Application of hybrid alkali-activated binders for chemical realkalization

Abstract

The repair of reinforced concrete structures affected by carbonation-induced corrosion is essential for the preservation of existing buildings. The chemical realkalization, using cementitious layers applied to the surface of carbonated concrete is a commonly used method to restore the passivity of the embedded steel reinforcement. Despite its practical relevance and low implementation effort, the mechanisms contributing to the realkalization process, especially when using low-CO₂ binders, remain insufficiently understood. In the present study, the applicability of hybrid alkaline-activated binders (HAAB), which enable a reduction of the clinker content while simultaneously adding additional alkaline components through alkaline activation, is investigated. Under defined exposure conditions, realkalization depths of up to 30 mm were achieved using HAAB. The application of alternative pH indicators allows a more precise analysis of the spatial and temporal evolution of the realkalized area, highlighting the critical role of the initial suction phase. The results provide new insights into the interaction between the binder chemistry and the realkalization effectiveness as well as the importance of the availability of alkalis.