The industrial SO2-induced corrosion: Investigation of the corrosion onset

Abstract

The stability of the passivation film on reinforcing steel is significantly influenced by the internal chemical environment of concrete under industrial sulfur dioxide (SO2) corrosion. This study aimed to investigate the electrochemical state of the reinforcing steel and the internal chemical environment (corrosion products, phase composition, and pore structure) of concrete by conducting indoor simulations of reinforced concrete specimens exposed to industrial SO2 environment. The results indicated a consistent trend in open circuit potential (OCP) and corrosion current density (icorr) of steel rebar in different types of concrete. A sudden reduction in OCP is accompanied by a significant increase in icorr when the rebars reach an active state. At this time, the ratio of sulphation depth to protective layer thickness ranges from 0.47 to 0.63. The main sulphation products were gypsum and ettringite, with their content decreasing as the cover layer depth, water-to-binder ratio, and fly ash content increased. Due to crystallization pressure and expansion, the impact of SO2 corrosion on the capillary pores of concrete was the most significant, followed by its effect on larger pores. After 96 days of corrosion, there was an increase of 191.7 % and 116.2 % in the quantity of pore sizes, respectively. Furthermore, the porosity growth rate in concrete with the incorporation of fly ash is lower than that of Portland concrete. This suggests that the rational use of fly ash to partially replace Portland cement is beneficial for enhancing the resistance of concrete to SO2 corrosion.