Field Evaluation of the Impact of Environmental Conditions on Concrete Moisture-related Shrinkage and Coefficient of Thermal Expansion

This study evaluates the impact of the environmental conditions on the moisture-related shrinkage and the coefficient of thermal expansion (CTE) of concrete. The evaluations are based on the strain measured in a series of unrestrained shrinkage prisms during fifteen months. The prisms included four concrete mixtures containing either portland cement or calcium sulfoaluminate cement. The prisms were fabricated in the field and left outdoors so that they were subjected to natural rainfall, sun radiation, and daily and seasonal changes in air temperature and relative humidity (RH). A strain model was used to divide the deformation measured in the prisms into its thermal and moisture-related components. By doing so, the evolution of concrete moisture-related shrinkage and CTE during the fifteen-month period was back-calculated. A strong correlation (R2 = 0.998) existed between the maximum moisture-related shrinkage that was back-calculated in the outdoor prisms and the ultimate moisture-related shrinkage measured in the laboratory under constant temperature and 50 percent air RH. Because of drying, concrete CTE reached values that were up to 50 percent higher than the CTE determined in the laboratory under saturated conditions. Concrete moisture-related shrinkage and CTE systematically decreased after the rainfall events, except when the concrete was already saturated. Rainfalls, rather than air RH, controlled the re-wetting of the concrete in the field.