Interfacial weakening mechanism and energy evolution of filling-type large-size cement-stabilized macadam for reflection crack mitigation

Reflection cracking is a critical issue affecting the durability of semi-rigid base asphalt pavements, primarily caused by the high shrinkage and limited crack resistance of conventional cement-stabilized macadam (CSM). To address this, a filling-type large-size cement-stabilized macadam (F-LSBC) base was developed, yet its interfacial weakening mechanism and corresponding impact on energy evolution remain unclear. This study combines micro- and macro-scale investigations to elucidate the crack resistance mechanism of F-LSBC compared with CSM. Nanoindentation testing was employed to quantify the micromechanical properties of the interfacial transition zone (ITZ), while splitting load–unload tests were conducted to analyze the releasable elastic strain energy and surface-layer energy evolution of the two materials. Results show that the ITZ in F-LSBC exhibits significantly lower elastic modulus (60%–75%) and hardness (55%) than in CSM, along with higher porosity and a 1.5-fold larger volume fraction, confirming a pronounced interfacial weakening structure. Correspondingly, the dissipated energy proportion in F-LSBC reaches about 75%, notably higher than the 60% observed in CSM, leading to a 50% reduction in its energy storage limit and a surface-layer energy less than 40% that of CSM. These findings indicate that the intentional interfacial weakening in F-LSBC effectively reduces the transmission of shrinkage strain energy to the surface layer, thereby suppressing the formation of reflection cracks. This study provides the first quantitative nanoindentation-based confirmation of ITZ weakening in F-LSBC and provides quantitative evidence supporting the linkage between ITZ weakening and the reduction of surface-layer energy peak, offering theoretical guidance for the design of anti-cracking semi-rigid base materials.