1 Dec 2017

Highways: asphalt or concrete?

Ronald writes*

Most highways in the Netherlands are made of asphalt. However, in the US only about 65% is made of asphalt,** while the rest is mostly concrete. Why is there such a difference in the materials used? Should there not be one clearly superior to the other?

While both materials are largely made up of aggregate (various fractions of crushed stone and sand), they are bound together differently.** In asphalt surfaces, the binding agent is bitumen, a refinement product of crude oil, while concrete is bound together by cement. These chemical differences create inherent distinctive characteristics. Asphalt, being a product of crude oil, emits various hazardous compounds to its environment during the period it is used. Some of the compounds that are of most concern are PAH’s. These compounds can be toxic for both humans and the environment, and this cost is not necessarily accredited for in the construction price. On top of this, the laying of asphalt is very energy intensive, both in pre-production as well as on-site. This brings in further environmental concerns, as especially on-site energy use usually relies heavily on fossil fuels. The pollution and CO2 emissions of burning fossil fuels are also externalities that should be accounted for.

However, the only serious alternative for highways is concrete roads. While cement is not such a contaminating substance as bitumen, is also creates a more brittle surface. For high-intensity roads, which highways usually are, large amounts of steel reinforcements are needed. The production of steel is very energy intensive, and might offset any benefits gained by using cement instead of bitumen. The combination of these two materials, concrete and steel, creates a much more durable road surface, more durable even than asphalt. This should be taken into consideration when assessing the total costs for society of using either of these materials. Reparations or early replacements will also have a cost, and an extra cost to society through the various externalities both options have. Partly due to this durability, concrete is considered to have a lower environmental cost than asphalt, while asphalt has a lower production cost. To do a proper cost-benefit analysis of both materials, environmental and social costs should be considered on top of the internalized costs over their entire normalized lifespan.

* Please help my environmental economics students by commenting on unclear analysis, other perspectives, data sources, etc. (Or you can just say something nice :)

** DZ: Sorry, but some of these links are behind a university firewall. Fucking Proquest