Research On The Technology Of C80 High-strength Concrete Prepared By Machine-made Sand

With the country’s vigorous construction of infrastructure and environmental protection requirements,natural sand resources are becoming scarce,and it is inevitable to use machine-made sand instead of river sand as fine aggregate to prepare concrete.There are big differences between machine-made sand and river sand.Machine-made sand has sharp grain type,large surface roughness,and is easily affected by powder content.Combining the above conditions,according to the difference between machine-made sand and river sand,the characteristics of machine-made sand are studied for concrete work.The influence of performance,mechanical properties,durability and volume stability.Combining the properties of raw materials,through systematic research on water-binder ratio,sand ratio,mineral admixture,etc.,the benchmark mix ratio of C80high-strength concrete is determined;through the analysis of the characteristics of machine-made sand,the fineness modulus and mud content of different machine-made sands are studied(MB value)on the working performance and mechanical properties of machine-made sand concrete;by analyzing the properties of machine-made sand and gravel powder,studying the influence law of machine-made sand and gravel powder content on the durability and volume stability of concrete,the following conclusions are drawn:(1)After mix design,experiment and trial mix,the recommended mix ratio of C80high-strength concrete prepared with machine-made sand:water-binder ratio 0.25,cement:mineral powder:fly ash:silica fume:machine-made sand:crushed stone=408:90:60:42:664:1036(unit kg/m~3).(2)The characteristics of machine-made sand have a direct impact on the working performance of concrete;the larger the fineness modulus of machine-made sand,the sharper the grain shape,the worse the working performance of concrete;the content of machine-made sand and gravel powder must be controlled within 7%,and the stone powder plays a filling effect,and the mechanism is optimized.Sand grading is beneficial to the workability of concrete;(3)For C80 high-strength concrete,the strength of the machine-made sand matrix has a greater impact on the strength of the concrete;at the same time,the content of stone powder also has a greater impact on the strength of the concrete,especially the early strength of the concrete.(4)When the content of machine-made sand and gravel powder is between 3%and7%,the elastic modulus of concrete increases with the increase of stone powder content,but after 7%,the higher the content of stone powder,the lower the elastic modulus of machine-made sand concrete.(5)The shrinkage value of machine-made sand concrete is generally greater than that of river sand concrete.The larger the water-binder ratio,the greater the drying shrinkage rate of high-strength machine-made sand concrete;before the age of 14 days,the drying shrinkage value of concrete increases at a greater rate,and the stone powder content is within 7%,The concrete shrinkage value increases with the increase of the stone powder content.After more than 7%,the concrete shrinkage value is reduced by the influence of the stone powder content.(6)Stone powder content of 3%-9%has little effect on the impermeability of machine-made sand concrete.The 6h electric flux of concrete is between 100C～1000C,which is very low and has strong resistance to chloride ion erosion;C80 high-strength machine-made sand Concrete has a low water-binder ratio and strong concrete density.