Use of finely ground fly ash as mineral admixture in blended Portland cement production

Abstract

Fly ash is an active mineral admixture used commonly in the production of blended Portland cement. Fly ash improves many important properties of cement and cement concrete: increasing late compressive strength, increasing sulfate resistance, reducing heat of hydration, reducing alkali-silica reaction and reducing water permeability. However, the current use of original fly ash has a disadvantage that it reduces the early compressive strength of cement, which limits the amount of fly ash blended into the cement. Theoretically, increasing fly ash fineness would increase the reactivity of fly ash. Therefore, the objective of this study was to evaluate the possibility of using finely ground fly ash as a mineral admixture in the production of blended Portland cement through determining the effect of original fly ash (Blaine fineness of 2600 cm²/g) and finely ground fly ash (Blaine fineness of 5000 cm²/g and 6500 cm²/g) on some properties of Portland cement. The investigated cement properties include water of consistency, setting time, and compressive strength at ages of 1, 3, 7, 28 days. The results show that, increasing the fineness of fly ash increased the water of consistency and setting time of the cement, but the increases were small. Increasing the fineness of fly ash significantly increased both early and late compressive strength of the cement. Therefore, finely ground fly ash can be used to minimize the disadvantage of fly ash, thereby allowing the use of higher fly ash content in production blended Portland cement.