Physicochemical studies on single and combined effects of latex and superplasticiser on portland cement mortar

Abstract

This article reports on the compressive strength, rate of hydration at 3, 7, 28 and 90 days; by thermogravimetry (TG), differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) of unmodified, latex-modified, superplasticiser-modified, and superplasticised latex-modified mortars. Two commercial superplasticisers and three copolymer type latexes (selected from an earlier compatibility study) have been used with a uniform flow range. It has been observed that addition of superplasticiser in three latexes had increased both the rate of hydration and the compressive strength up to 28 days. Formation of a comparatively lower quantity of Ca(OH) 2 was observed at a higher latex content. The addition of superplasticiser in a latex-modified mortar further reduced the quantity of Ca(OH) 2. This was confirmed by both XRD and DSC observations. In all modified samples the peak temperature for Ca(OH) 2 decomposition was at least equal to or higher than the unmodified one. Appearance of two maxima for exotherm of latex in superplasticised latex-modified mortar was indicative of a possible change in emulsion character in the presence superplasticiser. MIP revealed that addition of latex caused the pore size distribution to become more even in character. The presence of superplasticiser in latex-modified mortar reduced the total pore volume significantly.