Using Rock Dust from Asphalt Plants as a Supplementary Cementitious Material in Concrete

Asphalt-plant rock dust (RD) is a fine by-product generated during hot mix asphalt production and is often landfilled or ponded, although it has potential for beneficial use in concrete. This study evaluates RD generated at hot mix asphalt plants as a supplementary cementitious material (SCM) for concrete and examines how source mineralogy and fineness affect pozzolanic reactivity, alkali-silica reaction (ASR) mitigation, and concrete performance. Nine RD samples in their as-received state were characterized and screened using physical, chemical, and reactivity tests, followed by mortar and concrete evaluation of selected materials. Pozzolanic reactivity varied widely among the tested RDs. Based on rapid, relevant, and reproducible ( R 3 ) heat release and calcium hydroxide consumption, four samples were classified as moderately pozzolanic, while the others behaved primarily as inert fillers. The moderately pozzolanic samples also showed strength activity index values above 80% and provided greater ASR mitigation, with expansion reductions of up to 61% at 20% replacement and 71%–87% at 30% and 35% replacement levels. Concrete mixtures with selected RDs at 20% cement replacement showed improved workability but reduced 90-day compressive strength by 24%–35% relative to the control. Bulk electrical resistivity at 90 days remained comparable to the control, while drying shrinkage was controlled with the aid of a shrinkage-reducing admixture. Among the tested materials, DI-1 and QM-3 showed the greatest promise for structural concrete applications, whereas DI-3 and QM-1 appear better suited for lower-strength applications. Overall, based on the nine tested RD samples in this study, RD suitability as an SCM depends strongly on source characteristics and should be evaluated on a case-by-case basis, providing new guidance for screening asphalt-plant RD sources and supporting their potential use as regional SCMs in more sustainable concrete production.