Study On Dynamic Compression Performance And Mechanism Of Recycled Tire Polymer Fiber Reinforced Concrete At High Temperature

In high temperature environment,concrete is damaged under the action of pore steam pressure.Meanwhile,hydration products in concrete are decomposed under high temperature environment,which reduces the adhesive force between components in concrete and further reduces the strength of concrete materials,threatening the safety of building structures.In order to reduce the damage of concrete caused by high temperature and improve the static and dynamic mechanical properties of concrete after high temperature,recycled tyre polymer fiber,RTPF)was added into concrete,and the content of RTPF was different(0kg/m3,0.6kg/m3,1.2kg/m3,2.4kg/m3 and 4.8 kg/m3)after five temperatures(20 ℃,105℃,250℃,400℃ and 600℃)The internal pore vapor pressure test,thermogravimetric analysis(TGA),composition analysis(XRD),pore analysis(MIP)and microscopic morphology analysis(SEM)were carried out on RTPF concrete with different content.The results show that adding RTPF does not change the material change of concrete at high temperature,but will affect the pore structure of concrete,improve the air permeability of concrete and reduce the damage of pore vapor pressure to concrete.The damage analysis of RTPF concrete specimens subjected to different temperatures is carried out by using ultrasonic technology,and the sound velocity,waveform,spectrum and energy distribution of RTPF concrete subjected to different temperatures are obtained.The results show that after high temperature,the ultrasonic sound velocity in concrete decreases,the waveform is distorted,the main frequency amplitude decreases,and the ultrasonic energy gathers to the low frequency band.When the temperature reaches the melting point of RTPF,the concrete with fiber content of 1.2 kg/m3 has the highest sound velocity and the lowest ultrasonic energy in low frequency band.The static and dynamic compressive strength of RTPF concrete with different content is tested.The test results show that the static compressive strength of RTPF concrete decreases with the increase of RTPF content at room temperature,because the addition of RTPF will reduce the compactness of concrete.With the increase of fiber content,the dynamic compressive strength,dynamic reinforcement factor and fracture energy of RTPF concrete first increase and then decrease.When the content of RTPF is 1.2 kg/m3,the dynamic compressive strength of RTPF concrete is the highest,which indicates that RTPF can effectively enhance the dynamic compressive performance of concrete at room temperature.After high temperature,the static relative compressive strength of RTPF concrete increases first and then decreases with the increase of fiber content,and the relative compressive strength of RTPF concrete(RTPF 12)with 1.2 kg/m3 content is the highest.Under the same temperature and similar strain rate,the dynamic compressive strength,dynamic strength enhancement factor and fracture energy of RTPF 12 are all larger than those of plain concrete,which indicates that adding 1.2kg/m3 RTPF can effectively improve the dynamic compressive performance of concrete after high temperature.