Enhanced massivity index based on evidence from case studies: towards a robust pre-design assessment of early-age thermal cracking risk and practical recommendations

Abstract

Tensile stresses resulting from a combination of thermal volumetric changes, due to the heat of hydration and ambient conditions, autogenous deformations and boundary restraints, often induce a significant intrinsic load on massive concrete structures. Whenever such stresses attain the concrete tensile strength, cracking occurs, which may in turn impair the serviceability and durability of the structure. This study is an output of Working Group 7 of RILEM Technical Committee 254-CMS: Thermal cracking in massive concrete structures and is presenting case studies of early-age thermal cracking in massive concrete structures where internal restraining conditions often prevail, such as thick blocks, armour units, footings, dams and spillways, and large-sized columns. It covers the analysis of causes of this type of cracking together with the lessons learned from the collected evidence along with best mitigation practices (often resulting from forensic investigations by means of computer-based simulations). Based on the evidence retrieved from the analysed case studies, the concept of massivity used to indicate potential thermal crack proneness in massive concrete structures is significantly improved to account for binder type and content as well as casting and fresh concrete temperature, in addition to the geometrical characteristics of the element under investigation. The use of such an indicator may lead to a more robust pre-design assessment of the likelihood for thermal cracking occurrence in massive concrete elements, advising designers and contractors dealing with such structures whether more complex analyses should be performed already at the design stage.