Analysis of drying and saturating natural gypsum samples for mechanical testing

Authors

Mohammadhossein Sadeghiamirshahidi, Michigan Technological UniversityFollow
Stanley Vitton, Michigan Technological UniversityFollow

Document Type

Article

Publication Date

4-2019

Department

Department of Civil, Environmental, and Geospatial Engineering

Abstract

The stability of underground abandoned gypsum mines is dependent on the gypsum pillar's strength, and most abandoned mines are in a fully saturated condition. Moisture affects the strength of gypsum and is therefore commonly measured when testing rock strength. For most rocks, this is a simple task of weighing the rock's mass before and after oven-heating at a specified temperature and duration. For natural gypsum, however, this is not a straightforward process. Heating natural gypsum can result in dehydration and transformation of gypsum to hemihydrate and anhydrite, thus changing the physical characteristics of the gypsum such as its particle density which in turn affects the moisture content and strength measurements. To prevent transformation when determining the moisture content of gypsum, the American Society for Testing Materials (ASTM) recommends lowering the drying temperature from 110 °C to 60 °C. To investigate the temperature at which gypsum transforms to hemihydrate, we used a helium pycnometer to measure the particle densities of gypsum, hemihydrate and anhydrite. In this research, we suggest that a higher drying temperature of 80 °C can be used for drying gypsum without transforming gypsum to hemihydrate. Further, preparing saturated samples for mechanical testing, which is required in stability analyses of abandoned mines, is challenging due to the dissolution of gypsum when placed in water. To address this problem, we investigated the following methods to saturate gypsum cores taking into account the solubility of gypsum: (1) water immersion, (2) vacuum saturation, and (3) improved vacuum saturation. The research indicates that all the three methods are acceptable but they should be conducted using a saturated gypsum-water solution to minimize dissolution. Further, the research found that the improved vacuum saturation method saturated the test samples within 24 h, while duration of 30 h was required for the other two methods.

Publisher's Statement

© 2018 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. Publisher’s version of record: https://doi.org/10.1016/j.jrmge.2018.08.007

Publication Title

Journal of Rock Mechanics and Geotechnical Engineering

Recommended Citation

Sadeghiamirshahidi, M., & Vitton, S. (2019). Analysis of drying and saturating natural gypsum samples for mechanical testing. Journal of Rock Mechanics and Geotechnical Engineering, 11(2), 219-227. http://doi.org/10.1016/j.jrmge.2018.08.007
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p/6820

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.

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Publisher's PDF