Modeling early-age stress development of restrained concrete

The B3 Model is a compliance model that was designed and calibrated to estimate the instantaneous and time-dependent strain behavior of concrete with an age of 1 day or more. However, it was not designed to model the rapidly changing viscoelastic and elastic properties of early-age concrete between setting and 1 day. The early-age stress development, free strain, and mechanical property development of 28 concrete mixtures were measured to model the early-age stress development of concrete. The mixtures utilized three water–cement ratios, five coarse aggregate types, two curing temperature scenarios, and densities from 1,390 to 2,320 kg/m3 (87–145 lb/yd3). Modifications were made to the B3 Model to account for the early-age viscoelastic and elastic behavior of concrete. The effect of the modifications made to the B3 Model are limited to improving the early-age response and have minimal effect on the later-age compliance estimated with the original B3 Model. The modifications to the B3 Model significantly improved the unbiased estimate of standard deviation from 0.74 MPa (110 psi) to 0.39 MPa (57 psi) and coefficient of variation from 0.23 to 0.79 compared to the unmodified B3 Model.