Investigation on local deformation and cracking characterisations of grouting asphalt concrete using digital image correlation

Grouting asphalt concrete (GAC) is a multiphase composite whose local deformation and cracking behaviour remains unclear. This study prepared GAC-13 by grouting cement-based grouting material (GM) into porous asphalt concrete (PAC-13), with AC-13 as the control. Two-dimensional digital image correlation (DIC) and indirect tensile testing were used to capture full-field displacement and strain evolution in the specimen and crack zone, aiming to clarify the cracking mechanism of GAC under indirect tensile loading. Compared with those of AC-13, the peak load and failure displacement of GAC-13 decreased by 20.7% and 66.8%, respectively, while the horizontal and vertical strains at the peak load decreased by 68.2% and 65.9%, respectively. GAC-13, cracks originated from the central region of the specimen and propagated upward and downward along the mortar–GM interface, whereas in AC-13, cracks initiated from the bottom-middle region and extended upward through the mortar. Both concretes exhibited a two-stage horizontal strain evolution, with the transition corresponding to the peak load. In GAC-13, asphalt mortar showed greater horizontal strain than the interface and GM, indicating that restricted mortar deformability and weak mortar–GM bonding govern its poor cracking resistance. These DIC-based findings provide a basis for optimizing the cracking resistance of GAC.