"Better Road Building Paves Way for Energy Savings"

Warm-mix asphalt is not the usual topic which I would expect in the National Geographic Daily News , but it certainly is a sign of the commitment of the magazine to energy ssues. It piqued my interest about the true potential of this new roadmix to save energy and provide a more durable surface. I remember well the bathtub sized potholes in the streets of Chicago, and wonder if this mix might prove to be more resilient.

Red Rock Aggregate in Asphalt

In my previous life, I was on the concrete side of the concrete vs. asphalt debate. The argument was for a longer service life (ie lower LCA), lower heat island effect, higher load bearing, and ability to recycle old roadbeds (Recycled Concrete Aggregate - RCA). I’ve championed pervious pavement for the ability to resupply the water table. On the other hand, I have to admit that concrete surfaces can be quite noisy, and require a higher level of installation skill – which was notoriously missing on one of my neighborhood streets which is now infamously known as the “roller coaster.” On the other side of the debate, asphalt makes a good overlay, and can also be recycled (Reclaimed Asphalt Pavement - RAP. And, the lower temperatures of the new warm-mix asphalt not only improves the conditions of the workers, but also reduces emissions and has about 30% fuel savings. So which is the better choice?

Both. Recycling concrete is a good idea in principle, but the use of the aggregate has been limited to low grade applications like base materials, haul roads and staging areas. It is difficult to use it for ready-mix concrete, because the random and uncontrollable composition of the aggregate (porosity, impurities, chemical composition) makes it difficult to guarantee the ability of the Portland cement to bind the rock. However, the characteristics of the rock are far less of an issue when the binder is asphalt, which allows it to be used in a high grade application – such as the actual roadbed.

There are several possible combinations available - such as using the RCA as the road base, or mixing the RCA and RAP for the road surface. Or one can mix in crumb rubber, using up some of the mountains of tires accumulated in America, and gaining a quieter road surface in the process.

Swiss Concrete Asphalt + Cobbletone 

The lesson learned is that industries which have traditionally been fierce competitors (concrete vs asphalt), or even totally unrelated (rubber tires) can come together to provide better product – in this case using more recycled material, providing a more durable surface, and a smoother roadbed for improved fuel efficiency of the vehicles.

This is an example of innovation on the edge of the industries, where a strategy which has allowed the IT world to keep nimble and make rapid improvement. Maybe this feature in the National Geographic will inspire yet another connectivity of ideas, and figure out a way to make roads last as long as the old Appian Way.