Meaning
Mass transfer of water molecules through the complex pore network of a concrete element occurs under the influence of a concentration gradient. The moisture transport diffusion describes this physical process, which governs the rate of drying and the penetration of environmental agents. This movement is slower in high-performance concrete because of the disconnected capillary network.
Pore Structure
Liquid and vapor travel through pathways created during the mixing and hydration phases. The moisture transport diffusion slows down as hydration products block the larger pores, making the concrete more impermeable. Aggregates act as barriers, forcing the water molecules to take a tortuous path through the cement paste.
Durability Assessment
Incursion of chlorides and sulfates from deicing salts or soils threatens the integrity of steel reinforcement. Analyzing the moisture transport diffusion allows engineers to estimate the time required for these harmful ions to reach the steel. Long-term durability models rely on accurate diffusion coefficients to design infrastructure with a hundred-year service life.
If the diffusion rate is too high, reinforcement corrosion will begin decades earlier than expected. This analysis is especially important for marine structures and highway bridge decks.
Rate Calculation
Laboratory testing uses non-destructive electrical resistivity or gravimetric drying to evaluate transport properties. Calculating the moisture transport diffusion involves fitting measured weight loss curves to analytical solutions of transport equations. When environmental conditions vary, numerical methods are needed to solve the non-linear equations.
