Effects of silicon fume and latex on properties and hydration of modified mortars
Polybutadiene-graft-polystyrene (PB-g-PS) latex with a weight ratio of 50/50 was used to modify cement mortar. This study examines the effects of silicon fume content and the polymer-cement ratios (P/C) on the flow, compressive and flexural strength and water absorption rate of PB-g-PS latex modified cement mortar. The experimental results show that the flow of modified mortar is increased with increasing polymer-cement ratios, and it is decreased with increasing silicon fume content, PB-g-PS latex and suitable silicon fume content can markedly reduce capillary water absorption rate. PB-g-PS latex can marked influences much on the mechanical properties of modified mortars. The compressive of the polymer modified mortar decreased, and the flexural strength of a portion of polymer modified mortar increased. The suitble silicon fume can improve mechanical properties of modified mortats. The effect of PB-g-PS latex and silicon fume content on cement hydration was explored by XRD, the analysis results showed that the cement hydration was influenced by silicon fume content and P/C.
Study of cement mortars modified by emulsifier-free latexes
Abstract 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.
Interaction of polymers with portland cement during hydration: A study of the chemistry of the pore solution of polymer-modified cement systems
The mechanism of interaction of polymers with the hydration products of portland cement has been studied. The data were obtained by squeezing the pore solutions from cement pastes with an appropriate pore solution expression device, followed immediately by chemical analyses of the clear solution. Three latexes — a styrene acrylate, a styrene acrylate with a coupling agent, and a polyvinylidene chloride were used for the study. The results show that interaction occurs between the polymers and Ca2+, SO42−, and OH− released by the cement during hydration. The mechanism of interaction between the Ca2+ ions and the acrylic polymers is believed to be initiated by alkaline hydrolysis of the carboxylate groups of these polymers. This reaction, termed ‘saponification’ makes it possible for the carbonyl radicals of the acrylic polymers to ‘catch’ the Ca2+ ions from the liquid phase of the pastes whilst SO42− ions become ‘trapped’ in the latter. With regard to polyvinylidene chloride-modified pastes, the interaction results from dehydrochlorination of the polymer. The ‘catching’ of the Ca2+ ions from solution is believed to involve certain species of the broken-down’ polymer. The study also revealed that dosages of 5% or more of polyvinylidene chloride (v/v of cement composite) could release sufficient Cl− ions to exceed the tolerable corrosion limits in reinforced concrete.