Comparison of Cast-In-Situ and Prefabricated UHTCC Repair Systems under Bending

Abstract

Ultrahigh-toughness cementitious composite (UHTCC) is a new type of cementitious material that is suitable for durability repair of deteriorated concrete structures. One of the key issues in this repair technology is the behavior of interfacial bonds. In this study, the bond properties between the UHTCC and the old concrete were evaluated by conducting four-point bending tests. The UHTCC was prepared using two methods: cast-in-situ and prefabrication. The test parameters include the roughness of the concrete substrate, roughness of the prefabricated UHTCC, strength of the old concrete, primer, and bonding agent. Two-way analysis of variance was used to analyze the effect of these test parameters on the bond strength. Moreover, two regression formulae were proposed to predict the flexural bond strength of the composite beams. The results showed that the flexural bond strength of the repair system tended to increase with the increase in the roughness values of the concrete substrate and prefabricated UHTCC and strength of the old concrete. However, a very high roughness could damage the interfacial zone; hence, the roughness should be controlled in a particular range. The results also revealed that suitable primers and bonding agents, e.g., polymer-modified material and fly ash–silica fume-modified material, could improve the bond strength of the interface. Moreover, double-layer bonding configurations were found to exist in the prefabricated repair system. The flexural bond strength depends on the weaker bonding plane, and the interface control needs to be considered during the design and construction. In particular, two-way analysis of variance was proven a reliable tool in evaluating the experimental results. The predicted flexural bond strength was in good agreement with the experimental value.