Limestone as an accelerator and filler in limestone-substituted alumina cement

The effect of substitution of alumina cement by limestone up to 25% as well as its fineness on the physico-mechanical properties of the hardened cement pastes is studied. The results revealed that the replacement of alumina cement by limestone slightly decreases the water of consistency and the setting times (initial and final). The combined water content increases with the curing time and the fineness of limestone. The total porosity decreases, and accordingly the compressive strength improves with the content and fineness of limestone. Hence, the limestone has a little accelerating action on the hydration process of the alumina cement but acts only as a filler reducing the porosity due to its compact structure. Therefore, the compressive strength of the hardened cement pastes is enhanced. The addition of finely ground limestone filler only up to 15% gives better results on strength. The XRD and DTA analyses of samples cured up to 28 days show that the addition of higher amounts of limestone filler to the aluminous cement tends to decrease the conversion reaction due to the partial carbonation of C3AH6.