Experimental Investigation On Mechanical Property Of Concrete Exposed To Low Temperatures

Low-temperature concrete is studied in this thesis based on the analysisfor existing research results at home and abroad. Through the experiments ofultra-low temperature concrete mechanical properties and their result analysis,the variation regularities and computing formulas about compressive strength,tensile strength, elasticity modulus and other physical quantities on concreteat various low temperatures are obtained. These will provide an importantbasis for structural design with their concrete exposed to very lowtemperatures.The finite element analysis using the software ANSYS is used to estimatehow the temperature distribution of the prism specimen is affected by concretemoisture content, cooling rate and temperature-lasting time. The experimentalsetup, including cryogenic furnaces and loading devices, is fabricatedourselves for testing mechanical properties of concrete at very lowtemperature.The experiment focuses on the concrete mechanical properties with thedecrease of temperature. One factor, namely temperature T, is considered. Thecooling rate is set to1℃/min. A total of12target temperatures are given from－196℃to20℃with an interval of20℃. All specimens were kept for48hours after the temperature decreased to the target value to make specimensattain a uniform distributed temperature. From the strength experiment results,it can be shown that the compressive strength of concrete at ultra-lowtemperature changes non-linearly with the decrease in temperature, and can bedivided into three phases: rapid increase from－20℃to－100℃. Thecompressive strength will roughly linearly increase as temperature decreasesin this temperature range and reaches a maximum value at－100℃; slightdecline from－100℃to－180℃. The compressive strength will slightlydecay with the decrease in temperature in this temperature range; and re-increase with the temperature below－180℃. The compressive strengthwill recover and start to increase with the decrease in temperature. From thetensile strength experiment results, it can be shown that the tensile strength ofconcrete at ultra-low temperature increases non-linearly, and can be dividedinto two phases: rapid increase from－20℃to－100℃. The tensile strengthwill roughly linearly increase as temperature decreases in this temperaturerange and reaches a maximum value at－100℃; and slight decline from－100℃to－196℃. Tensile strength will roughly linearly decline astemperature decreases in this temperature range. From the deformation testresults, it can be shown that the stress-strain curve of concrete will becomesteeper at low temperature, and the most obvious at－140℃, indicating theplastic deformation capacity and ductility of concrete goes weaker at lowertemperature. The peak stress, peak strain and elasticity modulus of concrete atultra-low temperature increase non-linearly with the decrease in temperature,and the peak strain reaches the maximum value in－70℃and the elasticitymodulus in－140℃.The mechanical properties of concrete at ultra-low temperature from thetest results are similar over－100℃comparing with the existing researchresults at abroad, and have an obvious difference below the temperature.Based on the experimental results, the mechanism of concrete strengthvariation at ultra-low temperature is also discussed, and an incrementalcomputing model for the compressive strength is suggested. Thecorresponding calculation results have a similar trend with the experimentalresults.