Foamed warm mix asphalt mixture containing crumb rubber: Foaming optimization and performance evaluation

To address global concerns of global warming, environmental pollution, and rapid urban growth associated with the development of transportation infrastructure and the increasing accumulation of waste tires, warm mix asphalt and crumb rubber modified asphalt have been proposed as green technologies for environmentally-friendly pavement. However, limited research has devoted to the behaviors of the foamed warm mix asphalt with crumb rubber (FWMA-CR). This study aims to investigating the foaming condition of the FWMA-CR binder and evaluating performance of both FWMA-CR binder and mixture. It is recommended to fabricate the FWMA-CR binder at foaming temperature of 160 °C, water content of 2.0%, and air pressure of 0.70 MPa, achieving desirable foaming characteristics of expansion ratio, half-life, and foaming index. The manufacturing temperature of the FWMA-CR mixture is remarkably dropped by 17 °C in comparison with that of the hot mix asphalt mixture with crumb rubber (HMA-CR). It has also explored that the performance of the FWMA-CR binder is consistent with that of the mixture. The foamed rubberized asphalt binder and mixture exhibit better low-temperature performance and fatigue resistance, while present inferior high-performance performance in comparison with conventional rubberized asphalt binder and mixture. The statistical analysis verifies that the foaming imposes no significant impact on performance of rubberized asphalt. The environmental and economic analysis reveals that compared to hot mix asphalt mixture with crumb rubber, the production of the FWMA-CR mixture contributes to approximate 7.4% of energy saving, 0.78 $ of cost saving, and reduction of CO₂ emission by 7.2% per 1 ton of mixture. The outcomes facilitate the production and usage of the foamed warm mix asphalt with crumb rubber.