Synthesis of MNS@PDMS emulsion for enhancing hydrophobicity in cementitious materials with limited strength loss

Developing hydrophobic agents that minimize the strength loss of bulk hydrophobic cementitious materials (BHCM) remains a formidable challenge. Substances such as siloxanes can hinder cement mineral hydration and prevent the formation of an initial network structure during the early hydration stages. In this study, a novel hydrophobic emulsion in which polydimethylsiloxane (PDMS) wrapped with modified nano silica (MNS) is designed to enhance the hydrophobic property of cementitious materials while minimizing strength loss. The results show that BHCM exhibits good hydrophobicity (water contact angle 121.8°) while significantly reducing strength loss (decreased by 10.3 %). The presence of MNS effectively shields PDMS from direct contact with cement minerals during the initial stages. Moreover, MNS can react with portlandite (CH) to generate C-S-H phase and optimize the pore structure of hardened cement pastes. This study contributes to promoting the structure-function integration of cement composites and achieving an extended service life for concrete.