Impact of wet–dry cycles on concrete: chemical-phase and pore-structure changes and moisture distribution mechanisms observed via hyperspectral imaging

Wet–dry (W–D) cycles significantly impact concrete durability by influencing moisture distribution and microstructural evolution. This study employs hyperspectral imaging (HSI) as a rapid, non-destructive technique to visualise surface moisture profiles in concrete subjected to controlled W–D cycles designed to approximate field exposure conditions via short-term partial water penetration and ambient drying. Concrete specimens with varying water-to-cement ratios and curing regimes were examined. HSI effectively revealed moisture gradients, including capillary rise equilibration after initial cycles and drying retardation caused by aggregates. Gravimetric measurements validated the HSI results. Complementary X-ray diffraction and mercury intrusion porosimetry analyses indicated depth-dependent microstructural changes, such as enhanced hydration and porosity reduction in inner layers, contrasted by surface leaching. The findings suggest a moisture redistribution between pore size scales, which may influence pore connectivity during cyclic moisture exposure. This study offers new insights into moisture transport dynamics and microstructural responses under W–D cycling, approximating typical environmental exposure, and proposes preliminary guidance for establishing standardised W–D testing protocols to support improved durability assessments of concrete infrastructure. • Hyperspectral imaging visualises moisture profiles in concrete during wet–dry cycles. • Wet–dry cycles with partial water penetration simulate field exposure. • Aggregate content influences drying rates and moisture transport in concrete. • Moisture redistribution observed and linked to depth-dependent pore structure changes. • Integrated HSI, XRD, and MIP analyses clarify surface and bulk durability mechanisms.