Volume changes of gypsum-based lightweight mortar during the heating process

Abstract Gypsum-based lightweight mortar undergoes dehydration of gypsum when subjected to changes in external temperature, which macroscopically manifests as a change in volume. Based on the dehydration kinetics of gypsum, the phase transition during dehydration was investigated, and a volume evolution model driven by the expansion force of water vapor after dehydration was established. The model was subsequently refined through experiments. The results showed that the volume of gypsum-based lightweight mortar gradually increased with rising temperature. Additives such as hydroxypropyl methylcellulose (HPMC), hydroxypropyl starch ether (HPS), and redispersible latex powder (LP) had a relatively minor effect on the volume expansion of the lightweight mortar. After simulating the experimental data using the established mathematical model, it was shown to effectively represent the volume change of the gypsum-based lightweight mortar during the heating process. Based on this mathematical model, the thermal expansion of gypsum-based lightweight mortar with a larger volume was studied. Calculations revealed that as the volume expanded, the temperature difference between the interior and exterior of the mortar increased, which slowed down the dehydration rate of dihydrate gypsum and correspondingly reduced the volume expansion of the gypsum-based lightweight mortar.