Research On Mechanical Properties And Acoustic Emission Response Of Fiber Reinforced Concrete Under Thermal-mechanical Coupling

In recent years,frequent construction fires have pose a great threat to human's life and property safety.The current research on the high temperature resistance of concrete and fiber reinforced concrete materials mainly focuses on their performance after the processing of high temperature.When the project catches fire,the temperature change has an effect on the deformation of the force,at the same time,the deformation of the force has an effect on the temperature change.That is,the concrete material which as the main body of the structural load-bearing is under thermal-force coupling in the event of a fire in an actual construction project.The reference concrete,PVA fiber reinforced concrete,steel fiber reinforced concrete and PVA-steel fiber reinforced concrete were prepared,and the tests under high temperature and the thermo-mechanical coupling effect are carried out.Meanwhile,acoustic emission technology was used to track and monitor the heating process and the failure process of the specimens.At the same time,the high-temperature reinforcement mechanism of fiber reinforced concrete was explored by scanning electron microscope.The results showed that under the condition of high temperature,for mechanical properties,compared with the reference concrete,PVA fiber reinforced concrete has a higher temperature resistance performance.In addition,the stress-strain curve of PVA fiber reinforced concrete undergoes four stages:compaction,linear elasticity,plasticity,and failure.For acoustic emission,the ringing count of acoustic emission causes abrupt change near the peak stress corresponding to the specimen.The incorporation of PVA fiber can improve the ability of concrete to resist failure under high temperature,the damage D value of PVA fiber concrete is slower than that of the reference concrete and the value is lower than the reference concrete.Moreover,its high temperature resistance is stronger.A damage constitutive model of PVA fiber reinforced concrete is established under high temperature.Under the thermo-mechanical coupling effect,for macro performance,the apparent integrity is better after the incorporation of the steel fiber,the compressive strength of steel fiber reinforced concrete is the highest,the PVA-steel fiber reinforced concrete is second.In addition,the reinforcing effect of PVA fiber is not obvious,the compressive strength residual rate of fiber reinforced concrete is higher than the reference concrete at most temperature ranges.The incorporation of PVA fiber and steel fiber enhances the high temperature resistance of concrete.The effect of mixing PVA fiber and steel fiber on the longitudinal expansion deformation of concrete is optimal.For acoustic emission,in the process of temperature increase,the dense phenomenon of ringing count occurred at 400??500?,PVA-steel fiber reinforced concrete has higher temperature resistance performance,the mechanical properties of concrete and fiber reinforced concrete and their acoustic emission response have a good correspondence.The damage-inhibiting effect of fiber on concrete was verified by the established damage evolution equation.In the micromechanical aspect,the tensile strength of the PVA fiber cement-based specimens is higher than that of the reference cement specimens in the corresponding temperature range.At both temperature ranges of 20? and 100?,the bridging and fracture energy dissipation of PVA fibers enhances the tensile strength of cement-based materials.