Potential Use of Industrial Byproduct-Based Geopolymers in Asphalt Binders

Asphalt binder modification is a viable option to overcome the pavement performance problems, but the most commonly used commercial asphalt modifiers are expensive and non-eco-friendly materials. Globally many industrial by-products and waste materials are produced annually and disposed of in landfills increasing the pressure on our environment and leading to many environmental challenges such as climate change. The objective of this study is to investigate the potential of the incorporation of geopolymers, based on industrial by-products, in asphalt binders. Geopolymers based on two industrial by-products, namely fly ash (FA) and metakaolin-silica fume (MK-SF), were prepared in the laboratory. The binder was modified with 0, 4, 8, and 12% by weight of the binder. The effect of geopolymer type, composition, and curing time, within the binder, on binder behavior was studied in terms of rutting (G*/sin δ), fatigue cracking (G*sin δ), thermal cracking and aging potentials (ΔT_c). Asphalt binder short-term and long-term aging was simulated in the laboratory using the Rolling Thin Film Oven Test (RTFO) and the Pressure Aging Vessel (PAV), respectively. Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) were used to study the geopolymer-modified asphalt (GMA) performance. Results showed that GMA had higher viscosity (but still meeting the workability requirements), higher G*/sin δ, lower G* sin δ, and less ΔT_c than the virgin (unmodified) asphalt binder indicating an enhancement in terms of rutting, fatigue cracking and a compromised thermal cracking and aging resistance. The two optimum geopolymer-modified asphalt binders were 12% FA GMA of (PG76-28) and the 4% MK-SF GMA of (PG70-28) in reference to virgin (unmodified) asphalt binder of (PG58-22). Hence, GMA met the regional Superpave PG requirements whereas the unmodified asphalt binder failed to meet this specification of PG (70-10). The duration of geopolymer curing within the asphalt binder was observed to have a significant impact on the resulting GMA concerning both rutting resistance and thermal cracking behavior. Consequently, geopolymers, prepared using industrial by-products, gave initially promising results to modify the asphalt binder which can pave the way for further investigations.