Corrosion resistance of zinc in a low-carbon binder with belitic calcium sulfoaluminate cement

This study investigated the passivation ability and chloride-induced corrosion behavior of galvanized steel in the pore solutions of belitic calcium sulfoaluminate (BCSA) cement. Pure zinc was used to simulate the galvanized coating, and ordinary Portland cement (OPC) solution was also tested for the comparison purpose. A comparable passivation behavior was observed for pure zinc in the OPC solution and a mixture solution of 50 % OPC and 50 % BCSA cement (abbreviated as PSA solution). On the one hand, due to the high Ca²⁺ ion concentration and low alkalinity of the PSA solution, which is conducive to zinc passivity, a more stable protective layer of calcium hydroxyzincate (CHZ) was generated on the zinc surface. On the other hand, the passivation ability of zinc was reduced to some extent by the high SO₄²⁻ ion concentration in the PSA solution. During the corrosion stage induced by exogenous chlorides, a different variation tendency was found for the corrosion resistance of zinc in OPC and PSA solutions over exposure time. Owing to the synergetic attack by SO₄²⁻ and Cl⁻ ions, the critical chloride concentration of zinc in the PSA solution was only 0.3 M, as determined by a sharp drop of E_corr and R_p values, while zinc in the OPC solution exhibited a much higher chloride resistance with the critical chloride concentration of 0.8 M. However, this detrimental effect on the corrosion resistance of zinc in the PSA solution was less pronounced with prolonged exposure due to the formation of protective corrosion products.