Page 234 - Handbook of Thermal Analysis of Construction Materials

Section 3.0 - Non-Chloride Accelerators 217

gypsum is consumed in 30 minutes as evidenced by the decreasing intensity
of the peak at 130°C. After 30 minutes, the intensity of the endothermic
peak at 165–180°C increases substantially. This peak represents
monosulfoaluminate hydrate. XRD data confirm the presence of
monosulfoaluminate at 1 hour. In the presence of 12.5% gypsum and 12.5%
carbonate, the rate of disappearance of gypsum is accelerated. Gypsum is
consumed in 20 minutes. Formation of ettringite is accelerated by calcium
carbonated (peak at about 100°C). In the presence of calcium carbonate,
even at 10 minutes, ettringite lines appear in XRD. DSC results also
demonstrate that the ettringite peak occurs within 5 minutes in the presence
of the carbonate, but not in the sample with gypsum only.

Figure 24. Conduction calorimetric curves of C S hydrated in the presence of nitrobenzoic
3
acids.