Research on the Mechanical Properties and Durability Against Freeze–Thaw of Latex-Modified OPC-Based Materials

The intrinsic brittleness and poor crack resistance of OPC-based materials severely limit their service durability under complex environments. In this study, a composite latex polymer was fabricated via an ambient-temperature APS/STS redox initiation system, using N,N′-methylenebisacrylamide (MBA) as a cross-linking agent and incorporating reactive SiO2 and MgO as synergistic reinforcing fillers. The composite latex was incorporated into OPC paste, and its effects on the mechanical strength, freeze–thaw resistance, water permeability, and microstructural characteristics of the hardened composites were systematically evaluated. The results show that, at an optimal dosage of 0.2 wt%, the 28-day flexural and compressive strengths of the modified OPC specimens were respectively increased by 16% and 18% compared with the plain cement control, while the strength loss after freeze–thaw cycling was effectively controlled within 10% and the maximum impermeability pressure rose from 2.9 to 3.2 MPa. FTIR and XRD analyses confirmed that the incorporation of the latex polymer did not alter the phase composition of the OPC hydration products but promoted the generation of C-S-H gel. SEM observations further revealed that the polymer filled internal micro-pores and microcracks, yielding a denser organic–inorganic composite microstructure. The improved performance may be attributed to the potential synergistic interplay among APS/STS-triggered cross-linking, pozzolanic reaction of reactive SiO2, and the micro-expansion effect of MgO. This work provides a feasible technical approach for the development of high-toughness and frost-resistant latex-modified OPC-based materials.