Bonding between New and Substrate Concrete in Composite Beams subjected to the Effect of Repeated Loads

This study uses experimental methods to assess the bonding strength of aged concrete compared with several types of new concrete under the effect of repeated loads. The major goal of this study is to evaluate several methods for creating bonding behavior. Additionally, it evaluates the influence of altering stiffness and shrinkage rates at the interface between concrete layers poured at different dates. The experimental tests examined the impact of numerous parameters, including surface preparation, bonding agent type, age difference, and the kind of concrete utilized in the new concrete. The flexural test results show that the percent of Pu (repeated) / Pu (static) was about 85%, 95%, 98%, 95%, 97%, 92%, and 95% for the composite beam with the shear connector, SCC, steel fibers, rough surface, SBR, SIKA, and HSC, respectively. The ultimate load increased by 126% for the composite beams with stirrups as shear connectors with respect to the reference beam. So, using stirrups as shear connectors between new and old concrete significantly increased the load-carrying capacity of the beam subjected to repeated loads.