A hybrid laser thermography approach for quantifying concrete crack width

Accurately quantifying crack width is crucial for assessing concrete structure serviceability and durability, yet remains challenging for conventional non-destructive techniques. This study develops a rigorous Laser Spot Thermography (LST) methodology for the quantitative evaluation of surface crack width in concrete. A closed-loop framework integrating theoretical analysis, detailed finite element modelling, and experimental validation was established. A high-fidelity 3D transient thermal model with a Gaussian heat source was developed and experimentally validated to simulate heat-crack interaction, showing a mean absolute error below 2% for absolute temperature prediction at the laser spot centre and 4.3% for the crack temperature differential (ΔTc). Systematic parametric analysis using ΔTcidentified the laser-to-crack distance as the most critical parameter, with optimal sensitivity at 2.5 mm. A distinct saturation effect was observed for crack depths beyond 5 mm due to limited thermal diffusion in concrete. A robust quantitative model relating ΔTc to crack width (w) was formulated as a logarithmic function. This work establishes LST as a precise quantification technique, providing a practical pathway for its integration into structural health monitoring systems for non-destructive measurement of fine concrete cracks.