Composite fatigue failure of cold recycled material mixtures: new insights into the role of bitumen and cement

In pavement engineering, cold recycled material (CRM) mixtures allow implementing circular economy concepts by maximizing the reuse of reclaimed asphalt without heating. Along with bitumen emulsion and foamed bitumen, Portland cement is often added to CRM mixtures to improve the field performance. However, the role of cement on the fatigue failure is not sufficiently investigated. The objective of this research is to provide new insights into the fatigue failure of CRM mixtures produced with bitumen emulsion and cement. To this aim, two CRM mixtures prepared with different dosages of cement (1 and 2%) were subjected to uniaxial cyclic tension fatigue tests. Empirical and energy-based failure criteria, originally developed for asphalt concrete mixtures, were used to define the fatigue failure. The results showed that the fatigue failure mechanism of CRM mixtures was of a composite type, affected by both cementitious and bituminous bonds. A new criterion was proposed to identify the failure of the cementitious bonds.