Effect of calcium sulfate type and dosage on properties of calcium aluminate cement-based self-leveling mortar

In this paper, the influence of calcium sulfate type (α-hemihydrate, anhydrite and dihydrate) and amount (0%, 2%, 4% and 6%) on the performances of calcium aluminate cement-based self-leveling mortar (SLM) were investigated. The influence of calcium sulfate on fluidity and mechanical properties was investigated. Moreover, the impact of calcium sulfate on the hydration products, morphology and heat evolution of pastes hydrated up to 3 days were determined by using X-ray diffraction (XRD), Scanning electron microscope (SEM) and isothermal heat-conduction calorimeter. Test results revealed that SLM prepared with anhydrite exhibited the highest initial flow value (∼160 mm) and setting time and the lowest fluidity loss due to the slow dissolution rate of anhydrite compared to other calcium sulfate. In comparison to control formulation, the enhancement in flexural and compressive strength for T4 (dihydrate) was the highest and was found to be 485.71% and 437.5% respectively and hence it can be concluded that dihydrate is favorable to the early strength of SLM as compared to other SLM formulations containing α-hemihydrate and anhydrite respectively. The shrinkage compensating effect became more obvious with the increase in the amount of C$ in SLM samples. Due to the fast dissolution rate, mortar containing α-hemihydrate exhibited more expansion as compared to other calcium sulfate. SLM prepared with dihydrate showed the highest early strength due to the lowest influence on C₃S hydration while the influence of α-hemihydrate was more obvious. Hence, the hydration of PC in the ternary system can be limited by increasing calcium sulfate due to the formation of ettringite. Finally, the type of calcium sulfate has an important influence on the quantity and morphology of ettringite.