Effect of graphene oxide on rheology, hydration and strength development of cement paste Kavya Vallurupalli a , Weina Meng b , Jianhui Liu a,c , Kamal H. Khayat a,⇑ a Department of Civil, Environmental and Architectural Engineering, Missouri University of Science and Technology, Rolla, MO, USA b Department of Civil, Environmental and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ, USA c Key Laboratory for Green and Advanced Civil Engineering Materials and Application Technology of Hunan Province, Hunan University, Changsha, China highlights  Well-dispersion of GO in water requires the use of superplasticizer and sonication.  Higher GO content increased the superplasticizer dosage needed for dispersion.  Optimum superplasticizer dosage was found to be four times the mass of GO.  Use of 0.04% well-dispersed GO improved fresh and hardened properties of the paste. article info Article history: Received 3 December 2019 Received in revised form 10 July 2020 Accepted 19 July 2020 Keywords: Graphene oxide Dispersion Rheology Hydration Compressive strength Density of C-S-H abstract The aim of this paper is to investigate the effect of a well-dispersed graphene oxide (GO) on workability, rheological properties, hydration kinetics, density of hydration products, and compressive strength of cement paste. Paste mixtures were prepared with 0.42 water-to-cement ratio, and a well-dispersed GO was incorporated at contents of 0.04%, 0.15%, and 0.29%, by mass of cement. When coupled with sonica- tion time of 48 to 56 min, the optimum active superplasticizer (SP) dosage was found to be four times that of the GO. Compared to paste made with 0.16% SP and no GO, the addition of 0.04% GO increased yield stress and viscosity coefficient values of paste, total heat of hydration at 70 h, density of hydration products at 28 d, and compressive strength at 1, 3, and 7 d. The increase in rheological properties can be caused by the reduction in free water due to water absorption by the GO, while the increase in total heat and compressive strength can be associated with the nucleation effect of the GO. However, increasing the GO content from 0 to 0.15% with the SP dosage fixed at a higher dosage of 0.6% showed no effect on hydration kinetics but reduced yield stress, viscosity coefficient, and 1-d compressive strength. This behavior was attributed to the high dosage of the SP needed for dispersing the high content of GO. The beneficial effect of using 0.15% GO was evident from the increase in compressive strength at 3 and 7 d. Overall, the addition of well-dispersed GO improved the rheological properties, hydration kinetics, density of hydrates, and compressive strength of cement paste. However, the improvement achieved with GO at early age (1 d) was hindered by the retarding effect of SP used to maintain proper dispersion. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, there has been a growing interest in using nano- materials for improving the rheology and mechanical properties of cement-based materials [1–3]. This is due to the ability of the nanomaterials to modify the microstructure of the cement-based materials at nanoscale. The improvement in rheology with the addition of nanomaterials is due to increase in: i) absorption of free water on the high surface area of nanoparticles; ii) particle agglom- eration due to the increase in van der waal attractive forces; iii) interconnectivity among the binder particles in the presence of nanoparticles; iv) particle packing density [4]; and v) degree of hydration as a result of increased nucleation sites [5]. The improvement in mechanical performance with the addition of nanomaterials is mainly attributed to the increase in packing density and nucleation sites [6]. In the case of carbon-based nano- materials (i.e., carbon nanotubes (CNTs) [7–11], carbon nanofibers (CNFs) [10–12], and graphene oxide (GO)) [6,13–15]), the improve- ment in mechanical performance can also be due to the ability of https://doi.org/10.1016/j.conbuildmat.2020.120311 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: khayatk@mst.edu (K.H. Khayat). Construction and Building Materials 265 (2020) 120311 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat