Evaluation of a Warm Mix Asphalt Using a Blast Furnace Slag Treated with a Portland Cement

Abstract

Hot-mix asphalts (HMA) have limitations that are mainly related to environmental aspects: they use large amounts of natural origin aggregates (NA) and high manufacturing temperatures. There is a waste material obtained in the steel industry that could be useful for replacing NAs in HMAs, namely, blast furnace slag (BFS). Likewise, BFS can improve its performance (reducing its porosity and absorption) if it is previously treated with chemical additives that are compatible with asphalt such as Portland Cement (PC). On the other hand, manufacturing temperatures can be reduced by applying similar techniques to those developed for warm mix asphalts (WMA). This study replaced within HMA part of the NA by mass with blast furnace slag (BFS) (12.5%, 21% y 43%) that was previously treated with PC paste (BFS-PC). Likewise, the base asphalt was modified with a chemical additive called HUSIL, which foams the asphalt at 80°C, with the purpose of achieving a reduction in manufacturing temperature. All of this was done with the purpose of attempting to produce a more environmentally friendly asphalt mixture. A secondary objective was to avoid increasing the cost of HMA by using the same optimal asphalt content (OAC) in the control mix when substitutions were carried out. Because of these reasons, all mixes maintained a constant OAC. In order to evaluate the mix performance, their resistance under monotonic load was measured (Marshall and Indirect Tensile Strength – ITS) as well as moisture damage resistance (using Tensile Strength Ratio – TSR) and abrasion (Cantabro Test). As a general conclusion obtained, when substituting 21% of NA by mass (sieves ½”+3/4”) with BFS-PC and HUSIL modified asphalt is used, the mix manufacturing temperature can be reduced by 25°C, attaining an asphalt mixture with a better performance in all the evaluated properties, when compared to the control HMA.