Interface Shear Strength between Self-Compacting Concrete and Carbonated Concrete

An experimental test is proposed to investigate the interface shear strength between carbonated concrete substrate and self-compacting concrete (SCC) overlay. Thirty-nine Z-type specimens consisting of two L-type concrete members were designed and subjected to direct shear test. One L-type concrete member was cast as substrate and carbonated. Then the SCC was cast as overlay. The effects of carbonation of substrate, strength of SCC overlay, and interfacial treatment on shear strength were discussed and clarified. A coefficient was developed to consider the influence of carbonation on the shear strength prediction between old concrete substrate and new SCC overlay. Results showed that carbonation of substrate affects both the interface shear strength and cracking. The shear strength increased by 30% when the carbonation depth of substrate was deeper than 20 mm. The location of shear crack was changed from the bonding interface to the interface between the carbonated and uncarbonated layers within the substrate. The strength of new self-compacting concrete and the interface treatment also affected the interface shear strength. For specimens without interfacial planted bars, the shear strength increased with the strength of SCC overlay until it was more than 5 MPa greater than that of the substrate. The strength of SCC overlay, however, had negligible effect on the shear strength of specimens reinforced with interfacial planted bars.