A new multi-scale approach to characterize concrete creep and its implications in long-term durability

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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. Estimating the long-term creep of concrete (e.g., 30-50 years) using short term creep tests (e.g., 3-12 months) has been an unavoidable crux in civil engineering. In this context, novel microindentation techniques have been provided a breakthrough solution as they allow characterizing the logarithmic nature of the long term creep in few minutes. From a design point of view, the modern model code fib 2010 has recently adopted a logarithmic function for predicting the long term creep. This is extremely appealing for the proposed research program which intends to develop micro-indentation techniques to rapidly estimate the parameters of such logarithmic function for predicting the long term creep of concrete. The specific objectives of this research program are: (1) At the microstructure level, to fully characterize and better understand the effect of the temperature and possible damage on the creep behaviour of a cement paste by means of microindentation tests; (2) Upscale the properties measured at the level of a cement paste to the concrete level; (3) To implement a numerical model for predicting the long term deformation of a structure at different environmental conditions (e.g., temperature) and with possible damage due to durability issues; (4) To improve the current design methods on the prediction of the long term creep; (5) To develop an international network of excellence and train students in highly specialized competences. This innovative research direction will provide outstanding contributions to civil engineering, such as: (i) Fostering the current understanding on the long term creep of concrete with emphasis on its dependence on temperature and damage; (ii) Developing of ultra-rapid microindentation techniques for characterizing the long term creep of cement paste; (iii) Developing engineering tools for better predicting the long term creep of a concrete structures, such as bridges; (iv) Contribution to enhanced design recommendations for better predicting the long term creep of concrete structures and assuring the desired durability of the future Canadian infrastructure.