Better Roads Staff
Like the concrete paving industry, asphalt’s emissions-reducing progress is also being fueled by a need to reduce pavement costs.
For asphalt, the leading edge on this front centers on integrating ever-higher concentrations of reclaimed asphalt pavement (RAP) into mixes and on the use of reclaimed asphalt shingles (RAS) to counter the impact of higher costs for virgin asphalt cement.
Growing sophistication in engineering RAP mixes – and increased confidence in them among DOT pavement professionals – has brought a steady increase in RAP ratios. NAPA’s Kent Hansen says RAP currently comprises about 18 percent of asphalt placed in the United States, up from an estimated 12 percent in 2007.
The upward trend seems certain to continue as pioneering states are allowing 35- to 50-percent RAP mixes for base and intermediate courses, and up to 25 percent for surface courses. Some states have no limit — contractors just have to meet design standards set by the state.
The industry has also aggressively adopted recycled shingles in mix designs to supplant a portion of the virgin asphalt cement and thus reduce costs.
Asphalt advocates, like those for concrete, are working to reduce pavement thickness as a way to reduce costs and carbon footprints. In addition to supporting the adoption of AASHTO’s DARWin-ME, the industry has used Auburn University’s National Center for Asphalt Technology to establish new structural values for modern mix designs. The new values substantially reduce the thickness required for various load projects.
Perhaps no pavement development has won more friends in the environmental community than the advent of porous asphalt and pervious concrete.
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