Evidences of chemical interaction between EVA and hydrating Portland cement

In spite of the widespread use of ethylene/vinyl acetate copolymer (EVA) in mortar and concrete production, there is no agreement among various researchers about the kind of interaction that is developed between cement and polymeric phases. Therefore, the adoption of adequate measures for Final product quality achievement is impaired, as well as the adjustment of their properties to the desired performance. The purpose of this research is to fill this lack of knowledge through the microstructural characterization of cement pastes modified with EVA copolymer. Portland cement pastes were prepared with different EVA contents. The water/cement ratio was kept constant. The pastes were submitted to two different curing conditions, and analyzed at 28 days old. Thermal analyses (differential thermal analysis [DTA] and thermogravimetric [TG] analysis), Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) tests were performed, which permitted the evaluation of the EVA effects on the cement hydration. Some evidences of chemical interactions between cementitious and polymeric phases were identified. The results showed that the acetate groups of EVA copolymer undergo alkaline hydrolysis and interact with Ca2+ ions of the pastes to form an organic salt (calcium acetate). The calcium hydroxide content is decreased, the ettringite crystals appear to be well formed and many Hadley's grains were observed. A calcium-rich, porous and hexagonal structure phase was detected, probably due to acetic acid attack on calcium hydroxide crystals. (C) 2002 Elsevier Science Ltd. All rights reserved.