Recycling of RAP and steel slag aggregates into the warm mix asphalt: A performance evaluation

- RAP improves moisture sensitivity and resilient modulus of WMA mixes.
- No specific trend is detected for influence of steel slag on moisture sensitivity.
- Steel slag improves resilient modulus especially at high temperatures.
- RAP- and/or slag-incorporated mixes have a lower rutting potential.
- Incorporating RAP and/or steel slag into the WMA enhances fatigue resistance.

Incorporation of electric arc furnace (EAF) steel slag aggregates in asphalt mixes boosts their performance, but the high bitumen consumption is the primary obstacle that hinder their widespread application. To remove this barrier this research investigates the effects of concurrent recycling of reclaimed asphalt pavement (RAP) and steel slag aggregates into the warm mix asphalt (WMA) mixes. To this end, six types of WMA asphalt mixes with two coarse steel slag contents (0% and 40%) and three fine RAP contents (0%, 20% and 40%) were prepared and their moisture resistance, resilient modulus, dynamic creep and fatigue behavior were evaluated and statistically were compared to each other. Results showed that contrary to the steel slag, RAP clearly improves resistance to moisture damage of mixes. The addition of RAP to the WMA also increases the resilient modulus at all the temperatures; however, addition of steel slag only at intermediate and high temperatures leads to improvement in the resilient modulus. Nonetheless, sensitivity of resilient modulus to the temperature decreases with incorporation of both marginal materials. Moreover, it is found that adding RAP and/or steel slag significantly improves the number of cycles that the asphalt mix can tolerate in both dynamic creep and indirect tensile fatigue tests (ITFT). In addition, it is demonstrated that the fatigue behavior of RAP- and/or slag-incorporated mixes has a lower sensitivity to stress level, with the exception of mixes containing 40% coarse steel slag along with 40% fine RAP materials. Overall, simultaneous incorporation of steel slag and RAP materials into the WMA is proven to be an economic and environment-friendly option with a comparable or even better performance with respect to conventional WMA.