Cement equivalence factors for fly ash

Abstract

An investigation has been carried out into the cement equivalence factors for fly ash in concrete. The work was part of a pre-normative research aimed at taking the contribution of fly ash to strength development and the other properties of concrete into account on the minimum cement content and maximum water-cement ratio required to achieve these properties as by the Dutch Concrete Standards. Three cements were studied. These are ordinary Portland cement, rapid hardening Portland cement and Portland blast furnace slag cement. Four fly ashes, including two Low-NO x ashes, were used for the study. Concrete compositions with a range of water-cement ratios, two fly ash-cement ratios, and three curing regimes were studied as functions of concrete compressive strength development. The test results show that the contribution of fly ash to strength is strongly dependent on the water-cement ratio, the type of cement, the fly ash quality, and the concrete age. The equivalence factor increases when the water-cement ratio decreases. This dependance is highest for the rapid hardening Portland cement and lowest for the Portland blast furnace slag cement. For the latter cement the equivalence factor decreases with increasing age, while for the Portland cements investigated the reverse is the case. The period of curing has influence up to a period of 3 days.