Study of the Corrosion Behaviour of Reinforcing Bars in Biochar-Added Concrete under Wet and Dry Exposure to Calcium Chloride Solutions

This research investigates the mechanical behaviour and durability of biochar-added concrete, by comparing the results with those of a standard concrete, in the case of both dry and water curing. More in detail, the corrosion behaviour of rebars embedded in biochar-added concrete during wet and dry exposure (w/d) to calcium chloride solutions was studied by corrosion potential (Ecor) and potentiostatic polarization resistance (Rp) monitoring, and electrochemical impedance spectroscopy (EIS) and polarization curves recording. Chlorides concentrations were measured, in coaxial cores obtained from unreinforced samples. The results show that biochar addition improves compressive strength of short and long-term dry-cured samples compared to reference concrete. Chlorides diffusion tendency in biochar-added concrete is similar to that of the traditional one. However, the onset of localized corrosion is slightly earlier, because retained water in biochar macroporosities maintains a wet environment around rebars. The results suggest that under dry curing, typical of common structures, the beneficial effects of biochar on compressive strength and the comparable chlorides permeability with respect to reference, make biochar-added concrete an environmentally friendly solution potentially exploitable for reinforced concrete structures.