Development of a sample preparation procedure for Sr isotope analysis of Portland cements

The ⁸⁷Sr/⁸⁶Sr isotope ratio can, in principle, be used for provenancing of cement. However, while commercial cements consist of multiple components, no detailed investigation into their individual ⁸⁷Sr/⁸⁶Sr isotope ratios or their influence on the integral ⁸⁷Sr/⁸⁶Sr isotope ratio of the resulting cement was conducted previously. Therefore, the present study aimed at determining and comparing the conventional ⁸⁷Sr/⁸⁶Sr isotope ratios of a diverse set of Portland cements and their corresponding Portland clinkers, the major component of these cements. Two approaches to remove the additives from the cements, i.e. to measure the conventional ⁸⁷Sr/⁸⁶Sr isotopic fingerprint of the clinker only, were tested, namely, treatment with a potassium hydroxide/sucrose solution and sieving on a 11-µm sieve. Dissolution in concentrated hydrochloric acid/nitric acid and in diluted nitric acid was employed to determine the ⁸⁷Sr/⁸⁶Sr isotope ratios of the cements and the individual clinkers. The aim was to find the most appropriate sample preparation procedure for cement provenancing, and the selection was realised by comparing the ⁸⁷Sr/⁸⁶Sr isotope ratios of differently treated cements with those of the corresponding clinkers. None of the methods to separate the clinkers from the cements proved to be satisfactory. However, it was found that the ⁸⁷Sr/⁸⁶Sr isotope ratios of clinker and cement generally corresponded, meaning that the latter can be used as a proxy for the clinker ⁸⁷Sr/⁸⁶Sr isotope ratio. Finally, the concentrated hydrochloric acid/nitric acid dissolution method was found to be the most suitable sample preparation method for the cements; it is thus recommended for ⁸⁷Sr/⁸⁶Sr isotope analyses for cement provenancing.