Effect of Emulsifier Type on the Properties of SBR-Modified Cement-Based Materials

Styrene butadiene rubber (SBR) is a commonly used polymer modifier that can improve the mechanical properties and durability of cement mortar. However, the effects of different emulsifier types on cement hydration behavior and structural evolution still need to be systematically studied. To clarify the differences among anionic, cationic, and nonionic SBR emulsions on mortar performance, three types of SBR emulsion were selected in this study. Setting time, chemically bound water, mechanical properties, chloride ion diffusion, freeze–thaw cycles, and microstructure were tested to evaluate the effects of different types and dosages on cement mortar. The results show that all three types of SBR emulsion prolong the setting time of cement paste and reduce the early hydration degree. The cationic SBR emulsion shows a more obvious effect. At 28 d, the compressive strength of mortar with 10% cationic SBR emulsion increases from 38.5 MPa to 41.2 MPa, and the flexural strength also increases. In terms of impermeability, the chloride ion diffusion coefficient decreases from 7.47 × 10−12 m2/s to 5.12 × 10−12 m2/s after adding 10% cationic SBR emulsion. After 100 freeze–thaw cycles, the compressive strength loss of ordinary mortar is 16%, while it decreases to 7.2% with 15% cationic SBR emulsion, and the mass loss is also reduced. Microstructural analysis shows that the modified mortar has a denser internal structure, improved interfacial continuity, and reduced crack development after freeze–thaw cycles.