Vibratory compaction mechanisms in cold recycled mixtures with foamed asphalt: insights from aggregate migration to skeleton formation

Due to the lack of essential understanding of the compaction mechanisms of cold recycled mixtures with foamed asphalt, engineering problems such as uncontrolled compaction quality and mix design failures are prone to occur. The laboratory vibratory compactor was utilized to simulate field vibratory compaction conditions, integrated with Smart Rock technology for real-time monitoring of the internal aggregate movement and stress state within the mixture. The compaction process was analyzed multi-dimensionally through aggregate motion evolution, interlocked structure development, and compaction energy dissipation. Furthermore, the meso-scale voids and skeleton structure characteristics of mixtures are quantitatively characterized under different compaction conditions using X-ray CT three-dimensional reconstruction. As vibration frequency increased from 20 Hz to 28 Hz, the mixture’s Compaction Energy Index decreased by 71%, while the Traffic Densification Index rose by 108%, indicating improved workability and deformation resistance. The aggregate interlocking intensity increased 17 times, and void uniformity improved by 26%, reflecting a shift from dendritic to mesh-like skeleton structure. The most stable skeleton occurred with new fine aggregates, and best load-transfer with both new coarse and fine aggregates. These results provide valuable insights for elucidating the compaction mechanism and optimizing the compaction process of cold recycled mixtures with foamed asphalt.