**1. Introduction**

The construction sector is responsible for significant environmental stresses, consuming 48% of global supplied energy on an annual basis and depleting the natural resources [1]. In addition to exploitation of materials, manufacturing of construction materials and operational works are responsible for 38% of worldwide greenhouse gas emissions [2]. The sustainable development goals demand continuous monitoring of emissions and potential health risks of the implemented system. Understanding the environmental impacts of infrastructure and construction practices aids in developing efficient energy techniques. Moreover, low fatalities and injuries are common in the construction industry which encourages the automation of construction-related techniques. Furthermore, automation of construction activities is preferred to account for low productivity rates. More specifically, labour productivity, which is defined as construction workload expressed in units per man hour, plays a key role in the capital investment of the project as well as meeting the global

**Citation:** Abdalla, H.; Fattah, K.P.; Abdallah, M.; Tamimi, A.K. Environmental Footprint and Economics of a Full-Scale 3D-Printed House. *Sustainability* **2021**, *13*, 11978. https://doi.org/10.3390/ su132111978

Academic Editors: Pierfrancesco De Paola, Francesco Tajani, Marco Locurcio and Felicia Di Liddo

Received: 22 September 2021 Accepted: 26 October 2021 Published: 29 October 2021

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**Copyright:** © 2021 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/).

housing demand [3]. Current rates of productivity combined with an increase in urbanization has been a concern in sustaining the increasing housing demand which is estimated to reach 230 billion m<sup>2</sup> in the next 40 years [4]. As a result, additive manufacturing has been proposed as an alternative to conventional construction. Additive manufacturing or 3D printing is being assessed as a potential solution to current methods of construction for energy reduction, automation of construction methods, mitigation of environmental impacts, and cost savings [2].

In addition to the consideration of materials, the construction industries face a continuous challenge of having to complete construction of the structures within the shortest time, while still having to maintain safety and work quality. Innovations in the construction industry have explored different techniques to account for the technical drawbacks and environmental impacts associated with conventional construction techniques. Automation of activities in the construction site have been proposed, particularly additive manufacturing or 3D printing technology, to improve construction practices [5]. The additive manufacturing process operates by continuously adding a layer-by-layer extrusion paste. It is also defined as a method of digitally fabricating materials via printers [6]. Each 3D printed layer is a 2D representation from the computer aided design (CAD) or building information modelling (BIM) model that is deposited to the printer [7]. Digital fabrication enables customization and assembly of complex designs. Attempts have been made to utilize 3D printing techniques in the construction industry and evaluate the sustainability and implications on the economic, environmental and social aspects [5]. A case study in China demonstrated the potential of large-scale 3D printing, whereby several houses approximately 200 m<sup>2</sup> have been built using high quality cement alongside glass fiber to enhance strength [8]. Another application represented the functionality of 3D printing by prefabricating the components of a 5 storey building and later assembled on site [9]. Wu et al. [7] asserted the importance of selecting appropriate material to attain the desired level of detailing and withstand the loading on the structure. A Complex design of a 12 m × 12 m × 12 m house with complex details has been successfully implemented using 3D printing [7]. The house was printed with glass reinforced plastic extrusion paste which was able to resist corrosion, aging and water seepage.

Digital fabrication foresees the potential of mitigating the environmental constraints and reducing the materials used in building sector [4]. Moreover, utilization of 3D printing technology in the construction industry can potentially lead to a reduction of energy supply and overall emissions up to 5% by 2025 in large scale projects (i.e., large filament size) [4]. The environmental performance of implementing additive manufacturing methods in the construction sector has been explored. Several studies investigated the environmental impacts of additive manufacturing in the construction industry using life cycle assessment (LCA) systematic framework. Sinka et al. [10] explored the environmental impacts of different 3D printing cement and gypsum binders. The results revealed that gypsum-based mixes had an overall reduction in GWP of 84% as a result of lower energy use. Other studies investigated the performance of different construction elements. Mrazovi´c et al. [11] compared the environmental performance of conventional and 3D-printing of different metal building elements (such as steel frame and steel brackets). Additive manufacturing proved to be compatible for construction which achieved 40% lower environmental impact (compared to conventional manufacturing methods) [11]. Agustí-Juan et al. [12] utilized LCA to identify the viability of constructing walls with varying complexities using 3D printing compared to conventional construction techniques. The results revealed that complexity of structures did not increase the overall costs and the design of the structure was not responsible for environmental constraints as opposed to conventional building techniques. Moreover, the literature has been focused on studying the environmental impacts particularly, climate change potential and energy consumption as they have been reported to have the greatest effects [13]. The climate change impact of conventional walls was 75%, whereas the 3D-printed wall had negligible impact (2%). Climate change was reported to have significant environmental impacts as a result of the GHGs emissions

during the material production, manufacturing, transport and construction phases [12]. Another case study assessed the environmental impacts from the materials production and operation of 3D-printed wall and roof structures [14]. Results highlighted the minimal impacts of operation of fabrication robots, while the mainstream energy consumption originates from material production. Mohammad et al. [15] also investigated the environmental performance of 3D printed walls compared to conventional reinforced concrete ones. The 3D concrete printing (3DCP) scenarios yielded lower emissions in terms of global warming potential and acidification potential. The study further combined conventional reinforcement with 3DCP, and the environmental impacts were still lower than conventional construction techniques.

All of the above mentioned studies only assessed the environmental impacts of different structural elements, on the other hand, Han et al. [16] developed a 3D model simulating a 3D-printed house. The emissions were calculated using equations from the literature. The findings of the study revealed that construction using 3D printing technology resulted in higher emissions when compared to cast in-situ conventional concrete. Moreover, the study attributed the high emissions to cement production processes. Another study compared the environmental impacts of 3D printing and conventionally built house [17]. The study utilized concrete and cob (a sustainable material) to run the analysis. The 3D printing technology acquired lower impacts compared to conventional concrete construction. In terms of materials, cob attained lower impacts, nevertheless, 3DCP binder consumed less energy. In terms of economic viability, a case study in the United Kingdom investigated the financial feasibility of 3D printed residential structures using life cycle costing analysis (LCCA). The findings of the study revealed savings up to 35% when compared to conventional houses due to lower material consumption and eliminated labour cost [18].

Conventional construction is responsible for significant environmental and safety risks which compels introduction of new efficient and feasible alternatives. Digital technologies, particularly 3D printing, have been successfully implemented in the field of construction. Evaluation of the systems encompasses quantification of environmental impacts using the standard LCA tool and economic value of building structures using conventional manufacturing methods versus 3D printed methods. The capital and energy costs incurred over the life cycle of the examined structural systems are estimated using life cycle costing analysis. An eco-efficiency analysis is used to combine the results of the LCA and LCC into a single framework to assist decision makers with the choice of the optimum construction method taking account the environmental and economic perspectives. A search of recent publications (Table 1) in this field showed that most of the studies focus primarily on developing the 3D printing mortar and utilizing sustainable materials. The literature lacks comprehensive and integrated environmental and economic assessment of large-scale 3D printed buildings. Since this technology is under development, more studies are needed to optimize the materials and methods used from both environmental and economic perspectives. This study aims to enrich the literature with comprehensive assessment of such a knowledge base which is essential to drive the shift towards digital fabrication construction. This study provides a comparative assessment of a 3D-printed structure compared to conventional concrete construction. The comparative assessment is applied on an actual single-storey house located in Dubai, United Arab Emirates (UAE).


**Table 1.** Summary of life cycle assessment-based studies in the construction sector.
