Why is asphalt used for roads? Why is it better than concrete?

This is usually a matter of cost and the type of vehicles that use the roadway. Concrete is more expensive than asphalt, but has a longer life. It is also a matter of constructability and the ability to get production. Concrete companies think we should put concrete pavement everywhere. Asphalt companies think we should put asphalt pavement everywhere.

In Oregon, you will find that a portion of I-84 has asphalt pavement in the left lanes and concrete pavement in the right. Trucks generally use the right lane. The concrete can tolerate the loading of heavy trucks much longer than asphalt.

The concrete is typically reinforced, which lengthens the life of the pavement. In the case of Oregon’s concrete pavement, it is continuously reinforced. The asphalt is less expensive. So, Oregon may have extended their budget by using asphalt in the left lane.

It is becoming more and more common to use concrete at intersections. This is an area with lots of turning movements, starting and stopping, and, interestingly, where vehicles drip lots of fluids onto the pavement. These fluids tend to reduce the life of asphalt. This is actually one very important reason that use see bus stops with concrete pads. Concrete does not have the same reaction to these fluids. Due to concrete’s durability, it is used at these locations.

I have constructed miles of interstate with concrete pavement. When they can pave a long distance of concrete pavement at a time, meaning they get production, there is a cost savings. It is still more expensive, most of the time, than asphalt, but it lasts longer and can handle the truck loading.

On rural roads where there are lots of driveways and approaches, and where the road my be on rolling terrain, it makes more sense to use asphalt because you have to pay special attention to the driveways and approaches.

There are also different noise levels between concrete and asphalt. Some types of asphalt absorb the sound better than other asphalt, but asphalt, in general, is quieter than concrete. Some concrete pavement has lines in it, called tining. We used to tine across the roadway, perpendicular to the direction of travel.

This proved to help drainage, but was very noisy. Now, they tine in the direction of travel, except on bridges. This is much quieter. A road without tining is noisier than both. This is an important consideration when noise is a concern. Idaho typically has to construct noise walls where they have concrete pavement close to urban areas.

Picture: Tining in concrete pavement

Concrete can be place almost any time of the year. If it is too cold, it can be heated. This isn’t feasible for long distances. It would require a lot of blankets. Asphalt can only be placed in warm weather, if you want to get any significant quantities down. Generally, the temperature must be at least 50 degrees and rising to place asphalt. Typically, the oil isn’t even available in the winter. Cold patch is often used for small areas of asphalt paving in the colder months.

Incidentally, you actually don’t have to wait 28 days to allow traffic onto concrete pavement. In order to expedite construction, they want to get traffic on it as soon as possible, so you can pave other areas. Usually, the contractor will use a mix design that reaches the minimum strength rather quickly. As long as it has the required minimum strength of 3500 psi, small vehicles can get on the concrete.

The strength must be 4000 psi when all traffic is allowed on it. We either break concrete cylinders or use dataloggers to determine if strength has been reached. Usually, the concrete saw cutting trucks get onto the concrete within a couple of days. Concrete has to be cut in sections to control cracking. Then they seal the joint with a hot asphalt sealant. Traffic may be allowed onto the pavement within a week or so.