Effects of cellulose ether and polyvinyl alcohol on hydration and rheology of cementitious tile adhesives

摘要

The present work aims to provide a fundamental understanding of the effects of cellulose ether (CE) and polyvinyl alcohol (PVA) additions on the hydration and rheology of cementitious tile adhesives (CTAs). The first part of the thesis focusses on cement hydration and involves the following three stages.Stage 1: PVAs undergo hydrolysis in wet cement to release acetate groups into pore water solution. This stage, which focussed on the effects of these acetate groups on early cement hydration through the addition of the analogue acetic acid, showed that acetate addition had a mixed effect; the effect was enhanced with increasing acetic acid concentration up to the point at which surface adsorption of acetate reached the saturation level.Stages 2 and 3: Stage 2 focussed on the effects of the degree of hydrolysis (DH) and the degree of polymerisation (DP) of PVA on the kinetics of hydration of Portland cement pastes that were modified by polyvinyl alcohol (PVA) addition. Stage 3 focussed on the effects of the same factors on the kinetics of hydration of Portland cement pastes modified using a mixture of CE and individual PVAs. This work was able to produce a detailed model describing the effects of these factors on the heats of hydration of cement pastes during the first 24 h. Further, the impacts of the DH and DP of PVA on the kinetics of the hydration of C3S were assessed through measurement of the calcium hydroxide contents of cement pastes aged for 24 h.The second part of the thesis focusses on the rheology and involves the following two stages.Stage 1: This stage examined the impact of PVA on the rheology of Portland cement pastes as a function of the content and molecular weight (Mw). The addition of PVA increased the yield stress, shear stress, and viscosity of the cement pastes; these effects were enhanced with increasing contents and Mw of PVA.