materials Review Green Concrete for a Circular Economy: A Review on Sustainability, Durability, and Structural Properties Abathar Al-Hamrani 1 , Murat Kucukvar 2, * , Wael Alnahhal 1 , Elsadig Mahdi 2 and Nuri C. Onat 3   Citation: Al-Hamrani, A.; Kucukvar, M.; Alnahhal, W.; Mahdi, E.; Onat, N.C. Green Concrete for a Circular Economy: A Review on Sustainability, Durability, and Structural Properties. Materials 2021, 14, 351. https://doi.org/10.3390/ma14020351 Received: 24 December 2020 Accepted: 5 January 2021 Published: 12 January 2021 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional clai- ms in published maps and institutio- nal affiliations. Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Civil and Architectural Engineering, Qatar University, Doha 2713, Qatar; aa1205725@student.qu.edu.qa (A.A.-H.); wael.alnahhal@qu.edu.qa (W.A.) 2 Department of Mechanical and Industrial Engineering, College of Engineering, Qatar University, Doha 2713, Qatar; elsadigms@qu.edu.qa 3 Qatar Transportation and Traffic Safety Center, Qatar University, Doha 2713, Qatar; onat@qu.edu.qa * Correspondence: mkucukvar@qu.edu.qa; Tel.: +974-4403-4332 Abstract: A primary concern of conventional Portland cement concrete (PCC) is associated with the massive amount of global cement and natural coarse aggregates (NCA) consumption, which causes depletion of natural resources on the one hand and ecological problems on the other. As a result, the concept of green concrete (GC), by replacing cement with supplementary cementitious materials (SCMs) such as ground granulated blast furnace slag (GGBFS), fly ash (FA), silica fume (SF), and metakaolin (MK), or replacing NCA with recycled coarse aggregates, can play an essential role in addressing the environmental threat of PCC. Currently, there is a growing body of literature that emphasizes the importance of implementing GC in concrete applications. Therefore, this paper has conducted a systematic literature review through the peer-reviewed literature database Scopus. A total of 114 papers were reviewed that cover the following areas: (1) sustainability benefits of GC, (2) mechanical behavior of GC in terms of compressive strength, (3) durability properties of GC under several environmental exposures, (4) structural performance of GC in large-scale reinforced beams under shear and flexure, and (5) analytical investigation that compares the GC shear capacities of previously tested beams with major design codes and proposed models. Based on this review, the reader will be able to select the optimum replacement level of cement with one of the SCMs to achieve a certain concrete strength range that would suit a certain concrete application. Also, the analysis of durability performance revealed that the addition of SCMs is not recommended in concrete exposed to a higher temperature than 400 ◦ C. Moreover, combining GGBFS with FA in a concrete mix was noticed to be superior to PCC in terms of long-term resistance to sulfate attack. The single most striking observation to emerge from the data comparison of the experimentally tested beams with the available concrete shear design equations is that the beams having up to 70% of FA as a replacement to OPC or up to 100% of RCA as a replacement to NCA were conservatively predicted by the equations of Japan Society of Civil Engineers (JSCE-1997), the American Concrete Institute (ACI 318-19), and the Canadian Standards Association (CSA-A23.3-14). Keywords: green concrete; cement; ground granulated blast furnace slag; fly ash; silica fume; metakaolin 1. Introduction With the increasing risks of climate change and the depletion of natural resources due to their utilization in the construction industry, sustainability has gained wide importance and the term circular economy (CE) has emerged as one of the most important factors leading to sustainable development [1]. In contrast to the prevailing traditional economy system, which is based on a methodology of make, use, and finally, dispose of, the CE aims at continuous use of products by recycling and reusing instead of disposing to create a closed-loop system and reduce the resource consumption [2]. Materials 2021, 14, 351. https://doi.org/10.3390/ma14020351 https://www.mdpi.com/journal/materials