Don’t hate me. I’m just answering Tejash’s question. Blame him.

He asked the question the other day about the age old debate: Concrete or asphalt?

There really is no easy answer.

To start, when road construction really got underway in the country, the first roads that were actually paved, were paved with concrete. Why? It was readily available and was a tested commodity. Engineers knew what they would get with concrete. This is why many if not most of the original Interstates were constructed using concrete.

Eventually enough advances were made with asphalt paving that it became a viable option for road construction.

If you travel the interstates you will no doubt see portions under construction. Sometimes they will be widening/improving a concrete section and sometimes will be an asphalt section. The break points are usually at the county lines and the choice of materials is determined by several factors, the biggest being ultimate cost.

Building a road with concrete is incredibly expensive. The expense has increased in recent years because the cost of cement and steel has gone through the roof. Also, it is costing more and more for the aggregate used to make the concrete.

Using concrete also takes more time. Pay attention the next time you pass a construction zone where they are building a concrete road. You will notice massive amounts of steel being used as reinforcement, as shown in this picture:

It takes a lot of steel to provide the required reinforcing and it takes a lot of labor to install all that steel.

Concrete is very, very good in compression, but it absolutely sucks in tension. To make up for this tendency to suck, you need to add reinforcing steel to the areas where you are expecting tension. The problem with roads is that roads fail where the sub-base fails. When that happens with a concrete road, the concrete has to bridge over the failure, to do that, you need the steel. But often, if the sub-base failure is large enough, the concrete road will fail and form potholes.

To keep the sub-base from failing, you need to spend lots of time ensuring it is prepared properly and your base material is installed appropriately. This is usually graded aggregate base, or GAB for short. It is the grey sandy, rocky material you see them put down and compact. On top of that, you lay your steel and then you pour your concrete.

If done properly, a concrete road requires very little maintenance. You pay more up front, but the long term cost of maintaining the road are much less than an asphalt road.

Asphalt roads are easier to build. You still have to pay close attention to your base material, but there is no steel to worry about. This cuts down on the labor and the cost of materials. But there are tradeoffs. Asphalt is not as durable as concrete. It does not have the ability to bridge areas of bad base. Every base failure will have a dip in the road surface. Concrete can span most normal sized failures, but asphalt will conform to the failure and there will be a dip.

Asphalt also ruts. You may have noticed this at busy intersections. If there is a lot of truck traffic or a large number of turning movements, the asphalt will have a tendency to rut. This is because asphalt always maintains a certain level of fluidity. In other words, it don’t dry hard as a rock like concrete. On hot days or if there are heavy wheel loads making turns, the asphalt will run and buckle. Very similar to how your carpet reacts under heavy traffic and gets loose, requiring it to be re-stretched.

You can build an asphalt road cheaper than a concrete road, but you will have long term maintenance costs. You will need to resurface (repave) the road every 3 to 5 years and if heavy truck traffic is expected, you may have rutting issues.

Asphalt roads are much easier to repair. You can cut a section of road, fix the base and repave it and the final product will almost match the existing road. Not so with concrete. You may have noticed where the DOT has “fixed” areas on concrete roads and after they are finished, the ride is actually rougher than before they “fixed” it. This is happening on I-75 south of Cordele. They are completely removing the existing concrete road and rebuilding it. The soils down there are very poor and my guess is the base is pretty shot. So the only thing they can do is rip it up and start again.

Now, you can use concrete for parking lots as well, but the same issues apply to them. It costs more for concrete, but it lasts longer, but if you have repair needs, it is harder to fix a concrete parking lot. Also, you tend to have the need to dig something up in a parking lot. A pipe or conduit may have failed or you need a new something or other run to your building. If you have to dig through the concrete and then replace it, it’s going to cost an arm and a leg.

I’ve seen concrete parking lots for auto repair shops like Napa Auto Parts. You can pressure wash concrete and those types of businesses would have need for that to keep the grease and stains down. By and large I only see asphalt parking lots around here.

I guess it boils down to cost and usage. Standard residential streets do not see much traffic and can get by with only 6″ of base and 1.5″ of asphalt. The same goes for standard duty parking lots. Even higher traffic roads can get by with 8 to 10″ of base and a total of 3″ of ashalt. Concrete takes a minimum of 8″ of base and 6″ of concrete. Higher traffic would require reinforcing steel and thicker base and concrete. It adds up. But you have less maintenance with concrete.

My opinion:

Use asphalt for residential and collector roads; parking lots; and some major arterials.

Use concrete for higher traffic roads and parking lots which are expected to receive a lot of truck traffic.