Impacts of Milled Aggregate Gradations and Foamed Asphalt Contents of Cold In-Place Recycling Layer on the Performance of Asphalt Overlays

This paper presents gradations of both Hot In-place Recycling (HIR) and Cold In-place Recycling (CIR) and analysis of cores collected from CIR/Hot Mix Asphalt (HMA) overlay sections in Iowa. Milling samples were obtained from an HIR recycling project on IA 22 in Wellman, Iowa. It was concluded that the average gradation of HIR millings was coarser than that of CIR millings by retaining the original aggregate gradations. Cores were then extracted from CIR pavement with foamed asphalt overlaid by HMA at the right wheel path and between wheel paths at eight locations on US 34 in Mills and Wapello Counties. The cores were cut into discs to isolate the pavement layers, and the discs were fabricated into semicircular bending test specimens. Based on the Semicircular Bending (SCB) tests performed on both CIR and HMA specimens, CIR specimens with higher asphalt binder contents exhibited higher flexibility index values. Since CIR pavement layers were found to be more flexible than the HMA overlay layers, it can be speculated that CIR layers may serve as a stress-relieving layer and mitigate reflective cracking.