| Since the beginning of the 21st century,China's urbanization process has developed rapidly,producing about 10 million tons or even hundreds of millions tons of construction waste every year,and the trend of annual growth.At present,the way to deal with construction waste is relatively limited,most of the use of open-air stacking or direct landfill.The random dumping and stacking of construction wastes have caused a serious impact on the surrounding environment and the overall appearance of the city.The recycling of construction waste can not only protect the environment,but also reuse the waste building materials and improve the utilization rate of construction waste materials.As traditional building materials,concrete and clay bricks are widely used in all kinds of construction projects.These two materials also account for the largest proportion of construction waste.The recycling of waste clay brick and concrete has far-reaching significance for the recycling of construction waste.At present,many scholars at home and abroad have studied various types of materials in construction waste,but there are few studies on mixed aggregates composed of different aggregates,and there are few studies on recycled aggregates of concrete bricks.The physical and mechanical properties of concrete and clay brick are very different,and the interaction between the two materials when mixing and crushing is still unclear.In addition,to further analyze and study the actual application of recycled concrete aggregate and recycled clay brick aggregate,it is necessary to study the characteristics of the material itself.In this paper,the concrete and clay bricks in the construction waste generated during the demolition of a university teaching building in Taiyuan are used for the lateral compression test,and pretreatment is carried out.The gradation rules,fractal characteristics and crushing characteristics of recycled aggregates under different static pressure loading were studied.The specific research content and main research results are as follows:(1)The confined compression test was conducted by using recycled aggregates with a diameter of 19mm~26.5mm.The change of the gradation curve of the regenerated mixed aggregates under various pressures was discussed.After the aggregates were crushed under pressure,the aggregate gradation changed from a single gradation to a fractal gradation.Under different pressures,the sieve residue at 4.75mm particle size appears peak.(2)The influence of factors such as material strength and pressure on the fractal dimension is explored.The fractal dimension of aggregate is negatively correlated with material strength and positively correlated with pressure.The crushing mechanism of recycled mixed aggregate is"discarding weak and maintaining strength",that is to say,weak aggregate recycled clay bricks are broken preferentially,"protecting"strong aggregate recycled concrete,so that the amount of recycled concrete aggregate crushing is reduced.(3)The relative crushing rate Br of each sample group aggregate in this experiment was calculated using Hardin's relative crushing rate theory.The changes between relative breaking rate Br,stress level?,volume strain?_v,and fractal dimension D are analyzed.Studies have shown that there is a close relationship between the relative crushing rate of aggregate and volume strain and fractal dimension.(4)By analyzing the relationship between the fractal dimension of recycled mixed aggregate and gradation,the gradation curve of recycled mixed aggregate is obtained,and then the optimal gradation suitable for expressway and first-class highway is discussed.Through comparison and analysis with the mixed aggregate grading recommended in the specification,the maximum blending amount of recycled clay bricks applied to the pavement base or subbase is proposed.(5)The load applied to the recycled mixed aggregate of concrete brick is 600kN,and the fractal distribution is formed when the aggregate is broken. |
PDF Full Text Request