WS 2 nanotube – Reinforced cement: Dispersion matters Roey Nadiv a,⇑ , Michael Shtein a,b , Alva Peled c , Oren Regev a,b,⇑ a Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel b Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel c Department of Structural Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel highlights  Tungsten di-Sulfide NanoTubes (WS 2 NTs) enhance the cement flexural strength by 74%.  We developed a method to disperse WS 2 NT individually in cement paste.  Optimal enhancement occurs at extremely low WS 2 NT concentration (0.15 wt%).  WS 2 NTs inhibit crack propagation by bridging, and fail via pullout mechanism. graphical abstract article info Article history: Received 30 March 2015 Received in revised form 3 August 2015 Accepted 9 August 2015 Keywords: Cement Dispersion Fractography Mechanical properties Nano-composites Nanotubes abstract Nanotubes are considered as promising nano-reinforcement in cement-based materials. The main chal- lenge towards achieving a significant enhancement in cement properties is an effective dispersion of the agglomerated nanotubes. In this paper, we demonstrate a novel dispersion method of Tungsten di-Sulfide NanoTubes (WS 2 NTs) that results in substantial flexural and compressive strength enhancements at opti- mal nanotube concentration as low as 0.15 wt%. The reinforcement by WS 2 NTs remains significant after a variety of curing processes, suggesting a genuine nanoscale reinforcing effect. Finally, by employing a comprehensive fractography we found that the WS 2 NTs inhibit crack propagation by bridging with a pullout failure mechanism. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Cement, one of the most widely used composite materials, is characterized by high compressive strength on the one hand and by low tensile, flexural and fracture toughness properties on the other [1,2]. The latter properties are expected to improve by load- ing appropriate Nano-Materials (NMs) into the cement paste matrix [3]. A wide range of NMs were used in Cement Nano-Composites (CNC), including nano-silica [4–6], nano-titanium dioxide [4,7,8], http://dx.doi.org/10.1016/j.conbuildmat.2015.08.085 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved. Abbreviations: BSE, Back-Scattered Electron; CNT, Carbon NanoTube; CNC, Cement Nano-Composites; EDS, Energy-Dispersive X-ray Spectroscopy; NM, Nano-Material; NT, nanotube; PC, Plain Cement paste; SEM, Scanning Electron Microscope; TEM, Transmission Electron Microscope; WS 2 NT, Tungsten di-Sulfide NanoTube. ⇑ Corresponding authors at: Chemical Engineering, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel. E-mail addresses: roeynadiv@gmail.com (R. Nadiv), oregev@bgu.ac.il (O. Regev). Construction and Building Materials 98 (2015) 112–118 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat