Effect of mix ratio on modified epoxy mortar performance and field application

The development of high-performance repair materials for hydraulic infrastructure remains critical given the deteriorating effects of extreme environmental on aging concrete structures. Hence, this study proposes a performance-targeted inverse design strategy that integrates orthogonal experimental design, response surface methodology and a neural network algorithm (NNA) to formulate a modified epoxy mortar with balanced mechanical strength and thermal compatibility for hydraulic repair applications. The effects of epoxy resin, curing agent, medium sand and fine sand on the mechanical properties and deformation characteristics of epoxy mortar were studied. The results demonstrated that the resin-to-curing agent ratio (REC) is the primary determinant of mechanical strengths, while fine sand dosage served as a secondary factor affecting tensile and compressive performance. Medium sand dosage functioned as the secondary influence specifically on adhesive strength. NNA analysis identified an optimal REC of 14.5:1 to achieve the target linear expansion coefficient of 7.98 × 10−6/°C. The optimised proportion with 25% fine sand and 55% medium sand demonstrates enhanced mechanical strength while meeting expansion requirements. Field validation at a hydropower station’s silt-releasing tunnel in Henan Province, China, exposed the restored surface to sediment-laden flows with a maximum monitored sediment concentration of approximately 703.0 kg/m³. Follow-up inspections in 2023 and 2024 showed no visible cracking, hollowing, peeling or detachment in the repaired area, indicating good field applicability of the optimised epoxy mortar.