New insights into the use of particle-size sensors for asphalt mixture gyratory and roller compaction

Compaction is a critical phase in pavement construction, directly influencing early performance and long‑term durability. While field procedures aim to achieve target density levels, laboratory methods still struggle to fully replicate field compaction mechanisms. Although particle‑size sensors have recently been standardized for gyratory compaction through ASTM D8541, the reliability of the associated workability parameters remains uncertain due to machine‑specific mold kinematics. The first objective of this study is therefore to assess the consistency and interpretability of ASTM D8541 workability parameters. A second objective is to explore the feasibility of applying particle‑size sensors in roller compaction, where no established framework currently exists. To address these aims, two gyratory compactors, one roller compactor, three asphalt mixtures, an unbound granular material, and two sensor geometries were investigated to characterize particle motion under laboratory compaction. Results show that ASTM D8541 parameters are affected by rigid mold movement, leading to inconsistent outcomes across gyratory machines and indicating the need for compactor‑specific calibration. A new parameter, M‑S RRC, is introduced to quantify the relative motion between mold and sensor, providing an improved and locally measured indicator of compaction effort; in gyratory compaction, it exhibits a favourable indicative trend with the Compaction Energy Index (CEI). Finally, roller compaction tests demonstrate that spherical sensors are more sensitive than cubic ones to variations in mixture workability, supporting their preferential use for detecting subtle differences in compaction behavior.