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Table 20: Statistical quantification of total rainfall-duration during wet spell
STATION JODHPUR MADRAS BANGALORE KODAIKANAL NEW DELHI
[CLIMATIC ZONE] [HOT-DRY] [WARM-HUMID] [TEMPERATE] [COLD] [COMPOSITE]
Mean 19.0 hours 251.7 hours 232.2 hours 433.2 hours 96.4 hours
Range 17.8 hours 272.3 hours 140.3 hours 482.3 hours 87.1 hours
Standard deviation 6.4 hours 71.0 hours 37.4 hours 137.8 hours 32.0 hours
Coefficient of variation 0.34 0.28 0.16 0.32 0.33
Pearson’s index 0.29 0.57 0.92 0.84 1.07
95 percentile 29.62 hours 368.51 hours 293.69 hours 659.88 hours 149.06 hours
th

Table 21: Data pool of exposure conditions and adopted valued for sensitivity analysis
DATA POOL RAINFALL INTENSITY WDR INTENSITY RAINFALL DURATION
(PERCENTILE VALUES) (mm/hour) (mm/hour) (hours)
Station 95 th 50 th 5 th 95 th 50 th 5 th 95 th 50 th 5 th
Jodhpur 38.27 6.85 0.24 5.52 0.80 0.01 1.71 0.72 0.22
Chennai (Madras) 14.30 3.43 0.28 4.39 0.68 0.01 7.49 1.54 0.08
Bangalore 11.53 2.12 0.08 4.50 0.84 0.03 5.66 1.69 0.24
Kodaikanal 9.05 2.15 0.17 3.39 0.69 0.03 7.10 1.78 0.16
New Delhi 18.81 5.15 0.60 5.40 1.00 0.04 6.05 1.31 0.08

at wet bulb temperature, T a (K) is the dry bulb temperature of period for service life prediction. Hourly records of rainfall,
ambient air and T w (K) is the wet bulb temperature. The wet wind, temperature and relative humidity data spanning over
bulb temperature can be estimated from psychrometric chart the period of contemporary fifteen years were obtained
or empirical equations available in literature [66-68] . Latent heat from the archives of the Indian Meteorological Department
can be also from thermodynamic consideration [66,70-71] . In the for this purpose [66,81] . Jodhpur, Madras (Chennai), Bangalore,
context of drying constant rate, drying continues to a critical Kodaikanal, and New Delhi represent, hot and dry, warm and
moisture at the evaporating surface beyond which evaporation humid, moderate, very high precipitation and composite climate
front recedes and falling rate drying commences. The critical respectively. Rainy day and dry days are classified based on
moisture content again can be estimated through a series of the criteria that, when rain ≥ 2.5 mm/day, it is rainy and dry day
empirical equations [66,70-71] . In the falling rate drying, surface correspond to when rain < 2.5 mm/day. Utilizing the available
temperature of concrete is no longer wet bulb temperature, information, the wet spell for each station has been chosen to
but lower than the ambient temperature. Heat flux from the include the maximum number of wet rainy days while limiting
higher surrounding temperature into concrete occurs through the number of dry days to less than 2 % of the period. The
surface film conductance. From the surface to evaporation front delineated intervals exhibit clear distinction across stations and
heat transfer is happening by conduction for latent heat supply. have durations in the order of, Kodaikanal (270 days) > Madras
Detailed modelling is available in reference literature . (235 days) > Bangalore (218 days) > New Delhi (128 days) >
[66]
Jodhpur (107 days) [66,81] . The total duration of rainfall during
6.4 Rainfall intensity duration and wind velocity wet spell for the purpose of modelling of wetting and drying is
for design worked out and statistical quantification is given in Table 20. The
design of typical scenarios must account for the number and
Degradation period depicted in Figure 35, can be estimated manifestation pattern of rainy days, the intensity and duration of
when the rainfall intensity, rain duration, and wind velocity are individual rainfall events and the total duration of wet spell.
known. With these inputs, design boundary flux is calculated
and computation of wetting and drying period is possible. There are more than one wet spell and are spaced by dry spells
Five locations, namely, Jodhpur (26.28°N latitude, 73.02°E in-between except for Jodhpur, where rainfall is scanty. The
longitude), Madras (13.08°N latitude, 80.27°E longitude), effect of intermittent drying on moisture intrusion which occurs
Bangalore (12.97°N latitude, 77.57°E longitude), Kodaikanal due to the manifestation of dry days during the wet spell can
(10.23°N latitude, 77.48°E longitude) and New Delhi (28.61°N be modelled using average temperature and relative humidity
latitude, 77.21°E longitude) each pertaining to a distinct climatic characteristics. The influence is, however, expected to be
zone located within the vast geographical expanse of India, minimal owing to the inherently slow rate of the drying process.
are chosen as representative stations for design deterioration A more significant impact of drying could be expected during

36 THE INDIAN CONCRETE JOURNAL | JANUARY 2026