Interfacial bond behavior between concrete and precast hybrid fiber engineered cementitious composites

While engineered cementitious composites (ECC) have been widely employed for strengthening and retrofitting aging or deteriorated structures, they also exhibit great potential as permanent formwork for concrete in marine or other aggressive environments. However, limited attention has been devoted to the interfacial bond performance between precast ECC layers and cast-in-place normal concrete (NC). To address this gap, an experimental program comprising 21 ECC-NC composite specimens was conducted using push-out tests to investigate the effects of fiber hybridization and interfacial treatment methods on the bonding behavior. The damage evolution were monitored using non-contact digital image correlation (DIC) technique, while the hybrid fiber-bridging effect and microstructural characteristics were examined through scanning electron microscopy (SEM). Based on the bond–slip responses and the observed failure modes, the interfacial stress transfer mechanisms were clarified, and the effectiveness of various surface treatment techniques was evaluated. Furthermore, the experimentally measured interfacial shear strength, together with data reported in the literatures, were compared with predictions from existing international design codes. The findings of this study provide experimental evidence and mechanical insights to support the rational design and practical application of ECC–concrete composite systems.