Study On Physical Properties Of Sandstone Under Burning

Based on the engineering background of burnt rock in coalfield geology,high temperature heating experiment of sandstone was carried out.The influence of temperature range of 25-1300? on the chroma and wave velocity of sandstone was studied by instrument.At the same time,the compressive strength,tensile strength and acoustic emission experiments were tested,and the influence of temperature on the strength of samples and the development of internal cracks in sandstone under pressure were analyzed.In addition,the changes of mineral composition and physicochemical reactions in sandstone under different temperatures are studied by means of thermal analysis under two different thermal analysis environments of air and argon.The physical properties of rocks are analyzed from the macro-micro response angle.The research results in this paper provide theoretical support for the study of the formation mechanism and physical characteristics of burnt rocks.The main results are as follows:(1)The chroma of sandstone increases slowly from 100 to 400?,a* and b* increase rapidly.From 500 to 800?.a* and b* increase slowly.From 800 to 1100?,a* decreases rapidly and b* decreases slowly.L*,a* and b* decrease rapidly from 1100 to 1150?.The thermal conductivity of sandstone is relatively stable between 100 and 400?,rapidly declines between 400 and 1000?,and increases from 1000 to 1200?.(2)The failure mode of sandstone changes from brittle failure to plastic failure with temperature,which is reflected in the relationship between compressive strength and axial strain: with temperature rising,compressive strength decreases gradually,peak axial strain increases,and slope of strength-strain curve decreases.The variation of acoustic emission is consistent with the time stress curve of compression test.In the compaction stage,there is a small number of ringing,and in the destruction stage,there is a dense ringing stage.With the increase of temperature,the number of rings decreases and the ductility of rocks increases gradually.(3)In the process of thermal analysis of argon environment,according to the sample heating temperature,it can be divided into three stages: stage ?,stage ? and stage ?,which correspond to the three temperature ranges of 25-500? 600-800? and 1000-1300?.In stage ?,five physical and chemical reactions were successively observed,namely,adherent water dehydration,combined water dehydration,crystalline water dehydration,structural water dehydration and calcite decomposition.These reactions correspond to the valleys of DSC curves and are endothermic reactions.In stage ?,the dehydration process of sandstone samples treated at 600? and above is irreversible.In stage ?,calcite is completely decomposed in sandstone treated at 1000? and above.In the air environment,it can also be divided into five regions: a,b,c,d and e.However,regions a and b merge,the decrease in region c is smaller than that in argon atmosphere.(4)According to the macroscopic characteristics of samples and the relationship between parameters and temperature,100-1300? is divided into four stages: stage ?(100-400?),stage ?(400-800?),stage ?(800-1100?),stage ?(1100-1300?).It is found that the color of sandstone turns red in stage ? and stage ?,and the velocity is linearly correlated with the strength and thermal conductivity.In stage ?,there is a penetrating crack.In stage ?,the surface of sandstone gradually turns black,albite begins to melt,and the surface of sample gradually becomes smooth.In general,wave velocity,strength,chroma and thermal conductivity have good response to the change of micro-damage.