Corrosion protection performance of microsilica added concretes in NaCl and seawater environments

Abstract

In a hardened concrete structure, diffusion of oxygen, carbon dioxide, aggressive ions and moisture from the concrete/environment to the concrete/rebar interfaces takes place through the pores. This results in the failure of the passivation provided by the alkalinity of the cement to the rebars. Microsilica is a mineral that improves the corrosion protection and strength of concrete by reducing the permeability of the concrete and forming more calcium silicate hydrate (CSH) which provides strength and durability to concrete. In order to study the corrosion protection behavior of microsilica in ordinary Portland cement (OPC) and sulfate resistant cement (SRC), carbon steel reinforced concrete specimens of above cements containing 10% each of densified (DMS) and undensified (UDMS) microsilica were exposed to 5% NaCl solution and seawater. Corrosion of rebars was monitored using open circuit potential (OCP) measurements. Diffusion of ions into the concrete was studied by salt ingress, salt fog and rapid chloride permeability tests. It has been noted that densified microsilica provides better corrosion protection to the rebars than the undensified one. In addition to this its protective effect with SRC is much more than with OPC. An attempt has been made to explain the mechanism of corrosion protection behavior of microsilica added concrete immersed in seawater and NaCl solution.