M. J. Yadegari

Agenda 2030 is a plan of action adopted by the United Nations in 2015 to promote sustainable development and address global challenges such as poverty, inequality, and climate change. It includes 17 Sustainable Development Goals (SDGs) that aim to transform the world by 2030 through economic, social, and environmental sustainability [1].

In relation to use of industrial waste and reduce CO₂ emissions, two of the most relevant SDGs are SDG 9 and SDG 12. SDG 9 aims to build resilient infrastructure, promote sustainable industrialization, and foster innovation. The 9.4 target of SDG 9 is to upgrade infrastructure and retrofit industries to make them sustainable with increased resource-use efficiency and greater adoption of clean and environmentally sound technologies and industrial processes. An indicator connected to climate change is CO₂ emissions per unit of value added. SDG 12 aims to ensure sustainable consumption and production patterns. The 12.5 target of SDG 12 is to substantially reduce waste generation through prevention, reduction, recycling, and reuse. An indicator connected to this target is the national recycling rate and tons of material recycled [1].

Additive Manufacturing (AM) is an advanced technique used to produce mechanical and structural components that plays a crucial role in the 4th industrial revolution, also known as the digital industrial transformation. This technology has gained immense popularity in recent years due to its unparalleled advantages that have revolutionized traditional manufacturing methods. AM allows for close to optimal utilization of materials and even enables the use of waste industrial material, leading to a significant reduction in energy consumption and CO₂ emissions [2,3].

The most commonly used material in construction is concrete, which is made from inexpensive and easily accessible raw materials worldwide. Traditional methods of using concrete involve using simple and repeatable formwork to save money. However, scaffolding and molds can be expensive, accounting for half of the cost of concrete construction. Therefore, there has been significant development in additive manufacturing techniques for concrete, which offer many opportunities for cost savings. Concrete AM or 3D concrete printing (3DCP) is more advanced and widely used in construction than metal or polymer printing. So far, concrete AM has been used to construct residential and office buildings, as well as pedestrian bridges (Fig. 1) [4].

Fig. 1. 3d printing concrete structures, up) 2 floors building in Germany and below) pedestrian bridge in China

In a study conducted by Spadea et al. [5], the use of recycled nylon fibers as reinforcement for cement mortars was investigated. The researchers observed an improvement in tensile strength and a transformation from brittle to more ductile failure after reinforcing the mortar with nylon fibers. In another study by Colangelo et al. [6], the environmental impact of geopolymer mortars (alternative binders with low CO2 emissions) production was evaluated. The mixture of fly ash (FA) and ground granulated blast furnace slag (GGBFS) was found to have minimal impact on the environment.

Construction sector contributed to over 35% of total global CO₂ emission [7]. Thanks to Agenda 2030 to promote sustainable development, this research project aims to prepare mortars and concretes using industrial waste, such as fly ash, and low carbon emission binders, like geopolymer. The objective is to develop mixtures for 3DP that have excellent mechanical properties while being sustainable and eco-friendly in terms of CO₂ emissions.

Currently, the most advanced 3DCP technologies rely on extrusion of concrete filaments, although selective binding techniques have also been explored [8,9]. Extrusion-based 3DCP is currently the most extensively researched and utilized large-scale construction technology of its kind. This method involves digitally controlled printers depositing or pressurizing a well-designed cementitious material or concrete through a nozzle that can be shaped to create successive layers following a digitally programmed path based on the structure’s design. After each layer is completed, the nozzle returns to its starting point to print the next layer once the previous one has gained sufficient strength and moisture to bond with the subsequent layer (Fig. 2).

Fig. 2. Different types of 3D concrete printing techniques

It is important to acknowledge that creating intricate concrete structures using 3D concrete printing often requires using a large amount of cement. The mixtures used for printing typically contain more binding agents and fine materials than traditional concrete mixes. In the future, new mixtures with suitable supplementary cementitious materials and additives may be developed to achieve the necessary fast setting time for 3D printing (Fig. 3).

Fig. 3. An illustrative comparison of percentage materials (by volume) used in conventional concrete, self-concrete, and 3D-printable concrete [10].

The use of 3D printing in construction has become more popular in the last decade. Using industrial waste as a supplementary cementitious material (SCM) in traditional concrete is beneficial for sustainability and durability. The utilization of industrial wastes as SCMs is affected by two interrelated factors, namely cost and availability. In the past, fly ash was easily obtainable and inexpensive, but due to the shutdown of coal-fired power plants worldwide, this is no longer always true. On the other hand, slag is less abundant than FA and is not commonly accessible. Fig. 4 shows the availability of conventional and novel SCMs [11].

Fig. 4. Availability of commonly used SCMs. The * indicates that the material can be considered an industrial waste [11].

In 3D printed concrete, industrial waste can improve the extrudability or buildability, depending on the composition and dosage. However, some materials may negatively affect buildability due to their shape and size. Combining suitable waste and chemical admixtures can improve both extrudability and buildability. Recycled aggregates can improve green strength and interlayer bond strength due to their surface texture. Overuse of industrial waste can reduce early strength. Developing high volume SCM concrete will result in even more sustainable 3D printable materials. Structural optimization design strategies can optimize material use compared to traditional concrete structures [11].

Sustainable alternatives such as artificial aggregates and geopolymers are being considered for use. Other viable options for 3D printing concrete include composite cementitious materials, calcium sulfur aluminate, earth-based sustainable materials, binders based on geopolymers, and reactive magnesium oxide cement. It is important to find sustainable materials to reduce reliance on Portland cement, which is responsible for 8% of emissions and can increase material costs while compromising sustainability. While composite cementitious materials like calcinated limestone clay cement offer improved workability, they may have reduced mechanical functionality due to dilution effects. Earth-based binders are a potential sustainable alternative for 3D printing concrete [12].

References

[1]          R. Johnston, “Arsenic and the 2030 Agenda for Sustainable Development,” in Arsenic Research and Global Sustainability – Proceedings of the 6th International Congress on Arsenic in the Environment, AS 2016, 2016, pp. 12–14. doi: 10.1201/b20466-7.

[2]          P. Wu, J. Wang, and X. Wang, “A critical review of the use of 3-D printing in the construction industry,” Autom. Constr., vol. 68, pp. 21–31, 2016, doi: 10.1016/j.autcon.2016.04.005.

[3]          D. Delgado Camacho et al., “Applications of additive manufacturing in the construction industry – A forward-looking review,” Autom. Constr., vol. 89, no. December 2017, pp. 110–119, 2018, doi: 10.1016/j.autcon.2017.12.031.

[4]          C. Buchanan and L. Gardner, “Metal 3D printing in construction: A review of methods, research, applications, opportunities and challenges,” Eng. Struct., vol. 180, pp. 332–348, 2019.

[5]          S. Spadea, I. Farina, A. Carrafiello, and F. Fraternali, “Recycled nylon fibers as cement mortar reinforcement,” Constr. Build. Mater., vol. 80, pp. 200–209, 2015, doi: 10.1016/j.conbuildmat.2015.01.075.

[6]          F. Colangelo, I. Farina, M. Travaglioni, C. Salzano, R. Cioffi, and A. Petrillo, “Eco-efficient industrial waste recycling for the manufacturing of fibre reinforced innovative geopolymer mortars: Integrated waste management and green product development through LCA,” J. Clean. Prod., vol. 312, no. March, p. 127777, 2021, doi: 10.1016/j.jclepro.2021.127777.

[7]          L. Huang, G. Krigsvoll, F. Johansen, Y. Liu, and X. Zhang, “Carbon emission of global construction sector,” Renew. Sustain. Energy Rev., vol. 81, no. June, pp. 1906–1916, 2018, doi: 10.1016/j.rser.2017.06.001.

[8]          G. H. Ahmed, “A review of ‘3D concrete printing’: Materials and process characterization, economic considerations and environmental sustainability,” J. Build. Eng., vol. 66, no. January, 2023, doi: 10.1016/j.jobe.2023.105863.

[9]          P. Shakor, S. H. Chu, A. Puzatova, and E. Dini, “Review of binder jetting 3D printing in the construction industry,” Prog. Addit. Manuf., vol. 7, no. 4, pp. 643–669, 2022, doi: 10.1007/s40964-021-00252-9.

[10]        A. U. Rehman and J.-H. Kim, 3D Concrete Printing: A Systematic Review of Rheology, vol. 14, no. 14. 2021.

[11]        D. Dey, D. Srinivas, B. Panda, P. Suraneni, and T. G. Sitharam, “Use of industrial waste materials for 3D printing of sustainable concrete: A review,” Journal of Cleaner Production, vol. 340, no. February. 2022. doi: 10.1016/j.jclepro.2022.130749.

[12]        N. Singh, F. Colangelo, and I. Farina, “Sustainable Non-Conventional Concrete 3D Printing—A Review,” Sustainability, vol. 15, no. 13, 2023, doi: 10.3390/su151310121.