The United States spends 2.4% of its GDP annually on transportation infrastructure projects and this number has been in decline. The declining spending in transportation infrastructure is not due to infrastructure lasting longer, nor is it due to a lack of need of new infrastructure. A number of factors, including the American car culture, have contributed to transportation infrastructure costs rising faster than spending. This has created a situation where spending falls short by 60% annually of what is necessary to keep infrastructure in good repair.
A significant portion of transportation spending goes to building and repairing roads. More than 550 million tons of hot-mix asphalt is used annually in infrastructure and construction projects. The NSF has identified stronger asphalt and Portland concrete as a critical need for the future of American infrastructure. Premature failure of asphalt can be dangerous and it adds to the infrastructure deficit. Rutting and potholes are a large contributor to the US road fatality rate that is 60% higher than the OECD average, totaling some 30,000 plus deaths per year. The issue of stronger more resilient asphalt is a matter of public safety just as it is a matter of economics.
Adding Montmorillonite (MMT) nanoclay to asphalt binders has been shown to significantly increase the torsional stiffness and decrease the strain failure rate of asphalt, thus reducing rutting, potholes and cracking[fn]http://phys.org/news/2012-05-nanoclays-asphalt.html[/fn]. MMT is a smectite clay mineral, essentially composed of layered flakes of aluminum phyllosilicates. Each flake is about one nanometer thick and a few hundred nanometers wide. These flakes are separated via mechanical processes and then incorporated into the asphalt matrix. Studies were conducted with asphalt containing 2% and 4% MMT in two different types of fillers. The increased surface area of the MMT nanoclays versus conventional mineral fillers helps create better physical properties with less filler[fn]http://www.dtsc.ca.gov/TechnologyDevelopment/Nanotechnology/upload/Revie....
The addition of these nanoclays to asphalt increases the viscosity and reduces the strain failure rate in hot, cold, wet and dry conditions.
These nanoclays are naturally forming minerals, so would likely pose little risk to the environment. Furthermore, their platy structure makes them inherently safer than most nanoparticles in the context of human health. For these reasons, the risks are low and simple, and likely relate to any dust or air pollution created during the separation of the MMT platelets.