Modeling of Thermomechanical Damage of Early-Age Concrete

The phenomena that occur during the early age of concrete curing are complex, as the coupling between chemical-thermal-hydration and mechanical effects must be considered. Among the main attributes that govern the nonlinear behavior of early-age concrete are stiffness evolution, the development of thermal strains, creep, and cracking. To properly accommodate these effects in a finite-element analysis of a large structure such as a concrete dam, efficient computational strategies are needed. In this paper, a finite-element numerical algorithm is developed for analyzing thermomechanical damage in young concrete. Thermal analysis procedures include consideration of heat generation (hydration) and dissipation within mass concrete, including the effects of ambient temperature. The stress-deformation-damage analysis procedures include temperature-induced, creep, and autogenous deformations. Development of concrete properties, including Young's modulus, tensile strength, and limiting tensile strain is described by experimentally obtained functions. Damage in concrete is considered to be the result of crushing, cracking, and a mixed failure mode. Failure criteria for each failure mode, along with constitutive relationships for prefailure and postfailure states are developed for both loading and unloading conditions. The developed finite-element program is used to simulate the construction of the first four layers of a concrete dam. The cracking damage predicted by the finite-element analysis is shown to qualitatively match with field observations.