Automation in Construction 118 (2020) 103268 Contents lists available at ScienceDirect Automation in Construction journal homepage: www.elsevier.com/locate/autcon Review Additive manufacturing: Technology, applications, markets, and T opportunities for the built environment ⁎ ⁎ Ans Al Rashid , Shoukat Alim Khan, Sami G. Al-Ghamdi, Muammer Koç Division of Sustainable Development, College of Science and Engineering, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar ARTICLE INFO ABSTRACT Keywords: Additive manufacturing (AM) technologies (also known as 3D printing - 3DP) have been rapidly advancing into Additive manufacturing various industrial sectors, including aerospace, automotive, medical, architecture, arts and design, food, and 3D printing construction. Transitioning from the visualization and prototyping stages into functional and actual part re- Construction placement opens further design possibilities. Among the diverse applications of AM, construction applications Infrastructure have not yet seen a commercially available and widely used product in the market. Nevertheless, it has been a Construction materials subject of interest to researchers in recent decades. There are evident challenges and risks for the integration of AM towards large-scale construction. Therefore, progress in their commercialization seems to proceed at a slow pace, as only a few 3DP trials for large-scale construction can be found in the literature. This paper aims to provide a comprehensive and evidence-based baseline along with progresses in relevant disciplines related to 3DP in construction, which will provide an opportunity to experts in all domains to understand the multi- dimensional constraints and to specify the future research directions in these sectors. The distinct merit of this article is that it provides, for the first time, a diverse review on literature in the field of construction 3Dprinting. It offers up-to-date and in-depth information of hindrances (from processes, materials, structural designand standards) which add up towards low pace of automation in construction sector, identify deficiencies in the current research and provides future research trends for researchers. The findings from intensive literature re- view will guide engineers, designers and investors from construction sector to grab research gaps and business opportunities. First of all, the development of different 3DP processes in built environment are presented to highlight the process constraints along with the commercial applications of these processes for industrialists and investors to identify the business opportunities. Secondly, process parameters and difficulties in optimization of material mixtures are presented as a guide to civil engineers following the discussion on materials urging the need for development of eco-efficient and environment friendly materials. Conclusions drawn from discussion in individual sections along with issues/constraints and challenges involved are explained separately. 1. Introduction developed for more than three decades, the progress in the degree of automation for construction applications has been slow [4]. This is AM (a.k.a. 3D Printing) technologies have been considered pro- because AM processes, in their present form, cannot be directly utilized mising to take a significant role in design and construction of built in large-scale construction applications [5]. environment owing to their multiple benefits over conventional Despite recent advancements in AM processes and technologies, methods, including rapid production, custom products, reduction of there are still pressing needs and research issues to develop sustainable waste materials and labor costs, precision, and accuracy [1]. AM new materials for construction applications, obtain optimal process technologies can provide rapid housing solutions in cases of emergen- parameters and conditions, develop computational modeling techni- cies, and can be used to build exotic structures, which are not possible ques, introduce reinforcements and enhancements to AM structures, with conventional construction strategies [2,3]. Developed countries and develop new technologies [6]. Some researchers have tried to have been investing significantly in automation of the construction utilize conventional construction materials to print structures using AM sector to cope with shortages of skilled labor and to avoid vulnerable processes [7], whereas others have used some novel materials [8], in- situations at construction sites. Although AM processes have been cluding geopolymer concrete, natural fiber-reinforced materials, waste ⁎ Corresponding authors. E-mail addresses: [email protected] (A. Al Rashid), [email protected] (M. Koç). https://doi.org/10.1016/j.autcon.2020.103268 Received 17 February 2020; Received in revised form 11 May 2020; Accepted 14 May 2020 Available online 27 June 2020 0926-5805/ © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/). A. Al Rashid, et al. Automation in Construction 118 (2020) 103268 materials-reinforced construction materials, and recycled materials. research. Three main gaps were identified between academic, con- Although AM processes have been improved to adopt to construction struction industry and robotics industry along with the recommenda- requirements, there remains a need to develop materials that can re- tions to bridge these gaps. A. Darko et al. [22] performed a sciento- place conventional materials from the market, and that are integrable metric analysis and visualization of literature related to artificial to the above processes. intelligence in architecture, engineering and construction. Rakha and Researchers face difficulties in optimizing process parameters asAM Gorodetsky [23] provided a comprehensive review on utilization of processes require the material to be fluidic enough to pass a delivery system, unmanned aerial systems for built environment applications in auto- whereas rapid curing is required to ensure the structural integrity. Research mated buildings inspection followed by a case study to validate the efforts have been made regarding extrudability, buildability, printer nozzle proposed framework. G. D. Schutter et al. [24] published an article very design, printing speed and direction, aggregate sizes, optimum mixes, and specific to technical issues related to concrete 3D printing addingup the addition of reinforcements to the material. Nevertheless, the progress in economic and environmental potential related with technology. V. Li the standardization of AM processes in the construction sector is not ac- et al. [25] recently presented the study of process characteristics and ceptable for commercialization [6]. properties during fresh and hardened state of 3D printable cement- In this article, authors build upon and improve the previous reviews, based composites. V. Mechtcherine et al. [26] presented almost similar as summarized in the next paragraphs, by a systematic, thorough, and study for extrusion based processes, rather in this study the mechanical comparative analysis of the published literature. Review papers and properties of cementitious composite materials were discussed more in original research articles from well reputed journals were considered details. D. Asprone et al. [27] published a review article with special for this study to highlight the limitations and hindrances for utilization focus on reinforcement for 3D printed concrete structures. Review ar- of AM processes in construction sectors, as well as the guidelines to ticle presented by N. Roussel [28] accumulated literature to identify the future research directions for researchers. rheological requirements required for concrete printing. Although several review articles are present in this field, many of In the view of shortcomings of current literature, still there is a need to them fall short in bringing a multi-dimensional aspect and discussion. identify and address multi-disciplinary issues for proper utilization of AM For instance, the articles presented by R. Buswell et al. [12], S. Ghaffar processes. For implementation of AM processes in the construction sector, a et al. [13], D. Delgado et al. [14], J. Zhang et al. [15], G. D. Schutter current state-of-the-art needs to be established to highlight the constraints. et al. [24], V. Li et al. [25] and V. Mechtcherine et al. [26] discussed the AM processes, construction materials for AM, AM process constraints and material science involved in the process without extensive information commercialization of AM processes in built environment are the four target about development of the processes. On the other end, the processes sectors for this review, which would assist researchers from several back- were presented in detail with limited or no consideration to the issues grounds (including manufacturing, material science, designers and sus- related with implementation of materials to 3DP processes by F. Cra- tainability) to identify the future research directions. veiro et al. [17] and A. Paolini et al. [18]. Finally, I. Perkins et al. [9], F. This paper presents the development and adaptation of AM pro- Bos et al. [10] and Y. Tay et al. [11] are considered outdated reviews as cesses in the construction sector, with a more specific focus on built significant advancements in processes and materials have been wit- environment and infrastructure applications. The advancements and nessed