Performances of UHPC bonded cementitious composite systems containing styrene-butadiene rubber latex in a chloride-rich environment

Abstract

• The green and sustainable cement-based material—UHPC was used as the repairing material to strengthen the existing cementitious substrate. • Mechanical, electrochemical and microstructural characteristics of the bonded composite systems were investigated. • The performance developments of the composite systems in a chloride-rich environment were presented. • Styrene-butadiene rubber (SBR) latex were considered to enhance the bonding properties and the electrochemical performances of the composite systems. This study investigates the mechanical, electrochemical and microstructural characteristics of UHPC bonded cementitious composite systems concerning the influences of chloride attack. The bonded composite systems with styrene-butadiene rubber (SBR) latex content of 0, 2 %, 4 %, 6 %, 8 % in UHPC layers were prepared. The experimental groups were immersed in saturated sodium chloride solution whereas the reference groups were cured in clean water. The compressive, bonding and flexural strength of the bonded systems were tested at different curing ages. The free corrosion potential, AC impedance spectroscopy and polarization resistance were considered to figure out their electrochemical behaviors. Furthermore, X-ray diffraction (XRD), pore structure characteristics as well as scanning electron microscope (SEM) observations were employed to show some light on the internal mechanism at a microscale level. Results indicate that the chloride-rich environment demonstrated certain adverse effects on the system’s mechanical properties, especially the bonding strength, which could be reduced by 20 % on average at 56d. Proper content of SBR latex was conducive to the system’s bonding strength. However, when the dosage was too large, a remarkable adverse effect on compressive strength was seen. The addition of SBR latex could further delay the corrosion of the reinforcement inside the system, from 28d of the systems without latex to 42d with 4 % SBR latex. The microstructural investigations confirmed that in a chloride-rich environment, the total pore volume was reduced by 29.4 % at 28d. A dense transition zone was observed between the substrate and the UHPC layer with a width of about 0.1 μm in clean water curing, whereas it became relatively loose and obvious bonding holes appeared in this area under severe chloride attack.