Design of asphalt fine aggregate matrix based on aggregate model library and strain behavior analysis across the entire loading process

This research aims to clarify uncertainties in asphalt and filler proportions for Fine Aggregate Matrix (FAM) mix design and to determine the Nominal Maximum Aggregate Size (NMAS). The three-dimensional blue light scanning apparatus and high-precision balances were utilized to generate an aggregate model library encompassing four size ranges. The aggregate model library facilitated investigating the aggregates' distribution of various physical parameters. The model proposed using the short and middle axes of the minimum bounding box as particle size indicators. The aggregate particle size distribution conformed to a Gaussian pattern, and a power function relationship was identified between specific surface area and particle size. Nano-CT and image segmentation techniques were used to determine the thicknesses of the pure asphalt layer and asphalt mastic on aggregate surfaces. These data and aggregate distribution models helped calculate FAM mix proportions for NMAS of 4.75 mm, 2.36 mm, and 1.18 mm in AC-13, OGFC-13, and SMA-13, respectively. FAM beamlet specimens were created using rotary compaction and precision cutting, then tested with the Meso Scale Under Microscope Universal Load Frame (μTS) to observe strain behavior under three-point bending and uniaxial tension. The strain coefficient of variation was proposed to assess material homogeneity. The study found cohesive cracking in FAM with 1.18 mm NMAS and adhesive cracking at sizes above 2.36 mm. FAM with 1.18 mm NMAS is recommended as a dispersive medium, optimizing its function as a matrix material. • A method for designing asphalt fine aggregate matrix (FAM) mix proportions replicating the actual distribution state within asphalt mixtures is proposed. • The distribution of various physical parameters of aggregates was investigated through an aggregate model library. • At an NMAS of 1.18 mm, FAM primarily undergoes cohesive cracking, while at NMAS values of 2.36 mm and above, adhesive cracking becomes predominant. • Based on continuum theory, 1.18 mm is recommended as the nominal maximum aggregate size (NMAS) for the fine aggregate matrix (FAM).