AMOUNT OF WATER REQUIRED FOR COMPLETE HYDRATION OF PORTLAND CEMENT

Abstract

This point-of-view article discusses the amount of water that would be needed to completely hydrate portland cement. The ratio of the volume of water to the volume of cement is critical in the chemical reaction that causes concrete to stiffen, harden and develop strength. There is a misconception that it takes only the amount of water in a 0.2-water/cement (w/c) paste to hydrate all of its cement. However, for a given volume of cement to hydrate completely, there must be an amount of original mixing-water-filled space equal to 1.2 times the solid volume of the cement. This is because the hydration product has approximately 30% pore space that must be present, and water must be available to fill it. Not all of the cement can hydrate if the amount of original mixing water-filled space is less than that provided at a w/c of approximately 0.4, even though only half of the water will go into chemical combination. An analysis of data from 1948 and 1994 confirms that it takes approximately w/c = .04 to provide all of the hydroxide required to hydrate all of the reacting bits of a portland cement and also fill the gel pores.