Kilogram scale synthesis of C3A polymorphs and their hydration reactions

Abstract

Studies on the properties of pure C3A phases are often limited to methods requiring small sample amounts due to the lack of a convenient laboratory synthesis yielding sample amounts exceeding 100 g. Here, we report a simple and large scale lab method for the synthesis of C3A polymorphs with yields of up to 500 g per batch. Commercial calcium aluminate cement (CAC) was used to prepare cylindrical green bodies of CaCO3 and Al2O3 (and NaNO3 for orthorhombic and monoclinic polymorphs). The green bodies were sintered at 1300 °C and 1400 °C respectively. The chemical and mineralogical compositions of the obtained C3A polymorphs were analyzed by X-ray powder diffraction and X-ray fluorescence spectroscopy. The reactivities of these C3A polymorphs were compared to conventionally synthesized C3A (using mechanical powder compaction prior to sintering) via in-situ isothermal heat flow calorimetry. Additionally, we demonstrate that synthetic C3A retains its reactivity over one year if stored appropriately. As the new synthesis protocol yields hundreds of grams of C3A, it enables experimental methods such as slump flow testing with pure phases, which is also reported for all polymorphs.