Integrated Multimethod Characterization of Full-Scale Pore Properties in Asphalt Mortar

Pore structure is a critical feature of asphalt mixtures, with pore size distribution (PSD) strongly affecting material performance. Conventional PSD characterization methods are limited by restricted measurement ranges, necessitating integrated approaches for full-scale analysis. This study employed X-ray computed tomography (CT), mercury intrusion porosimetry (MIP), and low-temperature nitrogen adsorption (LTNA) to characterize asphalt mortar specimens prepared with 90# base asphalt or SBS-modified binder—compacted using 50 / 75 blows with a scaled device simulating field conditions—given varying freeze-thaw (F-T) treatments. A novel PSD integration method was developed by combining multitechnique data: LTNA-MIP curves were merged at 30 nm using intersection analysis, and MIP-CT data were aligned through equal-volume pore size coordinate transformation. Using this approach, full-scale pore characteristics and their dependence on asphalt type, compaction, and F-T cycling were analyzed. Asphalt mortars exhibited bimodal PSDs, allowing classification into micropores ( ≤30 µ m ), structural pores (30 μm–200 μm), and bulk cavities ( ≥200 µ m ) comprising approximately 3.2%, 79.4%, and 17.4% of total pore volume, respectively. Lower compaction increased all pore categories. High-viscosity asphalt hindered densification, enlarging structural pores and bulk cavities. F-T cycling primarily expanded structural pores; bulk cavities changed minimally due to high connectivity and low saturation, whereas water-resistant micropores remained stable. This study provides a robust framework for multiscale pore network characterization, enhancing the understanding of microstructure-property relationships in asphalt composites.