 The strength and water tightness of concrete improve with age as long as long as conditions are favorable for continued hydration of its Portland cement. Other qualities, such as weathering and resistance to freezing and thawing, are affected similarly. Improvement is rapid early and continues more slowly for an indefinite period as long as moisture and favorable temperatures are present. Fresh concrete contains more than enough water for hydration, but under most job conditions much of this water is lost by evaporation unless certain precautions are taken. Hydration proceeds at a much slower rate as the temperature drops until it stops altogether at about 14ºF(-10ºC). however, at about 40 ºF(4.4ºC), hydration becomes too slow for concrete work to proceed without special provisions to heat the ingredients so that the concrete so that moisture is not lost during the early stages of hardening, and it should be kept at a temperature that will promote hydration and also protect against injury from subsequent construction activities. |