Thermodynamical and Experimental Study of the Effects of Ball Clay-Silica Fume Combination on the Hydration and Strength

The production of ordinary Portland cement (OPC) as the most expensive constituent of concrete is associated with destructive environmental effects and significant energy consumption. Thus, the use of supplementary cementitious materials such as Natural or synthetic pozzolans is a fundamental solution that affects the kinetics of hydration of cementitious materials. In this article, to evaluate the effect of ball clay in the presence or absence of silica fume on the performance of cementitious materials, compressive strength and ultrasonic tests were performed at replacement weight percentages of 0, 10 and 20% for ball clay and 0 and 7% for silica fume. Also, thermodynamic modeling during hydration was carried out based on the Gibbs free energy minimization. The results showed that mere presence of ball clay does not have a positive effect, but it can improve the structure and strength of cement in the presence of silica fume, since it resulted in complete consumption of portlandite and consequently increasing C-S-H gel. In addition to examine the type and volume of phases formed during hydration, the optimum substitution of ball clay and silica fume was studied. Accordingly, the best overall performance of ball clay was observed in the 10% substitution in the presence of 7% silica fume.