Research On Mechanical And Thermal Properties Of Fine Recycled Aggregate Concrete At Elevated Tempretures

The emergence of recycled aggregate concrete has provided a new direction for the sustainable development of the construction industry.If the construction waste concrete can be applied to the preparation of recycled aggregate concrete,it will promote the solution of construction waste pollution and alleviate the pressure of sand and gravel resources exploitation.Prior to this,research was needed to understand the performance of recycled aggregate concrete.The research on recycled aggregate concrete began with the replacement of recycled coarse aggregate.Up to now,the replacement of coarse and fine aggregate has achieved a lot of results.Most scholars have concluded that the compressive strength and elastic modulus of recycled aggregate concrete at room temperature have different amplitudes as the replacement rate increases.However,the research on the mechanical properties and thermal properties of recycled fine aggregate concrete at high temperature is basically in a blank state.Therefore,This research will consider the replacement rate of recycled fine aggregate,temperature and replacement conditions of recycled coarse aggregate,and study the mechanical and thermal properties of recycled fine aggregate concrete at high temperature.The main contents of this research are as follows:(1)The material parameters such as apparent density,crushing index and water absorption of the aggregate used in this experiments were tested,and the concrete mix ratio was designed accordingly.The apparent density,water absorption and compressive strength of 18 recycled aggregate concrete cubes were measured.The axial compressive strength,elastic modulus and peak strain of 18 prisms at room temperature were measured,and the influence of temperature and fine aggregate replacement rate on these parameters was analyzed.(2)The temperature rise test was carried out to determine the constant temperature time required during the high temperature experiments;the mass loss rate of the test pieces with different replacement rates before and after the high temperature was measured;and the axial compression test of 72 recycled concrete prisms at high temperature was carried out.The failure mode was obtained,and the variation of axial compressive strength,elastic modulus,peak strain,stress-strain relationship with temperature and fine aggregate replacement rate at high temperature of recycled fine aggregate concrete was studied.It is recommended to use the calculation model of recycled coarse aggregate concrete at high temperature to predict the stress-strain relationship of recycled fine aggregate concrete at 20~?~800~?.(3)The thermal conductivity of 12 recycled aggregate concrete samples was measured by hot wire method.The specific heat of 18 recycled aggregate concrete samples was measured by differential scanning calorimetry.The thermal expansion of 12recycled aggregate concrete samples was measured by push-rod technique.The thermal properties of recycled fine aggregate concrete was analyzed with temperature and fine aggregate replacement rate.According to the test results,the thermal calculation model of recycled fine aggregate concrete at high temperature of 20?~800? was proposed.