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Concrete Grade Selection Guide

IS 456:2000 · Clause 6.1 — Grades of Concrete, Table 2 & Table 5

Quick decision guide for selecting the right concrete grade based on structural element, exposure condition, and application. IS 456 mandates minimum M20 for RCC and specifies higher grades for severe environments.

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By Application — Which Grade to Use?

Application	Grade	Reason	Exposure
Levelling course / blinding	M10 (1:3:6)	Non-structural, below footings	N/A
PCC below footings	M10 or M15	75–100mm thick, protects rebar	N/A
Compound wall, parapet	M15	Non-structural or lightly loaded	Mild
RCC — residential interior	M20 (minimum)	IS 456 minimum for RCC	Mild
RCC — residential (general)	M20 to M25	Slabs, beams, columns	Mild to Moderate
RCC — exposed to rain	M25 minimum	Balconies, external beams	Moderate
RCC — basement / retaining wall	M30 minimum	Contact with soil + water	Severe
Water tank / overhead tank	M30 minimum	Impermeability critical, IS 3370	Severe
Swimming pool	M30 to M35	Chloride exposure	Very Severe
Foundation in aggressive soil	M35 minimum	Sulphate / chloride in ground	Very Severe
Coastal structure (<500m from sea)	M35 to M40	Chloride-induced corrosion risk	Very Severe
Bridge deck / pier	M35 to M45	IRC 112, heavy loads + exposure	Severe to Very Severe
Marine structure (tidal zone)	M40 minimum	Direct sea water contact	Extreme
Bored cast-in-situ pile	M25 to M35	Tremie placement, durability	Severe
Precast elements	M30 to M50	Early strength, durability	Varies
Post-tensioned slab	M35 to M45	High early strength needed	Moderate
High-rise columns (>15 floors)	M40 to M60	High axial loads	Moderate
Road pavement (PQC)	M30 to M40	IRC 44, flexural strength governs	Severe
Industrial floor (heavy traffic)	M30 to M40	Abrasion + impact resistance	Severe
Nuclear/containment structure	M50 to M60	Radiation shielding + strength	Extreme

Quick Decision — Minimum Grade by Exposure (IS 456 Table 5)

Application	Grade	Reason	Exposure
Mild (protected interior)	M20	IS 456 minimum for RCC	w/c ≤ 0.55
Moderate (sheltered from rain)	M25		w/c ≤ 0.50
Severe (rain, wet/dry cycles)	M30		w/c ≤ 0.45
Very Severe (coastal, chemicals)	M35		w/c ≤ 0.45
Extreme (sea water, acids)	M40		w/c ≤ 0.40

Notes

• IS 456 mandates MINIMUM M20 for all RCC work — M15 is only for PCC/mass concrete

• Nominal mix (1:1.5:3 etc.) is permitted only up to M20 — higher grades require design mix per IS 10262

• Grade selection is governed by EXPOSURE first, then STRENGTH requirement — use whichever demands the higher grade

• For water-retaining structures, use IS 3370 in addition to IS 456

• Flexural strength (for pavements) ≈ 0.7 × √fck MPa — design for modulus of rupture, not compressive strength

• Specifying a higher grade than needed wastes cement and increases cost — design mix optimization is key

• Always specify: grade, max w/c, min cement content, max aggregate size, slump, exposure condition

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