New Admixture for Foamed Warm Mix Asphalt: A Comparative Study

Abstract

Construction of flexible pavements with hot mix asphalt (HMA) consumes a huge amount of energy, which exhausts the resources and impacts the environment. Warm mix asphalt (WMA) has advantages over HMA in terms of mixing and compaction temperature reduction, which saves energy and money and reduces pollution. Foaming of asphalt using aspha-min is the most common manner to produce WMA. However, using this additive involves additional production costs. Therefore, providing an economical alternative capable of performing a similar role without affecting the properties of the asphalt mixture is in high demand. This paper covers the adoption of Alum as a new alternative to traditional additives in this domain. A comparative study was performed between HMA, WMA produced with aspha-min, and WMA produced with Alum to evaluate its effects on asphalt viscosity at mixing and compaction temperatures and on mixture properties using Marshal method, track wheel rut depth test, and indirect tensile strength test (ITS) under dry and saturated conditions as well as tensile strength ratio (TSR). The results exhibited that Alum is capable of reducing mixing and compaction temperatures by average values of 25.5 °C and 20 °C, respectively. These reduction values are higher than those attained by aspha-min (20 °C for mixing and 18.5 °C for compaction). Hence, Alum can reduce about 5.5 °C more than aspha-min can do. In addition, the engineering properties of the three mixes mentioned above were investigated according to Marshall method. The results expressed that Alum has advantages over aspha-min in terms of density, stability, and stiffness. In comparison with the control mixture, the mixture produced using Alum exhibited density, stability, and stiffness results represent 99.7%, 95.9% and 94% respectively, whereas the comparable values of the mixture modified with aspha-min represented 99.3%, 93.8%, and 85% respectively. In addition, WMA produced with Alum exhibited rutting susceptibility less than that of WMA produced with aspha-min. The final rut depth values (after 20,000 wheel passes) for HMA, WMA produced with Alum, and WMA produced with aspha-min were 7.9 mm, 9.7 mm, and 10.2 mm, respectively. The rut depth value of WMA produced with Alum is higher than that of HMA and lower than that of WMA produced with aspha-min. These results reveal the capability of WMA produced with Alum to control thermal cracking due to its flexibility and to resist distortions due to its stability. Moreover, WMA produced with Alum exhibited ITS values in dry and saturated condition and TSR values higher than those in the case of WMA produced with aspha-min. Therefore, Alum can be adopted as a new effective alternative for traditional additives in the domain of the study.