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.

Autogenous shrinkage may also contribute to early contraction. 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's new guidance "Early-age thermal crack control in concrete" (C660) provides a method for estimating the magnitude of crack-inducing strain and the risk of cracking; and where cracking is predicted guidance is provided on the design of reinforcement to control crack widths. For specific situations where cracking should be avoided, or where the use of reinforcement to achieve acceptable crack widths is uneconomic or impractical, measures are described to minimise the risk including selection of materials and mix design, planning pour sizes and construction sequence, the use of insulation to reduce thermal gradients, the use of movement joints, and cooling of the concrete either prior to placing or in situ.

For further information and to buy a copy of 'Early-age thermal crack control in concrete' (C660) visit www.ciriabooks.com, contact CIRIA on 020 7549 3300 or email enquiries@ciria.org

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