Performance Improvement of Asphalt Concretes Using Steel Slag as a Replacement Material

Abstract

The increased proportion of traffic volumes on roads is often the cause of distress to the pavement structure. The use of strong and durable steel slag (S) as an aggregate material in asphalt concrete can enhance the load-bearing capacity while at the same time conserving natural resources, resulting in a sustainable asphalt pavement system. This research evaluated the feasibility of using S to replace natural limestone (L) at various aggregate sizes in asphalt concrete. The measured performance of the L-S asphalt concretes was compared with that of L asphalt concretes and granite (G) asphalt concretes. Two types of asphalt cements, Penetration Grade AC60/70 and polymer-modified asphalt (PMA), were utilized in this research project. The mix proportions were prepared by separating each original aggregate (S, L, and G) into four bins, Bin 1 (<4.75 mm), Bin 2 (<12.50 mm), Bin 3 (<19.00 mm), and Bin 4 (<25.00 mm), and trial mixing them together. Five types of aggregate included L:L:L:L, L:G:G:G, L:S:S:S, L:L:S:S, and L:L:L:S, where the first, second, third, and fourth letters denote the types of aggregates in Bins 1–4, respectively. The asphalt concretes were prepared at 4% air voids using the Marshall compaction method. The performance tests included indirect tensile, fatigue life, resilient modulus, dynamic creep, and wheel tracking tests. S was found to improve the Marshall stability properties of the asphalt concrete by a maximum of 50%. The fatigue life, resilient modulus, and rut depth resistance of the L:S:S:S-AC60/70 were found to be 1.6, 1.4, and 1.4 times higher than that of L:L:L:L-AC60/70, respectively. The fatigue life and resilient modulus values of the L:S:S:S-AC60/70 concrete were found to be close to those of L:L:L:L-PMA concrete. The performance of L:S:S:S-AC60/70 concrete was found to be comparable to that of the costly L:L:L:L-PMA concrete, and had a longer service life than L:L:L:L-AC60/70 concrete with the same thickness. The research outcomes of this study will promote the use of S as a sustainable aggregate for pavement concrete construction.