Investigation into methods of chloride analysis of South African cement and cement-related materials with low chloride concentrations

This paper describes the findings of an investigation into the preferred method of chloride analysis on South African cement, clinker and raw materials, with low levels of chloride. The investigation entailed two parts. In the first part the reproducibility of the results obtained with the standard method (EN 196-21), employing an indirect Volhard titration to determine the total chloride content of the samples, were investigated. In the second part the reproducibility of the results obtained, employing alternative dissolution methods and an automated potentiometric titration, was investigated. It was found that the Volhard method produced highly variable results. The alternative procedures were found to be more precise and reliable. It was found that chloride measurements with an ion-selective electrode is more sensitive and yield better results in an acetate-containing medium than in a nitrate containing one. These conclusions were verified by statistical manipulation, using analysis of variance (ANOVA). The work performed showed that best results for chloride determinations at low levels are obtained if the method of standard additions is employed.