond grinding to improve the roads there are minimal traffic closures and disruptions. Concrete roads have a much higher upfront cost but over the lifespan of the road, concrete is significantly less than an asphalt road.