Effect Of Ceramsite On Mechanical And Thermal Properties Of Ultra High Performance Concrete For High-rise Shear Walls

In recent years,traditional concrete has become the construction material with the largest amount of consumption,energy consumption and environmental damage in China's industry.Based on the development requirements of green buildings,it is necessary to encourage innovation and development of green,low-carbon and environmentally friendly high-performance lightweight aggregate concrete.Therefore,high-strength lightweight aggregate concrete should be one of the development directions of concrete structural materials in this century.With the rapid advancement of urbanization in China,in order to cope with the problem of decreasing land resources caused by the rapid population growth,high-rise buildings have increased rapidly,and steel bars Concrete shear wall is widely used in the structure of high-rise buildings because it can effectively resist the effect of horizontal loads.However,high-rise buildings are facing a greater fire threat during construction and use.Because of its excellent characteristics such as light weight,high durability,and high fire resistance,ceramsite concrete is used to replace the coarse aggregate in the concrete to prepare high resistance.Hot concrete,which slows down material performance during a fire,protects the internal steel bars,improves the structure's ability to resist high temperature damage and degradation,prevents structural damage and collapse,and earns time and provides security for fire rescue.It has important theoretical and practical value.(1)Preparation and research of ultra-high performance cement-based composite materials.The results show that using local materials and conventional manufacturing equipment and curing conditions,ultra-high-performance concrete with ultra-high strength and good workability can be formulated.Choose cement content 60%,silica fume content 10%,fly ash content 20%,mineral powder content 10%,rubber-sand ratio1: 1,steel fiber(length 13mm)The volume content is 1% as the benchmark concrete mix ratio.of which the slump at 0h and slump at 1h were 230 mm and217mm,and the expansion at 0h and 1h were 605 mm and 591 mm respectively.(2)Experimental research on the influence of ceramsite density grade and its equivalent volume replacement crushing rate(referred to as "replacement rate")on the compressive strength and apparent density of benchmark concrete.The results show that the substitution rate of ceramsite directly affects the strength of the benchmark concrete.As the substitution rate increases,the strength of the concrete gradually decreases.The 800-grade shale ceramsite concrete has the highest compressive strength.When the substitution rate is 60%,the side length The compressive strength of the 100 mm cube test block reached 88.6 MPa at 28 days.(3)Experimental study on the effect of temperature on the compressive strength and stress-strain curves of 800-grade shale ceramsite concrete.The results show that ceramsite becomes a weak interface for concrete failure under vertical load after being heated(150 ?-350 ?).In addition,the replacement rate of ceramsite has a direct effect on the morphology of concrete failure;as the replacement rate of ceramsite increases,The compressive strength and axial compressive strength of lightweight high-strength concrete cubes that are large and heated(150 ?-350 ?)gradually decrease,while the elastic modulus gradually decreases,and the Poisson's ratio becomes larger;Calculation formulas of elastic modulus and stress-strain constitutive equations of lightweight high-strength concrete with different substitution rates.(4)The finite element analysis software ABAQUS is used to simulate the temperature field under standard fire and the compressive bearing capacity of the shear wall after high temperature for light weight high-strength concrete shear walls with different replacement rates.The results show that by selecting appropriate material thermal properties and establishing a reasonable finite element model,the temperature field of a lightweight high-strength concrete shear wall under high temperature can be well simulated;when the specimen is exposed to one side for 180 minutes,the replacement rate The ultimate bearing capacity of 30% grade 800 ceramsite concrete shear wall is 3340 kN,which is relatively small compared with the reference concrete shear wall ultimate load of 3472 kN,which meets the fire resistance requirements of the Code for Fire Protection for Architectural Design.Compared with the bearing capacity,it has a large margin and can be used inhigh-rise shear wall structures.