The conditions under which concrete is poured and cures have a large impact on the ability of the concrete to reach its maximum rated strength and maximum lifetime. Many concrete structures such as bridge decks and roadways are under the influence of the ambient atmospheric conditions during this critical pouring and curing time. Under conditions adverse to the curing, stress fractures may form, limiting the durability of the concrete slab. While much information about the chemistry of concrete is known, little detailed information is available regarding the interaction of the curing concrete and its ambient environment.
The New York State Department of Transportation has an ongoing research endeavor studying the effects of ambient conditions and different concrete mixtures on the resulting cured concrete. As part of this project, we made atmospheric and structural observations during the pouring and curing phases of several concrete bridges in New York State. The measurements included atmospheric wind speeds and directions, temperatures and humidities above and below the bridge deck, top and bottom bridge surface temperatures, incoming and reflected solar radiation, precipitation, net radiation above and below the bridge deck, and the amount of water sprayed onto and running off of the bridge. The curing of concrete is an exothermic reaction, so much heat is liberated from the concrete slab during the curing phase. To determine how this heat is removed from the bridge and thus how it is interacting with its environment, we have examined the surface energy budget of the bridge decks for up to 96 hours after the pour was initiated. The energy budget includes the net radiation and heat removed as sensible and latent heat, and heat removed by water running off of the bridge. We have found that during the early stages of the cure the enhanced upward longwave radiation provided by the curing concrete can significantly reduce the net radiation gained by the bridge top surface during the daylight hours. The net radiation loss below the bridge is not a significant fraction of the total heat removed from the bridge. Within roughly 72 hours after the pour, the bridge returns to being a passive participant in its environment. We have also found that sensible, latent, and water runoff heat fluxes from the top surfaces of the decks are all significant components of the energy budget. With this information and with a model of concrete curing, we draw several inferences about the ideal atmospheric conditions under which to initiate a pour.