Prediction of dam concrete structural properties based on wet-screened test results and mesoscale modelling

Abstract

Dam or full-mixed concrete is produced with large aggregates which implies the use of large specimens, heavy laboratory equipment and non-standard embedding monitoring devices. The wet-screened concrete, obtained from the full-mixed concrete by sieving the larger aggregates while the concrete is still fresh, is used to cast smaller specimens and embed standard monitoring devices. This thesis focuses on the prediction of the structural properties of dam concrete based on wet-screened concrete experimental results, analytical models and detailed particle models in which the mesostructure is represented. In order to study the effect of wet-screening, an in situ experimental setup and a series of laboratory tests were carried out for both dam and wet-screened concretes. Three sets of creep cells were installed in a dam which allowed for the improvement of the experimental setup and the testing procedures, aiming to reduce costs, to facilitate the installation in situ and to increase the reliability of the results. The test results revealed the differences between the two types of concrete and the influence of the coarse aggregate on the deformability and strength properties. Different analytical models based on composite models, on the equivalent age method, on size effect and on the Abrams law were developed to describe the instantaneous and delayed behaviour of concrete using the composition data and to establish a practical relationship between dam and wet-screened concrete behaviour. Similarly, a numerical solution based on the discrete element method applied to particle models was developed to predict the behaviour of dam concrete. A new fast numerical procedure for long-term analysis taking into account the aging viscoelastic behaviour of cementitious material is proposed. Particle models are especially suited for modelling dam concrete since the coarse aggregate structure can be explicitly represented, allowing the study of stress distribution inside the specimen and the study of complex failure patterns both in tension and compression. For the two types of approaches, the obtained experimental results were used to calibrate the main parameters and to validate the analytical and numerical prediction models. The experimental results and the development of physically-based models highlighted the particular properties of dam concrete, allowed for a significant contribution to the analysis of concrete instantaneous and delayed behaviour and presented new approaches for the prediction of dam concrete behaviour based on the wet-screened properties.