Mechanical properties and damage evolution of cemented coal gangue-fly ash backfill under uniaxial compression: Effects of different curing temperatures

A high geothermal heat affects the physical properties of cemented coal gangue-fly ash backfill (CGFB). The mechanical properties, damage evolution, elastic modulus, and peak strain of CGFB under uniaxial compression were investigated at different curing temperatures (20 degrees C, 35 degrees C, and 50 degrees C) and curing ages (3, 7, 14, and 28 days), and the stress-strain curves were obtained. The results show that the elastic modulus and peak strain of CGFB exhibit an increasing overall trend with a rise in the curing temperature; the 14th day of curing is the inflection point of the elastic modulus curve of the CGFB specimens. The theoretical results based on the piecewise damage constitutive model are in good agreement with the experimental results, indicating that the model is reasonable. Four damage stages of the CGFB are observed: no damage, initial damage formation, accelerated damage growth, and stable damage development. The CGFB specimens cured at 35 degrees C and 50 degrees C suffer complete damage, whereas the CGFB specimens cured at 20 degrees C are not completely damaged, with a damage value of only 0.5409. The damage trend under uniaxial compression indicates that the damage value increases slowly from 0 at the initial stress, rapidly increases after the peak stress, and increases slowly until the damage value reaches 1, and the CGFB suffers a complete failure. This paper lays a foundation for analyzing the stability of CGFB in a high geothermal environment.