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A high ambient temperature increases the temperature of the fresh concrete, resulting in more rapid hydration of the cement and leading to accelerated setting. Rapid evaporation of moisture from exposed surfaces may cause plastic shrinkage cracking and crazing, see also main entry Cracking and subsequent sub-headings. Thus greater care needs to be taken with curing than under normal ambient conditions.
Higher temperatures for the fresh concrete will lead to higher early age maximum temperatures. This will result in higher thermally induced stresses as the concrete cools to the ambient temperature, with a correspondingly higher risk of cracking. In addition, differential temperatures between the interior and the surface of the concrete may be increased, again increasing the risk if cracking. Design Standards, give guidance on maximum differential temperatures; generally a figure of 20oC is considered acceptable.
In areas with extremely high ambient temperatures, such as in the Arabian Peninsula, it may be necessary to cool the concrete prior to placing it, for example by replacing part of the water in the mix flaked ice.
A good reference document is Early age thermal crack control in concrete. Report C766 published by CIRIA (2019), which replaces C660 (2007).
Acknowledgement: The Concrete Society
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