Mechanical Properties And Permeability Of Recycled Brick-Concrete Aggregate Pervious Concrete

The rapid development of China's construction industry has brought a large number of construction waste,of which brick-concrete waste is the mainstay.The use of construction brick-concrete waste as recycled aggregate and the preparation of recycled permeable concrete can effectively solve the problems of urban construction waste stacking pollution and lack of natural gravel aggregate resources;On the other hand,it can also alleviate the urban heat island effect and urban waterlogging caused by dense population activities,and bring significant economic,social and environmental benefits to the development of the building materials industry.Therefore,it is of great practical significance to study on the preparation of recycled brick-concrete aggregate pervious concrete.Based on reading a large number of relevant literatures at home and abroad and conducting preliminary experiments,this paper studies on proportion of recycled brick-concrete aggregate pervious concrete mixture and its propertie.The main work and results are as follows(1)Taking ordinary recycled concrete with 100%recycled brick-concrete aggregate replacement rate as the research object,the effect of aggregate water treatment method and cement aggregate ratio on the mechanical properties of concrete at 7 days of age was explored.The results show that the 7-day compressive strength and flexural strength are positively correlated with the cement aggregate ratio,and the aggregate can be used to improve the compressive performance of recycled brick-concrete aggregate concrete after water floatation treatment.(2)Combining the additional water consumption of recycled aggregate and the porosity index requirements of permeable concrete,the traditional volume method is optimized for design,and the design method of the mix ratio of permeable concrete based on the replacement of part or all of the recycled brick-concrete aggregate Afterwards,a trial calculation is conducted for specific cases(3)Recycled aggregate replacement rate,cement aggregate ratio,water-cement ratio and sand ratio were used as test factors,and the mechanical properties and water permeability were used as the test indicators for orthogonal tests,and the comprehensive balance method is used to determine the optimal combination ratio that meets the mechanical properties and permeability of recycled brick-concrete aggregate pervious concrete:the replacement rate of recycled aggregate is 40%,cement aggregate ratio is 0.20,water-cement ratio is 0.26,and sand ratio is 15%.Based on this ratio,the compressive strength of the specimen with the best mix ratio can reach 15.70MPa in 3 days,19.65MPa in 7 days,23.40MPa in 28 days,porosity of 8%,and water permeability coefficient of 0.104cm/s.At the same time,the relationship between each test index and index,test factor and index is determined through fitting analysis,and an empirical formula is obtained to guide the application.Finally,through X-CT technology and SEM scanning electron microscopy,the pore structure and microstructure of recycled brick permeable concrete were studied to analyze its strength and water permeability mechanism.(4)Based on the two methods of adjusting the concrete molding method and incorporating different proportions of fly ash,the experimental study on the performance improvement of the recycled brick-concrete aggregate pervious concrete is obtained:The pressure forming method can improve the macro mechanical strength of the recycled brick-concrete aggregate pervious concrete,and the permeable performance will be reduced accordingly;At the same time,as the replacement rate of fly ash increases,the macro-mechanical strength of recycled brick-concrete aggregate pervious concrete shows an increasing trend as a whole,and the permeability coefficient and effective porosity gradually decrease.Finally,the microscopic morphology and hydration products of different test groups at different ages were observed by SEM scanning electron microscopy,combined with EDS spectroscopic analysis to analyze element types and content,and the improvement mechanism of the two performance enhancement methods was analyzed.