A new multi-scale approach to characterize concrete creep - Phase 2: drying effects, application to emerging concretes and micro-to-macro validation

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A recent survey on 71 concrete bridges monitored over a period of about 20 years showed that the creep deflection increases incessantly and it overestimates by far the predictions of several national codes. A wake-up call was then launched stating that the current national design recommendations and codes "are not only theoretically obsolete, but also indefensible". The proposed research program aims at better understanding and characterizing the long-term creep of concrete, and finally, to enhance the current design methods for predicting the long-term behavior. The reason is that concrete creep depends on many factors so that published results are often controversial. Predicting the creep deflection of structure after decades from experimental compression creep tests lasting few months is a tremendous and error-prone challenge. Current methods to characterize concrete creep are time consuming and rarely applied in practice (3). Furthermore, there is a limited availability of creep data on emerging modern concretes, such as ultra-high performance concretes (UHPCs), which have enormous potentials for fostering the design lifetime and reduce the maintenance cost towards a more sustainable infrastructure system (4). By pioneering an innovative new research direction, this research program aims setting-up a groundbreaking multi-scale approach for enhancing current knowledge on concrete creep in terms of characterization methods, design accuracy and advanced material development. The specific objective of this research program is six-fold: (1) Foster the knowledge on the mechanisms of concrete creep under environmental changes by innovative micro-mechanical testis; (2) Develop a multiscale method to upscale the measured properties from the cement paste level to the concrete level; (3) Validate the proposed two-scale method (2SM) for characterizing cement paste, mortars and concrete at different water-to-cement ratios with emphasis on modern concretes and emerging UHPC; (4) Contribute to the Canadian design for predicting long-term deflection of concrete structures and improve the current practise; (5) Develop an international network of excellence on concrete micromechanics; (6) Train students in highly specialized competences requested for innovating industry.