Crack Width (RCC)

Crack width is the serviceability check that limits the surface width of flexural/tension cracks in reinforced concrete so that durability (reinforcement corrosion), watertightness and appearance are not compromised. Some cracking is inherent to RCC working under service loads; the design objective is to keep crack widths within acceptable limits by detailing — adequate, well-distributed reinforcement at moderate bar spacing and stress, rather than fewer large bars.

IS 456 Cl. 35.3.2 sets a surface crack-width limit of 0.3 mm for normal members, reduced for aggressive exposure, with a calculation method in Annex F; deemed-to-satisfy bar-spacing rules (Cl. 26.3.3) usually achieve this without explicit calculation. For liquid-retaining structures the criterion is much stricter — IS 3370 limits crack widths (typically 0.2 mm, or 0.1 mm for severe exposure) and often drives the design via the direct/flexural tension and shrinkage-temperature reinforcement. Crack width is sensitive to bar stress, cover and bar spacing, so detailing — not concrete grade alone — is the lever.