THE COMPRESSIVE STRENGTH OF STRUCTURAL FLY-ASH CONCRETE

In this paper, an adaptation of a previous model (generalized Feret's law, taking account of maximum paste thickness) for structural fly ash concrete is presented, beginning with an equation for the 28 day compressive strength of Portland cement concretes. A kinetics term is introduced to predict the strength development between 7 and 365 days. Then, an equivalent cement dosage is defined, by considering the fly ash as a silica fume of lower quality. The cementing efficiency of the fly ash at each age is described by a further coefficient. Then, the model is calibrated using published data, a set of 26 mixtures with w/c ranging from 0.31 to 0.66 and fly ash replacement from 0 to 30%. The mean accuracy of the model (on 156 results) is equal to 2.1 MPa. The formulae incorporate a limited number of parameters that can be determined easily from standard mortar or concrete tests. Therefore, the model appears to be suitable for computer-aided concrete mixture proportioning software.