Coal gangue based geopolymer as an additive of warm mix asphalt: preparation and properties

Abstract In contrast to conventional hot mix asphalt technology (HMA), warm mix asphalt technology (WMA) permits the mixing and compaction of asphalt mixture at lower temperatures. This innovative approach is characterized by significant energy savings and reduced emissions, making it a sustainable choice for asphalt mixture production. This paper used coal gangue to prepare a WMA additive. By leveraging the free water in its zeolite-like structure, which evaporates upon heating, bubbles form within the bitumen. This causes bitumen to expand and lose viscosity, thereby achieving the purpose of warm mixing. Both achieve a decline in the asphalt mixture’s mixing temperature and provide an effective method for utilizing coal gangue resources. It helps mitigate the environmental hazards associated with the massive accumulation of coal gangue, including soil contamination and water resource pollution. Therefore, based on alkali activation theory, this paper aimed to develop a novel coal gangue geopolymer (CG) WMA additive. CG was characterized through microscopic testing and analysis of water storage stability. The impact of varying CG dosages on the conventional performance of bitumen was examined. The bitumen foaming test elucidated the warm mixing mechanism and foaming behavior of the CG. Additionally, the road performance of the WMA was analyzed. The findings indicate that CG has abundant pore structures, providing an effective water storage space, and CG as a WMA additive exhibits good water storage stability at ambient temperature. When the CG dosage is 5% by the mass of bitumen, the viscosity of bitumen at 130∼140 °C is appropriate, and the WMA results in good road performance. Compared with HMA, the mixing temperature is reduced by a range of 20∼50 °C.