Effect of Different Fillers on Performance Properties of Asphalt Emulsion Mixture

The objective of this study is to evaluate the effect of different fillers on the performance properties of asphalt emulsion mixtures (AEM). Six types of fillers were used, including limestone filler (LF), hydrated lime (HL), fly ash (FL), slag powder (SG), composite Portland cement (CPC), and ordinary Portland cement (OPC). The AEM design was conducted using a two-stage process to allow for determination of the optimum water content (OWC) and optimum emulsion content (OEC). The effect of the fillers on the mixture performance was evaluated based on moisture susceptibility as measured by the indirect tensile test and rutting resistance measured by loaded wheel testing. To better understand observed differences in performance, the environmental scanning electron microscope (ESEM) was used to obtain the microstructure of different filler-emulsion combinations. Test results indicate that the physical and chemical properties of fillers significantly affect both mixture design and performance. Furthermore, the most effective fillers are found to be materials that include cement or hydrated lime as the reaction between these materials, and the water in the emulsion has a reinforcing effect on binding the aggregates together. Conversely, with replacement of a portion of the limestone filler with fly ash or slag powder, no effects on moisture susceptibility or rutting resistance relative to the control mix were observed. ESEM images confirmed that hydration products are formed when the water in the emulsion reacts with cement or slag, causing the increase in performance properties. The proposed mechanisms by which the hydration reaction improves performance include increasing the degree of compaction and rigidity of AEM as well as increasing the strength of the adhesive bond at the asphalt emulsion aggregate. Based on the findings of this study, it is recommended that filler chemical and physical properties should be used to select materials most appropriate for use in AEM.