Effect of severe sulfate exposure on the bonding behavior of hybrid engineered composite systems

Abstract

This article examines the sulfate resistance of composite concrete systems (CS) combining self-consolidating concrete (SCC) in compression and engineered cementitious composite (ECC) in tension, with special focus on the bonding properties at SCC/ECC interface. The effect of different fibers in the ECC tension area was investigated considering the use of PVA, steel and hybrid PVA/steel fibers at the same content. SCC and ECC layers were hot-jointed at fresh-to- fresh state and the hardened systems were tested under repeated cycles of concentrated sodium sulfate immersion and oven drying at a high temperature of 80 °C. Samples were assessed for physical, mechanical, and microstructural changes, including visual state, failure mode, mass, compressive strength, flexural properties and tensile bond strengths at different immersion-drying cycles. In addition, using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) and backscattered electron imaging, sulfate profiles and phase assemblage methods were applied to investigate the concentration of reaction products of each SCC/ECC system. The long-term exposure results confirmed the advanced sulfate resistance of all CSs as compared to monolithic SCC. Considering the different degradation levels of CSs, the use of PVA demonstrated slightly enhanced physic-o-mechanical properties due to its greater interfacial effect at the SCC/ECC bond. Microstructural studies revealed that there were high concentrations of reaction products in the SCC layers that also affected a limited area near the interfacial bond with the ECC layers, particularly when steel fibers were included in CSs.