Diffusion Potentials in Cement Mortars with pH Differences Due to Carbonation

Corrosion investigations of steel-reinforced concrete structures are often based on half-cell potential measurements, in which the diffusion potentials can be a significant source of measurement errors. Therefore, the diffusion potentials must be taken into account in order to enable accurate half-cell potential measurements. This study covers the measurement of the diffusion potentials in cement mortars with pH differences due to carbonation and various mortar moisture conditions. The effect of chloride exposure of the mortars on the diffusion potentials is outside of the scope of this study. The mortars consisted of ordinary Portland cement (OPC) and blast furnace cement (BFC) with water–cement ratios of 0.5–0.7. The use of color indicators allows for the observation of the pH drop around the carbonation front, which propagates as the carbonation progresses. The diffusion potentials in the mortars under study have measurement values between 10 and 240 mV. The measured diffusion potentials seem to correlate with the magnitude of the pH drop rather than the progress of the carbonation depth. The moisture condition of the mortars significantly affects the magnitude of the arising diffusion potentials.