Full-Field Infrared Visualization of Surface Apparent Freeze–Thaw Front Evolution in Water-Filled Fractured Granite

Coupled water–heat transport and water–ice phase transitions are key processes in the freeze–thaw deterioration of fractured rock, but their continuous surface-thermal manifestations remain poorly characterized. Infrared thermography was used to monitor the surface temperature fields of 100 mm saturated granite cubes containing one artificial fracture during freezing at −20 °C and subsequent natural thawing, with saturated intact specimens used for comparison. The surface 0 °C isotherm was tracked as an apparent thermal front; it was not treated as a direct measurement of the internal three-dimensional ice–water phase boundary. The fractured specimens exhibited strongly non-uniform apparent-front propagation, unlike the approximately linear behavior of intact granite. During freezing, the apparent front expanded in a fan-shaped pattern and accumulated near the fracture, whereas during thawing it propagated in a horseshoe-shaped pattern. Apparent-front velocities changed sharply near the fracture, consistent with fracture-induced redistribution of heat flow and the sensible- and latent-heat storage of fracture water. Because water content and liquid-water displacement were not measured independently, the results are interpreted as specimen-scale surface-thermal signatures rather than direct visualization of internal water migration. The findings establish a controlled laboratory benchmark for this specimen geometry and boundary condition. Extrapolation to natural fracture networks, frost-heave damage, or engineering-scale prediction requires additional tests across fracture geometries, rock types, stress states, moisture conditions, and thermal boundaries, together with internal hydraulic and mechanical measurements.