Calibration of New Concrete Shrinkage and Creep Model for ACI Committee 209

Abstract

A new semi-empirical concrete shrinkage and creep model is proposed and calibrated in which creep ages according to solidification theory. The impetus for this CRC-funded research is to propose new creep and shrinkage design guidelines for ACI Committee 209; previous guidelines were published in 1982 and are no longer up to date with modern understanding of time-dependent behavior. The new model proposes a coupling between autogenous and drying shrinkage using a volume-average pore relative humidity and treats drying creep as an additional stress-dependent shrinkage, linking together all these phenomena. The proposed expressions are designed to facilitate traditional integral-type analysis, but also uniquely support rate-type calculations that can be leveraged by analysis software. Model calibration uses the Northwestern University (NU) database of creep and shrinkage tests to determine new model parameters. Profile likelihood curves for each individual mix in the database are computed to quantify the sensitivity of the fitting parameters to the available data and to mix design inputs.