EFFECT OF THERMAL TREATMENT ON THE DYNAMIC MECHANICAL BEHAVIORS OF LIMESTONE IN QUASI-VACUUM AND AIR-FILLED ENVIRONMENTS
AbstractTHERMAL DAMAGE IN ROCK ENGINEERING OCCURS IN THE AIR-FILLED AND QUASI-VACUUM ENVIRONMENTS OF ROCK MASS LOCATED NEAR OR FAR FROM THE FREE SURFACE. MEANWHILE, DYNAMIC LOADS ARE ENCOUNTERED FREQUENTLY IN ENGINEERING PRACTICE. IN THIS STUDY, 39 LIMESTONE SAMPLES ARE PREPARED, AND A SERIES OF LABORATORY TESTS, INCLUDING SPLIT HOPKINSON PRESSURE BAR (SHPB), NUCLEAR MAGNETIC RESONANCE (NMR) AND OPTICAL MICROSCOPY ANALYSES, ARE CONDUCTED TO INVESTIGATE THE EFFECTS OF TEMPERATURE AND THE ENVIRONMENT ON THE DYNAMIC MECHANICAL PROPERTIES OF LIMESTONE. THE RESULTS SHOW THAT THE MACRO-PHYSICAL AND DYNAMIC MECHANICAL PROPERTIES OF LIMESTONE AFTER THERMAL TREATMENT CAN BE DIVIDED INTO TWO STAGES BY A CRITICAL TEMPERATURE OF 450°C, AT WHICH THE THERMAL DAMAGE FACTOR IS 0.71 AND 0.75 IN THE QUASI-VACUUM AND AIR-FILLED ENVIRONMENTS, RESPECTIVELY. IN THE FIRST STAGE, WITH TEMPERATURES VARYING FROM 25°C TO 450°C, THE THERMAL DAMAGE DUE TO EXPANSION AND FRACTURING SLIGHTLY INFLUENCES THE RELATED PARAMETERS, EXCEPT THE P-WAVE VELOCITY. HOWEVER, IN THE SECOND STAGE, WITH TEMPERATURES RANGING FROM 450°C TO 900°C, THE THERMAL DAMAGE CAUSED BY MINERAL DECOMPOSITION AND HYDRATION LEADS TO A REMARKABLE DECREASE IN THE DYNAMIC BEARING AND ANTI-DEFORMATION CAPACITIES. THE ENVIRONMENT PLAYS A NEGLIGIBLE ROLE IN THE FIRST STAGE BUT AN IMPORTANT ROLE IN THE SECOND STAGE, AND THE DYNAMIC COMPRESSIVE STRENGTH AND MODULUS OF SAMPLES AFTER THERMAL TREATMENT IN THE AIR-FILLED ENVIRONMENT ARE MUCH LOWER THAN THOSE IN THE QUASI-VACUUM ENVIRONMENT. BOTH THE TEMPERATURE AND ENVIRONMENT OF THERMAL TREATMENT SHOULD BE CONSIDERED IN ENGINEERING PRACTICE, ESPECIALLY WHEN THE TEMPERATURE EXCEEDS 450°C.
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