Comparative assessment of the effect of micro- and nano- fillers on the microstructure and linear viscoelasticity of polyethylene-bitumen mastics Claudia Roman, Moisés García-Morales ⇑ Departamento de Ingeniería Química, Centro de Investigación en Tecnología de Productos y Procesos Químicos (Pro2TecS), Campus de ‘‘El Carmen”, Universidad de Huelva, 21071 Huelva, Spain highlights  Mastics obtained by combination of micro/nano-fillers showed enhanced rheology.  Polymer dispersion improved with addition of nanoclay.  Polymer droplets size decreased as the microfiller approached its limiting content.  Fluorescence Optical Microscopy enabled visualization of polymer-rich domains.  Atomic Force Microscopy provided information on the filler reinforcement. article info Article history: Received 12 January 2018 Received in revised form 23 February 2018 Accepted 24 February 2018 Keywords: Bitumen Polymer Mastic Filler Nanoclay Rutting Microscopy Rheology Microstructure abstract In order to minimize permanent deformation in bitumen mastics, the combined addition of traditional mineral filler and an organo-modified nano montmorillonite to different bitumen/polymer matrices was evaluated by dynamic shear/torsional tests and microscopy techniques. Individual addition of micro- filler or nanoclay was also studied. The most remarkable result corresponded to a polymer modified mas- tic containing a mix of 40 wt% microfiller and 5 wt% nanoclay. As compared to a reference mastic with 45 wt% microfiller, the complex modulus at 65 °C increased more than two decades. The nanoclay has thereby shown high reinforcing potential if combined to standard mineral filler in bitumen mastics. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction Mineral fillers with a typical average particle size in the 10–50 mm range have traditionally been used in hot asphalt mixtures for road construction [1]. They provide contact points between larger aggregate particles in order to strengthen the mixture. It is note- worthy to mention that the composite formed when bitumen and filler are mixed, termed mastic, is the actual binder which holds the aggregates together. The rheological characterization of this composite is therefore essential to improve the understanding of the asphalt pavements performance [2,3]. The macro-mechanical behavior of flexible bituminous pave- ments is conditioned by the morphology and physical properties at the smaller meso- and micro-scales [4]. As the volume, speed and load of traffic have dramatically increased over the last dec- ades, the use of polymer modified bitumens (PMBs) is very often required in order to enhance pavements performance and, so, to prolong their in-service life and reduce maintenance costs [4,5]. Numerous studies [6–10] have reported increased shear complex modulus of bitumen upon addition of polyethylene (PE). Moreover, PE is the most popular commodity plastic and, so, is abundantly available as waste material. Its addition to bitumen represents an environment-friendly alternative approach for the future of waste PE valorization. https://doi.org/10.1016/j.conbuildmat.2018.02.188 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: moises.garcia@diq.uhu.es (M. García-Morales). Construction and Building Materials 169 (2018) 83–92 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat