Performance characterization and optimization of cement-lithium powder-grain slag composite cementitious materials

Abstract

In this study, cement, lithium powder and grain slag were selected for compounding design with the aim of developing high performance cement-lithium powder-grain slag composite cementitious materials (CLG). Based on Mixture Design, 13 mixing ratios were designed and used to study the effect of CLG on the workability, mechanical properties, carbonation resistance, and chlorine ion penetration resistance of concrete through response surface plots (3D Plot), and a mathematical model between concrete properties and CLG was fitted. The hydration products and microscopic morphology were investigated using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the single mixing of lithium powder had a positive effect on the 28d compressive strength and carbonation resistance of concrete, but it was unfavorable to the fluidity and chlorine ion penetration resistance of concrete. Single admixture of grain slag has mainly improved the workability of concrete. The highest 28d compressive strength (47.3 MPa) of concrete with excellent workability and durability was achieved when cement, lithium powder and grain slag were compounded in the ratio of 75 %, 20 % and 5 %. Microanalysis showed that the hydration reaction at 28d was higher when lithium powder and grain slag were compounded, producing more hydrated calcium silicate (C-S-H) and enhancing the compactness of the concrete matrix. As a result, the late strength, chloride penetration resistance and carbonation resistance of the concrete were optimized. The results of multi-objective optimization showed that the best overall performance of concrete was obtained with the ratio of cement, lithium powder and grain slag of 79.3 %: 10.3 %: 10.4 %. Therefore, the design method of CLG provides new ideas for the efficient utilization of industrial wastes and the development of other high-performance composite cementitious materials.