Title: Nonevaporable Water and Degree of Cement Hydration in Silica Fume-Cement Systems
Author(s): E. H. Atlassi
Publication: Symposium Paper
Appears on pages(s): 703-718
Keywords: hydration; pozzolans; silica fume; water of hydration; Materials Research
The most common way of estimating the degree of hydration of cement in practice has been to measure the Nonevaporable water content (W n) using the relation W n = 0.25 * C. However, when silica fume is incorporated in a mixture, some of the nonevaporable water is converted to evaporable water. More specifically, the water originally bound in the Ca(OH) 2, which reacts with the amorphous silica, is released in a polymerization process. This was shown in a study of mature cement-silica fume systems in which a new quantitative thermogravimetric method was used. Thus, for the same degree of hydration of the cement, the total nonevaporable water content is lower in a mixture with reacted silica fume than in one without. Moreover, the degree of hydration of the cement is slightly increased when moderate amounts of silica fume are added, provided sufficient water is present in the pore system, either by water curing or a high initial water-cement ratio. In mixtures with low w/c, the faster self-desiccation and the reduced permeability caused by silica additions affect the moisture state in a larger specimen (even if it is water cured) and, consequently, the degree of hydration of the cement.