Investigation of fatigue and fracture properties of asphalt mixtures modified with carbon nanotubes M. AMERI 1,2 , Sh. NOWBAKHT 1 , M. MOLAYEM 1 and M. R. M. ALIHA 3 1 School of Civil Engineering, Iran University of Science and Technology, Narmak 16846–13114, Tehran, Iran, 2 Center of Excellence for PMS, Transportation and Safety, Iran University of Science and Technology, Narmak 16846–13114, Tehran, Iran, 3 Welding and Joining Research Center, School of Industrial Engineering, Iran University of Science and Technology, Narmak 16846–13114, Tehran, Iran Received Date: 2 October 2015; Accepted Date: 9 January 2016; Published Online: 19 February 2016 ABSTRACT Load-induced cracking is one of the primary forms of distress in asphalt pavements at intermediate temperatures. Binder modification is a good alternative to promote the cracking resistance of asphalt mixtures. In the current research study, the effects of carbon nanotubes as a binder modifier on the fatigue and fracture performance of asphalt mixtures are investigated. The carbon nanotubes are added at five different percentages ranging from 0.2% to 1.5% to the base binder to study their effects on the fracture resistance and fatigue life of the asphalt mixtures. Using the cracked semi-circular bend specimen, the critical value of J-integral (Jc) was obtained for the investigated modified asphalt mixtures. Also, the fatigue behaviour of asphalt mixtures was studied using flexural beam fatigue test specimen. By employing the ratio of dissipated energy change approach, the plateau value of tested mixtures was determined as a measure of fatigue performance. Results showed that the carbon nanotubes can enhance both fracture resis- tance and fatigue performance of tested asphalt mixtures especially at higher percentages of the carbon nanotube. Keywords asphalt; carbon nanotube; dissipated energy; fatigue behaviour; fracture; strain energy release rate. NOMENCLATURE a = crack length or notch depth CNT = carbon nanotube DE = dissipated energy J = J-integral J c = critical strain energy release rate PV = plateau value RDEC = ratio of dissipated energy change SCB = semi-circular bend W = strain energy density INTRODUCTION Fatigue cracking is one of the main forms of deterioration in asphalt pavements. This kind of distress is the outcome of repetitive vehicular loads or the application of heavy loads that induce stresses or strains, which are greater than the material’s strength. 1 The fatigue phenomenon in asphalt mixtures encompasses two consecutive major stages. In the pre-localization stage, micro-cracks nucleate and grow followed by formation and propagation of macro-cracks, which occur during the post-localization of critical stresses or strains. 2,3 Addressing the two aforementioned phases is usually performed through the fatigue and fracture tests, respectively. 2–4 In the mechanistic-empirical design of asphalt pavements, it is re- quired to predict the material’s responses to the induced loads. Therefore, more comprehensive information about the fracture and fatigue properties of asphalt mixtures can lead to a more compatible pavement structure against the applied loads. Correspondence: M. Molayem. E-mail: molayem@iust.ac.ir © 2016 Wiley Publishing Ltd. Fatigue Fract Engng Mater Struct, 2016, 39, 896–906 896 ORIGINAL CONTRIBUTION doi: 10.1111/ffe.12408