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We calculated the equivalent ages of concrete for a wide variety of atmospheric and construction conditions for the first 24 h of the active phase of the hydration reactions. The equivalent ages were computed using Eq. ( 1) starting at the end of the induction period of the hydration reactions and the concrete was allowed to mature as long as there was water available for reaction at a given point. The atmospheric variables considered were air temperature and relative humidity (Ta and RH), wind speed (U), and cloud cover fraction (clf) which affects radiation (16). The range of values chosen represents typical atmospheric conditions. Diurnal variations of the atmospheric variables were approximated with simple cosine functions that capture the main features of typical diurnal variations (9). Ta and U generally peak during the late afternoon while RH reaches a minimum during this time. The simulations were run for Albany, NY in early June with the concrete being placed at 0700 local time (LT). The length of the induction period of the hydration reactions was set at eight hours.