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Flaky and elongated aggregate

Short answer

Flaky: thickness <0.6 mean dimension; elongated: length >1.8 mean dimension. They reduce strength (weak planes), workability (more water needed) and durability (trapped bleed water, porous interface), and increase cement demand.

Define flaky and elongated aggregate. How do these aggregates affect the strength, workability and durability of concrete? Explain.

Flaky aggregate: a particle whose least dimension (thickness) is less than 0.6 times its mean dimension (the mean of the sieve sizes between which it falls) (IS 2386 Part 1). The flakiness index is found using the thickness gauge.

Elongated aggregate: a particle whose greatest dimension (length) is more than 1.8 times its mean dimension; the elongation index is found with a length gauge.

Flaky and elongated particles are together called poorly shaped particles. Aggregate should preferably be cubical, and IS 383:2016 limits the combined flakiness and elongation index to 40 per cent.

Effect on concrete

PropertyEffect of flaky / elongated particles
StrengthReduced; they tend to break under load and create weak planes; poor bond and interlock
WorkabilityPoor: higher surface area, so more water and paste are needed for the same slump; harsh mix, difficult compaction
DurabilityLower: water gathers under flat particles (bleed pockets), giving a porous interface zone and higher permeability; flaky pieces orient horizontally
EconomyMore cement is needed to make a workable mix
OtherTendency to segregate; difficulty in pumping

Therefore, flaky and elongated aggregate is limited, and cubical, well-shaped crushed stone is preferred.

✓ Answer checked by Claude Opus 5.5 (high effort)

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