Use of fine aggregate matrix to analyze the rheological behavior of cold recycled materials

Nowadays, one of the main challenges to a wider application of cold recycling techniques is the lack of reliable information on the mechanical behavior of cold recycled materials (CRM). In this context, measurement and modelling of the complex modulus of CRM mixtures may give an important contribution to the design and analysis of pavements including cold recycled layers. In this study, we analyzed the rheological behavior of CRM mixtures produced using bitumen emulsion and cement through the study of their fine aggregate matrix (FAM). Starting from a fixed CRM mixture composition, we compared different FAM mortars, focusing on the effect of water and air content. Then, we selected a composition as representative of the FAM in the mixture and investigated the evolution of both materials during a fixed curing period. Next, we measured the complex modulus of the CRM mixture and FAM at two curing stages and applied a rheological model to simulate and compare their behavior. Results showed that the properties of CRM mixtures are comparable to those of FAM mortars produced using all the binding agents (bitumen emulsion and cement) and a fraction of the voids contained in the mixture. Despite the huge difference in volumetric compositions, the FAM mortar controlled the curing and the thermo-rheological behavior of the CRM mixture, while the coarse reclaimed asphalt aggregate fraction and the voids mainly affected the asymptotic properties (equilibrium and glassy moduli) and the non-viscous dissipation component.