Influence of Deformation Amplitude and Fatigue Cycles on the Tensile Behaviour of Cold-Recycled Asphalt Mixtures

In this study, the modulus response and evolution, and damage behaviour of cement bituminous treated materials (CBTM) stabilized with 2% Portland cement and 4% bitumen emulsion during two test methods, including indirect tensile deformation sweep test (ITDST) and indirect tensile fatigue test (ITFT), were investigated. The ITDST was performed at 15 °C and 35 °C through six incremental strain steps ranging from 3–30 μm to evaluate stiffness reduction under increasing horizontal deformation. ITFT was performed at 15 °C to monitor stiffness reduction, and failure under cyclic loading. A stiffness damage index (E/E0) allowed direct comparison between the two tests, indicating consistent degradation patterns despite different loading modes. The ITDST results indicated a stiffness breakpoint threshold between 12–14 μm, potentially reflecting a shift from cement to bitumen-dominated mechanical response. A comparison of damage evolution in both test methods (increase in the strain level and number of cycles) at 15 °C showed consistent reduction trends. The equivalent damage states were identified by interpolating strain levels in ITDST that equalled the stiffness loss observed at the measured fatigue cycles in ITFT. The results suggest a highly correlated link between deformation-induced and fatigue-induced damage behaviour.