Evaluation of mechanical performance, corrosion behavior, texture characterization and aggressive attack of OPC-FMK blended cement pastes modified with micro Titania

Abstract

Building constructions are vulnerable to a major financial loss due to the dangerous degrading process of steel corrosion in reinforced concrete, which requires frequent repairs. This study examined the durability of steel cement-based covers and steel corrosion in two severe media, NaCl and MgSO4. The degree of penetration of these harmful ions was determined by monitoring the mechanical properties and porosity profile (using the N2-adsorption/desorption technique) of cement-based steel covers made from OPC and fine metakaolin (FMK) reinforced by micro-titania (MT). Additionally, after the immersed steels were exposed to solutions containing 7% NaCl and 7% MgSO4 for four months, the steel corrosion rates (CR, mpy) were assessed. The results demonstrated that blending OPC by FMK up to 30% could develop mechanical properties similar to plain OPC at later hydration periods of 28 and 90 days. XRD and TGA/DSC analyses connected this behavior to the emergence of novel phases, namely strätlingite and hydrogarnet, in OPC/FMK combinations. Better mechanical performance was demonstrated by blended mixes containing between 1% and 3% MT in all curing media. The replacement of OPC with 30% FMK in the presence of 3% MT resulted in significant changes in the porous system from macro to meso-nature, as confirmed by the BET and BJH models. Under normal, sulphate, and chloride curing, respectively, the maximum pore diameters (dpmax) decreased by 66.19%, 78.40%, and 79.14%. When CSH clusters were observed under a scanning electron microscope (SEM), they seemed to be symmetrical and organized, similar to floral crystals. This development is partially attributed to micro TiO2. Based on CR values, it was found that steel corrosion was higher in MgSO4 solutions than in NaCl solutions. Steel coverings made of OPC/FMK composites with 3% MT were able to reduce CR by 65.8% in MgSO4 solutions and by 56% in NaCl solutions.