Effect of defoaming agent on the properties of cement mortars with hydroxyethyl methyl cellulose through adjusting air content gradient

Abstract

Pore structure plays one of the most important role in the properties of cement-based materials. Hydroxyethyl methyl cellulose (HEMC) has the air entrainment effect, which may significantly change the pore structure and further affect the performance of this materials. Incorporating defoaming agent (DA) may weaken this effect, due to its defoaming effect which needs to be fully evaluated. Therefore, the working efficiency of DA and the changes of pore structure caused by stepwise adjustment of the air content were mainly studied. The results show that incorporating DA can effectively eliminate air bubbles, while the defoaming effect is weak with the air content approaching to 6.0%. There is a certain negative correlation between fresh bulk density and air content, and a positive correlation between fluidity and air content. Incorporating an appropriate dosage of DA is beneficial to control the air content of the cement mortars with HEMC, so as to ensure the cement mortars have better mechanical strengths and low drying shrinkages. With the increase of DA dosage, the large capillary pores, macro pores and total porosity all show a gradual decreasing trend due to the air content decreasing. The content of connected capillary pores in cement mortars tends to increase as the air content level decreases, but shows a small decrease at the low air content of less than 6.0%.