Rheology of cement paste: Role of excess water to solid surface area ratio

Although many attempts have been made in previous research to identify the various parameters governing the rheology of cement paste, there has been little progress in evaluating the combined effects of these parameters. In this paper, a new parameter, the excess water to solid surface area ratio, is proposed to evaluate the combined effects of water content, packing density, and solid surface area on the theological properties of cement paste. For the purpose of determining the value of this new parameter, a new wet packing method has been developed to measure the packing density of cementitious materials so that the voids content of the cementitious materials and the amount of excess water in the cement paste can be quantified. A number of cement paste samples containing different proportions of cement, pulverized fuel ash and condensed silica fume, and different water contents have been tested and their theological properties, as measured by a rheometer, correlated to the new parameter. The correlation revealed that the excess water to solid surface area ratio, which serves as an indicative measure of the average water film thickness, is the single most important factor governing the rheology of cement paste.