Deformation behavior Investigation of gypsum materials with variation moisture and stress

Due to the complex behavior of materials containing gypsum, loading of structures containing these materials such as dams and bridges, etc. is very important. Therefore, it is important to pay attention to the deformability of these materials under different environmental conditions such as humidity and stress. The present study has investigated the effect of moisture and stress changes on the samples extracted from the Marash Dam site located in Mahneshan city of Zanjan province. For axial loading, a device similar to uniaxial device was designed and built and 9 samples were exposed to different loads in three modes of humidity percentage of 30, 50 and 80%. Loads were applied at different time intervals and sometimes up to 45 days for creep testing. The results showed that with increasing stress, the amount of creep strain increases and with the stresses approaching the uniaxial strength of the sample, the values of creep strain increase so that with increasing stress from 1.3 to 3.5 MPa, the values of creep strains sometimes Increases up to 2.5 times. According to the results, most creep strains occur in the early days. Also, with increasing humidity, the strain of the sample increases and the behavior of the sample changes so that in low humidity the strain is elastic and reversible and in higher humidity the strain is plastic. Increasing the relative humidity increases the deformation of these materials so that as they approach the saturation state, the sample showed a very large volume change. The results also showed that when the sample is placed in water for a longer period of time, water easily penetrates into the microcracks and joints of the sample and reduces the integrity of the sample and its loosening.