Interaction of polymers with portland cement during hydration: A study of the chemistry of the pore solution of polymer-modified cement systems

Abstract

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 Ca 2+, SO 4 2−, and OH − released by the cement during hydration. The mechanism of interaction between the Ca 2+ 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 Ca 2+ ions from the liquid phase of the pastes whilst SO 4 2− 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 Ca 2+ 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.