Prevention of air void formation in polymer-modified cement mortar by pre-wetting

The air voids that form when cement and aggregates are mixed with an aqueous polymer solution are not easily removed because they tend to be stabilized by the polymer. Antifoaming agents can be used to prevent air void formation, but they often cause problems of poor adhesion. An alternative approach is suggested for reducing air void formation in polymer-modified mortar, which is to pre-wet the cement and sand with water, and then add a concentrated polymer solution. The air content of a PVA-modified cement mortar prepared in this way was as low as 6%, which was lower than the 13% air content of the PVA-modified mortar with an antifoaming agent, and it was much lower than the 32% air content when a PVA solution was mixed with dry cement and sand. (C) 1997 Elsevier Science Ltd.