Viscoelastic age-dependent analysis of restrained shrinkage stress development in early-age concrete

In this study, effort has been placed to better understand the behavior of early-age concrete with respect to the restrained shrinkage stress development during the first days after casting. Procedures and material coefficients associated with the analysis of drying, shrinkage, and restrained stress development were refined for early-age concrete. The analysis of drying resulted in an estimation of a continuous change in the humidity profile of the concrete as a function of time and position. By measuring unrestrained free shrinkage, the shrinkage coefficient was determined for the concrete tested in this study that links the humidity changes to shrinkage deformation. The predicted free shrinkage becomes a driving force of stress development in restrained concrete.; For the calculation of stress development, a new aging viscoelastic material model was proposed for early-age concrete based on the result of tensile creep tests. The degree of hydration was selected as an aging parameter of the model. For the implementation of the model for stress analysis, the incremental constitutive equations for aging viscoelastic materials were derived and encoded in a FORTRAN program named VISCON. Using this program, the response of early-age concrete subjected to restrained shrinkage was estimated in terms of stress. The results of the viscoelastic analysis showed good agreement with the test data obtained in this study.