A method for predicting alkazi ion concentrations in cement pore solutions

Abstract

Synopsis A method is described for predicting the sodium, potassium and hydroxyl ion concentrations in the pore solutions ofhydrated OPC or Portland-pfa (pulverized-fuel ash, fly ash) concretes, mortars or pastes more than about 1 day old. The minimum data required are the total Na 2 O and total K 2 O contents of the Portland cement component and of the pfa, if present, the relative amounts of Portland cement, pfa and water, and the age. Other data, especially the contents of water-soluble Na 2 O and K 2 O in the cement and pfa, may be introduced with advantage. The calculation, which rests on the principle of mass balance combined with empirical equations and constants to represent kinetics and equilibria, may be carried out on a microcomputer. The validity of the results is tested by comparing calculated and observed concentrations for all the cases in which the relevant experimental data were available. Some aspects of the chemistry underlying the method are discussed.