Unveiling the anomaly water uptake in concrete: Coupled pore evolution and swelling-induced crack closure

Anomalous water transport in concrete presents significant challenges to conventional durability models, owing to limited understanding of mechanisms involving the dynamic evolution of transport pathways. To elucidate the microscopic origin of this phenomenon, we integrated X-ray computed radiography, digital image correlation, and single-sided nuclear magnetic resonance spectroscopy to monitor moisture ingress, strain field evolution, and pore-scale water redistribution in concrete simultaneously. A two-stage water uptake process, comprising an initial capillary filling, followed by capillary narrowing and crack closure driven by calcium–silicate–hydrate (C–S–H) swelling was observed. This study offers the first experimental evidence of temporal alignment of water redistribution, volume expansion, and dynamic crack closure, which governs the macroscopic anomaly. By incorporating this two-stage evolution of transport pathways into a one-dimensional uptake model, we quantitatively reproduced the anomalous behavior, offering a mechanistic foundation for designing more durable concrete structures for infrastructure and climate-resilient applications.