Calculation of Shrinkage Stress in Early-Age Concrete Pavements. I: Calculation of Shrinkage Strain

Abstract

This paper focuses on modeling of the distribution of shrinkage strain in early-age concrete pavements. In the modeling, an integrative model for autogenous and drying shrinkage predictions of concrete at an early age is introduced first. Second, a model taking both cement hydration and moisture diffusion into account synchronously is used to calculate the distribution of the interior humidity in concrete. The previous two models are experimentally verified independently by a series of shrinkage and interior humidity tests on three types of concretes with different compressive strengths. Using the models, the distribution of shrinkage strain in early-age concrete pavement (with respect to drying of the pavement surface) is calculated. The model results show the development of interior humidity inside of the pavement because the concrete cast obeys a two-stage mode, i.e., a vapor-saturated stage with 100% relative humidity (Stage 1) and a stage with the relative humidity gradually decreasing (Stage 2). The duration of Stage 1 increases with respect to the location, i.e., from the slab top to bottom. Within Stage 1, a uniform shrinkage strain is expected throughout the slab. By contrast, the shrinkage gradient along the slab depth is obvious in Stage 2. The maximum and minimum shrinkages occur at the slab top and bottom, respectively. The distribution of the shrinkage strain along the pavement depth is nonlinear and the nonlinearity is strong where it is close to the drying face. Concrete strength can significantly influence the magnitude of the shrinkage strain within the slab. For a given age and location, an increased concrete strength corresponds with an increased shrinkage strain and shrinkage gradient.