Report R 91 Early-age thermal crack control in concrete (revised edition)

Publication Year

1992

Document Status

Withdrawn

Abstract

Early-age thermal cracking occurs when the restrained thermal contraction strain exceeds the tensile strain capacity of the concrete. The restraint to thermal movement is the product of the coefficient of thermal expansion of the concrete, the temperature fall from a peak level during cement hydration, a restraint factor and a factor to account for the simplifications of the model. This Report discusses each of these factors in turn, and shows how early-age thermal strains can be reduced by taking appropriate measures during the design and construction of reinforced concrete elements. The concrete temperature rise is shown to depend on a number of factors: cement and addition type and content, type of aggregate, as well as ambient temperature, formwork used and section thickness. Restraint is a function of the construction sequence and the constraint of neighbouring elements. If early-age thermal cracking cannot be prevented, crack widths can be controlled with reinforcement. Equations for the control of crack widths are developed. The concept of a restraint factor is introduced and it is suggested that the crack widths are only controlled within an effective zone around the reinforcement and not necessarily throughout the section thickness.

Document History

First published in 1981. Replaced by CIRIA C660, Early-age thermal crack control in concrete, 2007.

ISBN

9780860173298

Publisher Information