Flexural and Interface Behaviors of Reinforced Concrete/Ultra-high Toughness Cementitious Composite (RC/UHTCC) Beams

This paper presents an experimental investigation on the response of reinforced concrete (RC) beams with the use of ultra-high toughness cementitious composite (UHTCC) in the tension zone. Two parameters, the longitudinal reinforcement ratio and the depth of UHTCC layer, were varied. The failure mechanism, flexural behavior, interface performance, and cracking pattern were compared between RC and RC/UHTCC beams as well as between RC/UHTCC beams with different depths of the UHTCC layer. The experimental results revealed that the yielding load was improved apparently for beams with a reinforcement ratio of 0.67%, and the macro wide cracks in concrete turned into multiple tight cracks in the UHTCC layer depending on the prominent crack dispersion capacity of the UHTCC. However, RC/UHTCC beams with 1.0% and 1.73% reinforcement ratios showed shear-interface debonding failure prior to the yielding of reinforcement, and the failure resulted from the accumulated interface crack extension up to the support and the crush of concrete. Moreover, the theoretical analysis indicates that the interface cracking strength and ultimate interface bonding strength are related with the reinforcement ratio and UHTCC depth. The tensile stress difference of reinforcement in the UHTCC layer plays a controlling role in the interface debonding between concrete and UHTCC. The present study provides significant insights for the engineering application of hot-casting RC/UHTCC composite beam.