Oil shale waste (OSW), as fine aggregate in the mixture (particle size less than 4.75 mm), can effectively improve the overall properties of open grade friction course (OGFC), but the reinforcement mechanism is not clear. Thus, a comprehensive investigation of the reinforcement mechanism of OSW as fine aggregate is essential to provide better understanding for promoting its engineering application. In this paper, the reinforcement mechanism of OSW was explored through numerical calculations and laboratory tests from three aspects: macroscopic mechanical characteristics of mixture, micromechanics of asphalt mortar containing OSW filler, and adsorption characteristics of OSW. Numerical simulation results showed that the aggregate with a particle size greater than 4.75 mm in OGFC is the skeleton, which is the main loading bearing aggregate, and the skeleton bears more than 85% of external loads. The beam bending test and indirect tensile test results illustrated that the introduction of OSW improves the shear resistance and flexure-tension resistance properties of asphalt mortar, which is beneficial the overall properties of OGFC. From the Brunauer Emmett Tell test and Scanning Electron Microscope test, it was known that OSW has large specific surface area, dense pore structure, and various mesoporous shapes, which means a larger adsorption area and stronger adsorption with asphalt binder. Three self-developed tests containing asphalt adsorption capacity test, infiltrated asphalt saturation test and aggregate-bitumen interface observation test manifested that the existence of “claws”-pointed synapses at OSW-bitumen interface is the main reason for the significant improvement of properties of asphalt mortar containing OSW filler.
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