Study On Damage Evolution At Elevated Temperatures Of Thermal Insulation Concrete With Recycled Aggregates Based On CT Image Processing

High temperature(fire)will reduce the structural performance of concrete buildings.Under the action of high temperature,concrete macroscopic mechanical properties are reduced due to the difference of material properties of each component and the influence of preparation process.High temperature damage is serious on the surface of the structure,and through CT scanning,the internal meso-structure will be damaged under the action of high temperature.Due to the material property and process of regenerated thermal insulation aggregate and vitrified microsphere thermal insulation aggregate,the high temperature macro and micro damage damage and mechanical properties of regenerated thermal insulation concrete are different from those of ordinary concrete.This paper studies the influence of high temperature on the macroscopic mechanical properties of RATIC and the damage law of meso-structure and the relationship between them.Through the analysis of the CT image characteristics of recycled thermal insulation concrete,the characteristics of damage change of concrete internal mesostructure were studied,and the relationship between high temperature meso-damage and macro mechanical properties of recycled thermal insulation concrete was studied in combination with the experiment of macro mechanical properties of recycled thermal insulation concrete after high temperature.(1)The high temperature mechanical performance test was carried out on the100mm×100mm×100mm cubic recycled thermal insulation concrete specimens with different replacement rates of recycled aggregate and different mixing amounts of glass glass beads.The experimental results show that the apparent color of the specimen gradually deepens with the increase of temperature,and gradually turns red from cyan gray.The apparent damage of the specimen gradually appeared serious Angle missing,skin peeling and loose phenomenon from no obvious crack,and accompanied by serious crack damage.(2)Due to the material properties of recycled aggregate,the mass loss rate increases with the increase of the replacement rate of recycled aggregate.When glass bubbles are added,the mass loss rate increases with the increase of glass bubbles because of the change of water usage during preparation.The residual compressive strength of all RATIC specimens showed obvious two-stage characteristics,and the critical temperature was 300℃.Reclaimed coarse aggregate and glass bubbles have little effect on the compressive strength of recycled thermal insulation concrete.The addition of vitrified microspheres can alleviate the effect of temperature on cement slurry and reduce the high temperature damage.By analyzing the variation characteristics of the relative residual compressive strength of concrete at different temperatures and combining with the tests,a two-stage thermal damage calculation model was established.(3)The high temperature CT test was carried out for the 50mm×500mm cylinder recycled thermal insulation concrete specimens with different replacement rates of recycled aggregate and different mixing amounts of glass glass beads;Through CT image analysis,it is found that the internal meso-structure damage of recycled thermal insulation concrete at high temperature increases with the increase of temperature.The main reason is the steam pressure caused by a series of physical and chemical reactions in the concrete at high temperature.Because of the moisture content of reclaimed aggregate,RATIC suffered serious high temperature mesodamage.The addition of vitrified microspheres can obviously alleviate the high temperature damage of cement slurry and pore boundary.Due to the special honeycomb structure of the glass bubbles,the pore damage data in the experimental CT images were intensified with the increase of the mixing amount of the glass bubbles.However,it was verified by the compressive test that the pore damage data had no obvious effect on the residual compressive strength.The damage of high temperature pores in the middle part of RATIC specimen is reduced compared with that in the edge.After adding glass bubbles,the damage reduction phenomenon is more obvious because of the material properties of glass bubbles.By means of high temperature RATIC mesoscopic structure damage and the correlation between mechanical performance degradation characteristics analysis found that the residual compressive strength after high temperature and cause the degree of pore coarsening roughly the present linear relationship,but only through the porosity for the analysis of the high temperature performance of concrete is not comprehensive,high temperature performance of concrete is caused by multiple factors comprehensive,The porosity of concrete at high temperature can only reflect the changing trend of its properties to a certain extent.