Frost Resistance of Redispersible Polymer Powder–Modified Fast-Hardening Cement Mortars under Simulated Climatic Conditions

Polymer-modified fast-hardening cement mortar is widely used as road repair material due to its excellent performance attributes of shorter setting time and good workability as well as high adhesive strength. However, in the complex actual service environment, whether it can still maintain stable performance has become a concern. Therefore, this study performed an indoor freeze–thaw cycle test to investigate the frost resistance of polymer-modified fast-hardening cement mortar under winter climate conditions in Lanzhou. The macro properties of the fabricated mortar were characterized by compressive strength and flexural strength, and the microstructures were investigated by MIP, FTIR, and SEM. It was found that with increasing polymer doses, the frost resistance of the fast-hardening cement mortar was improved, and the flexural strength increased gradually, but the compressive strength showed an opposite evolutionary trend. The overall performance of mortars was best when the content of polymer admixture was 4%, by mass, of the cementitious material. In addition, the polymer significantly refined the pore structure in the range of 3–10 nm, which made the total porosity of the system increase. Meanwhile, the polymer could be involved in the chemical reaction to generate polymer film and interlap with the needlelike ettringite (AFt) to form a spatial network structure, as shown by FTIR and SEM analysis. This means that incorporating polymer 5010N improved the microstructure of the fast-hardening cement mortar, leading to improved frost resistance.