Determination of the chloride ion content in concrete under simultaneous chloride and sulphate ion attack

This paper proposes a modified testing method for the determination of chloride ion concen-tration of concrete, which is a significant parameter for the durability design and service life prediction of concrete structures in marine environment. The existence of sulphate ions and allied cations in the seawater not only alter the diffusion and distribution of chloride ions in the con-crete, but also effect the accuracy of chloride ion concentration measured by silver nitrate titrate method. In the modified testing method, barium nitrate was used to eliminate the adverse effects of sulphate ions. Besides, the influences of barium nitrate addition and allied cations on both free and total chloride ion concentration test results were investigated respectively. The results demonstrate that the sulphate ion released from ettringite in dilute nitric acid, leading to a larger tested chloride ion concentration, and the error became larger with increasing sulphate ion concentrations. The addition of barium nitrate in immersion process reduced the error in the measurement of total chloride ion concentration. However, for determination of free chloride ion concentration, the addition of barium nitrate resulted in a lower test result since part of free chloride ions were replaced with sulphate ions in ettringite. Thus, addition of barium nitrate is only suitable for the determination of total chloride ion concentration, and traditional water-soluble method is more accurate for free chloride ion concentration measurement.

Automated summary

This paper proposes a modified testing method using barium nitrate to determine the chloride ion concentration of concrete in marine environment. It investigates the influences of sulphate ions and allied cations on the accuracy of chloride ion concentration measurement. The results show that barium nitrate is suitable for determining total chloride ion concentration, while traditional water-soluble method is more accurate for free chloride ion concentration measurement.