|Red Rock Aggregate in Asphalt|
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.