LABORATORY EVALUATION OF HOT MIX ASPHALT PERFORMANCE USING LOCALLY PRODUCED STEEL SLAG AS A REPLACEMENT FOR DOLOMITIC COARSE AGGREGATE

The depletion of natural aggregates has increased the need for sustainable alternative materials in asphalt pavement construction. This study investigates the use of locally produced steel slag from Helwan Steel Factory, Egypt, as a partial replacement for dolomitic coarse aggregate in hot-mix asphalt. Six asphalt mixtures containing 0, 20, 40, 60, 80, and 100% replacement of the coarse aggregate with Helwan factory blast furnace steel slag (HFBFSS) were prepared at an optimum bitumen content of 5.0%. The mixtures were initially evaluated in terms of air voids (AV), voids in mineral aggregate (VMA), Marshall stability and flow, loss of stability, and indirect tensile strength to determine the most suitable HFBFSS/dolomite blending ratio. Although the mixtures containing 80 and 100% HFBFSS exhibited higher mechanical strength, their VMA decreased to 14.70 and 14.00%, respectively, below the adopted minimum requirement of 15%. Consequently, the mixture containing 60% HFBFSS and 40% dolomite was selected as the optimum blend, providing the highest acceptable replacement level while satisfying the volumetric requirements. Its performance was subsequently compared with the conventional 100% dolomite mixture through moisture-susceptibility, Hamburg wheel-tracking, and semi-circular bend tests. The selected mixture increased dry and wet indirect tensile strength by 42.0 and 48.6%, respectively. After 14,000 wheel passes, rut depth decreased from 14.70 to 11.90 mm, corresponding to a 19.0% reduction in permanent deformation. Moreover, the average semi-circular bend peak load increased from 2.567 to 3.188 kN, representing a 24.2% increase in fracture-load response. The results demonstrate that replacing 60% of dolomitic coarse aggregate with locally produced steel slag provides a balanced enhancement in mechanical performance, moisture resistance, rutting resistance, and fracture-load response while maintaining the required volumetric characteristics. The proposed replacement therefore offers a promising approach for reducing natural-aggregate consumption while beneficially utilizing a locally available industrial by-product in asphalt pavement construction.