Influence of defoaming agents on mechanical performances and pore characteristics of Portland cement paste/mortar in presence of EVA dispersible powder

The present study reports the influence of defoaming agent (DA) on the mechanical performances and pore characteristics of cement paste/mortar in presence of ethylene and vinyl acetate copolymer (EVA) dispersible powder. To make a comparative investigation, two various types of DA including silicone and ether DA are introduced. Fluidity, air content, volume density and strengths experiments are performed to evaluate the development of workability and mechanical performances. The hydration kinetics, phase composition and pore structure are characterized by isothermal calorimetry (ICC), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and mercury intrusion porosimetry (MIP) techniques. The experimental results indicate that the initial fluidity is increased with addition of EVA, while it is decreased with the content of defoaming agents. The DA enhances the development of strengths and volume density of hardened paste/mortar in presence of EVA. The fact that EVA participates in the chemical reaction and promotes the formation of carboxyl-containing substance (e.g. calcium acetate), ettringite and calcium hydroxide can be found. MIP results shows that the porosity and more-harmful pore are increased with the incorporation of EVA. DA significantly reduces the porosity and quantity of more-harmful pore, contributing to the higher mechanical properties. This study can be viewed as a valuable reference for the improvement of pore structure by using DA in the EVA modified cement-based materials.

Automated summary

This study shows that the addition of EVA increases initial fluidity, while the addition of defoaming agents decreases it. Defoaming agents enhance the strength and volume density of hardened paste/mortar and reduce porosity and harmful pore quantity.