Mechanical properties and drying shrinkage of graphite tailing-basalt fiber cement mortar

Abstract

By replacing part of standard sand with graphite tailings (GT) and adding green basalt fibers (BF) together to prepare cement mortar, it could effectively alleviate the environmental problems caused by the massive discharge of tailings and the shortage of resources caused by the massive use of natural river sand. In this study, graphite tailings and basalt fibers were added to cement mortar, and the impact of mixing GT and BF fibers on the mechanical characteristics and drying shrinkage properties of cement mortar were analysed through experimental studies. The hydration of cement mortar was investigated by using techniques such as energy spectroscopy (EDS), differential thermogravimetric analysis (DTG-TG), electron microscopy (BSEM, SEM), and x-ray diffraction (XRD). And the microstructures of the matrix, fiber, and fiber–matrix interface underwent evaluation. The findings demonstrated that the cement mortar with a 20 % GT substitution rate and 0.1 % BF by volume admixture was the most optimized combination, and the compressive strength and flexural strength at an estimated 28 days of curing time were improved the most, by 13.89 % and 14.08 %, respectively. And the early drying shrinkage performance could be improved more substantially; the drying shrinkage at the age of 7 days was 54 % that of cementitious sand. According to the microscopic test results, it was known that GT would adversely affect cement hydration due to higher sulphide levels, but it had a pozzolanic effect. The appropriate amount of GT could give full play to the pozzolanic effect, reduce the porosity of cement mortar and lower the Ca/Si value within the matrix–matrix fiber interface transitional region, improve the adverse effect of its sulphide on cement mortar, and help improve the mechanical and crack-resisting properties of cement mortar.