The effect of saturation Methods on natural gypsum rocks

When the gypsum rock is exposed to the relative humidity in a closed environment for a continuous period, the result is an increase in the weight of these rocks after the passage of the first 24 hours, and there is no effect on the percentage of gypsum that the rocks contain, as the weight increase occurred at the same time for the different gypsum ratios. For rocks submerged in potable water and located within a humid environment, most of these rocks witnessed weight gain, with some exhibiting dissolving behavior. As for the gypsum rocks submerged with water saturated with aqueous calcium sulfate salt, they witnessed weight gain without any solubility. It is worth noting the important effect that relative humidity plays in the atmosphere at high levels, as it stimulated the saturation property to cover and overcome the famous property of gypsum rocks, which is the melting at high humidity.

Correlation between the mineral composition and strength properties of sulfate rocks

The literature review confirms that the effect of mineral composition on the strength properties of rocks has rarely been studied. One of the most problematic sedimentary rocks is sulfate rocks, which cause engineering problems in the infrastructure sites such as reservoir dams. In this paper, for the first time, the effect of mineral composition on the strength properties of sulfate rocks was investigated. The rock blocks were collected from the Gachsaran Formation outcrops at the four under construction reservoir dam sits in Iran. After preparing, drying and saturation the rock cores samples (329 samples), uniaxial compressive strength tests were performed in accordance with ASTM and ISRM standards. The results of this study confirmed that firstly, there is a correlation between the mineral composition and the strength properties of the sulfate rocks, but the obtained relationships do not have the necessary certainty to be used as predictive equations. Secondly, by increasing the amount of anhydrite or microcrystalline carbonates in a gypsum rock, its strength properties are increased. Thirdly, in a dry condition the dominant failure mode in gypsum and anhydrite rocks is a shear and dilatation mode, respectively, but after saturation, the failure mode tends to shear mode.

Experimental investigation into the effects of composition and microstructure on the tensile properties and failure characteristics of different gypsum rocks

The present work investigated the differences in the composition and internal microstructure of four types gypsum rock—fiber gypsum, transparent gypsum, alabaster, and ordinary gypsum by X-ray fluorescence spectrometry, X-ray diffraction, scanning electron microscope and Brazilian split test, and analyzed its effects on the tensile strength and fracture characteristics of gypsum rock. For alabaster, fiber gypsum, transparent gypsum, and ordinary gypsum, CaSO4·2H2O is the main component with 72.78%, 72.72%, 72.57%, and 71.51% content, and tensile strength of 1.79, 2.22, 3.22, and 4.35 MPa, respectively. In addition, the fracture line is arc-shaped, vertical, and zigzag for fiber gypsum, ordinary and transparent gypsums, and alabaster, respectively. On the microscopic level, fiber gypsum has an evident striated structure while the gradual increased pore development for alabaster, transparent gypsum, and ordinary gypsum. Gypsum rock has an obvious layered crystal structure with the increase of CaSO4·2H2O, contributing to the phenomenon with a larger grain size and lower tensile strength. In addition, the number of particles for alabaster, transparent gypsum, and ordinary gypsum increased in turn, while their particle size decreased uniformly, indicating that the lower CaSO4·2H2O content, the more sufficient energy accumulation and release. This paper can provide a theoretical basis for the analysis of the mechanical properties of rocks with different mineral composition and contribute to the design for different ore grades mining.

Effect of Microstructure and Relative Humidity on Strength and Creep of Gypsum

The wide range of gypsum facies observed all over the world and the strong heterogeneity that may be present even within a single facies often cause an inhomogeneous mechanical response that, if neglected, may be particularly dangerous in the framework of underground excavations. In addition, gypsum is particularly sensible to the presence of water. The high relative humidity conditions often registered in underground gypsum quarries may imply an additional worsening of mechanical properties. In the present study, the strength and the creep response of a natural gypsum rock facies are investigated, considering the influence of material heterogeneity and relative humidity conditions. The heterogeneity of the material, quantified with MIP and SEM analyses, is observed to strongly affect the mechanical response. To this intrinsic mechanical variability, the influence of an external parameter as the relative humidity is observed to generate an additional reduction of material strength and to increase the creep strain rate in the long-term tests. The effect of all these elements in the underground quarry framework is discussed and a constitutive model of these experimental results is provided.

Influencing Factors for the Instability and Collapse Mode of the Goaf Structure in a Gypsum Mine

Large-area goafs in a gypsum mine tend to collapse after 10 or more years, but the influencing factors are still unclear, and the effects of multiple factors have not been comprehensively considered. In this study, the failure mechanism and collapse mode of the room-pillar goaf structure were analyzed, and the uniaxial compressive strength tests of the pillars under different conditions were carried out in a laboratory. The influences of water, temperature, and time on the strength of the gypsum rock were considered. These three factors weakened the gypsum rock in different degrees. After 120 days of immersion, water had the greatest effect with a strength-weakening rate of 52.61%. After 20 temperature cycles, changes in temperature had little effect with a strength-weakening rate of 12.60%. After 25 years of aging, the strength-weakening rate of time was 25.13%. These results show how different factors affect the instability and collapse of the goaf structure, which are of great significance for predicting and preventing this from happening.

The use of natural clay-carbonate gypsum in the production of sulfate-containing cements

The purpose of the article is to study the raw materials located in the deposits of Kyrgyzstan and used in the production of sulfate-containing cements. The article aims to identify features of the technological process of clinker formation. An analysis of deposits of gypsum raw materials in Kyrgyzstan was carried out. For the most common raw materials of limestones, their chemical and mineralogical composition was studied using the chemical, derivatographic and X-ray methods. By calculating raw mixtures, a charge was produced for obtaining sulfate-containing cement from limestone of the Tashkumyr deposit, local loams and clay-carbonate gypsum. The temperature regime of the clinker formation of sulfate-containing cements using local clay-carbonate gypsum awas studied. The article analyzes an effect of high temperatures on clay-carbonate gypsum whose chemical and mineralogical composition decreases the decarbonization temperature and causes the partial decomposition of CaSO4 and the early formation of primary clinker minerals. The use of gypsum rock with a high content of carbonates and clay impurities as a sulfate component in the preparation of sulfoclinkers helps to reduce the decomposition temperature of calcium carbonate and sulfate during burning. The data on the intensification of clinker formation are presented. They depend on the composition of charge components and the burning temperature, which correspond to the low-power technology. The technology can save energy, reduce CO2 emissions and improve the environmental safety.