In 2009, FHWA’s Exploratory Advanced Research (EAR) program hosted a workshop to identify interests and capabilities for nanoscale research that can be applied to highways. The workshop attracted experts from FHWA, university transportation research centers, federal labs and other organizations that are conducting nanoscale research.

The workshop helped shape the scope of FHWA’s further investment in nanoscale research, and supported the development of strategic roadmaps that could outline funding needs for future nanoscale research for highway infrastructure.

“We expect the nanoscale workshop to lead to an overall increase in research targeted at highway program needs,” says David Kuehn, EAR program team director at FHWA. “The workshop was an ideal opportunity to collaborate and leverage nanoscale technology that is being developed for other industries and to accelerate our ability to solve long-term highway research questions.”

“There are multiple potential nanoscale applications in highways,” FHWA says in a 2010 report on the workshop, Nanoscale Approaches for Highway Research. “For example, concrete is a material containing pores on a nanoscale, a result of the chemical reaction between cement and water. Repeated exposure to deicing chemicals causes oxidation, cracks and long-term deterioration to occur in the structure. Utilizing nanotechnology to create smart self-healing materials and structures could lead to less-frequent and faster construction, as well as to increased durability and improved performance, all helping to prevent catastrophic failure.”

Nanotechnology’s ability to produce minuscule MEMS, or microelectronic and mechanical systems, would permit stakeholders to constantly monitor materials, and also could offer improved predictive performance models. “During construction, nanotechnology can allow for embedding increasingly smaller sensors throughout a structure or pavement,” FHWA says. “These sensors could be used for long-term monitoring of corrosion and could offer an invaluable tool in monitoring bridges. By using a car-mounted data reader, information from the embedded sensors could then easily and safely be collected as the vehicle passes.”

As Alvarez, Lee and Mahendra observe, some of this research should be aimed at the environmental aspects of widespread use of nanotechnology, FHWA says. There is concern that unleashing these products on a widespread basis could have unanticipated consequences like something out of a science fiction novel.

Yet nanotechnology in transportation infrastructure also offers environmental benefits, FHWA observes. “[Nanomaterials have the] ability to monitor mobile source pollutants during construction and operations by using nanoscale devices to bind with road-based pollutants,” FHWA says. “Low-cost environmental sensors could monitor the air, water and soil quality, and the technology could allow large-scale monitoring of the operation to continually map pollution levels.”

In a new line of research, nanomaterials such as thin-film technologies may boost use of recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP), in addition to reducing alkali-silica reactivity (ASR) in concrete.

“Nanoscale research could lead to an increased use of recycled materials in pavements through a better understanding of bonding at the boundaries of different materials and the design of very thin coatings to improve the workability and durability of recycled materials, which would also help to reduce costs,” FHWA says. “Nanoscale research also could result in the development of smaller, lower-cost sensors, which would use substantially less energy. Self-powered sensors also would contribute to the efficiency and reduced environmental impact of the highway network.”

Concrete Leads Nanoresearch

By far, the most activity in nanotechnology research for pavement and bridge infrastructure has taken place in the concrete industry. There, research is aimed at optimizing concrete strength and durability using nanomaterials, and condition monitoring via MEMS imbedded in the concrete matrix.

For years, the minuscule size of a particle of microsilica admixture has benefited concrete, as the smaller the silica particle size, the greater the surface area that is presented for reaction within the curing concrete. The much smaller size of nanoparticles now makes possible a geometric increase in performance, and that’s one of the areas of research.

Research in concrete nanotechnology has been well-organized. A workshop at the University of Florida in August 2006 was attended by more than 70 participants, with more than 30 presentations, and focused on the development of a Roadmap for [Nanotechnology] Research for Concrete-Based Materials. The roadmap is destination-oriented, with clearly defined outcomes that will greatly enhance concrete technology and the uses of concrete in structures, including housing, bridges, tunnels and pavements.

That 2006 roadmap identifies research needs such as:

• development of high-performance cement and concrete materials as measured by their mechanical, durability and shrinkage properties;

• development of sustainable and safe concrete materials and structures through engineering concrete for different adverse environments, reducing energy consumption during cement production, and enhancing safety with nanoengineering of concrete materials;