Effect Of Lithology And Gradation Of Manufactured Sand On Chloride Ion Permeability Of Concrete

With the large-scale construction of infrastructure in China in recent years,20-50%of the natural sand resources occupying concrete raw materials are becoming scarcer,and the demand for construction sand is increasingly prominent.Replacing natural sand with manufactured sand as a fine aggregate of concrete has become a common trend in the current construction industry.Although the application of manufactured sand can reduce energy consumption and reduce environmental pollution,it can help alleviate the supply of sand resources and environmental pressure.However,the manufactured sand is not only versatile in lithology,but also has different characteristics,and the gradation curve is unreasonable and fineness modulus is slightly larger,the porosity is larger,the edges and corners are more rough,and the high content of rock-powder is significantly different from natural sand.These problems lead to the great hindrance of the application of manufactured sand in important parts of concrete structures.Therefore,it is of great significance to systematically study the influence of manufactured sand on concrete performance in order to develop and popularize the market application of manufactured sand.In this paper,granite and diabase are studied,and the influence of lithology on the working performance and mechanical properties of mortar and concrete is discussed.The different grain sizes are screened on the basis of undisturbed sand and redesigned.Furthermore,the influence of gradation of manufactured sand on the performance and mechanical properties of mortar and concrete was studied.On this basis,the mechanism of lithology,gradation and rock-powder was applied to the concrete against chloride ions.The performance study analyzed the correlation of chloride ion permeability of sand concrete under different test methods（electric flux method and natural infiltration method）.The main conclusions of this paper are as follows:（1）In the case of the same water consumption,the fluidity of the mortar prepared by the three fine aggregates is diabase>natural sand>granite,but the cohesiveness and water retention of the diabase mixtures is the worst.This is because the manufactured sand has a more irregular shape than the natural sand,with a larger specific surface area and more water demand.（2）Under the same grading condition,the working performance of manufactured sand,mortar and concrete with different lithology is greatly influenced by rock type,texture structure and particle morphology..Layered cleavage of diabase mixed with sand and concrete has poorer fluidity and slump than granite.（4）The flexural and compressive properties of manufactured sand mortar with good gradation are better than those of natural sand mortar.especially the flexural strength is 10%～40%higher than that of natural sand.This may be because the surface of the manufactured sand is rough,multi-angular,more tightly bonded to the cement stone matrix,the Interfacial bonding effect is enhanced,and there is better mechanical meshing force between the particles.（5）Under the same conditions,the concrete prepared by natural sand has better resistance to chloride ion permeability than granite and diabase.Poor gradation of manufactured sand concrete has more internal structural voids,which connects the chloride ion transportion channels,makes the specimens have poor resistance to chloride ion penetration.（6）With the increase of the content of rock-powder content,the permeability of concrete against chloride ion increases first and then decreases.When the rock-powder content is 10%,the chloride ion diffusion coefficient is reduced by 3.77×10^-9 cm³/s,and the total chloride ion content is reduced by 73.8%,which greatly improves the chloride ion permeability of the concrete structure.（7）The electric flux method can better reflect the chloride ion penetration tendency of the manufactured sand concrete,but as a semi-quantitative analysis method,its accuracy and applicability need further research.