To elucidate the mechanisms of microstructural changes in ultra-high-performance concrete (UHPC) under microwave exposure, this study characterizes the microstructure at multiple scales using a combination of microscopic experiments and molecular dynamics simulations. The hydration products, pore structure, morphology, and interface transition zone (ITZ) of UHPC specimens were analyzed using mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Molecular dynamics simulations were employed to investigate the uniaxial tensile behavior, free volume, and radial distribution of calcium silicate hydrate (C-S-H) gel, the primary hydration product. The results indicate that microwave curing significantly reduces the pore volume of specimens, with a daily average reduction of 0.15% in the early stages. This accelerated reduction in porosity effectively diminishes the number of high-risk pores. The hydration products formed under microwave curing exhibit higher density and enhanced internal pore optimization. Simulation findings suggest that the non-thermal effects of microwaves play a more significant role in the structural evolution. The molecular orientation of C-S-H changes after oscillation, leading to more ordered molecular arrangements. Mechanical oscillation also expels free volume from the crystal cells, promoting a more compact overall structure and increasing the tensile strength by up to 1 GPa.

The insufficient skeletal stability of porous asphalt mixtures (PAM) stems critically from the poorly understood dynamic evolution of aggregate gradation during compaction. The differential impacts of distinct compaction methods remain inadequately characterized. This study systematically investigates the effects of Marshall Compaction (MC) and Superpave Gyratory Compaction (SGC) on gradation variation in PAM-13 and PAM-16, incorporating key parameters such as asphalt addition states and compaction energy levels. Specimens were prepared under both with asphalt and without asphalt conditions, subjected to multi-level compaction energy, and subsequently analyzed through sieve analysis. Key findings reveal that MC induces more pronounced coarse aggregate breakage (up to −15.06 %) and fine aggregate generation (up to 101.64 %); SGC better preserves fine aggregate integrity; asphalt provides protective effects predominantly for fine aggregates; and increasing compaction energy continuously exacerbates fine aggregate fragmentation. The findings elucidate the gradation variation patterns induced by different compaction methods, thereby providing a critical theoretical foundation for optimizing the design and construction control of PAM.