Study of cement mortars modified by emulsifier-free latexes

Cationic copolymer latex of vinyl acetate (VA) with methacryloxyethyl trimethylammonium chloride (MTC) and anionic copolymer latex of VA with sodium acrylate (SA) were prepared via emulsifier-free emulsion copolymerization. Modifications of cement mortars by these copolymer latexes were studied, and the results were compared with mortars modified by homopolymer of VA (PVA) as well as with blank mortars. The experimental results showed that flow of the mortars modified by PVA homopolymer and P(VA-MTC) copolymer latexes were increased compared with the blank, whereas a decrease was observed for that modified by P(VA-SA) anionic copolymer latex; a volume expansion was detected in polymer modified mortars by PVA and P(VA-MTC), while no volume expansion was observed in the anionic P(VA-SA) modified mortars; the flexural strength of mortars modified by P(VA-MTC) increased by 79.5% compared to unmodified mortars after 5 day water curing plus 21 day air curing. This value reached 95% when the curing process was followed by a supplementary 24 h vacuum curing. These polymer modified mortars were then subjected to hydration analysis through X-Ray diffraction (XRD). Mechanisms of the mortar modification are discussed based on the characterization results.