Evaluating the effect of laboratory aging on fatigue behavior of asphalt mixtures containing hydrated lime

Hydrated lime (HL) is typically used as an additive to enhance the anti-stripping resistance of asphalt mixtures. As a result, this particular feature of hydrated lime has received the greatest share of academic attention, and its other long-term effects such as the resulting resistance against fatigue cracks have been relatively neglected. In the present study, effects of different quantities of HL (by weight of aggregate) on the fatigue properties of asphalt mixtures was investigated by four-point bending fatigue testing of unaged and aged specimens. Laboratory long-term aging procedure was carried out in accordance with AASHTO PP2 (120 h of treatment at 85 °C). Fatigue tests were conducted in strain-controlled mode with a sinusoidal load applied with frequency of 10 Hz (without rest) at 20 °C. Fatigue life was analyzed with the stiffness reduction and dissipated energy methods. Test results showed that fatigue life of asphalt mixtures is sensitive to their HL content. Addition of 1%, 1.5% and 2% of hydrated lime to mix design was found to improve the fatigue life of unaged asphalt specimens. For the aged specimens, adding of 1% and 1.5% HL increased the fatigue life by, respectively, 25% and 50%, but use of 2% HL led to 40% reduction in this property. For all asphalt mixtures, the best improvement in the fatigue life was achieved by mixes containing 1.5 of hydrated lime.