Study On Mechanical Properties Of Concrete After Sub-high Temperature Cycle

Concrete is the dominant material in the construction field and plays a supporting role in major engineering structures such as ordinary civil buildings,bridge tunnels,water conservancy hubs and reactors.Compared with other building materials such as steel,concrete exhibits excellent high temperature resistance,but its mechanical properties are still greatly affected by high temperature.The research on the influence of high temperature on the mechanical properties of concrete is mainly focused on the high temperature with fire as background.Concrete chimneys,support structures for high-temperature equipment,industrial cooling towers,and some high-temperature industrial plants will be subjected to sub-high temperature cycles from normal temperature to about 150 °C during normal use.Whether the sub-high temperature cycle in this temperature zone affects the mechanical properties and durability of concrete is still unknown.Up till now,there is no enough experimental data and theoretical research support.Based on this,this paper carried out the mechanical properties test and numerical simulation of concrete under normal temperature to sub-high temperature(150 °C~200 °C).The main contents include:1.Uniaxial compression tests of different strength concretes were carried out.The axial strength of the three batches of concrete is in the range from 20 MPa to 70 MPa.Through the test,the apparent characteristics of concrete with different strengths under different sub-high temperature cycles were recorded.The mechanical parameters such as elastic modulus,compressive strength,peak strain and Poisson’s ratio were obtained by uniaxial compression test.The evolution law of the sub-high temperature cycle affects the macroscopic mechanical properties of concrete;the prediction formulas of mechanical parameters such as compressive strength and elastic modulus with the number of sub-high temperature cycles are fitted according to the experimental data.2.A model concrete uniaxial compression test was carried out with two different aggregate volume fractions.The mechanical model of concrete specimens is simplified,and the variation of mechanical properties of materials with different mass fractions of sub-high temperature cycles is studied.The effects of two aggregate volume fractions on the sub-hightemperature cycle are studied.Image processing technology(DIC)traces and analyzes concrete cracks during the test,studies the mechanism of concrete failure caused by sub-high temperature cycle,and studies the influence of sub-high temperature cycle on the performance of each phase from the concrete component level.3.A thermodynamic coupling analysis of the meso-concrete model was performed.The mesoscopic model of modeled concrete was established,and the damage evolution and stress development of aggregate,mortar and interfacial transition zone under sub-high temperature cycle were studied from the mesoscopic level.From the perspective of numerical simulation,the sub-high temperature cycle effect was further explored.The influence mechanism of the mechanical properties of various phases of concrete.Based on the above experimental and numerical simulation studies,this paper systematically establishes the evolution law of concrete mechanical properties with sub-high temperature cycle,and reveals the mechanism of the degradation of mechanical properties of concrete caused by sub-high temperature cycle from macro and mesoscopic scales.The research results are of great significance for the analysis and prediction of the mechanical behavior of concrete structures circulating under sub-high temperature conditions.