Physical properties and tensile strength evolution of gypsum materials under different water content conditions

•Three strength criterions were improved and the tensile strength of the gypsum materials was evaluated.•The reasons for the different failure modes of the samples under different water content conditions are discussed.•The plane stress distribution of Brazilian disc samples was discussed.•The plane strain distribution of the Brazilian disk sample was analyzed. To investigate the physical properties and tensile strength evolution of gypsum materials under different water content conditions, three groups of gypsum standard samples were prepared, including natural, saturated and dehydrated gypsum samples. Electron microscopy, composition analysis, Brazilian splitting tests and numerical simulation analysis were carried out. The results are as follows. The larger the water content of the samples is, the higher the content of CaSO4·2H2O, the more flocculation structures on the surface, and the higher the longitudinal wave propagation speed. Saturation and dehydration change the composition of the sample and cause a change in its tensile strength and failure mode. The fitting effect of the modified Hoek-Brown criterion is obviously better than that of the modified Mohr-Coulomb criterion because it considers the influence of uniaxial compressive strength. The Balmer criterion introduces the index b and greatly improves its regression accuracy. The vertical compressive stress exhibits a concentrated distribution. At x = 0, the peak value of the vertical load appears at the two ends of contact between the specimen and the indenter and gradually decreases from both ends to the centre. The horizontal stress is mainly tensile stress, and the value at x = 0 is the theoretical tensile strength. It is uniformly distributed on the line directly affected by the vertical load and decreases to both ends of the specimen along the line. It is reduced to 0 at the left and right ends. The horizontal deformation arises from both sides of the disk tip and then spreads downwards in an arc during loading. The horizontal strain in the upper part of the disk is always larger than that in the lower part. The upper part reaches its tensile strength and then fails due to the continuous loading.