Effects of packing density, excess water and solid surface area on flowability of cement paste

Abstract

Although it has been postulated for many years that it is excess water rather than whole water that lubricates the cementitious materials and governs flowability of paste (excess water is water in excess of that needed to fill up voids), there has been no detailed investigations to study the actual effects of excess water. This was due to the lack of a suitable method for measuring the packing density and voids content of cementitious materials. To resolve the problem, the authors have recently developed a new wet packing method that was applied herein to measure the packing densities and voids contents of cementitious materials containing different amounts of cement, pulverised fuel ash and condensed silica fume. The flowability properties of the paste formed of the cementitious materials with different water contents were also measured and correlated to the excess water contents, each determined as water content minus voids content. The results revealed that whereas an improvement in packing density would increase excess water content, flowability is governed mainly by excess water to solid volume and excess water to solid surface area ratios.