A computational model is developed for predicting nonuniform internal relative humidity distribution in concrete. Internal relative humidity distribution is known to have a direct effect on the nonuniform drying shrinkage strains. These nonuniform drying shrinkage strains result in the buildup of internal stresses, which may lead to cracking of concrete. This may be particularly true at early ages of concrete since the concrete is relatively weak while the difference in internal relative humidity is probably high. The results obtained from this model can be used by structural and construction engineers to predict critical drying shrinkage stresses induced due to differential internal humidity distribution. The model uses finite elment-finite difference numerical methods. The finite element is used to space discretization while the finite difference is used to obtain transient solutions of the model. The numerical formulations are then programmed in Matlab. The numerical results were compared with experimental results found in the literature and demonstrated very good agreement. 1. Introduction Cracking is detrimental to the serviceability, durability, and the aesthetic quality of concrete structures. A major driving force behind cracking is the nonuniform early-age drying shrinkage [1]. Drying shrinkage can be defined as the volume reduction that concrete suffers as a consequence of the moisture migration when exposed to a lower relative humidity environment than the initial one in its own pore system. During production of concrete, more water is added to the concrete mix than necessary for hydration for the sake of workability. This leads to having two types of moisture in concrete. The first type is structural water, chemically bound within the cement paste. As the concrete hydrates, some shrinkage takes place in absence of additional water as hydration takes up some free water. This shrinkage is referred to as autogenous shrinkage and is typically about 50 to 100 microstrains [2]. The second type is the excess water that does not take part in the hydration product and as a consequence it will not be chemically bound to the solid phase. This water is contained in the pore structures. Drying shrinkage in concrete is due to drying of the water contained in the pore structures and the associated decrease in moisture content. Therefore, it is necessary to estimate the moisture loss as accurately as possible in order to study drying shrinkage in concrete members. Accurate prediction of drying shrinkage in concrete requires knowledge of the concrete
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