Characteristics of Alkali-Activated Slag Filler and Its Effects on Rheology of Asphalt Mastic

Attributes of filler play a significant role in the overall performance of asphalt mixtures through their direct influences on asphalt mastic. Alkali-activated slag (AAS), which is currently in the beta stage of development, is a promising and innovative cementitious replacement material. However, mass production AAS for experimental use generates significant quantities of waste discharge. The purpose of this study was to explore the potential of using AAS waste as a mineral filler in asphalt mastic. Properties of AAS waste were assessed and compared to limestone (LS) filler using scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, X-ray fluorescence (XRF) spectrometry, laser particle size analysis, hydrophilic coefficient, mesoscopic void characteristic, and Rigden void tests. The penetration, softening point, Brookfield viscosity, and rheological properties of the asphalt mastic samples made, respectively, using AAS and LS fillers, were examined using complex modulus (G*), phase angle (delta), and rutting factor (G*/sin delta) results and two interaction indices (delta G* and K-B-G*). Furthermore, models used to test relative viscosity (eta(r)) were applied to predict the complex viscosity (eta*) of the samples. Results indicated that comparing to LS filler, AAS filler was shown to deliver superior compatibility to asphalt matrix, and the properties of the asphalt mastic containing AAS filler were superior to those of the asphalt mastic containing LS filler. Of particular note, the models used to predict relative viscosity demonstrated validity in predicting the complex viscosity of asphalt mastics. The results support using AAS filler as a replacement for LS filler in asphalt mastic. Further research should be conducted to maximize the potential benefits of using AAS filler in asphalt mixtures.