Georgia Department of Transportation's Progress in Open-Graded Friction Course Development

Abstract

To improve the safety of motorists on Georgia highways, the Georgia Department of Transportation (GDOT) has continued to use the most advanced and effective pavements available, including the open-graded friction course (OGFC). Since OGFCs were conceived in the 1950s and 1960s, GDOT has used these mixes as thin porous wearing layers primarily on Interstate highways. In the past, GDOT encountered problems with OGFC use, including asphalt cement (AC) draindown, rapid oxidation, raveling, and stripping of underlying layers. Consequently, GDOT placed a moratorium on OGFC use in 1982. Since that time, however, several modifications have been made to improve the performance of OGFC mixes. Hydrated lime is added as an antistripping agent to OGFC and to all other mixes used on the Georgia state route system, including dense-graded mixes that underlie OGFC. Fibers are added to eliminate AC draindown. Polymer-modified AC is added to improve the durability of the pavement by reducing problems associated with premature oxidation and raveling. Production temperatures are increased to more thoroughly dry aggregate components and thus improve AC adhesion. Finally, coarser gradations and thicker layers are used to improve permeability. With the modifications made to these mixes in the last few years, significant improvements in mix performance have already been noted. Agencies that have used this mix in the past and experienced problems similar to those experienced by GDOT should consider using this modified OGFC on high-volume traffic facilities.