Research On Mechanical Properties Of Ultra-high Toughness Cement-based Composites Of Low Temperature Curing Recycled Concrete Powder

With the development and innovation of my country’s construction industry,new high-performance,sustainable building materials will become my country’s current and future development direction for a long period of time.For my country’s North,Northeast and Northwest regions,due to the long duration of winter,concrete projects are constructed in this severely low temperature environment.Failure to meet the maintenance conditions will cause problems such as a decline in project quality and delays in construction.In the past ten years,with the continuous deepening of my country’s supply-side reform,the pace of urban modernization and urban-rural integration has accelerated,and the transformation of the old city has produced a large amount of waste concrete blocks and other construction waste.Construction waste is stacked randomly without treatment,which not only takes up farmland but also pollutes the environment,which has become a problem in the development of urban modernization in my country.In order to reduce environmental pollution caused by large-scale demolition,ECC can be used to repair aging buildings.Research on lowtemperature curing and green recycling ECC can effectively solve the problem of a large number of construction waste disposal,and also provide a theoretical reference for the winter construction of ECC restoration of concrete buildings in the Three North areas of my country.In this paper,under the condition of low-temperature curing,the use of waste concrete block crushing,ball mill concrete powder instead of quartz sand to prepare ultra-high toughness cement-based composite material(ie ECC).Determine the best replacement rate of concrete powder under low-temperature curing conditions(based on the average winter temperature in North China:-10℃),and then design orthogonal experiments to study the effects of water-binder ratio,fiber output,fly ash,temperature and other variables under low temperature The impact of ECC mechanical properties,and conduct the inter-subject effect test to determine the size of the effect of the influencing factors.The research on recycled concrete powder ECC not only responds to the national sustainable development strategy,solves the problem of a large amount of construction waste being piled up everywhere,but also broadens the development ideas of new high-performance materials.Winter construction provides a theoretical basis,which has a good guiding significance for the engineering practice of ultra-high toughness cement-based composite materials and the formulation of construction specifications in the future.The main research contents and conclusions of this paper are as follows:(1)Under the curing condition of-10℃,using recycled concrete powder instead of quartz sand,comparing the mechanical properties of concrete powder at 0,25%,50%,75%,and 100% replacement rate,under comprehensive consideration of each replacement rate After the various mechanical properties of the test piece,the best replacement rate is finally selected as the replacement of 50% quartz sand by concrete powder.(2)Based on the results of orthogonal experiments,SPSS statistical analysis software was used to obtain the influence of temperature,water-binder ratio,fiber content and fly ash content on the bending properties of the material.The results show that the ultimate deflection of the material is the largest at-10°C,which is 53.6mm.The ultimate strength is the largest at 0°C,which is 5.326 MPa.By comparing the F value of the intersubjective effect,it is found that the order of influence on deflection is fly ash content> temperature> water-binder ratio> fiber content.(3)Based on the results of orthogonal experiments,SPSS statistical analysis software was used to obtain the influence of temperature,water-binder ratio,fiber content and fly ash content on the flexural strength of the material.The test results show that the flexural strength gradually decreases with the decrease of curing temperature.Increasing the water-binder ratio will reduce the flexural strength of the material,and increasing the amount of fiber and fly ash will increase the flexural strength of the material.(4)Based on the results of orthogonal experiments,SPSS statistical analysis software was used to obtain the influence law of temperature,water-binder ratio,fiber content and fly ash content on the tensile properties of the material.The results show that the ultimate tensile stress at a curing temperature of 0℃ is the largest,which is2.34 MPa.The ultimate strain is the largest at-10°C,reaching 5.35%.By comparing the F value of the inter-subject effect,it is found that the order of influence on the ultimate tensile strain of the material is temperature>fiber content>water-binder ratio>fly ash content.(5)Based on the results of orthogonal experiments,SPSS statistical analysis software was used to obtain the influence of temperature,water-binder ratio,fiber content and fly ash content on the compressive strength of the material.The test results show that the compressive strength is the largest at a curing temperature of 0°C,which is 25.3 MPa.The compressive strength gradually increases with the increase of temperature and fly ash content,but increasing the water-binder ratio will reduce the compressive strength of the material.