Detection of homogeneity indicators in the blending process of fresh and RAP bitumen by using multivariate analysis of IR mapping data

To support sustainability in road construction and reduce the use of non-renewable resources, this study investigates the homogeneity between virgin and aged binders in asphalt mixtures – a key factor influencing mechanical performance and durability. Unlike conventional approaches that rely solely on bulk testing or extraction methods, this work applies a combined methodology using infrared (IR) mapping and X-ray diffraction (XRD) to analyse asphalt components. A multivariate analysis of IR hyperspectral data enabled the differentiation between bitumen and aggregates based on C–H bond vibrations, and between virgin and RAP aggregates through variations in CaCO3 C=O bond signatures. Results reveal notable heterogeneity in the blending of fresh and RAP binders, highlighting the limitations of standard mixing protocols. This study introduces a novel microscale assessment method that avoids binder extraction and offers direct insight into blending quality. Further research is needed to quantify the effects of temperature, mixing time and binder compatibility.