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Early-age thermal cracking occurs when the tensile strain, arising from either restrained thermal contraction or a temperature differential within the concrete section, exceeds the tensile strain capacity of the concrete. Numerous factors influence the risk of early-age cracking including the temperature rise, the coefficient of thermal expansion of the concrete, the restraint to movement offered either by adjacent elements or by differential strain within an element, and the ability of the concrete to resist tensile strain.
CIRIA guide C766, Early-age thermal crack control in concrete (2018) which supersedes CIRIA Report C660 (2007) and CIRIA R91 (1992) provides a method for estimating the magnitude of crack-inducing strain and the risk of cracking. Where cracking is predicted, guidance is provided on the design of reinforcement to control crack widths in accordance with current European Codes. For specific situations where cracking should be avoided, or where the use of reinforcement to achieve acceptable crack widths is uneconomic or impracticable, measures are described to minimise the risk.
Acknowledgement: The Concrete Society
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