sand. However, those materials sometimes will not work for demanding applications. In many cases, there is plenty of good local rock already on roadways that are being resurfaced. Whenever possible, in preparation for resurfacing, the old surface materials (RAP) should be recovered by milling it up and returning it to the asphalt plant. Contractors and DOTs should work together to maximize the use of RAP, thus stretching the remaining available virgin rock further.
LIQUID ASPHALT
Most liquid asphalt is the residual of petroleum refining processes. Natural deposits, such as the well-known Trinidad Lake asphalt repository, do exist, but they are minor sources by comparison. If fossil fuel use diminishes, the availability of liquid AC—also called bitumen—would also diminish. Ironically, the opposite situation—increasing demand for fossil fuels—is also a threat to the liquid AC supply. With increasing oil demand or decreasing supply, at some point, operating coker units that extract more fuels from petroleum refinery residuals, leaving no asphalt, would increase in number and capacity. Because RAP includes both aggregate and high quality AC, maximizing its use will help deal with future shortages of virgin AC.
ASPHALT ROOFING SHINGLES
The asphalt shingles enthusiasm seems to have diminished. Some contractors found them difficult to use. When processing shingles for use, dealing with size reduction and the resulting high moisture content, various problems are encountered. Nevertheless, shingles consist of some good materials, especially liquid asphalt. The asphalt content is about 18 percent in the southern tier of the United States and up to about 22 percent in the northern tier of the United States and Canada. Prepared, processed and incorporated into the mix correctly, shingles contribute to excellent mix and effectively replace some liquid asphalt. In as much as using shingles solves the used shingles disposal problem as well as providing a useful asphalt pavement material, it seems to me we should continue to use them and just keep improving our technology, based on science.
RUBBER TIRES
The accumulation of rubber tires continues to be a problem; however, the asphalt industry alone cannot solve it. We can and do take some of the tires and can make excellent special-purpose mixes with them by incorporating fine rubber powder. Special-purpose pavements can bring in a good return, thus we can contribute to the solution.
PLASTICS
Plastic packaging material rubbish has become a huge environmental problem and may be an opportunity for the asphalt industry. Polymers, as everyone in the industry knows, can be beneficial to asphalt pavements. Plastics are polymers, but not all polymers are created equal.
www.THeAsphaltpro.com // 27