Bonding between New and Old Concrete in Composite Beams under the Effect of Static Loads

This study experimentally investigates the bonding strength of aged and other forms of new concrete. Its primary objective is to assess several methodologies for achieving effective bonding behavior. Additionally, the present study examines the impact of varying stiffness and shrinkage rates at the boundary between concrete layers poured at different times. The experiment on bonding strength included examining the effects of several factors, such as surface preparation, bonding agent type, age difference, and the type of concrete used in the new layer. The flexural test results show that the ultimate load decreases by 16.2%, and 13.3% for composite beams with new concrete of Self-Comparing Concrete (SCC), and steel fibers, respectively, compared to the reference beam. However, the ultimate load increases by 6.5% and 9% for composite beams with new concrete of Sika and High-Strength Concrete (HSC), respectively, compared to the reference beam. So, using new concrete with Sika or HSC is the best choice. The composite beam with shear connectors has the highest ultimate load in the test, whereas the beam with SCC as a new layer has the lowest value.