Effect of water saturation in hardened mortar around a steel bar on corrosion considering exposure history

The corrosion rate of steel bar in carbonated concrete is dependent on the presence of water. However, there are few studies on corrosion rate considering the hysteresis behavior, which illustrates the difference between the water contents of concrete in the drying and wetting processes for the same RH. Therefore, this research was done to study the corrosion rate of hardened mortar exposed to various drying and wetting process. In the experiment, thin mortar specimens with an embedded steel plate were fabricated to represent changes in the water state around the steel bar in the mortar. Then, moisture desorption test using saturated specimens and moisture adsorption or dry-wet cycle test using dried specimens that is constant at 40 °C were carried out. The water saturation and corrosion rate were obtained by mass change of mortar specimen and weight loss of steel plate, respectively. The result shows that corrosion was barely observed in non-carbonated specimen but observed in carbonated specimen and the corrosion rate in moisture desorption process was larger than that in moisture adsorption process. In addition, arranging the relationship between water saturation and corrosion rate, constant relations can be seen being independent of process and as water saturation increased, corrosion rate increased by about 60 % and then became constant. •Corrosion rate in carbonated concrete is discussed considering water content.•Water hysteresis behavior is taken into account even in same RH.•Even in the presence of water, corrosion cannot observed in non-carbonated mortar.•In same RH, corrosion rate in desorption process is larger than that in adsorption.•Corrosion rate is proportional to water saturation by 60 % regardless of process.