Mechanical Properties And Microscopic Evolution Of Rubber Concrete At High Temperature And After High Temperature

In recent years,with the increasing demand for cars,the number of waste tires is also growing rapidly.Due to the low recovery rate of waste tires in China,serious ’black pollution ’ has been caused,which restricts the realization of China ’s ’ double carbon ’ goal.Therefore,waste tires are added to concrete as building materials,which can not only solve the problems of low recovery rate of waste tires and environmental pollution,but also improve the mechanical properties of concrete.However,the use of waste tires in concrete structures has brought many problems to the fire safety of concrete structures.The existing research on the mechanical properties of rubber concrete at high temperature mostly stays in the relevant tests after high temperature,which cannot accurately describe the mechanical properties of rubber concrete at high temperature.Therefore,it is necessary to study the mechanical properties of rubber concrete at high temperature,which is not only beneficial to evaluate the fire resistance of rubber concrete structure and ensure the safety of rubber concrete structure under fire,but also conducive to the wide promotion and application of rubber concrete in practical engineering.In this thesis,through the method of equal volume replacement of fine aggregate by rubber particles,by controlling the three variables of rubber particle size(10 mesh,40 mesh and 150 mesh),rubber content(0 %,10 % and 20 %)and temperature conditions(28 °C,100 °C,150 °C,200 °C,250 °C,300 °C and 400 °C),a total of 49 groups of rubber concrete specimens were made,and the high temperature mechanical properties of rubber concrete and the mechanical properties of rubber concrete after high temperature were tested.The apparent change and failure mode,stress-strain curve,compressive strength,elastic modulus and peak strain of rubber concrete specimens under high temperature and high temperature were analyzed and compared.Finally,the multi-scale analysis method is used to scan the initial state of the meso-morphology of the rubber concrete by SEM electron microscope,and the macro-failure mechanism and mechanical property attenuation mechanism of the rubber concrete are interpreted from the meso-perspective.The main research results are as follows :The incorporation of rubber particles will not change the shape of the dimensionless stress-strain curve of concrete at high temperature and after high temperature,but it can deteriorate the mechanical properties of concrete and improve the deformation ability of concrete,which is reflected in all temperature conditions,and the phenomenon is more obvious with the increase of rubber content.In addition,under the same temperature condition and rubber content,the mechanical properties of concrete containing 150 mesh rubber deteriorate the most at high temperature and after high temperature,and the deformation ability is the strongest,while the concrete containing 40 mesh rubber is the opposite.The incorporation of rubber particles reduces the compressive strength of concrete at high temperature and after high temperature,but under the same conditions,the compressive strength of each rubber concrete after high temperature is higher than that at high temperature.Moreover,the test results show that the compressive strength of rubber concrete with 40 mesh decreases the least at high temperature and after high temperature,followed by 10 mesh,and 150 mesh decreases the most.In addition,the compressive strength of rubber concrete at high temperature shows a complex nonmonotonic fluctuation(decrease-increase-decrease),and the compressive strength of rubber concrete after high temperature shows a change rule of increase-decrease.The above phenomena are also reflected in the elastic modulus of rubber concrete after high temperature and high temperature.The incorporation of rubber particles can reduce the peak strain of concrete at high temperature and after high temperature,and the effect is more obvious with the increase of rubber content.Under the same temperature condition and rubber content,the peak strain of 40 mesh rubber concrete decreases the least at high temperature and after high temperature,and the peak strain of 150 mesh rubber concrete decreases the most.Moreover,the peak strain and temperature condition curves of rubber concrete after high temperature and high temperature show an increasing trend with the increase of temperature,and the overall trend of peak strain rise of rubber concrete is significantly stronger than that of ordinary concrete.In addition,under the same conditions,the peak strain of each rubber concrete specimen after high temperature is higher than the peak strain at high temperature.There is an obvious interfacial transition zone(ITZ)between rubber particles and cement paste,and the smaller the rubber particle size,the smaller the thickness of ITZ between rubber particles and cement paste.However,at the same rubber content,when the rubber particle size is too small,it will have more specific surface area and form more ITZ.By calculating the ITZ volume between rubber particles and cement paste under the same rubber content,it is found that the ITZ volume of rubber concrete with40 mesh is the smallest and 150 mesh is the largest.This explains the phenomenon that the mechanical properties of rubber concrete with 40 mesh are the best and the mechanical properties of rubber concrete with 150 mesh are the worst in this experiment.By scanning the microscopic morphology of H-R20-D10 specimens after different high temperatures,it was found that the rubber particles still had a clear contour shape at 150 °C.As the temperature continues to rise,the secondary hydration of cement makes the microstructure of cement paste more dense,but at this time,the rubber particles gradually lose their initial contour shape,and the interface between rubber particles and cement paste becomes blurred,especially at 300 °C.Until 400 °C,the rubber particles completely melted and cracked,only some pyrolysis products were retained,and irregular holes of the same size were formed in the original place,and the meso-structure of rubber concrete was seriously deteriorated.It is also because of the evolution of the meso-structure of rubber concrete at different high temperatures that the mechanical properties of rubber concrete after high temperature and high temperature are changed.