Corrosion behavior of steel rebar embedded in hybrid CNTs-OH/polyvinyl alcohol modified concrete under accelerated chloride attack

Abstract

This study evaluated the mono and hybrid effects of hydroxyl carbon nanotubes (CNTs-OH) and polyvinyl alcohol (PVA) on the corrosion behavior of steel rebars embedded in concrete under accelerated chloride attack by an impressed voltage technique. The contents of CNTs-OH and PVA were fixed at 0.5% and 1% by weight of cement, respectively. Mechanical tests showed that hybrid CNTs-OH/PVA improved the flexural strength and compressive strength by 20% and 9%, respectively. The Mercury Intrusion Porosimetry test showed that adding CNTs-OH/PVA reduced the total porosity and macro-pore content of concrete by 29.9% and 83.2% over the control concrete, respectively. The impressed voltage corrosion test indicated that hybrid CNTs-OH/PVA significantly delayed the deterioration progress of the steel rebar in concrete, as the corrosion level of the steel rebar decreased by 94% and the exposure time increased by 60% before the generation of the surface crack compared to those of the control concrete. The mechanisms for the hybrid effects of CNTs-OH and PVA on enhancing the steel corrosion resistance in concrete include: 1) uniform dispersion of CNTs-OH in PVA colloid; 2) pore-filling effect of both CNTs-OH and PVA; and 3) PVA coated CNTs-OH form electric capacitors to restraint the transport of free ions. The findings in this study reveal the potential of hybrid CNTs-OH/PVA modifiers to improve the corrosion resistance of steel rebars in concrete.