Behaviour of Ca(OH)2 in polymer modified mortars

Abstract

This paper deals with the effect of polymer modification on the behaviour of Ca(OH)₂ in modified mortars. The polymer modified mortars were prepared using powdered emulsions and aqueous polymer dispersons at various polymer-cement ratios; they were then tested for air content, moulded into specimens and cured. The cured specimens were tested for compressive strength. The fine powder samples obtained from broken specimens were subjected to X-ray diffraction, differential thermal analysis and thermogravimetric analysis. From the test results, it is concluded that formation of Ca(OH)₂ in the polymer modified mortars is reduced possibly because of the absorption of Ca(OH)₂ on polymer films formed in the mortars. The extent of reduction in the quantity of Ca(OH)₂ depends upon the polymer-cement ratio, polymer type or both. Generally powdered poly(vinyl acetate-vinyl carboxylate), poly(ethylene-vinyl acetate) emulsions and aqueous poly(ethylene-vinyl acetate) emulsion were found to be more effective than styrene butadiene rubber latex in reducing the quantity of Ca(OH)₂ in the modified mortars. The cement modifiers did not cause any detrimental effect on the degree of hydration as indicated by their higher compressive strength. Estimation of the quantity of Ca(OH)₂ in the polymer modified mortars therefore, does not provide a proper means for predicting their degree of hydration.