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 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 m2
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 m2
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. Mrazović 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).
5. Sensitivity Analysis
Several factors such as system boundaries, assumptions, and accuracy of inventory data affect the certainty of LCA and LCC results. Moreover, the 3D printing technology is still in the exploration and development stage and the data were compiled from the literature. A sensitivity analysis was conducted to account for the uncertainties in this study where the selected parameters are listed in Table 9
. Different 3D printing binder mixtures were evaluated in the analysis to investigate the environmental impact of cement and coarse aggregates as they acquired the highest scores in the LCA results. The conventional concrete mix was also evaluated to investigate the effect of varying concrete and steel quantities [2
The concrete, steel, and cement production accounted for the highest environmental scores in the performed LCA. Figure 7
illustrates the results of the sensitivity analyses for the different 3DCP and Conventional mixtures. The results are presented relative to the conventional base scenario which obtained the highest impacts in all categories. The analysed mixtures had relatively small impacts contributing to 0–3% in all categories. Nevertheless, the 3DCP mix 1 and 2 contributed to the highest water consumption (474 and 391 m3
, respectively), followed by conventional mix 1 (390 m3
), conventional base scenario (233 m3
), the 3DCP base scenario (184 m3
), and the least water consumption was attained by conventional mix 2 (110 m3
). These results led to the conclusion that reducing cement quantities in 3DCP binder can reduce the overall environmental impacts by 90%. In conventional construction techniques replacing some concrete elements with bricks (such as conventional mix 2) can also reduce the environmental deterioration.
The LCC results of the different mixtures reveal significant differences from the original scenarios (Table 10
). The 3DCP mix 1 and 2 showed almost similar results with a decrease of 20% from the original mix. This decrease can be attributed to the reduction of cement in mix 1 and mix 2. Conventional concrete mixtures 1 and 2 obtained a total cost of USD 33,073 and 31,451, respectively which is almost 60% less than the base scenario. Moreover, the cost of the 3D printer was added to the 3D printed house scenario while keeping all the other parameters constant. The present value was found to be USD 225,391 (82% increase in expenditures). Since the technology is still in the exploration stage, a renting cost is yet to be accounted for in future 3D construction projects. Different electricity tariffs ranging between 0.07 to 0.1 were investigated. For low electricity tariffs, the costs of the 3D printing scenario decreased by 5% and increased up to 25% for higher ranges. Similarly, the costs of the conventional scenario decreased by 7% and increased up to 7% for higher ranges.
Data uncertainty and limited availability typically affects the life cycle assessment results. Figure 8
shows a +10% variation of the LCC and LCA parameters studied in the current research. The figure revealed a correlation of operation of both 3D printed and conventional scenarios. Nevertheless, the construction of conventional system had the greatest environmental impact and greatest cost with the variation.
6. Study Limitations
Based on the conducted structural, environmental, and economic assessments, 3D printing is a viable alternative to conventional construction techniques. However, the findings of this comparative study were limited due to the unavailability of some important data, such as, (1) characteristics of the mortar used in 3D printing process, (2) varying ratios of conventional concrete ingredients, (3) limited number of investigated structural elements, (4) exclusion of sub-structure system and end of life phase, and (5) the common processes and components among the examined alternatives were not included, thus only relative environmental impacts were quantified, (6) inadequacy in 3D printing speicifc processing and (7) data inventory was calculated from diverse sources as a result of lack of data.