Comparative study on mechanical and environmental properties of coal gangue sand concrete

To reduce the adverse impact of coal gangue heaping and save natural resource, artificial coal gangue sands are utilized as fine aggregates in the concrete preparation. The mechanical and environmental properties of coal gangue sand concrete were studied experimentally and theoretically by considering concrete strength grades (C30, C50) and replacement ratios (0, 25%, 50%, 75%, 100%). The results show that coal gangue sand will weaken the adhesion performance of the transition zone between cement mortar and coarse aggregate. The elastic modulus and axial compressive strength of coal gangue sand concrete were decreased by increasing the replacement ratio regardless of concrete grade. When the replacement ratio is 100%, the elastic modulus and axial compressive strength of C30-grade concrete were reduced by 2.9% and 12.6% respectively whilst the values of C50-grade concrete were 5.0% and 21.5% respectively. Based on the tested results, the prediction formulas of the mechanical properties and the uniaxial compressive stress–strain model of the coal gangue sand concrete under different replacement ratio are proposed. Through life cycle assessment, it is found that the replacement ratio of the coal gangue sand is negatively correlated with environmental impact and willingness to pay (considering transport cost), and positively correlated with willingness to pay (without considering transport cost). The balance point is defined by the environmental influence of coal gangue sand concrete when the willingness to pay (considering transport cost) of coal gangue sand concrete under different replacement ratio is equal. According to the tested results, the prediction formula of the balance point under different transport distance is proposed. When the consistent transportation distance of gangue sand and natural sand exceeds 140 km, the utilization of coal gangue sand can produce good environmental benefits.