This code provides a comprehensive framework for durability-based design of concrete structures, introducing service life design principles and detailed environmental exposure classes. It moves beyond the prescriptive durability rules of IS 456 to a performance-based approach, aiming to ensure structures achieve their intended service life by considering long-term degradation models.
Provides guidance on designing and detailing concrete structures to ensure long-term durability and resistance to degradation.
Quick Reference Values
Target service life for normal buildings50 years
Target service life for monumental structures/important bridges100 years
Allowance in design for deviation of cover (Δc dev)10 mm
Minimum grade for 'Tidal, splash and spray zones' (XS3)M40
Maximum W/C ratio for 'Very Severe' exposure (XD3/XS2)0.40
Minimum cement content for 'Very Severe' exposure (XD3/XS2)360 kg/m³
Minimum grade for 'Extreme' exposure (XF4)M40
Key Formulas
x_c(t) = k_c * sqrt(t) — Simplified formula for depth of carbonation
C(x,t) = C_s * [1 - erf(x / (2*sqrt(D_app,Cl*t)))] — Fick's 2nd Law for chloride ingress
c_nom = c_min + Δc_dev — Calculation for nominal cover
c_min = max(c_min,b; c_min,dur + Δc_dur,add; 10 mm) — Calculation for minimum cover
Practical Notes
This code supplements, not replaces, IS 456. Its durability provisions (especially for cover and mix design) are more stringent and should be followed for important structures or those in aggressive environments.
The selection of the correct exposure class from Table 1 is the most critical first step as it dictates all subsequent durability design choices.
The nominal cover (c_nom) is calculated by adding a 10 mm allowance for deviation (Δc_dev) to the minimum cover (c_min), a key difference from the direct values in IS 456.