Citation: Maglad, A.M.; Zaid, O.; Arbili, M.M.; Ascensão, G.; S , erb˘ anoiu, A.A.; Gr ˘ adinaru, C.M.; García, R.M.; Qaidi, S.M.A.; Althoey, F.; de Prado-Gil, J. A Study on the Properties of Geopolymer Concrete Modified with Nano Graphene Oxide. Buildings 2022, 12, 1066. https://doi.org/10.3390/ buildings12081066 Academic Editor: Abdelhafid Khelidj Received: 26 June 2022 Accepted: 20 July 2022 Published: 22 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). buildings Article A Study on the Properties of Geopolymer Concrete Modified with Nano Graphene Oxide Ahmed M. Maglad 1 , Osama Zaid 2, * , Mohamed M. Arbili 3 , Guilherme Ascensão 4 , Adrian A. S , erbănoiu 5 , Cătălina M. Grădinaru 5 , Rebeca M. García 6 , Shaker M. A. Qaidi 7 , Fadi Althoey 1 and Jesús de Prado-Gil 6 1 Department of Civil Engineering, Najran University, Najran 55461, Saudi Arabia; ammaglad@nu.edu.sa (A.M.M.); fmalthoey@nu.edu.sa (F.A.) 2 Department of Civil Engineering, Swedish College of Engineering and Technology, Wah Cantt 47080, Pakistan 3 Department of Information Technology, Choman Technical Institute, Erbil Polytechnic University, Erbil 44001, Iraq; mohamed.arbili@epu.edu.iq 4 RISCO, Department of Civil Engineering, University of Aveiro, 3810-193 Aveiro, Portugal; guilhermeascensao@ua.pt 5 Faculty of Civil Engineering and Building Services, Gheorghe Asachi Technical University of Ias , i, 700050 Ias , i, Romania; serbanoiu.adrian@tuiasi.ro (A.A.S , .); catalina.gradinaru@tuiasi.ro (C.M.G.) 6 Department of Mining Technology, Topography and Structures, University of León, Campus of Vegazana s/n, 24071 Leon, Spain; rmartg@unileon.es (R.M.G.); jesusdepradogil@gmail.com (J.d.P.-G.) 7 Department of Civil Engineering, College of Engineering, University of Duhok, Duhok 42001, Iraq; shaker.abdal@uod.ac * Correspondence: osama.zaid@scetwah.edu.pk Abstract: This paper reports the results of a study conducted to examine the impacts of adding graphene oxide (GO) to GBFS-fly ash-based geopolymer concrete. The geopolymer concrete’s compressive strength, thermal conductivity, and modulus of elasticity were assessed. X-ray diffraction (XRD) analysis was conducted to understand the differences in mineralogical composition and a rapid chloride penetration test (RCPT) to investigate the changes in the permeability of chloride ions imposed by GO addition. The results showed that adding 0.25 wt.% GO increases the modulus of elasticity and compressive strength of GBFS-FA concrete by 30.5% and 37.5%, respectively. In contrast, permeability to chloride ions was reduced by 35.3% relative to the GO-free counterparts. Thermal conductivity was decreased as GO dosage increased, with a maximum reduction of 33% being observed in FA65-G35 wt.% samples. Additionally, XRD showed the suitability of graphene oxide in geopolymer concrete. The present research demonstrates very promising features of GO- modified concrete that exhibit improved strength development and durability compared to traditional concrete, thus further advocating for the wider utilization of geopolymer concrete manufactured from industrial byproducts. Keywords: graphene oxide; geopolymer concrete; alkali-activated materials; nanomaterials 1. Introduction Approximately 8% of the world’s carbon dioxide (CO 2 ) emissions can be related to clinker manufacturing [1], and the global cement production has been growing 10–12% per year over the last decade [2,3]. In order to reduce the outflow of CO 2 emissions, it is vital to restrict clinker manufacturing [4,5] and partially replace it with supplementary cementitious materials (SCM) [6,7]. Granulated blast furnace slag (GBFS) [8] and fly ash (FA) are both industrial by-products [8–10] that have been extensively utilized as SCMs to diminish the clinker factor in cement formulae [11]. However, SCMs have a limited ability to substitute clinker with a current threshold limit at approximately 25–35% of cement weight due to the significant decrease in concrete strength at an early age. Recently, clinker- free binders are attracting increasing attention [4], with several studies been conducted on alkali-activated materials (AAMs) and geopolymers. Geopolymer binders might be an Buildings 2022, 12, 1066. https://doi.org/10.3390/buildings12081066 https://www.mdpi.com/journal/buildings