Road-gripping technologies already in place in Europe and Asia are now being implemented in the United States. Learn what this means for material producers.
by Robert N. Dingess
High-friction surfacing, which uses a specialized epoxy binder into which processed calcined bauxite is dropped, is being found to improve the gripping of road surfaces on curved roads, dramatically improving safety.
Roughly 33,000 people are killed annually in motor vehicle crashes on U.S. roadways. According to the National Highway Traffic Safety Administration (NHTSA), the annual economic costs of motor vehicle crashes is $277 billion. Thanks to renewed efforts by the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO), a technology used in Europe and Asia is being applied to improve roadway safety at high-risk locations such as curves and certain intersections. The technique, known as high-friction surfacing, uses a specialized epoxy binder into which processed calcined bauxite is dropped. The result is a dramatic increase in the grip provided by the roadway surface.
Calcined bauxite
Calcined bauxite is provided in 3,400-pound bags.
Calcined bauxite is used in the refractory process in the iron and steel industries. High-end calcined bauxite is also the key component in a high-friction surface. Creating a calcined bauxite that meets the standard for roadway application requires heating the bauxite to 2,732 degrees Farenheit (1,500 degrees Celsius). The current minimum aluminum oxide content requirement in AASHTO’s specification is 87 percent. The resulting material has a hardness just below that of diamonds.
Most calcined bauxite is shipped from Chinese producers processed, bagged, and ready for distribution to customers.
The process for applying high-friction surfacing is similar to that of sealing bridge decks. The key difference is that most bridge deck surfaces are not subjected to the friction demand levels found in horizontal curve or intersection applications. The binding systems for high-friction surfacing are required to account for this additional friction demand through higher compressive strength. A properly installed high-friction surface treatment is expected, on average, to last up to 10 years.
FHWA “Every Day Counts”
While comprising only about 5 percent of roadway miles, roughly 25 percent of all fatal crashes occur at horizontal curves. The FHWA initiated a number of test projects using high-friction surfacing at curves with a history of severe crashes. The crash reductions following application were so remarkable that in 2012 the FHWA included high-friction surfacing as part of its “Every Day Counts” initiative. The FHWA has partnered with AASHTO and the American Traffic Safety Services Association (ATSSA) on a number of projects designed to increase the use of high-friction surfacing around the United States.
Although there were a small number of high-friction surfacing projects in 2012 and 2013, a dramatic increase in the number of projects in 2014 and 2015 is expected as state transportation departments develop specifications and locate potential project sites. Nearly a dozen states have projects scheduled for 2014 and expect more than double that number for 2015. Kentucky, Tennessee, Florida, West Virginia, Oklahoma, and California are aggressively working on large-scale programs. Texas, Utah, Georgia, Alabama, Virginia, and Illinois are well on their way to developing significant high-friction surfacing programs as well.
Sourcing calcined bauxite
Nearly all calcined bauxite used for roadway surfacing is imported from China and India. In developing the AASHTO Standard Specification for High-Friction Surfacing, it was decided that refractory-grade calcined bauxite would be required. The single greatest benefit of using refractory-grade calcined bauxite stems from quality control. The material cost for a unique specification would have increased cost and decreased availability. Refractory-grade material has easy-to-access supply chains and creates transparency and accessibility through globally available pricing options.
Given the foreign sourcing of this material, some have speculated that the market may not be able to provide sufficient quantities to meet demand. Ken Jones, plant manager at C-E Minerals, in Newell, W.Va., disagrees. “Supply of calcined bauxite should remain strong, and prices are likely to drop over the next few years due to the slowing of global demand for refractory materials.” C-E Minerals has already provided calcined bauxite for use in high-friction surfacing. “We did not even know that this market existed until we were approached a couple of years ago,” Jones says. “We will certainly be monitoring its progress as we attempt to gauge demand.”
The calcined bauxite is provided in 3,400-pound bags. Most suppliers are having materials shipped to them from Chinese producers processed, bagged, and ready for distribution to customers. Others are securing raw calcined bauxite and processing the material at their own facilities. Price and timing seem to be key drivers for U.S. aggregate providers. It takes approximately three to four months for orders to be processed and shipped.
Other aggregates
As the FHWA started its examination of high-friction surfacing as a safety countermeasure, there was a strong effort initiated to find domestic aggregates that provided friction numbers and polishing resistance similar to refractory grade calcined bauxite.
The National Center for Asphalt Technology conducted a side-by-side tests of eight aggregates (calcined bauxite, flint, granite, basalt, silica, taconite, emery, and coal slag). While calcined bauxite was the most durable and retained the highest friction numbers, there may be opportunities for local aggregates that provide high initial friction numbers at locations with low traffic volumes.
The FHWA’s Office of Pavement Technologies’ Surface Enhancements at Horizontal Curves (SEAHC) project funded the installation of demonstration projects throughout the country. In addition, the National Center for Asphalt Technology conducted a side-by-side evaluation of eight aggregates (calcined bauxite, flint, granite, basalt, silica, taconite, emery, and coal slag). The results confirmed that refractory-grade calcined bauxite is the most durable and retains highest friction numbers. There may be opportunities, however, to use certain local aggregates that provide high initial friction numbers at locations with low traffic volumes.
Cost/benefit
There have been a number of cost/benefit evaluations conducted on the use of high-friction surfacing. Some evaluators attempt to compare it to other friction improvement options. Others push for the use of lesser aggregates, citing cost reductions. The bottom-line is that high-friction surfacing using calcined bauxite should be compared with the cost of engineering reconstruction, not against other friction materials. When compared with the cost of redesigning and straightening a horizontal curve, high-friction surfacing is a quick, low-impact solution. Unlike reconstruction, there are no environmental impact studies and no long periods in which the roadway is taken out or provides reduced service. No land purchases or other expensive measures need to be addressed. Instead of years of delay, high-friction surfacing provides agencies with a relatively low-cost and quick solution to make roadways safer.
Information
ATSSA has developed a website containing information about high-friction surfacing. The website, www.highfrictionsurface.net, contains updates on research, specifications, press coverage of high friction surfacing, case studies, and publications. The frequently asked questions section has videos from industry leaders answering questions related to installation and testing.
Future
The effort to find low-cost, systemic methods to make roadways safer continues. In addition to high-friction surfacing, the use of colorized aggregates and binders will soon be in wide use to designate bicycle lanes (green), transit lanes (red), and electronic toll lanes (purple). The push by agencies to find ways to use local aggregates for some of these systemic solutions should provide new use for a variety of traditional aggregates. The time for material suppliers to get educated and monitor the potential for these new markets has arrived.
Robert N. Dingess is the president of Fredericksburg, Va.-based Mercer Strategic Alliance, Inc. and serves as chair of ATSSA’s High-Friction Surfacing Council.