Fracture behavior of grouted composite pavement mixtures: Effects of grout morphology and distribution using image processing techniques

Grouted composite pavement (GCP) offers high rutting resistance but suffers from poor cracking resistance, largely governed by the meso‑morphology and distribution of hardened grout. This study employed image processing to quantify grout morphology (characteristic diameter ( r c ), aspect ratios AR₁ and AR₂ ) and uniformity index ( UI ) in GCP mixtures. Segmentation errors of 6.6–14.1% validated the method for meso‑scale analysis. Semicircular bending tests and multi-factor ANOVA revealed that void content dominates equivalent diameter, while asphalt‑aggregate ratio critically controls distribution uniformity. Increasing void content reduces aspect ratio; higher water/cement or asphalt‑aggregate ratios increase aspect ratio and interfacial stress concentration, thereby reducing fracture energy and toughness. Uniformity deteriorates when asphalt‑aggregate ratio exceeds 3.5%.Considering both fracture energy and fracture toughness, the optimal mix is 0.30 w/c, 3.5% asphalt‑aggregate, and 26% void content. AR₁ and AR₂ are proposed as primary morphological controls, with UI as a supplementary uniformity check, together offering a meso‑scale basis for designing cracking‑resistant GCP.