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| Grading of Aggregates |
Grading of
aggregates consists of proportioning the fine and coarse aggregates in such a
ratio, so as to get strongest and densest mix 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.
The grading
of aggregates are done by the following methods
·
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
method, the samples of both coarse and fine aggregates are passed through a set
of nine standard sieve and the percentage of sample retained on each of the
said sieves is determined. The total of these percentages divided by 100 gives
the finesses modulus of sample
·
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. 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: It is a commonly adopted method
of propitiating the aggregates in a concrete mix for small works of moderate
importance. This method is not recommended for large works 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.
Ex: 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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