Fly ash–limestone ternary cements: effect of component fineness

Composite cements in which the ordinary Portland cement (OPC) is partly replaced by limestone powder and/or siliceous fly ash (FA) at levels up to 35% were studied using three different finenesses for each material. The aim was to evaluate the influence of fineness and replacement level on the development of the compressive strength, the amount of bound water and calcium hydroxide and the heat of hydration of the composite cements. Replacing up to 10% of the fine OPC by fine limestone powder did not impair the compressive strength. Using 5% fine limestone powder instead of 5% fine FA in a cement containing 35% FA resulted, on the other hand, in a considerable strength increase of 13% at 28 days, indicating a synergetic effect between limestone powder and fly ash. The OPC fineness was the major parameter regarding the early hydration. At 28 days the fineness of the fly ash also played an important role due to its contribution to the pozzolanic reaction. Indeed, intensive grinding of the fly ash appeared to render the fly ash more reactive. The fineness of the limestone powder within the tested range (362–812 m²/kg) had no effect on the hydration of the OPC and the composite cement.