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TECHNICAL PAPER

Table 19: Proposed durability zones for service life prediction

MAIN ZONES SUB ZONES BASIC DETERIORATION MECHANISMS RELEVANT BOUNDARY CONDITIONS
TO SERVICE LIFE
Chloride Diffusion in saturated concrete and/or May be sudden exposure to constant chloride
Submerged (MZ1) sea water attack and leaching followed by rebar concentration, exposure to hydrostatic pressure,
corrosion but lack of oxygen polarizes rebar corrosion
Chloride Diffusion and solution ingress in un-
Marine zone Periodic boundary condition varying with time,
Splash zone (MZ2) saturated concrete, and/or sea water attack and
leaching followed by rebar corrosion velocity flux, wetting and drying
On shore (5-10 km) Chloride accumulation at the surface followed by Wind driven rain induced velocity flux, wetting
(MZ3) ingress with rainwater and drying
Wind driven rain induced velocity flux, wetting
Moisture ingress induced carbonation, corrosion
Hot dry desert (NMD) and drying and also periodic wetting and drying in
of rebar or any other deterioration
case of partially submerged structure
Wind driven rain induced velocity flux, wetting
Moisture ingress induced carbonation, corrosion
Warm Humid (NMW) and drying and also periodic wetting and drying in
of rebar or any other deterioration
case of partially submerged structure
Non-marine zone
Wind driven rain induced velocity flux, wetting
Composite Monsoon Moisture ingress induced carbonation, corrosion
(NMM) of rebar or any other deterioration and drying and also periodic wetting and drying in
case of partially submerged structure
Wind driven rain induced velocity flux, wetting
Very high precipitation Moisture ingress induced carbonation, corrosion
(VHP) of rebar or any other deterioration and drying and also periodic wetting and drying in
case of partially submerged structure
the main issue is moisture ingress through wind driven rain for 6.3 Wind driven rain induced wetting and
exposed concrete. The wetting and drying are the phenomena. drying
This is because all the deterioration process in concrete
involves ingress of water and conducive relative humidity In tropical climates, e.g., hot dry desert climate, warm humid
for degradation. Carbonation may peak around 55-60 % RH. climate, and composite monsoon climate etc., rainy season
lasts for maybe a few days in hot dry desert climate, for 2-3
Conducive RH for active corrosion may peak around 90 % RH. In
months in composite monsoon climate and up to six months in
both carbonation and active corrosion, processes are inhibited
some cases in warm humid climate. Exposed concrete surfaces
in 100 % saturation due to low concentration of CO 2 and oxygen
during monsoon in India would be subjected to wetting due
respectively. Hence there is conducive saturation condition for to rain flux during rainy season leading to intermittent wetting
both carbonation and rebar corrosion. The degradation would followed by drying in the absence of rain. Thus, wetting-
occur in steps and increase progressively with cycles of wetting drying cycle is typically constituted by a period of rainfall
[63]
and drying as shown in Figure 35 . followed by subsequent evaporative drying. Wetting involves

Figure 34: Proposed durability zones for India (Tropical) Figure 35: Annual wetting drying cycle and degradation period

34 THE INDIAN CONCRETE JOURNAL | JANUARY 2026