Evaluation of the degradation of gypsum subjected to natural aging

Abstract

This research aims to evaluate the properties of gypsum with and without water repellent, with water/gypsum hemihydrate ratios of 0.7 and 0.9, when subjected to natural aging in both indoor and outdoor environments. For this purpose, in addition to the characterization of the materials and evaluation of the microstructure of the samples, the axial compressive strength, total immersion water absorption, mass loss, and capillary absorption of the test specimens were assessed. The properties were evaluated before aging, at zero age, and after 6, 12, 18, 24, 30, and 36 months of aging. It was observed that the microstructure of the dihydrate presents interwoven prismatic needles. Furthermore, the presence of the water repellent was identified both in the matrix and on the surface of the material, even after 36 months. The test specimens of type GR9 and GH9 exhibited the lowest mechanical strengths and highest absorption, both in indoor and outdoor environments. The mass loss assessed in the material exposed to the outdoor environment increased over time, indicating material dissolution caused by leaching from rainfall. This research concluded that the water/gypsum hemihydrate ratio, the addition of water repellent, and the exposure environment directly influence the percentage of water absorption and the mass loss of the material. Moreover, gypsum exposed to outdoor environments requires greater protection through the combination of water repellent and painting systems to reduce its degradation and early performance loss, contributing to greater durability.