Role of ternesite on the hydration of C3A in the presence and absence of gypsum

Abstract

In the search for new eco-cements it has been found that ternesite (2C2S·CaSO4), which has traditionally been regarded as a hydraulically inactive phase, can be activated by aluminum hidroxides (AH3) and some calcium aluminates. This research, in particular, studies the role of ternesite on C3A hydration, with and without gypsum. After laboratory synthesis, C3A was blended with ternesite, gypsum and ternesite+gypsum. The early hydration of those blends was monitored with isothermal conduction calorimetry at 25 °C for 7 days. The resulting pastes were analysed with XRD, FTIR and DTA/TG. Additionally, mixtures of C3AH6 and ternesite in water were prepared in order to study their compatibility. The calorimetric results showed a higher total heat per gram of aluminate in the sample containing gypsum and ternesite than in the sample C3A+ternesite. XRD diffractograms and DTG-TG analysis revealed the presence of AFm in all the samples with gypsum but not in C3A+ternesite which shows no evidence of ternesite activation by C3A.