Criteria for Rational Prediction of Creep and Shrinkage of Concrete

Abstract

The paper discusses the problem of formulation and evaluation of 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 comparisons to the complete existing data bank easy. However, statistics based on the data bank are insufficient. There are three further criteria : (1) After optimizing its coefficients, the 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, high ages at loading, large thicknesses etc. The last criterion is very important 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 and GZ models 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 the way to move ahead.