260 / 2022-08-07 16:18:05

Bond performance and mechanisms of sulphoaluminate cement-based UHPC for reinforcing old concrete substrate

Keywords: repair materials; bond strength; bond performance; interfacial microstructure; interfacial agents; assessment;

One of the major problems facing reinforced concrete structures nowadays is their repair and reinforcement. Sulphoaluminate cement (SAC)-based material is an effective repair material. This paper examined the bond performance between SAC-based UHPC with low water to cement ratio and old OPC concrete substrate using the bond strength test and SEM analysis. It was found that SAC-based UHPC has beneficial mechanical properties, including compressive and flexural strength, at an early age (Fig. 1). This paper provided a reference   for the reinforcement of reinforced concrete structures that are exposed to the marine environment.



SAC-based UHPC mixture could rapidly bond the old OPC substrate, and the bond strength of all the cylinder and prism specimens at 1 day reached over 8MPa (Fig. 2). The bond strength of the cylinder and prism increased greatly significantly with more curing time and achieved more than 10 and 12 MPa at 28 days, respectively，which can be attributed to the early strength properties of SAC. Comparing the cylinder and prism specimens, the bond strength of the latter is higher than that of the former.



The bond strength when using the cylinder specimen was lower than that of the prism. A linear trend was obviously demonstrated between the bond strength of the cylinder and prism specimen (Fig. 3). The findings indicated that it was feasible to measure bond performance using the cylinder specimen when the shrinkage around the interface of old concrete needed to be considered and that SAC-based UHPC could be applied in repair work that required high-early strength repair material.



For both cylinder and prism specimens, the prepared bonded specimens whose interface was covered without any agents had higher bond strength than that of samples using different bonding agents, including waterborne epoxy resin and modified epoxy resin in different recipes (Fig. 4).



The SEM diagrams of interfacial microstructure showed that there were some small fiber-like AFt crystals that were produced by the hydration of SAC in the interface of the specimen with no agents when magnified to 20,000 times (Fig. 5). For the specimens with different kinds of agents, visible cracks at the interface were observed. The observations were consistent with the evaluated bond strength of the specimens applied with different interfacial agents.