J. Cent. South Univ. (2013) 20: 256−266 DOI: 10.1007/s11771-013-1483-1 Long term performance of warm mix asphalt versus hot mix asphalt Ziari Hasan, Behbahani Hamid, Izadi Amir, Nasr Danial School of Civil Engineering, Iran University of Science and Technology, Tehran, 1684613114, Iran © Central South University Press and Springer-Verlag Berlin Heidelberg 2013 Abstract: The fatigue behavior, indirect tensile strength (ITS) and resilient modulus test results for warm mix asphalt (WMA) as well as hot mix asphalt (HMA) at different ageing levels were evaluated. Laboratory-prepared samples were aged artificially in the oven to simulate short-term and long term ageing in accordance with AASHTO R30 and then compared with unaged specimens. Beam fatigue testing was performed using beam specimens at 25 °C based on AASHTO T321 standard. Fatigue life, bending stiffness and dissipated energy for both unaged and aged mixtures were calculated using four-point beam fatigue test results. Three-point bending tests were performed using semi-circular bend (SCB) specimens at –10 °C and the critical mode I stress intensity factor K I was then calculated using the peak load obtained from the load–displacement curve. It is observed that Sasobit and Rheofalt warm mix asphalt additives have a significant effect on indirect tensile strength, resilient modulus, fatigue behavior and stress intensity factor of aged and unaged mixtures. Key words: warm mix asphalt; hot mix asphalt; fatigue behavior; resilient modulus; tensile strength; stress intensity factor; ageing Received date: 2012–02–06; Accepted date: 2012–04–04 Corresponding author: Izadi Amir; Tel: +98–9111279814; E-mail address: amirizadi60@gmail.com 1 Introduction Ageing in asphalt pavements occurs due to bitumen oxidation and volatilization when it is exposed to air especially at high temperatures. This phenomenon causes hardening and material embrittlement with time, which eventually leads to fatigue and thermal cracking as common types of distresses in asphalt pavements. The amount of ageing (ageing rate) has been found to vary significantly depending upon crude source, additives, climate, and characteristics of the mixture. Furthermore, aged mixtures might be less durable than original mixtures in terms of wear resistance and moisture susceptibility [1–3]. In recent years, several technologies have been developed to produce asphalt pavements. Warm mix asphalt (WMA) is one of the newest ones which have recently gained wide popularity. This technology was proposed to address the Kyoto protocol agreement in lowering emission in construction phase. Employing WMA technique also improves working conditions for production and paving workers due to reduced fumes, emissions and odors. Furthermore, the ability to transport it over longer distances to pave at lower temperatures, and a longer paving season are the additional benefits of this technology. The most promising advantage of this technology is reducing asphalt binder ageing due to lowering the mixing and paving temperatures which in turn results in less cracking, etc [4]. All in all, few investigations are performed on the ageing property of the mixtures. Fatigue cracking is one of the most important damages in asphalt concrete pavements and causes structural damages. In Ref. [5], a four-point beam fatigue test from IPC global company was utilized to conduct the fatigue test in accordance with AASHTO T321 standard. Ageing of asphalt mixtures is the controlling factor leading to the failure in asphalt layers. In this work, the simulation of asphalt mixtures at different ageing levels namely short term and long term was run in a forced-draft oven in accordance with AASHTO R30 standard [5–6]. During the course of short term ageing, asphalt mixture was short-term aged, compacted and then kept in an oven at 85 ºC for 120 h. In this work, the effect of ageing on indirect tensile strength, resilient modulus, moisture susceptibility, fatigue performance and fracture toughness of WMA and hot mix asphalt (HMA) mixtures with two different aggregate gradations was evaluated. 2 Experimental 2.1 Materials The mineral aggregate used in this work was obtained from a limestone source. Table 1 demonstrates engineering properties of the aggregate used. Two different aggregate gradations (A and B) with nominal