Title: Concrete Creep and Shrinkage Numerical Modelling of Test Results

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Publication: CIA

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Date: 2/13/2011

Abstract:
The paper describes an investigation of concrete creep and shrinkage, including advanced numerical models and an extensive series of laboratory tests. Numerical modeling, based on models of humidity diffusion, unrestrained shrinkage and concrete compliance (including basic creep), has indicated that significant tensile stresses can develop quickly on the surface of drying concrete due to non-uniform shrinkage. The strain-softening effects of surface cracking were modeled, and calculated shrinkage strains were reduced by about 20% as a result of strain-softening for unloaded drying shrinkage specimens of three sizes (small, medium and large). Modelling also showed that an increase in diffusivity due to cracking could have a significant effect on shrinkage strains and partly offset the effects of strain-softening. It was shown that the numerical model could easily be calibrated to fit the shrinkage test results for specimens of any given size (small, medium or large), but attempts to model the observed size-effect for shrinkage strains were unsuccessful. Total strains for medium sized drying loaded specimens were modeled using a combination of the basic creep model (calibrated for medium-sized specimens) and the shrinkage model (as calibrated for small specimens). The numerical model underestimated the strains for the drying loaded specimens, but the match was closer than for shrinkage alone.