Chloride transport in mortar at low moisture concentration

Abstract

Chloride penetration into cementitious structures with a steel reinforcement results in corrosion of the steel. Concrete columns of bridges, which are in frequent contact with sea water, are an example of these structures. Understanding the chloride transport in cementitious materials can lead to improving their durability. In this paper, the chloride transport driven by moisture transport in various specimens is compared experimentally. Standard mortar specimens, with a water cement ratio of 0.5, are immersed into sodium chloride solutions to obtain specimens with the chloride mass percentage of 2.0%. The specimens, with initial chloride of 2.0%, are exposed to relative humidities of 55% at the top and 70% at the bottom, to obtain a moisture transport through the specimen, during 10 months. The chloride profiles before and after the experiment are compared. The concentration is measured with three techniques; Titration, Ion Chromatography and XRF. The results show that the chloride concentration measurement with Titration and Ion Chromatography are similar while the measurement with XRF is approximately 30% higher. Furthermore, due to the moisture transport through the specimen during 10 months, the total chloride content of the specimen seems to be decreased. Although that at the beginning of the experiment the chloride concentration at the surface is higher than the average concentration, this surface concentration at the end of the experiment is surprisingly lower than the average concentration.