Justification and refinements of model B3 for concrete creep and shrinkage 2. Updating and theoretical basis

Following statistical evaluation in part 1, this part deals with the improvement of prediction by updating one or two parameters of the model on the basis of short term tests and theoretical derivation of some formulae. The updating of model parameters is particularly important for high strength concretes and other special concretes containing various admixtures, superplasticizers, water-reducing agents and pozzolanic materials. For the updating of shrinkage prediction, a new method is presented in which the shrinkage half-time is calibrated by simultaneous measurements of water loss. This approach circumvents the ill-posedness of the shrinkage extrapolation problem. Theoretical justifications of various aspects of the model are given and a new formula for the additional creep due to drying (or stress-induced shrinkage) is derived. The new model should allow a more realistic assessment of the creep and shrinkage effects in concrete structures, which significantly affect durability and long term serviceability of civil engineering infrastructure.