Effect of polymer modification on flexural performance and microstructure of biomimetic cementitious composites for marine infrastructure

Owing to the superiority of strength-toughness synergy, the previously developed nacre-inspired biomimetic cementitious composites (BCC) demonstrate promising application prospects in marine engineering. Studies have indicated that ethylene-vinyl acetate copolymer (EVA) crucially contributes to the flexural behavior of BCC, but the effect of EVA modification remains unknown. Herein, this study adopts aminopropyl triethoxy silane (APTES) and nano-silica (NS) to modify EVA and investigates the flexural performance and microstructure of unmodified and modified BCC. Results show that single APTES modification increases flexural strength and toughness, but exhibits brittle fracture. Single NS modification also improves flexural strength and toughness, and simultaneously maintains ductile fracture. Compound APTES and NS modification cannot further enhance flexural strength and toughness, and remains brittle fracture. Single APTES modification causes extensive hydrolysis and alcoholysis of EVA, resulting in its poor film formation. The film formation of EVA is not affected by single NS modification, but is still inhibited after compound modification. The strengthening mechanism of APTES is manifested as the chemical bonding with cement matrix after its hydrolysis and condensation, while NS mainly displays an interfacial optimization effect, but these might be weakened after compound modification due to the interactions between APTES and NS. This work can offer some guidance for future material designing of high-performance BCC for marine infrastructure.