Experimental investigation of the fatigue phenomenon in nano silica- modified warm mix asphalt containing recycled asphalt considering self- healing behavior Saber Kie Badroodi a , Mahmoud Reza Keymanesh a , Gholamali Shafabakhsh b a Department of Management, Payame Noor University, P.O.Box 25359-3650, Tehran, Iran b Faculty of Civil Engineering, Semnan University, Semnan, Iran highlights  By increasing the RAP in samples the stiffness of the specimens was increased.  Samples containing 5% nano-silica had a higher rate of self-healing.  The strain level is very much related to self-healing rate.  Applying rest periods would have a very significant effect on self-healing potential. article info Article history: Received 16 February 2019 Received in revised form 29 October 2019 Accepted 8 November 2019 Keywords: Warm mix asphalt Fatigue Self-healing RAP Nano-silica Aging abstract This study investigates the fatigue performance of nano silica-modified warm mix asphalt containing recycled asphalt pavement (RAP) with self-healing properties. To achieve this goal, Sasobit was added at 2 wt% and nitric oxide at 3 wt%, 5 wt% and 7 wt% to the bitumen and mixed with a high shear mixer. In order to simulate aging in warm asphaltic mixtures, 0, 70 and 100 wt% of the RAP were used to prepare four-point bending test slabs. Then, the beams obtained from the slabs were evaluated under constant strain at two strain levels of 400 and 800 mm. The results showed that addition of nano -silica can signif- icantly improve the self-healing behavior of warm asphalt mixtures. Furthermore, the healed specimens showed significant flexural stiffness. On the other hand, the self-healing behavior of asphalt samples with and without RAP and nano-silica were substantially different under constant strains of 400 and 800 mm. Ó 2019 Published by Elsevier Ltd. 1. Introduction 1.1. Self-healing of asphalt mixtures Self-healing engineered materials were first designed in 2001 by introduction of a catalyst and microcapsules containing a heal- ing agent in a polymer matrix [1]. The self-healing process can be explained as follow: by growth of cracks, the microcapsules break in the self-healing polymer structure and release the healing agent into the crack; the healing agent starts to polymerize upon it con- tact with the catalyst therefore, the two sides of the cracks mouth will close together leading to the overlap of the two sides of the crack [2]. Review of literature indicates that the self-healing mech- anism in asphalt mixtures can be categorized into two types: a) improving the coherence between the aggregates in the asphalt mixture; b) improving the bonding and adhesion of the bituminous binder. Some of the researchers suggest that when the cracks are connected to each other by the Van der Waals force, the molecules will be propagated from one side to another until the cracks become completely restored, and the asphalt regains its original resistance [3]. Bitumen plays a vital role in self-healing of asphalt mixtures. Furthermore, the temperature and healing time depends on the type of applied bitumen [4,5]. The stiffness and strength of bitumen materials may reduce when they are exposed to repetitive loading [6]. The main issue of the self-healing process is its very slow pace at ambient temperature; in a way that the cracks growth rate exceeds the pavement recovery rate and the asphalt mixture can’t be automatically recovered. In addition, traffic flow on the road can’t be blocked to improve the self-healing [7–9]. The initia- tion and growth of microcracks under cyclic loading have been investigated by several researchers [10,27–32]. The stiffness recov- ery of materials, increased fatigue life and strength recovery were https://doi.org/10.1016/j.conbuildmat.2019.117558 0950-0618/Ó 2019 Published by Elsevier Ltd. Construction and Building Materials 246 (2020) 117558 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat