Creep and shrinkage of concrete: physical origins and practical measurements

Subcommittee 4 of RILEM TC 107-CSP has established recommendations for shrinkage and creep tests. These recommendations are based on physical and mechanical analysis of these tests, to ensure that they provide reproducible and objective results. However, the complete specification of these tests must also make it possible to respond to diversified needs: in particular, industrial users (contractors, suppliers of materials, etc.) are increasingly led to request such tests, and the type of experimental data they expect can be quite different from what is expected by people who draft regulations or develop numerical models. This paper therefore presents, in a first part, thinking about these needs, which are found to be highly varied and rapidly evolving. In a second part, we review the importance of the scale effect that makes it tricky to attempt any extrapolation of the available experimental results in two directions (to the long-term and to large thickness). In the absence of a satisfactory explanation of this scale effect, a practical method is proposed that can be used to get round this difficulty experimentally and to deal with certain engineering problems.