Question

What is the maximum aggregates size of a concrete mix for a slab of depth 100
mm and main reinforcement having spacing of 150 mm.

Answer 1

Maximum size of aggregates as per Indian Standards ( IS 456:2000) page 14 clause 5.3.3 is the

1. Less than 1/4 of the minimum thickness of the member

2. 5mm less than the minimum distance between the main bars

3. 5 mm less than the minimum cover

Hence the size of aggregate should be less than

1. 100/4 = 25mm

2. 150- 5 = 145 mm

Least of the 2 cases and hence the minimum size of the aggregates should be less than 25 mm. Also assuming a minimum cover of 30 mm for moderate conditions.