Increased monocarbonate formation during long-term hydration of CAC-limestone binder by calcium sulfate addition – A temperature-dependent XRD study

Abstract

The long-term hydration of a mix with and without gypsum addition was investigated at 10, 23 and 40 °C by QXRD analysis. In addition, thermodynamic modelling was performed on all systems using GEMS to determine the stable phase composition and the influence of water loss during hydration. The results show that the formation of conversion-sensitive phases such as CAH10 is accelerated at 10 °C and hindered at 23 and 40 °C by the addition of gypsum. Moreover, at all different temperatures, monocarbonate forms next to AH3 as the main hydrate phase and the final phase composition is reached after at least 14 d (at 23 °C and 40 °C already after 2 d). Formation of low amounts ettringite only occurs at 10 and 23 °C during the entire storage time. At 40 °C, however, ettringite is not observed, which is probably due to water loss in the mix until 2 d.