Modeling Early-age Drying and Moisture Transfer in Concrete for Practical Applications in Nordic Climates

Moisture in concrete is a critical issue for durability and indoor air quality in buildings. The building industry has faced challenges with excess moisture in concrete slabs for decades. Ensuring adequate drying before applying moisture-sensitive materials is essential, yet moisture control often fails. Nordic climates add complexity, with outdoor conditions like rain, snow, and low temperatures influencing concrete properties and drying processes. This study investigates the modeling of drying behavior of early-age concrete, focusing on the period from casting to the operational phase. A major research gap is the lack of general guidelines and benchmark data.

The research builds on existing models to simulate early-age drying, considering self-desiccation (hydration), temperature dependence, and wetting. The study examines changes in relative humidity (RH), as in Nordic, the adequate drying of concrete is assessed mainly based on RH. The study addresses three key research questions: the applicability of existing models, the computational evaluation of temperature-dependence on RH in concrete, and the requirements for test sets when calibrating models based on RH measurements. The findings emphasize the importance of calibration with measured temperature and RH data and the impact of environmental factors. Thus, critical test set requirements for calibration are described, along with approaches to determine concrete material parameters. Model application varies based on intended use and specific material parameters, which are discussed especially regarding temperature dependence.

The research results improve modeling methods for estimating drying times and assessing moisture-related risks, while also offering guidance for the design of drying experiments intended for calibration or validation purposes. The results apply to specific concrete material parameters under certain boundary conditions. Comprehensive data for various grades were not generated. Further testing of drying behavior in different concrete grades is needed and recommended as part of manufacturers' quality management.