Effect of composition on basic creep of concrete and cement paste

A two-level composite model for predicting the basic creep of aging concrete from its composition and the properties of its constituents is proposed. On the macroscale, concrete is treated as a composite of elastic aggregate embedded in the matrix of creeping hardened cement paste. The composite action is described by a combined series-parallel model in which a portion of the paste acts in parallel with the aggregate and the remaining portion in series with this parallel coupling. The portion of the paste coupled in parallel is determined as the amount of paste needed to fill the voids when the aggregate is at its maximum possible compactness, and the remaining portion of the paste then corresponds to the series coupling. On the microscale, the hardened cement paste is considered as a composite of elastic anhydrous cement grains embedded in a matrix of cement gel with voids filled by water and air. The aging is considered by an extension of the previously proposed solidification theory, in which the creeping constituent, the gel, is considered to have nonaging viscoelastic properties, and the aging caused by the chemical reaction of cement hydration is totally ascribed to the volume growth of the load-bearing (bonded) portion of hardened cement gel. The model is calibrated and verified by means of a comprehensive data set reported by Ward, Neville and Singh.