Jiahan Liu

Scratch tests have emerged as a promising technique for evaluating the fracture behavior of cementitious materials. However, conventional fracture toughness (K_c) 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 K_c averages 0.21 MPa⋅m^1/2, 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 K_c 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.