Why do we still use concrete and asphalt for our roadways? Why have we not found a better material that is less prone to potholes and always feels smooth to drive on?
In: 674
We use them because they work. Concrete can get the bumps from the joints. Asphalt is by far cheaper and, done properly give you a lasting, and smooth ride.
The problem is not the surfacing materials being used… they are appropriate. There are a lot of factors at play. One of these is existing material and the subgrade materials. Another is proper drainage. It does not matter if you lay 20” of asphalt or what mix design you use… if you lay it over muck, heaving clays, or next to a shallow ditch that allows for perched water conditions to occur under the surfacing, under the base (base layer stoically stone, lime treated or other stabilized base like soil cement) and can cause “pumping” or movement under everything due to saturated soil. This will cause deep failures that will mirror through to whatever surfacing you have.
Another huge problem is the existing conditions in comparison to what that state or county or parish has for a work program budget. For example in a state like Florida – you would some pretty decent conditions… dense sand, readily available source for lime stone and some granite sourced aggregates to the north… and a hefty budget to meet the needs.
Then you could look at a state like Louisiana or Mississippi in contrast. Heaving clays plague their roads… and they are at the mercy of the 80/20 federal aid program jobs to fund most jobs. They do asphalt surface treatments (AST) to roads to try to squeeze a couple extra years out of them when they really are overdue a patch, mill, and overlay. An AST is basically a shot of emulsion (such as CRS-2P) with a graded aggregate such as a size 2 or 3 spread across the top.
If you looked at a cross section of roadway from Florida and either of those states, you’d see a huge huge difference. Significantly better subgrade, 2-3x more stabilized subgrade, more aggregate or stone for proper flexible pavement design and less “dead” hotmix under the surface of poorer states. You’d see far more in depth investigation from a geotechnical scale because again the money is there to fund it.
You will see even worse roads in the off-system, or town/county maintained roads. Even in better funded states yiu can see some counties with lack luster roads… but even still there are “giveback” projects or projects for local entities like the county that get 80%federal and 20% local funding that the FHWA has the appropriate state DOT oversee the administration of said work to facilitate the use of federal dollars to the county’s contractor.
The point is that when properly applied, in well improved or existing conditions, maintained properly, and replaced within the RIGHT time of the service life cycle asphalt and concrete are excellent materials. And really the only reason you see concrete still used in most states?… it’s because the states make commitments to local “stewards” or “organizations” representing the concrete industry to allocate x amount of roadway miles or xx $ of their budget to concrete roadway. Not saying concrete is bad but it is expensive and just observing a good hotmix operation compared to concrete… there is a clear winner in efficiency.
Latest Answers