Conversion from metastable phase to stable phase in calcium aluminate cement (CAC) causes volumetric instability, resulting in loss of compressive strength. This study investigated the effect of CaSO 4 on the phase conversion of calcium aluminate cement. The specimens with different dosage of CaSO 4 were exposed to 60 °C to trigger the phase conversion of CAC after curing at 20 °C for 7 days. Analysis with X-ray diffraction, thermogravimetry, mercury intrusion porosimetry, and scanning electron microscopy were conducted. The incorporation of CaSO 4 inhibited the formation of unstable CAH 10 by direct precipitation of ettringite. As a result, the reduction of strength of CAC specimens due to the increased pore volume by conversion was inhibited by ettringite and monosulfate formation.
