Reusing waste coal gangue to improve the dispersivity and mechanical properties of dispersive soil

The disposal of waste coal gangue (WCG) is still a serious problem for areas that rely on the coal mine industry, especially in the northern part of China. This paper investigated the improving behavior and corresponding mechanism by waste coal gangue on the dispersivity, water stability and mechanical properties of dispersive soil. Dispersive soil samples with different contents of natural waste coal gangue, varying from 1% to 10%, were prepared and cured for 0, 1, 3, 7, 14 and 28 days. Dispersivity and water stability of soil samples were evaluated by pinhole test, cube sample crumb test and remoulded sphere sample crumb test. Electric conductivity and pH of soil samples were monitored during 28 days of curing. Unconfined compression test and splitting test were performed to determine the compressive and tensile strength of soil samples. Microstructural and mineral analysis methods such as SEM, EDS and XRD were conducted to determine the microstructural and mineral changes during curing time. Experiments show that waste coal gangue could restrain the dispersivity and enhance the water stability of dispersive soil, subsequently changing dispersive soil into nondispersive soil. Increases of 591% and 192% are observed when WCG content increases from 1% to 10% and curing time increases from 0 to 28 days for compressive and tensile strength, respectively. Increasing in waste coal gangue content and curing time would better promote the positive effect of waste coal gangue, on both the dispersivity modification and strength improvement of dispersive soil. Microstructural and mineral analyses show that newly generated products among soil particles increase the friction and cohesion between soil particles. Results indicate that reusing of waste coal gangue as an admixture in dispersive soil is a feasible way, which would solve the disposal of waste coal gangue and optimize the poor properties of dispersive soil at the same time. Enhancing water stability of dispersivity soil would ensure the safety and normal operation of soil structures.