How the IS 456 Quick Tables works
The IS 456 values site engineers look up every day, in one place: minimum cement content, maximum water-cement ratio and minimum grade for each exposure (Table 5), nominal cover (Table 16), workability and slump (cl. 7.1), target mean strength (IS 10262), bar weights, and a search across common IS codes.
Frequently asked questions
What does IS 456 Table 5 specify?
Table 5 gives, for each exposure condition, the minimum cement content, maximum free water-cement ratio and minimum grade for plain and reinforced concrete with 20 mm aggregate. For example, RCC in moderate exposure needs at least 300 kg/m³ cement, w/c not more than 0.50 and grade M25.
What is the nominal cover as per IS 456?
Table 16 gives 20 mm for mild, 30 mm for moderate, 45 mm for severe, 50 mm for very severe and 75 mm for extreme exposure. Columns need at least 40 mm cover to longitudinal bars and footings at least 50 mm.
What slump is required for RCC work?
IS 456 cl. 7.1 suggests 25–75 mm for lightly reinforced slabs, beams, walls and columns, 50–100 mm for heavily reinforced sections, 75–100 mm for pumped concrete and 100–150 mm for in-situ piling.
How is target mean strength calculated?
IS 10262:2019 uses the higher of fck + 1.65s and fck + X. For M25: s = 4, so the target is the higher of 31.6 and 30.5, i.e. 31.6 N/mm².
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