Effect Of MB Value On Performance And Pore Structure Of High Strength Manufactured Sand Concrete

Mud powder will be produced in the mining and processing of manufactured sand.Mud powder,due to its own characteristics,will affect the workability of concrete and have a negative impact on the strength and durability of concrete.The MB value is used to represent the content of mud powder in the manufactured sand in the construction sand.With the expansion of China ’ s infrastructure scale,the applicable surface of high strength and high performance concrete is expanded,and the requirements for the quality and service life of concrete structures are improved.It is necessary to study the influence of mud powder on the performance of manufactured sand concrete.Mineral admixtures such as metakaolin and fly ash can significantly improve the performance of concrete and play an important role in the preparation of high strength and high performance concrete.In this paper,C90 high strength manufactured sand concrete was prepared by adding mineral admixtures and polycarboxylate superplasticizer.By controlling the amount of mud powder,the mechanical properties,durability and microstructure of manufactured sand concrete within the MB value of 0.85～2.0 were studied,which provides theoretical support for the formulation of MB value limit value of high strength manufactured sand concrete and the promotion of manufactured sand concrete in cold regions.The specific research results are as follows:(1)The MB values of stone powder and different types of mud powder were tested.The results showed that the MB values of stone powder and mud powder increased linearly with the increase of content.stone powder has little effect on MB value;mud powder has a great influence on MB value,and the adsorption capacity of methylene blue from large to small is montmorillonite,mud powder and mud stone powder.(2)The addition of Metakaolin has a certain improvement on the workability of concrete.The mechanical properties,dry shrinkage performance,resistance to chloride ion penetration and frost resistance of manufactured sand concrete were significantly improved by adding 8% metakaolin.(3)The workability of manufactured sand concrete gradually deteriorates with the increase of MB value.The mechanical properties of manufactured sand concrete increased first and then decreased with the increase of MB value.When MB value was 1.1,the compressive and tensile strength of 28 d age reached the maximum,and the drying shrinkage and frost resistance of manufactured sand concrete were improved.When the MB value is0.85,the chloride ion permeability coefficient is the minimum,and increases with the increase of mud powder content.(4)Grey entropy correlation analysis reveals that the compressive strength of manufactured sand concrete has a good correlation with the pore structure.When the MB value is 1.1,the microscopic pore structure is the best.There is a good correlation between fractal dimension and compressive strength.The compressive strength decreases exponentially with the increase of fractal dimension.When the MB value is 1.1,the fractal dimension reaches the minimum 2.3202 and the compressive strength reaches the maximum.