Influence Of Machine-made Sand Quality On The Performance Of High Strength And Large Flow Concrete

With the rapid development of the construction industry,the requirements for concrete performance are also increasing.The most widely used concrete in practical engineering is large flow concrete.As an important part of the concrete raw materials,the quality of fine aggregate has a critical influence on the workability of concrete.In the past,natural sand was mainly used for construction sand,but with the increasingly exhausted natural sand resources and the implementation of the stricter policy of no mining and excavation in river channel,the application of machine-made sand has gradually become the most widely used sand.However,due to the uneven quality of machine-made sand in today’s market.The influence of lithology,gradation,rock fines content and flaky particle content of different machine-made sand on concrete performance is different,which leads to unsatisfactory performance of machine-made sand concrete in engineering application.Compared with ordinary concrete,high strength and large flow concrete has stricter requirements on the quality of machine-made sand,so it is necessary to clarify the influence of various indicators of machine-made sand on the performance of high strength and large flow concrete and determine its control limit.In this paper,the problems existing in the practical application of machine-made sand are systematically studied,including the common problems of concrete performance caused by the broken grading of machine-made sand,more rock fines content,more flake particles content and different lithology.Under the condition of ensuring that other indexes of machine-made sand are the same,the control limits of various indexes of machine-made sand are obtained,which provides a reference for the application of machine-made sand in high strength and large flow concrete.As for the gradation of machine-made sand,the gradation of machine-made sand is within the range of zone 2,and the content of intermediate particles is basically reasonable.Moderate change of the gradation of machine-made sand has little effect on the workability,cube compressive strength,shrinkage and durability of C60,C70 and C80 concrete,which can basically meet the design requirements of concrete.Under the condition of the same fineness modulus,the segregation and bleeding of the concrete gradually appear with the decrease of0.6 mm and 0.3 mm particles sieve residue in the sand,the cube compressive strength,shrinkage rate and durability of concrete also have negative effects,As the high strength and large flow concrete is dense,the overall durability of concrete is well.With the same gradation of machinemade sand,the performance of limestone machine-made sand concrete is slightly better than granite machine-made sand concrete in all aspects.Considering the influence of machine-made sand gradation on the overall performance of concrete with three different strength grades,the proportion of 0.6mm and 0.3mm aggregate sand is controlled in 30%-55%.In terms of rock fines content of machine-made sand,for C60 concrete,the control of rock fines content from 7% to 10% is better in all aspects of concrete.For C70 concrete,the concrete with rock fines content at about 5% has better performance;for C80 concrete,the concrete with rock fines content at about 3% has better performance.With the same strength gradation and rock fines content,the workability,cubic compressive strength and durability of limestone machine-made sand concrete are slightly stronger than that of granite machine-made sand concrete,and the overall shrinkage rate of limestone machine-made sand concrete is greater than that of granite concrete.In terms of flake particle content of machine-made sand,with the increase of flake particle content of machine-made sand,the workability,cubic compressive strength and durability of the concrete with three different strength grades gradually become poor.Because the flake particle limits the shrinkage of concrete to a certain extent,the shrinkage of concrete decreases in the early stage and increases in the later stage.With the same flake particle content,the performance difference between limestone and granite sand concrete is not obvious.In order to ensure the concrete performance meets the engineering requirements,the flake particle content of machine-made sand should not exceed 20%.