Evaluation of the influence of the pH of concrete pore solution on the corrosion resistance of steel reinforcement

Abstract

Partial replacement of Portland cement by supplementary cementitious materials results in decreased concentration of calcium hydroxide, leading to a reduction in the pH of the pore solution and influencing the formation of passive films on steel. Decreases in pH are often equated to lower-quality passive films, but, as has been recently shown, that is not always the case. This study evaluates the effect of partial replacement of cement Portland by silica fume, both on the pH of pore solution and corrosion resistance of reinforced concrete. Three concrete mixtures with variations of cement replacement by silica fume (0, 5 and 10% by volume) were produced. Pore solution chemical composition, corrosion current density and polarization resistance were measured up to 91 days. Results show that, especially in early ages—when concrete resistivity remains low and unchanged among the different mixtures tested—partial replacement of cement by silica fume led to an improved passivation process and increased corrosion resistance, even with a related decrease in calcium hydroxide concentration and pH.