Validation of Modified B3 Model to Predict Early-Age Stress Development of Concrete

The B3 Model is a compliance model that was designed and calibrated to estimate instantaneous and time-dependent strain behavior of concrete with a loading age of 1 day or more. Modifications were developed to correct the B3 model for rapidly changing viscoelastic and elastic properties of early-age concrete between setting and 1 day. Early-age stress and mechanical property development of 72 concrete mixtures with different materials, mixture proportions, and temperature histories were measured and compared to early-age stresses calculated using the Modified B3 Model. The unbiased estimate of standard deviation decreased from 0.78 to 0.42 MPa (113 to 60 psi), and the coefficient of determination increased from 0.59 to 0.80 when predictions with the Modified B3 Model are compared to the unmodified B3 Model. This magnitude of improvement is similar to that obtained when the Modified B3 Model was originally developed, which thus validates the Modified B3 Model.