Grading of Aggregates by Using Different Methods

Grading of Aggregates by Using Different Methods

Grading of aggregates consists of balancing the fine and the coarse aggregates in such a ratio, in order to obtain the strongest and densest mixture with the least amount of cement.

Grading the aggregates is so graded as to have minimum voids when mixed with all ingredients, and water should render a concrete mass of easy workability.

• By Trail
• By sieve analysis method
• By minimum voids method
• By arbitrary standards

By trail

In this method, proportioning of aggregates as to give heaviest weight for same volume, yield the
densest concrete.

By finesse modules method (sieve analysis method)

In this process, the samples of both coarse and fine aggregates are passed through a series of nine standard sieves, and the percentage of the sample retained on each of those sieves is determined. The sum divided by 100 of these percentages gives sample modulus of finesses.

By minimum voids method

This method is based on the fact, that so obtain dense concrete the quantity of cement should also be slightly in excess of voids more that the fine aggregates.

Also in this method the voids in the fine and coarse aggregates are separately found out with the help of graduated cylinder and water.

The percentage of voids I aggregate, “X” given by the equation.

X = (V₁ – V₂) x 100/V₂

Where V₁, volume of water filled
Where V₂, volume of aggregates.

By arbitrary standards

Its a commonly adopted method of propitiating the aggregates in a concrete mix for small project of moderate importance.

This method is not recommended for large projects  or important works in this method, the volume of cement, sand and coarse aggregates are taken in the proportion of 1:n:2n respectively.

The quantity of water to be used a varied suit the workability descried.

For Example:

1:1:2 – M250 rich mix for columns, beams

1:1:3 – M200 Water retaining structures etc

1:3:6 – M150 slab’s columns roads etc

1:3:6 – M100 – foundations

1:4:8 – For mass concrete

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