Long-term fatigue performance and damage evolution of emulsified asphalt cold recycled mixtures

As load cycles increase, the fatigue evolution of cold recycled mixtures damage becomes complex due to internal damage accumulation and strength gain in nondestructive state. To investigate the long-term fatigue performance, indirect tensile fatigue tests were conducted. Using the inflection point of vertical displacement curve and dissipated energy, the early-stage and long-term fatigue lives under different stress ratio conditions were compared to analyze combined effects of performance growth and damage accumulation. Results indicate that the standard method primarily reflects early-stage strength and fatigue performance under high stress ratios, thereby significantly underestimating actual fatigue resistance of cold recycled mixtures. Under identical stress ratio conditions, the improved method representing long-term state exhibit significantly longer fatigue life, confirming the progressive enhancement of fatigue resistance during long-term service. For single stress ratio, the evolution of fatigue damage follows distinct three-stage pattern. Across different stress ratios, the improved specimens show slower damage accumulation, resulting in superior fatigue performance. When two-stage loading is considered, the curves of damage and cycle ratio show that the cumulative cycles is greater than that of single-stage loading. However, if the early-stage performance is inadequate, repeated loading can accelerate damage accumulation, thereby significantly reducing final fatigue life. It highlights the importance of designing cold recycled mixtures with sufficient early strength and enabling a timely transition to improved long-term performance. ● Propose the improved curing method for simulating long-term condition of cold recycled mixtures. ● Consider the influence of RAP and aged asphalt on long-term performance in mixture design. ● Establish two-stage loading fatigue test for analyzing stress transitions and fatigue evaluation. ● Reveal the fatigue damage and growth of fatigue life under early stage and long-term conditions. ● Based on long-term performance development, the existing design tends to be conservative.