Experimental Study On The Compressive And Fracture Behaviors Of SFRAC After Exposure To Elevated Temperatures

In mainland China,there is increasing amount of updating of infrastures with the accelerated urbanization process since the beginning of21st century, as a result, it is significant to study the recycling of old concrete. Recycled aggregate concrete (RAC) refers to the concrete in which the recycled concrete aggregates (RCA) are used to partly or fully replace the natural conconrete aggregates. Because of the existence of cement past in RCA, RAC usually has lower strength,more internal pores and defects compared with normal concrete (NC). A detrimental effect of the more loose structure of RAC is that stress concentration is more prone to be induced, so the compressive strength splitting and bending strength of RAC is usually lower than the NAC with same water-to-cement ratio Steel fiber reinforced concrete (SFRC) is a new type of building material by adding an appropriate amount of steel fibers into NC, which can be fabricated by casting and injecting. Against the above background, this study carried out an experimental study on the compressive properties and fracture properties of steel fiber reinforced recycled aggregate (SFRAC) subjected to elevated temperature. In the present study, the replacement rate of recycled coarse aggregate is100%. Effects of two variable parameters, namely steel fiber volume content (0%,0.5%,1%and0.5%) and exposed temperature (room temperature,200℃,400℃and600℃) on compressive mechanical properties (strength and ductility) and fracture properties were investigated by uniaxial compression test on concrete cylinders (D×h=150mm×300mm) and three-point bending test on ndddotchded beams (t×h×l=100mm×100mm×515mm), respectivly. The test results were shown in this thesis to clarify the effects of the two parameters (i.e. exposure temperature and steel fiber content) on the uniaxial compression failure mechanism、fracture energy and fracture toughness of SFRAC. The main research work reported in this thesis are outlined as follows:1) A total of60cylinder specimens and60notched beams divided into5groups were prepared and subjected to different target temperature (elevated temperature). Based on the test observations and the experiment results, some basic issues of SFRAC after exposure to high temperature, including appearance color changes, spalling behavior, cracking behavior and mass loss were summarized;2) Uniaxial compression test on concrete cylinders after exposure to high temperature were carried out. Based on the test results, the effects of the two parameters, i.e. exposure temperature and steel fiber content, on the axial compression failure mechanism of SFRAC, including failure mode, residual strength (fc), elasticity modulus (E) and ductility (toughness), were discussed;3) Three-point bending test on notched beams were carried out. Based on the test results, effects of the above two parameters on facture behaviors (fracture energy and fracture toughness) of SFRAC, including elasticity modulus (E), fracture energy (GF), fracture toughness(KIc), initiation fracture toughness(KIcini), unstable fracture toughness(KIcun) were discussed.