Biennial International Lecture: Early behaviour of concretes in large dams

Overview

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 middle part of the 20th century, consequential cracking was relatively common in large concrete dams.

With the development of Roller Compacted Concrete (RCC), a renewed focus was placed on the thermo- mechanical behaviour of concrete during the early hydration heat development and dissipation cycle and advances in thermal analysis systems additionally enabled improved modelling of temporal temperature distributions. The thermo-mechanical behaviour materials models often subsequently used, however, failed to replicate actual behaviour, sometimes producing a significant misinterpretation.

Through back-analysis of RCC and particularly RCC arch dams, a 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 (SRC).

The related findings have implications across all types of large-scale mass concretes 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.

In his lecture, Quentin Shaw will discuss the early behaviour patterns observed in different concretes and how these influence the consequential structural behaviour and the associated design requirements for dams. He will subsequently illustrate how this principle will influence the selection of cementitious materials and the optimal processing of aggregates, etc, to improve the behaviour and increase the predictability of mass concrete thermo-mechanical performance.