How Do Isothermal Calorimeters Age? Repeatability and Reproducibility Across Calorimeter Generations

Reliable experimental data is essential for reproducible science. As our lab has access to five instruments of the isothermal (heat conduction) type of different age and product generations, we became interested in the quality of experimental data obtained from the different instruments. Each instrument consists of 8 individual calorimeters. An intralaboratory study of the first 72 hours of cement hydration was conducted with all five instruments. The objective was to determine the differences between the available instruments with respect to repeatability (precision of the 8 calorimeters within one instrument) and reproducibility (precision between the different instruments). The experimental program comprises 120 calorimetry runs in total (5 instruments each with 8 calorimeters, triple measurement performed). Results show that the oldest instrument version with its 8 calorimeters has a stronger higher standard deviation of the heat released after 72 hours compared to the latest state‐of‐the‐art instrument model (246.7 ± 2.7 vs. 232.3 ± 0.5 Jg^–1). This is attributed to the technical design differences of the instruments and continuous use over time. In terms of reproducibility, an increasing standard deviation for the heat released from 1 day to 3 days (136.2 ± 2.6 and 236.4 ± 5.9 J g^–1) is observed. From our point of view, this test study indicates that isothermal heat conduction calorimetry is a robust and precise measurement method to determine the heat of cement hydration for 72 hours.