Unique Declining Trend in the Corrosion Deterioration of Steel Reinforced Concrete at Elevated Temperature and Moisture Conditions

摘要

Chloride induced corrosion under coupled environmental effects of high humidity and high temperature often found in gulf marine environment is a very serious threat for durability of reinforced concrete structures. There exist different schools of thought between various researchers and the data in high relative humidity and high temperature range is also limited. Therefore, the objective of this research paper is to investigate the impact of coupled effects of humidity and temperature on corrosion of reinforcing steel in concrete structures. This effect is investigated by laboratory controlled experimentation under three different temperature conditions (30, 40 and 50°C) and a high ambient relative humidity of 85% in environmental control chambers. Specimens were prepared having total chloride concentration in mixing water varying from 0-5 % by mass of binder. From the experiment results interesting and novel observations, trends and behaviours have been obtained. A non-uniform and non-linear corrosion reaction was observed even after the breaking of passive layer. Furthermore, a decrease in corrosion potential and corrosion mass loss at 50°C in comparison to 40°C temperature conditions was seen. This may be due to the reduction of oxygen solubility in the pore solution at high temperature and blockage of concrete pores at high relative humidity. Thus, producing a reversing trend in corrosion mass loss as a function of chloride concentration at high temperature condition of 50°C and high relative humidity of 85%. It is expected that a stable oxide layer may have developed under limiting oxygen controlled corrosion reaction. This can form basis for the development of a new technique to passivate steel bar embedded in chloride contaminated concrete. The paper also presents qualitative analysis of the microstructure of corrosion products under coupled varying temperature-chloride conditions and identifies the dividing line and turning point chloride concentration.