Modeling of the early-age concrete behavior is a very complex task, as the phenomena of chemical-thermal-hydration and their effects on the mechanical behavior must be considered. However, since the behavior of early-age concrete directly determines the performance of the concrete in the later dates, the development of a mathematic model for the early age concrete becomes important. In this paper, the mathematic model treats the thermal and stress-strain calculation separately. The thermal analysis is carried out first, which is followed by the computation of stress evolution, including the initialization and propagation of microcrackings. The stiffness and strength evolution, the development of thermal and creep strains, and microcracking behavior are covered in a transient nonlinear finite element model. The thermal analysis procedures include the consideration of heat hydration in concrete, heat exchange between concrete surface and ambient air. The maturation of concrete properties, including Young's modulus, tensile strength, and creep, is described as a set of age-related functions, which can be calibrated with test data. The emphasis of this paper is placed on the following aspects: (1) a coupled elastoplastic creep model for the nonlinear failure problem related to the cementitious interface materials; and (2) a practical but powerful interface element is introduced to allow for FEM simulation of the intricate interface behavior. The related numerical examples are given to confirm the validity and accuracy of the proposed model and the FEM algorithm.
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