Programmatic Data Analysis for Quantitative Isothermal Heat Flow Calorimetry of Cementitious Materials

Isothermal heat flow calorimetry is a powerful method for studying chemical processes. In cement research, it has become indispensable for quantifying the heat release during cement hydration. It is used to study the reactivity of cementitious binders and the effect of admixture chemistry and dosage. Most isothermal calorimetry data on cementitious materials is analyzed qualitatively, i.e., by graphical comparison of heat flow curves. This is a missed opportunity, as the method delivers precise quantitative data with clearly defined chemical meaning. This work presents a lightweight open-source toolchain for quantitative analysis of isothermal calorimetry data. Using this toolchain, we quantify the effect of three retarders, sucrose, etidronic acid, and racemic tartaric acid, on the hydration of Portland cement. In particular, we determine characteristic times and kinetic parameters such as the maximum heat flow, the duration of the dormant period, or the maximum acceleration and the corresponding time. The results reveal that the efficiency of the retarders ranks in the order sucrose > etidronic acid > DL-tartaric acid. Further, we find that the end of the dormant period of cement hydration is exponentially dependent on the dosage of etidronic acid. In contrast, sucrose and tartaric acid show a small deviation from an exponential relationship which indicates differences in the retardation mechanism. This is also reflected in the acceleration of the main silicate reaction. Increasing amounts of etidronic acid lead to a significantly more substantial reduction of the C3S hydration acceleration than sucrose. Additionally, the Vicat set times of the cement pastes were determined, and an excellent correlation was found with the time of the maximum acceleration of the silicate reaction.