Optimizing steel slag and reclaimed asphalt incorporation in hot mix asphalt: From lab validation to full-scale application towards circular economy

Abstract

The transition towards a circular economy in road construction requires maximizing the use of alternative materials to reduce reliance on natural resources and minimize environmental impacts. This study develops and validates an innovative Hot Recycled Mix Asphalt (HRMA) incorporating Steel Slag Aggregates (SSA) and Reclaimed Asphalt (RA), significantly reducing the need for natural aggregates and virgin binder. The goal was to achieve over 75 % replacement of raw materials while ensuring high mechanical performance and industrial-scale feasibility. A recycled asphalt mixture for the binder course was validated in the laboratory, produced in an industrial asphalt plant, and applied in a full-scale road trial. The methodology included material characterization, volumetric and mechanical performance tests, and field validation. Results demonstrate that HRMA outperforms an equivalent conventional hot mix asphalt with natural aggregates, showing higher rutting resistance, improved durability, and comparable fatigue performance. The successful full-scale implementation confirms that high SSA and RA contents can be used without compromising quality. The viability of this solution is further supported by a material circularity indicator (MCI) of 0.84, a 25 % cost reduction per kilometer, and a composite circularity index (CCI) of 0.73 proposed to integrate the previous dimensions. These findings reinforce the relevance of circular economy principles in pavement engineering, promoting resource efficiency and sustainable road construction.