Effect of Long-Term Binder Draindown on Performance of Open Graded Asphalt Friction Courses with BOF Steel Slag Aggregates

Abstract

The open graded asphalt friction course (OGAFC) is a hot mix asphalt wearing course designed and constructed to mainly achieve the benefits of quick surface water drainage, high skid resistance, and low tire-pavement noise. OGAFC thus offers advantages of reduced hydroplaning, reduced splash and spray, reduced noise, and enhanced skid resistance and visibility (especially in wet weather). These mixes demand a uniform/open aggregate gradation for high permeability; establishment of proper stone-on-stone contact for good structural stability; and higher relatively stiff binder content for adequate resistance to moisture damage and binder draindown. Due to the lack of fines and higher binder content in OGAFC mixes, the asphalt binder tends to move down vertically under the influence of gravity when exposed to high temperatures during production (production-stage draindown) and over time at high pavement service temperatures (long-term draindown). This study evaluates long-term binder draindown of OGAFC mixes with both natural aggregates and basic oxygen furnace (BOF) steel slag, a waste/by-product of steel making, as a replacement for natural aggregates. OGAFC mixes with five replacement percentages (0%, 25%, 50%, 75%, and 100%) of BOF steel slag and two types of modified binders (polymer and modified crumb rubber) were subjected to different long-term binder draindown–conditioning protocols and then evaluated through determination of permeability characteristics, moisture susceptibility, raveling potential, and permanent deformation. The results revealed that aging in terms of temperature and duration has a significant effect on binder draindown. OGAFC mixes with higher BOF steel slag content showed better raveling, rutting, and moisture performance compared with a control mix after being subjected to long-term draindown. The inclusion of BOF steel slag up to 100% in OGAFC mixes produced encouraging results, with overall improvement in performance.