Three-Dimensional Geometry Correction of Scratch Grooves via X-Ray Computed Tomography for Fracture Characterization in Cementitious Materials.

Scratch tests have emerged as a promising technique for evaluating the fracture behavior of cementitious materials. However, conventional fracture toughness (Kc) calculations rely on empirical groove geometry models, which may not accurately represent the actual scratch morphology. In this study, X-ray computed tomography (X-CT) and probe profilometry were employed to characterize the three-dimensional morphology of scratch grooves in white cement paste. Scratch tests were conducted under a linearly increasing load up to 30 N. Groove boundaries were identified through grayscale statistical analysis of X-CT images, and the obtained morphological parameters were incorporated into a linear elastic fracture mechanics framework to evaluate fracture toughness. The results showed that the indentation depth increased with the applied load, whereas the lateral force exhibited a nonlinear power-law relationship with the normalized penetration depth. X-CT measurements yield an average elastic recovery rate of 26.05% relative to instantaneous sensor depths, and 15-20% larger groove widths than empirical predictions due to edge spalling and debris accumulation, with discrepancies that amplify with increasing load. The X-CT-corrected Kc averages 0.21 MPa⋅m1/2, about 30% lower than values derived from empirical geometric fitting. Good agreement between X-CT and probe profilometer measurements validated the reliability of the proposed approach. The main contribution is the correction of the Kc calculation using actual geometry. The results demonstrate that X-CT is an effective and non-destructive method for accurately characterizing fracture toughness evaluation of cementitious materials.