Hydration Characteristics of Limestone Filled Cement Pastes

The physico-mechanical properties of hardened limestone-filled cement pastes were studied. Five filled-cements were prepared from 0, 5, 10, 15 and 20 wt. % of limestone and OPC. The water of consistency of filled-cement pastes was 0.275, 0.275, 0.275, 0.272, and 0.270, respectively. The pastes are moulded into one inch cubic moulds and left within the moulds at 100% relative humidity for 24 h, then demoulded and cured under tap water for 3, 7, 28, and 90 days. At each hydration time, the combined water, bulk density, total porosity and compressive strength of the hardened filled-cement pastes were determined. Some selected filled-cement pastes were investigated using differential thermal analysis (DTA) and scanning electron microscope (SEM) Techniques. Addition of limestone to Portland cement causes an increase of hydration at early ages inducing a high early strength, but it can reduce the later strength due to the dilution effect. The results indicate that the addition of limestone up to 5 wt. % improves the physico-mechanical properties of ordinary Portland cement which acts as a nucleating agent and accelerates the hydration of filled cement pastes. The addition of 5 wt. % limestone can be used in the production of portland cement according to the international specifications. On the other side, the addition of 10-20 wt. % limestone can be used in the production of blended or mixed cements