CONCEPT:As per IS 456: 2000, Clause 26.5.2.2,Maximum Diameter:The diameter of the reinforcing BAR shall not exceed one-eighth of the total thickness of the slab.Minimum Reinforcement:The mild steel reinforcement in either direction in slabs shall not be less than 0.15 per cent of the total cross-sectional area.For high strength deformed bars, the above VALUE can be reduced to 0.12 per cent.Calculations:Maximum diameter = \({1\over8}\times total \; thickness \;of\;the\; slab\)Maximum diameter = \({1\over8}\times 75 \;cm=9.375\;cm\)So, the diameter of the bars to be used should not be greater than 8 MM.