Study of the influence of defoamers on the main properties of plasticized cement paste

The use of self-compacting concretes has become widespread in recent years. To achieve high flowability in mixtures, highly effective polycarboxylate based plasticizers are used. However, the use of superplasticizers in self-compacting concrete mixes without adding a defoamer can lead to a well-known problem: increased air entrainment and the formation of air bubbles. This can cause deterioration in the surface appearance. This article presents studies on the effects of various defoaming agents and air-entraining additives on the basic technological and rheological properties of plasticized by polycarboxylate plasticizers cement pastes, made from a blended binder which includes Portland cement and a microfiller based on ground blast-furnace granulated slag, in proportions of 25% and 40% respectively. The aim of this study was to investigate the spread diameter, expiration time, and dynamic viscosity of the cement paste with and without chemical additives, as well as to determine the type of defoaming agent that was most effective. The results of the experiments showed that a glycol ester-based defoamer was the most efficient. This type of agent reduced the number of surface pores in the paste. Optical microscopy was used to measure the size of these pores. It was found that glycol-ether defoamers were the most effective when used in concentrations of 0.02% and 0.04% in a cement mixture containing ground blast furnace slag (25%) and a polycarboxylate plasticizer. These additives changed the size and number of surface pores. It was also found that increasing the content of glycol-ether additives increased the mobility of the cement paste, but did not change the viscosity. There was a slight increase in average density and decrease in pore size and number by 0.28–0.29%, respectively. The study showed that using a defoaming agent in combination with a polycarboxylic acid ester-based additive can help reduce consumption and enhance plasticizing effects, thus predicting concrete behavior during construction.