Synergistic hydrophobic modification of cement mortar using SBR and PDMS: Performances and mechanisms

The inadequate water resistance of conventional mortar poses a significant risk to building durability and safety, especially in the context of rapid urbanization and evolving construction technologies. This study proposes a synergistic modification of mortar using Styrene-Butadiene Rubber (SBR) latex and Polydimethylsiloxane (PDMS). A series of tests was conducted to study the effects of their combination on waterproofing performance, mechanical properties, and microstructure. Results show that the co-incorporation of SBR and PDMS significantly enhanced the waterproofing performance of mortar. At an optimal dosage (5% SBR and 3% PDMS), the 12 h immersion absorption decreased by 80%, and the capillary absorption coefficients (S1 and S2) were reduced by 72.8% and 56.6%, respectively, with the contact angle exceeding 120°. Although mechanical strength was decreased, the optimal dosage of 28 d compressive strength was 22.3 MPa, resulting in minimal strength loss of 33.4% compared to unmodified mortar. Microstructural analysis revealed the synergistic mechanism, that is, the SBR seals water transport pores through film formation, while PDMS creates a hydrophobic chemical layer by reducing surface energy. Their synergy establishes a dual mechanism that significantly improves the mortar's waterproofing performance.