Modification study of underwater epoxy-cement mortar with polyacrylate latex: Engineering performance optimization and microstructure analysis

Cement mortar with waterborne epoxy resin (WEP) is extensively utilized in the underwater repair of hydraulic structures . However, this material encounters challenges in fluidity retention and the coordination of underwater self-compacting and non-dispersive properties. While the addition of superplasticizer can improve the underwater workability, the epoxy-cement mortar still struggles in well restoring the engineering performance, mainly due to the absence of effective bonding between the superplasticizer and the WEP. Hence, the current study trials to introduce the polymer composite modification strategy. Based on a typical epoxy-cement mortar, 0–25 wt% of highly extensible and strongly hydrophobic polyacrylate latex (PAE) was added to prepare the PAE-modified epoxy-cement mortar (PECM). The study measured the workability and mechanical properties of PECM cast underwater and on land. Microstructure characterization and hydration analysis were used to explore the modification mechanism of PECM. Results indicated that incorporating 20 % PAE into the repair mortar optimized both underwater and on-land interfacial bonding strength and bending toughness, while maintaining flexural and compressive strengths . The 7d interfacial bonding strength increased by 60.2 % for underwater application and 54.1 % for on-land application. Similarly, the 7d bending toughness improved by 25.1 % underwater and 74.6 % on land. Microstructural characterization analysis revealed that the improved underwater fluidity and fluidity retention ability of PECM primarily resulted from the rapid film formation effect of the PAE and the WEP. The hydrophobic polymer films created a ball-bearing lubrication effect, enhancing mortar fluidity. Simultaneously, the polymer films encapsulated unhydrated cement and early hydrates, controlling the hydration process and fluidity retention of PECM by impeding the transport of species across the polymer film interfaces. The resulting polymer films optimized early structural defects in the mortar, enhancing the early-age interfacial bonding strength and toughness of PECM. By leveraging the hydrophobic and self-lubricating properties of the polymer film when combined with PAE and WEP, this study has successfully developed a novel repair mortar that exhibits superior underwater workability and mechanical properties compared to conventional epoxy mortars , offering an effective solution for the repair of underwater damage to hydraulic structures. • PECM exhibits good compatibility, enhancing the workability of repair mortar. • PECM features rapid film formation, improving early toughness and bonding. • PAE enhances hydration product interpenetrating network's continuity and density. • The films hinder full C3A hydration, leading to AFm formation in early process.