Distinct dual-interface strengthening mechanisms of KH560 and EVA in PVA fiber-reinforced rubberized concrete

Previous studies have shown that KH560 and ethylene-vinyl acetate (EVA) can modify rubberized cementitious interfaces, but their effects on the coexisting rubber/cement and PVA fiber/cement interfaces remain unclear. Here, two parallel L9 (3 4 ) orthogonal designs were established for KH560- and EVA-modified PVA fiber-reinforced rubberized concrete (RUBC), considering rubber replacement ratio (5–15%), PVA fiber length (6–18 mm), PVA fiber dosage (0.5–1.5 kg/m 3 ), and modifier dosage (0–1.0%). Compressive, shear, and flexural properties were evaluated together with SEM, XRD, FTIR, and molecular dynamics simulations of the RH/C–S–H and PVA/C–S–H interfaces. Compressive strength ranged from 25.42 to 30.73 MPa for KH560 and 25.17–30.58 MPa for EVA; shear strength ranged from 8.43 to 10.44 and 8.28–10.48 MPa, respectively, while flexural strength ranged from 4.24 to 6.07 and 4.24–6.52 MPa. The two series showed similar overall compressive and shear responses, whereas EVA produced higher flexural strength in eight of nine corresponding runs; no inferential superiority between modifiers was claimed. SEM showed reduced visible interfacial separation after modification, while FTIR revealed more pronounced Si–O-related spectral changes with KH560. In the non-reactive MD models, KH560 increased the magnitude of interfacial interaction energy by 18.9% for RH/C–S–H and 10.96% for PVA/C–S–H, compared with 8.3% and 4.58% for EVA. Corresponding interfacial water–water hydrogen-bond counts were 1.97 versus 1.36 and 1.66 versus 1.06. Overall, KH560 and EVA exhibited property- and scale-dependent modification responses rather than a universal superiority relationship, distinguishing modifier-controlled interfacial stabilization from fiber-controlled crack bridging.