Effect of dispersibility of carbon nanotubes by silica fume on material properties of cement mortars: Hydration, pore structure, mechanical properties, self-desiccation, and autogenous shrinkage Chiwon Song, Geuntae Hong, Seongcheol Choi ⇑ Department of Civil and Environmental Engineering, Chung-Ang University, Seoul 06974, Republic of Korea highlights  CNTs can be effectively dispersed during the mixing process using silica fume.  CNTs change pore structure and hydration kinetics for greater dispersion.  Well-dispersed CNTs increase compressive strength and modulus of elasticity.  Well-dispersed CNTs decrease IRH drop by increasing capillary pore volume.  Well-dispersed CNTs decrease autogenous shrinkage of cement mortar. article info Article history: Received 17 September 2019 Received in revised form 16 May 2020 Accepted 19 July 2020 Keywords: Autogenous shrinkage Carbon nanotubes Dispersibility Hydration kinetics Mechanical properties Pore structure Self-desiccation Silica fume abstract In this study, the effect of dispersibility of carbon nanotubes (CNTs) by silica fume on the material prop- erties of cement mortars were experimentally analyzed. Cement mortar specimens incorporating differ- ent proportions of silica fume and CNTs were fabricated, and tests were conducted to measure their hydration kinetics, pore structure, compressive strength, elastic modulus, internal relative humidity, and autogenous shrinkage. Additionally, scanning electron microscopy analysis was performed to observe the morphology of the CNTs in the cement matrix. The results revealed that the dispersibility of the CNTs was enhanced with the increasing replacement ratio of silica fume. Furthermore, well- dispersed CNTs resulted in a decrease in the self-desiccation by varying the pore structure and hydration kinetics, and an increase in the modulus of elasticity, thereby reducing the autogenous shrinkage of the cement mortar specimens. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction With the advancement of nanotechnology, carbon nanotubes (CNTs), which are widely used in various fields, have been success- fully employed in construction materials. Existing studies [1–4] indicate that the performance of cementitious materials can be enhanced by incorporating even a small amount of CNTs. Improve- ment in the mechanical properties, such as compressive strength and elastic modulus, of cementitious materials was achieved [5– 7] when the incorporated CNTs were adequately dispersed in the materials. Manzur et al. [8] reported that the compressive strength of cement mortars was dependent on the dispersibility of CNTs with different proportions; for instance, incorporating 0.3% of CNTs resulted in a strength increase of 17.4% after 28 days, whereas incorporating 0.5% of CNTs resulted in a strength decrease of 14.3% owing to poor dispersion. Falara et al. [9] observed that the Young’s modulus of cement paste incorporating 0.048% and 0.075% of CNTs increased by 28.4% and 47.8%, respectively, in com- parison with that of reference specimens. These results can be attributed to the changes in the pore structures, which are affected by the dispersibility of CNTs in the materials. Owing to the strong van der Waals forces between the nanotubes and the high aspect ratios, CNTs exist in a bundled form [5]. It has been reported that the performance of cementitious materials dete- riorates if bundled CNTs are used without proper dispersion treat- ment [6,7]. In general, the dispersion of nanomaterials in cementitious materials is achieved by a combination of acid treat- https://doi.org/10.1016/j.conbuildmat.2020.120318 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: schoi@cau.ac.kr (S. Choi). Construction and Building Materials 265 (2020) 120318 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat