Effect of waterborne polymer on mechanical properties, carbonation resistance and freeze-thaw resistance of cement mortar

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The performance of concrete infrastructure deteriorates with the extension of service time. Traditional cement repair materials have defects such as brittleness, poor interface bonding and insufficient durability. In this paper, a kind of waterborne epoxy resin emulsion (WEP) was designed and synthesized. The effects of WEP, vinyl acetate powder (VAE), styrene butadiene rubber emulsion (SBR) and waterborne polyurethane emulsion (WPU) on the properties of cement mortar were systematically studied, and the modification mechanism was explained. The experimental results show that the bending strength of WEP modified cement mortar is 13.47 MPa, which is 17.1 % higher than the control, and the bond strength is 1.69 MPa, which is 164.06 % higher than the control. VAE modified mortar showed similar excellent performance, while SBR and WPU modified effect was relatively weak. The uniform particle size distribution and optimal epoxy value of WEP synthesized by phase inversion emulsification technology enable it to form a continuous interpenetrating polymer network in the cement matrix, and significantly improve the carbonation resistance and chloride ion penetration resistance of the material. The microstructure analysis revealed that the epoxy group of WEP formed a chemical bond with the hydration product of cement, creating a strong and tough interface structure, and the molecular characteristics of different polymers determined the difference of their modification effects. When the P/C ratio is 15 %, the polymer network and cement hydration products form the best synergistic structure. The comprehensive performance evaluation shows that WEP and VAE modified mortar are especially suitable for repair applications with high performance requirements such as marine and hydraulic engineering, while SBR and WPU are more suitable for general maintenance engineering. • Four waterborne polymers (WEP, VAE, SBR, WPU) compared for cement mortar modification with comprehensive evaluation. • WEP and VAE enhanced flexural strength by 17.1 %and bond strength by 164.06 % and 153.13 % respectively. • Optimal 15 % P/C ratio achieved superior mechanical properties through controlled polymer network formation. • Microstructural analysis revealed polymer bridging, chemical bonding, and pore structure optimization mechanisms. • Cost-effective modification provides tailored solutions for marine engineering and high-performance applications.