Experimental Study On Basic Mechanical Properties And Mix Design Of Ultra-high Performance Concrete Prepared By Recycled Fine Powder

With the implementation and continuous deepening of China’s sustainable development strategy,research on the resource utilization of construction waste is also continuing to heat up.Using crushed construction waste as aggregate to prepare recycled concrete is one of the important ways to use construction waste as a resource.During the crushing process,construction waste will produce a large amount of fine powder with a particle size of less than 0.16 mm,which accounts for about 15% of the total mass of construction waste,that is,recycled fine powder,which has a certain potential activity.Compared with recycled coarse aggregate and recycled fine aggregate,the recovery and application research of recycled fine powder is insufficient.At the same time,with the rapid development of China’s economy,new construction projects continue to emerge,posing new challenges to the performance of cement-based materials.Aiming at the shortcomings of traditional cement-based materials,researchers have developed ultra-high performance concrete(UHPC).Ultra-high performance concrete not only have high strength,but also have excellent long-term performance and durability.However,their high cementitious material consumption increases the use cost and affected the application in practical engineering.In this context,this paper selects waste sintered bricks in construction waste to prepare recycled brick fine powder.Firstly,the recycled brick fine powder is activated and then used it to replace cement to prepare ultra-high performance concrete.Research and analyze the effects of different excitation methods on the activation of recycled brick fine powder,and the effect of the replacement rate of recycled brick fine powder after excitation on the working performance and basic mechanical properties of ultra-high performance concrete materials(compressive,flexural,and split tensile strength).The research results can provide basic experimental basis and theoretical guidance for the utilization of construction waste as a resource and the promotion and application of ultra-high performance concrete.It has good engineering value and socio-economic significance.The main findings are as follows:(1)After using mechanical excitation,chemical excitation and high temperature excitation,the activity index of recycled brick fine powder is improved to varying degrees.Among them,mechanical excitation and high temperature excitation have better effects,with the highest activity index reaching 71%.However,considering the excitation effect,energy consumption,economy and practical operation difficulty,mechanical ball milling for 45 min is a more reasonable excitation method.(2)The expansion of the recycled brick fine powder ultra-high performance concrete mixture is 480-590 mm,and the working performance is good.As the replacement rate of recycled brick fine powder increases,the degree of expansion shows a downward trend,and the trend gradually intensifies,that is,an increase in the replacement rate will cause a decline in the working performance of the mixture.When the replacement rate is 10%,the work performance of recycled brick fine powder ultra-high performance concrete is the best.(3)Recycled brick fine powder ultra-high performance concrete has better compressive,flexural and split tensile properties.The 28 d compressive,flexural and split tensile strengths all exceed 120 MPa,18 MPa and 11 MPa.As the replacement rate increases,the compressive,flexural,and split tensile strengths show an overall downward trend.The older the age,the more obvious the downward trend.As the age increases,the compressive,flexural and split tensile strengths show an overall increasing trend.The greater the replacement rate,the less obvious the increasing trend.That is,the replacement rate of recycled brick fine powder has little effect on the early strength of ultra-high performance concrete,the higher the replacement rate,the less the late strength increase of recycled brick fine powder ultra-high performance concrete.When the replacement rate is 10%,the basic mechanical properties of recycled brick fine powder ultra-high performance concrete are optimal.