Concreting in Extreme Weather Condition

Over the last 30 years, scientific research has increasingly implicated human activities in contemporary regional- to global-scale climatic change. Over the last decade, this research has extended to the detection of the fingerprint of human activities on individual extreme weather events. Is it possible to say that this or that weather extreme was caused by human activities Pursuing answers to this question raises many difficult philosophical, epistemological and political issues. High temperatures affect concrete at all stages of the production and placing process and most of the effects have consequences for long-term strength or durability. Some of the problems resulting from high temperatures are presented in the chapter. Concrete at high temperature loses workability at a faster rate because of the combined effects of loss of water through evaporation and the more rapid rate of the hydration reaction. Hydration of cement in concrete is an exothermic reaction, that is, it produces heat. A number of different methods are used to alleviate the effects of hot weather. They are mostly aimed at reducing the temperature of the concrete at the time of placing by either cooling the ingredients, reducing the heat gain experienced during mixing, transit and placing or by cooling the concrete itself. Furthermore, in cold water effects concrete which is placed at low temperatures, but which is not allowed to freeze and receives good curing, develops higher ultimate strength, greater durability and is less subject to thermal cracking than similar concrete placed at higher temperatures. The main problems associated with cold weather are frost damage to immature concrete and slow gain in strength leading to later stripping times and the possibility of increased damage when the shutters are removed.