The early behaviour of concretes in large dams

Abstract

Surface gradient and mass gradient thermal effects have always substantially complicated the design and construction of large concrete dams. Despite generic rules of thumb and systems to control allowable thermal gradients being developed largely empirically during the early to mid-twentieth century consequential cracking has been relatively common in large concrete dams. While this is primarily a reflection of difficulties inherent to adhering to the related requirements, realistically, a similar level of causative effect can be attributed to a poor understanding of the associated early concrete behaviour mechanisms. Through back-analysis of roller compacted concrete (RCC) and particularly RCC arch dams, a more realistic picture of the actual early thermo-mechanical behaviour of concrete was progressively developed, identifying different behaviour for different concrete compositions and particularly different cementitious materials and supplementary cementitious materials. The key behaviour parameter was defined as a stress–relaxation creep. The related findings have implications across all types of large-scale mass concrete structures and impact the way in which we should think of concrete materials and structural composition and even how we should approach mix design for mass concrete.