Impact of supplementary cementitious materials and fibers in ECC on the fire resistance of hot-jointed SCC/ECC composites

This research examines the influence of various supplementary cementitious materials (SCMs) and fibers on the fire resistance of composite systems (CS) that combine engineered cementitious composites (ECC) in tension with self-compacting concrete (SCC) in compression. The study was designed to determine the ECC formulation ideally suitable for optimizing mechanical properties and bonding performance at ambient and elevated temperatures. The SCC and ECC were hot-joined without vibration or surface preparation, using a fresh-to-fresh casting method. Modifications to the chemical composition of ECC included the addition of Class-F fly ash (FAF), Class-C fly ash (FAC), or slag (SL), as well as polyvinyl alcohol (PVA) or steel reinforcing fibers. Subsequently, the samples were exposed to temperatures of 200 °C, 400 °C, 600 °C, and 800 °C, followed by comprehensive testing to evaluate their flexural strength, tensile strength, and interfacial properties. The results indicate that the incorporation of an ECC layer within the SCC system significantly improved mechanical strength, and thermal stability, both at ambient temperatures and under high-temperature conditions. Notably, the utilization of FAF in the ECC layer offered superior thermal stability and ensured the retention of desirable residual mechanical properties compared to FAC and SL. Moreover, steel fiber reinforcement greatly improved the bonding between SCC and ECC, outperforming PVA reinforcement at elevated temperatures.