Concrete grading of machine-made sand application technology
(1) Select graded machine-made sand that meets the technical requirements, which can replace river sand, and mix according to a reasonable mix ratio design method. The resulting machine-made sand concrete has advantages in workability, surface research and finishing, strength, wear resistance, and resistance to In terms of shrinkage and other properties, it can meet the design and construction process requirements of general concrete engineering.
(2) The technical requirements for preparing the machine-made sand of general concrete are: hard texture, clean, gradation conforming to the specification, its larger particle size is not more than 10mm, and the content of stone powder less than 0.08mm is not more than 7%.、
(3) The machine-made sand used for coagulation should be subjected to alkali activity test. After the alkali-aggregate reaction test, the specimen should be free of cracks, cracks, and overflow of the rubber. The expansion rate during the specified test age should be tested. Less than 0.1%. Preventive measures include: ①Limit the alkali content of cement (Na, 0·eq%), select “low alkali cement” with cement alkali content=0.6%; ②Use inactive aggregates; ③Incorporate suitable mineral ballast and powder Mixed materials such as coal ash and silica fume.
(4) The fineness modulus of machine-made sand should be controlled in the range of 2.8 to 3.6. Data shows that the range of 3.0 to 3.3 is better.
(5) The strengthening of the mechanism of stone powder on cement is manifested in two aspects: ① Stone powder acts as a nucleus in the cement hydration reaction, inducing the separation of cement hydration products and accelerating cement hydration; ② The powder participates in the cement hydration reaction and generates hydration. Carbon anchor calcium, and ettringue is converted to monosulfur type hydrated calcium sulfoaluminate.
(6) The workability of machine-made sand concrete is worse than that of natural river sand concrete. The workability can be improved by changing the sand ratio or adding an appropriate amount of stone powder (less than 7%).
(7) Mixing and feeding materials should be separated by crushed stone: cement, crushed stone, machine-made sand or machine-made sand, crushed stone, cement, which is beneficial to mix with aggregate and avoid segregation.
(8) When used for pumping concrete, machine-made medium sand should be used. The content of particles passing through the 300um sieve should not be less than 15%, and the content of particles passing through the 150um sieve should not be less than 5%.
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