Study on frost resistance and deterioration law of manufactured sand coal gangue concrete

Abstract

Coal gangue is one of the largest industrial solid wastes produced and discharged in China. The coal gangue manufactured sand made by crushing and screening can not only alleviate the shortage of natural sand resources, but also reduce the environmental pollution caused by gangue discharge. In view of the characteristics that coal mines in China are mainly distributed in cold areas, this study configured manufactured sand coal gangue concrete with different coal gangue manufactured sand replacement rates (0 %, 20 %, 40 %, 60 %, 80 %, 100 %). The mechanical properties of structures and the deterioration mechanism under freeze-thaw cycles were analyzed by macro and micro test methods. The results show that with the increase of coal gangue manufactured sand replacement rate, the mechanical properties and frost resistance of structures decrease. When coal gangue manufactured sand replacement rate is 100 %, the compressive strength, splitting tensile strength, flexural strength decrease by 18.1 %, 22.4 % and 28.7 %, respectively, and the frost resistance is the worst. When the coal gangue manufactured sand content is less than 40 %, the mechanical properties of structures are superior, and the damage degree before and after F-T is small. Compared with the unreplaced, the proportion of the harmful pores decreased by 3.9 % and 3.3 % respectively when the coal gangue manufactured sand replacement rate was 20 % and 40 %, and the proportion of the harmless pores increased by 10.4 % and 2.8 %. At this moment, the secondary hydration of coal gangue manufactured sand and coal gangue optimizes the aggregate gradation and pore structure, enhances the interfacial transition zone, and improves the frost resistance of structures. The damage of structures is due to the initial defects of interfacial transition zone, and the frost heaving stress further leads to the deterioration of interfacial transition zone structure and the stripping of aggregate-mortar, resulting in the degradation of macro performance. Finally, the structures damage evolution equation under different coal gangue manufactured sand replacement rates was established by the two-parameter Weibull probability distribution model. This study provides reference and guidance for the popularization and application of manufactured sand coal gangue concrete in cold areas.