Concrete Technology (General Engineering) (SSC JE)

Bulking of sand–The increase in the volume of sand due to the presence of moisture up to certain extent, is called bulking of sand.
• Increase in the volume of sand due to presence of surface moisture. As the moisture content of a fixed weight of sand increase, the volume also increases, which is known as bulking. The entrapped air escalates the sand volume between 5 to 10% depending on the grain size and shape of the sand particle. Increase in moisture content by 5% to 10% can escalate sand volume between 15 to 40%.
• Variation in bulking of sand in coarse, medium and the grain sand with increase in moisture content.

As per IS : 456-2000 clause 10.2–
The accuracy of the measuring equipment shall be within ±2% of the quantity of cement being measured the accuracy of the measuring equipment shall be within ±3% of the quantity of aggregate admixtures and water being measured.

Effect of Fly ash on cement concrete–
• Its reduce segregation and bleeding.
• Its improve workability of concrete.
• A 30% substitution of fly ash may result in an increase of initial setting time up 2 hours.
• Fly ash reduces the heat of hydration in concrete.
• Fly ash slightly improves the resistance of concrete to sulphate attack.
• The permeability of concrete reduces on addition of fly ash to cement.
• Addition of fly ash upto 30% may result in lower strength at 7 and 28 days, but may be about equal at 3 month and may further increase at ages greater than 3 months provided curing is continued.