Effects of Supplementary Cementitious Materials on Early-Age Tensile Creep and Shrinkage of Concrete

Determination of early-age tensile creep properties is critical for the performance of mass concrete structures at an early age. Due to the stress relaxation that tensile creep induces in concrete structures, accurate quantification of creep deformation is needed to determine the stress profile of the structure. Conventional methods of measuring tensile creep include the direct tension test where the concrete is subject to constant tensile stress. This method requires large quantities of concrete with embedded strain gauges which can only be used once. In this paper, the tensile creep parameters of concrete are found by using the restrained concrete ring test. The effect of Class F fly ash and ground granulated blast furnace slag on the concrete tensile creep properties was investigated. By measuring the free drying shrinkage properties of concrete using rectangular prisms, a shrinkage model was created. The main driving force behind concrete shrinkage is the loss of moisture in the ambient environment. The shrinkage model required the relative humidity inside of concrete to be known at any given time. To determine the humidity profile of concrete, experiments were conducted by inserting wireless humidity sensors inside of concrete. By using Fick’s law, a humidity model was calibrated using the experimental data. ABAQUS was used to simulate the effects of drying shrinkage and then a stress model was created. Using the modified double power law and B4 model for tensile creep of concrete, the stress relaxation parameters were varied until the modeled strains of the inner steel ring matched the experimental data. The results were compared to the creep compliance measured by dog-bone specimens subject to a constant tensile load. Results show that the modeled creep parameters obtained from the ring test match reasonably well with the creep compliance of the dog-bones. Furthermore, the modeled cracking predictions for the concrete rings match well with the experimental observations