Question:
Published on: 30 January, 2023

What are flaky and elongated aggregates? How can the shape of aggregate influence strength of concrete? Following is the result of a sieve analysis of 500 gm aggregate:

 IS sieve size 10 mm 4.75 mm 2·36 mm 1·18 mm 600 micron 300 micron 150 micron lower than 150 micron Weight retained in gm 0 10 50 50 95 175 85 35

Find out the 'Fineness Modulus' of the sample

FLAKY AGGREGATES:- This agg. Are those whose least dimension i.e. thickness is less than 3/5 th of their mean dimension.

ELONGATED AGGREGATES:- This agg. are those whose greater dimension i.e. length is greater than 9/5 th of their mean dimension.

According to shape                                        voids

Rounded aggregate                                    32 – 33 %

Irregular aggregate                                    35 – 38 %

Angular aggregate                                     38 – 40 %

Rounded aggregate gives better workability and Angular aggregate gives better strength.

total wt. = 500gm.

 Sieve Wt. retained in each sieve(gm) % wt. retained cumulative % of wt. retained % finer 10 mm 0 0 0 100 4.75 mm 10 2 2 98 2.36 mm 50 10 12 88 1.18 mm 50 10 22 78 600 µ 95 19 41 59 300 µ 175 35 76 24 150 µ 85 17 93 07 <150 µ 35 7 100 00 Ƹ = 346

So, F.M. = 346/100 = 3.46

F.M. of coarse aggregate is3.46.

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