ABSTRACT

Changes in temperature due to global warming could increase the risk of corrosion damage to critical reinforced concrete (RC) infrastructure and impose challenges to the corrosion protection of bridges exposed to extensive amounts of de-icing salt in the winter. The chloride threshold limit (CTL) of a steel reinforcing bar (rebar) indicates its corrosion resistance to chlorides. CTL is one of the governing parameters determining the time to corrosion initiation. This study presents an experimental investigation of the temperature dependency of CTL for six types of rebar, including four grades of stainless steel subjected to pitting corrosion characterized by the potentiodynamic polarization method. The temperature was an important influencing factor on the CTL of alloys. As expected, the corrosion resistance of the rebars (i.e., CTL) decreased with higher temperatures.

Additionally, the temperature dependence of the CTL was found to vary significantly among the six alloys. This study suggests that the temperature variation in the atmosphere can affect the corrosion resistance of rebar materials used in concrete, hence, changing the service life of these structures. The effect of temperature on CTL of reinforcing steel materials should be further understood and considered when selecting these alloys for more extended service design of concrete structures.

INTRODUCTION

Steel rebar in concrete is in a passive state due to the high pH of concrete. The hydroxyl (OH) ions in highly alkaline concrete pore solution act as inhibitors and promote passive film stability, while chloride ions lead to passive film breakdown. Leckie and Uhlig1 first explained the counter effect of inhibitor action with chloride concentration. They proposed a competition between the inhibitor and chloride anions for adsorption on the passive surface. At sufficiently high chloride concentrations, known as chloride threshold limit (CTL), oxygen which makes up the passive film, is displaced locally by Cl ions, thus, causing the breakdown of the passive layer.

Changes in climates may further increase the risk of corrosion damage to critical reinforced concrete (RC) infrastructure and impose more challenges to the corrosion protection and mitigation of bridges exposed to extensive use of de-icing salt in winter. Wang et al.2 pioneered the specific modelling of climate change's impact on the corrosion of concrete structures by taking into account the changes in CO2 concentration in the atmosphere and temperature effect on the diffusion of chlorides into concrete. Zhang et al. 3 studied the corrosion initiation of reinforcing steel in a changing climate while considering the impact of temperature on chloride diffusion in concrete and embedded steel rebars. It was shown that a temperature increase of 1.3-3.1 °C may decrease the expected CTL of a rebar by 8-19%. Canada's average annual temperature has risen by 1.7 °C since 1948, double the global rate.4 An experimental study by Deus et al. 5 suggested that temperature plays a significant role in the passive film's stability and the pore solution's chemistry.

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