A. Kazlagic, F. F. Russo, J. Vogl, G. J. G. Gluth, D. Stephan

¹ Federal Institute for Materials Research and Testing, Division 1.1 Inorganic Trace Analysis, Richard-Willstäter-Straße 11, 12489 Berlin, Germany

² Federal Institute for Materials Research and Testing, Division 7.4 Technology of Construction Materials, Unter den Eichen 87, 12205 Berlin, Germany

³ Technische Universität Berlin, Department of Civil Engineering, Building Materials and Construction Chemistry, Gustav-Meyer-Allee 25, 13355 Berlin, Germany

To identify the geographical origin of ordinary Portland cement (OPC) commonly used in concrete structures, its major constituent – OPC clinker – has to be investigated. Clinker is mainly produced from local materials in a rotary kiln at ~1450 ᵒC from two main types of raw materials: calcareous material, typically limestone or chalk, and to a lesser degree argillaceous material, such as clay or shale. Each of these materials contains strontium, an element whose isotopes provide information on the geographical origin. Therefore, clinkers can be considered as specific and unique materials regarding their isotopic signature, particularly the ⁸⁷Sr/⁸⁶Sr isotopic fingerprint. Besides clinker, whose mass percentage in OPC is about 95 %, about 5 % of cement is gypsum, anhydrite, limestone or other additives. Since those materials also contain strontium, it is very important to gain information on their influence on the final ⁸⁷Sr/⁸⁶Sr isotopic ratio of cement. Therefore, the development of a suitable sample preparation procedure, which ideally removes the additives and in first approximation returns the ⁸⁷Sr/⁸⁶Sr isotopic fingerprint of the clinker only is of primary importance. In this research, four different approaches have been tested with the aim of finding the most appropriate sample preparation procedure for Sr isotope analysis in cement. The selection of the most suitable sample preparation procedure is realized by comparing the ⁸⁷Sr/⁸⁶Sr isotope ratios of fifteen differently prepared OPC samples with those of the corresponding clinker samples. The final goal is to develop a procedure for preparing Portland cement in such way that its ⁸⁷Sr/⁸⁶Sr ratio gives the closest value to the ⁸⁷Sr/⁸⁶Sr ratio of the corresponding clinker, which is the target value.