Evaluating Influences of Alkali-Activated Slag Filler on the Engineering Properties of Asphalt Concrete Using Monotonic Indirect Tensile Tests

The search for alternatives to filler used in asphalt pavement has been focused on recently due to the lack of traditional materials sources and the aim of sustainable development goals. Novel environmental protection material—alkali-activated slag (AAS) with a prospective substitution for cementitious binder—has been developed widely; however, the possibility of application of AAS in practice is still under investigation, and hence, mass production of AAS for the testing phase generates significant quantities of solid laboratory waste materials. This study paved the way for safe disposal and evaluating the potential of utilizing AAS as filler in asphalt concrete mixes. To understand the influence of filler types on the performance of asphalt concrete, the physical and chemical properties of AAS filler were analyzed and compared to the conventional limestone (LS) filler by applying laser particle size analysis, scanning electron microscope (SEM), x-ray diffraction (XRD) analysis, and x-ray fluorescence (XRF) spectrometry. The monotonic indirect tensile test (IDT) was adopted to characterize the behavior of asphalt mixes over a range of performances at low, intermediate, and high temperatures; additionally, to practice the balanced mix design (BMD) into quality assurance (QA) of asphalt mixes. Testing methods involving monotonic IDT used in this study are indirect tensile strength (ITS), indirect tensile asphalt cracking test (IDEAL-CT), toughness index (TI) and fatigue index (fi), low-temperature IDT, high-temperature indirect tension (HT-IDT), and moisture susceptibility test. The results indicated that asphalt concrete using AAS filler delivers superior engineering performance, such as resistance to cracking, rutting, and moisture damage, compared to the one made with LS filler. This supports the use of AAS filler as a potential substitution for LS filler in the production of asphalt concrete. Besides, the practice of BMD by implementing monotonic IDT for QA of asphalt mixes showed high feasibility.