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Effect of w/c ratio on durability

Short answer

Higher water-cement ratio leaves more capillary pores, greatly increasing permeability and ingress of water, chlorides, and CO2, thus lowering durability. IS 456 limits maximum w/c from 0.40 to 0.55 depending on exposure, with minimum cement content of 300–360 kg/m³.

How does water cement ratio affect the durability of concrete?

The water-cement ratio is the main factor controlling the durability of concrete. Water in excess of that needed to hydrate the cement (w/c above about 0.38) leaves capillary pores. A higher w/c gives more and larger interconnected pores, so permeability is higher, strength is lower, and water, chlorides, sulphates and CO2_2 enter faster. This leads to corrosion, carbonation, freeze-thaw damage and chemical attack.

Hence IS 456 (Table 5) limits the maximum w/c for reinforced concrete: 0.55 (mild), 0.50 (moderate), 0.45 (severe and very severe) and 0.40 (extreme exposure), with a minimum cement content of 300 to 360 kg/m3^3.

✓ Answer checked by Claude Sonnet 5.5

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