| With the beginning of China’s 14th five year plan,infrastructure construction across the country is booming,and river sand,which is the rigid demand for engineering construction,after decades of extensive mining,many areas are facing the situation of depletion.The contradiction between supply and demand of construction sand has become increasingly prominent.Therefore,machine-made sand has gradually replaced river sand and occupied the leading position of fine aggregate.However,due to the influence of many factors such as the type of parent rock,sand-making technology and equipment,its physical properties are quite different from river sand.Whether the machine-made sand concrete prepared according to the existing standard system can meet the actual needs needs to be further studied.Based on the above situation,this paper starts with the characteristics of machine-made sand,the paper compares and analyzes the difference in physical properties between machine-made sand and river sand;According to the existing mix design system,study the influence rules of the preparation parameters such as gradation,sand ratio and water consumption on the performance of machine-made sand concrete,realizes the parameter optimization,and propose technical measures;through the study of the homogenity of concrete and the micro-structure of the cross-section,the selection principle of reasonable mixing time of machine-made sand concrete under traditional mixing technology and the optimization of mixing technology are studied.The main research results are as follows:(1)The parameters of roundness,axle length ratio and feret diameter ratio are selected to quantitatively analyze the grain shape characteristics of fine aggregates.The results show that the partical shape parameters of machine-made sand prepared by the combination of vertical impact crusher and impact crusher are closer to river sand.The partical shape is relatively smooth and round,while the machine-made sand partical shape of a hammer or cone crusher is poor,with more edges and corners and needle-like particles,and the surface texture is rough;this paper recommends that the roundness,axial length ratio,and feret diameter ratio of the newly manufactured sand should be controlled within 1.26,1.32,and 1.35,respectively.(2)For C50 concrete,the high content of particles larger than 1.18mm in machine-made sand should be controlled between 30%and 40%.It will improve workability and strength;the content of particles smaller than 0.3mm should be controlled between 15%and 25%,It mainly affects the cohesiveness and water retention of the mixture.(3)Under the same conditions,when preparing machine-made sand concretes with similar workability to river sand concrete,the unit water consumption should be increased by 4kg～8kg than that of river sand concrete,and the strength still remains above the design strength.(4)When the sand ratio is slightly reduced,the concrete mixture is easy to bleed and segregate.If it’s too high,the mixture will be viscous,the test shows that the C30and C50 machine-made sand concrete are the sand ratio should be controlled at 44%and 40%respectively;It can be increased by 2%～3%based on the selection of river sand ratio,and it has the same performance as the river sand concrete.(5)A proper amount of stone powder can improve the workability,strength and resistance of Cl~-penetration of machine-made sand concrete.The best stone powder content of C30 and C50 machine-made sand concrete is 9%and 6%,respectively.(6)Under the same mixing ratio,using traditional mixing technology to prepare machine-made sand concrete with similar workability to river sand concrete,its mixing time should be increased by 20s～30s compared with river sand concrete.Under the traditional mixing technology,the best mixing time is 60s for dry mixing and 120s for wet mixing.At this time,each component of the mixture has high dispersion uniformity,the strength reaches the peak,and the workability is excellent;the SEC technology can significantly improve the workability of machine-made sand concrete,made the structure of ITZ more dense and solid,and its compressive strength increased by 11.6%compared with the traditional mixing technology. |
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