Theoretical Time Evolution of Critical Chloride Content in Concrete

The critical chloride content for corrosion initiation is a crucial parameter in determining the durability and integrity of reinforced concrete structures, however, the value is still ambiguous. Most studies reporting the critical threshold of the chloride content have involved experimental measurements of the average amount of the total chloride content at an arbitrary time. Although carbonation can significantly impact on critical threshold chloride content, the majority of the researches have not dealt with this issue in combination with carbonation of concrete. Furthermore, many studies have tried to define the critical chloride content within the scope of their experimental concrete mix proportion at arbitrary time. However, the critical chloride content for corrosion initiation is known to be affected by a lot of factors including cement content, type of binder, chloride binding, concentration of hydroxyl ions, and so on. It is necessary to define a unified formulation to express the critical chloride content for various mix proportions of concrete. The purpose of this study is to establish an analytical formulation of the critical chloride content of concrete. In this formulation, affecting factors, such as mix proportion, environment, chemical evolution of the pore solution with elapsed time, carbonation of concrete and so on are taken into account. Based on Gouda's experimental results, the critical chloride content is defined as a function of [Cl−] vs. [OH−] in the pore solution. This is expressed as the free chloride content per unit of mass to consider time evolution of [OH−] content in the pore solution using the numerical simulation program for cementitious materials, HYMOSTRUC. The results are compared with other experimental studies and with various codes. It is believed that the approach suggested in this study could provide a good solution to determine the critical chloride content with the original source of chloride ions, for example, marine sand at initial time, and sea water penetration later on.