Criteria for rational prediction of creep and shrinkage of concrete

This paper, supplementing the exposition of model 83 in this volume, examines various basic questions in fommlating and evaluating a prediction model for creep and shrinkage of concrete. Verification by comparisons to a few subjectively selected data sets is no longer justifiable because computers have made statistical compatisons to the existing intemationally accepted comprehensive data bank very easy. The statistics based on the data bank alone, l1owever, are insufficient. There are three further criteria: ( 1) After optimizing its coefficients, the prediction model should be capable of providing close fits of the individual test data covering a broad range of times, ages, humidities, thicknesses, etc.; (2) the model should have a rational, physically justified theoretical basis, and (3) should allow good and easy extrapolation of the short-time tests into long times, at high ages at loading, large thicknesses etc. The last criterion is paramount because good long-time predictions can be achieved only through updating based on short -time data for the given particular concrete. Various aspects of the B3 model and the GZ model (also appearing in this volume), recently considered by ACI Committee 209, as well as some aspects of the CEF-FIP model, are briefly analyzed in the light of these criteria, clarifYing their advantages and differences.