Civil Engineering - Concrete Technology - Discussion

1)The aggregate is said to be elongated if its greater length is greater than 9/5th of its mean dimension.

Flaky means have less thickness, elongated means having more length.
A flaky aggregate is said to be elongated if its length is twice the mean size.

Elongated aggregates are unsuitable for pavement design.

Elongated aggregates can be found with the help of a length gauge.

Important Points:

An aggregate is said to be flaky is its least dimension is less than 3/5 of the mean dimension and the aggregate is said to be elongated if its greatest dimension is greater than 1.8 times the mean dimension.


So, the option B is the correct answer.

Mean of flaky aggregate is (3+5) /2=4.
Ellongated agg. 5/8.
So elongated length 8 but mean of flaky 4.

Then 2 times.

Flaky * X = Elongated.
3/5 * X = 1.8.
Solved, X=3

Flaky aggregate least dimension = 3/5 of the mean dimension.
= 0.6times
so flaky aggregate elongated to = 0.6 * 3 =1.8.

(so answer is thrice the mean size).

Let's suppose we have an aggregate with a mean size X.

So, for it to be elongated, its length should be greater than 1.8X and also for it to be flaky it's least dim should be less than 0.6X.

So, for aggregate to be both flaky and elongated, both conditions should be fulfilled and if the question says that the aggregate is flaky, so for it to be also elongated, its length should be 2X>1.8X.

Every particle has 3 dimensions.

In the Definition of flaky particles, we use the least dimension (it could be any) as a reference that has to be less than 0.6X (X is the mean size).

But in the definition of elongated particles, we use max dimension (it could be any but not least dimension) as a reference that has to be greater than 1.8X (approximately 2 times mean size).

So When we discuss flaky particles as elongated particles we are discussing a particle's max dimension and the least dimension can't be compared to the maximum one.

Any aggregate is said to be elongated if its length is more than 1.8 * mean dimension hence the correct answer is B only. It does not matter whether it is flaky or whatever and the answer would have been 3*least dimension if the length is asked compared to the least dimension i.e. thickness in the flaky aggregate.

It should be thrice as 3/5*3= 9/5.

Twice is the Correct answer because mean size is not 0.6 it is the length but we have calculated with respect to mean size so 9/5 is the correct answer.

Option C is correct according to IS456.