Influence Of Shape Characteristics Of Machine-made Sand On Working Performance Of Concrete And Experimental Research On Mix Proportion

With the development of engineering construction in China,the amount of concrete is increasing,and the natural sand resources are becoming increasingly scarce.Using machine-made sand to partially or completely replace natural sand as concrete fine aggregate has become a general trend in the current concrete industry.However,most of the machine-made sand particles are irregular and the surface is rough,which is different from natural sand concrete.By testing the basic physical properties of machine-made sand and natural sand,mainly including sand shape parameters,particle gradation,apparent density,bulk density,porosity and methylene blue value,the author has comprehensively studied the basic physical properties of machine-made sand.By testing and analyzing the mechanical properties of machine-made sand and natural sand cement mortar and concrete,the influence law of machine-made sand on concrete performance is revealed.The effects of particle characteristics and gradation of machine-made sand on the workability and mechanical properties of concrete are studied;The mix proportion of machine-made sand concrete is optimized and improved by statistical method,which provides a new guidance for promoting the application of machine-made sand in concrete.The details are as follows:(1)Based on the shape parameters,particle gradation,apparent density,bulk density,porosity,methylene blue value and other indicators,the characteristics of machine-made sand and natural river sand are compared and analyzed to confirm their similar physical characteristics.Through the mortar mechanical test,it is concluded that the strength of machine-made sand cement mortar with the same mix proportion is higher than that of natural sand cement mortar.(2)Taking pebble manufactured sand and natural river sand as fine aggregate,four groups of concrete specimens are designed according to the different strength of C30 and C40,and their mechanical properties are analyzed and studied.Based on the statistical analysis of cube compressive strength test and axial compressive strength test of machine-made sand concrete,it is suggested that the conversion coefficient of C30 pebble machine-made sand concrete is 0.72 and that of C40 pebble machine-made sand concrete is 0.76.The average value of the theoretical elastic modulus of machine-made sand concrete calculated according to the calculation formula of the code is 16.69% lower than the average value of the measured elastic modulus.Therefore,the elastic modulus of concrete calculated according to the code is conservative.(3)The internal relationship between particle shape,gradation and workability of concrete is studied and analyzed.By means of comparative research,the effects of particle characteristics and gradation of pebble manufactured sand and natural sand on the properties of mortar and concrete are studied.Manufactured sand has poor workability and stronger mechanical properties than natural sand.(4)Through the statistical analysis of a large number of data,it is concluded that the relationship between the preparation strength of machine-made sand concrete and the water cement ratio is:(?)...