The construction industry has yet to embrace the technological advancements seen in other sectors. Instead, it continues to rely on outdated methods to manage complex modern projects, resulting in high costs and inefficiencies. For instance, in traditional concrete, over 60% of the total cost is spent on formwork and labour. A promising technology that could transform the industry is the 3D printing of concrete. This innovative process builds solid parts layer by layer and has been recognised by the European Parliament as one of the most significant technologies. In addition, the cement industry is responsible for approximately 25% of all CO2 emissions from industry and generates the highest amount of CO2 per dollar of revenue. The production process of Portland cement involves decomposing carbonates, such as limestone and coal, at a high temperature of 1500 °C. It has been reported that every ton of OPC production releases 0.73-0.85 tons of CO2. As a result, CO2 emissions from raw materials and fuel combustion account for 5-7% of global total CO2 emissions. Furthermore, the extraction of construction virgin aggregates, such as sand and gravel, accounts for the majority of global non-metallic mineral consumption (41% gravel and 31% sand), which reached approximately 5 billion tons in 2010. Construction materials' use and impact on CO2 emissions, global warming, and natural resource conservation necessitate critical tools to minimize environmental effects. Therefore, research priorities should focus on employing innovative technological solutions to address specific needs, such as utilising 3D printing of prefabricated building blocks and using recycled construction materials obtained from demolition of buildings. DigiMat has been a collaborative training project for the past 2 years that brought together academia and industry to merge the expertise of diverse disciplines and cutting-edge 3D printing technology. The goal was to create a sustainable cementitious feedstock derived from construction and demolition waste as well as industrial by-products, which could be utilised to produce eco-friendly cast and 3D printed load-bearing building blocks. The main objective of the proposed plan was to develop a diverse collection of alkali-activated cementitious composites that could be used for both traditional and 3D printing construction processes. These materials would be designed explicitly for load-bearing applications that possess exceptional mechanical properties or non-load-bearing applications with superior physical characteristics, such as thermal and sound insulation. The goal of this project was to gain a scientific understanding of the relationship between design, material, process, environmental impact, and the overall quality of the end product. An interdisciplinary approach was taken, employing experimental techniques and trial and error on both micro and macro scales. We have successfully created various alkali-activated cementitious composites which can be 3D printed or conventionally cast. These innovative composites utilise waste materials from industrial by-products, construction and demolition waste, end-of-life plastics, and mining waste, serving as eco-friendly replacements for both ordinary Portland cement and natural sand aggregates in low-carbon concrete. We have identified a diverse array of potential waste resources and crafted tailored mix designs for each material. This marks the inception of a new era for feedstocks in 3D printable objects, characterized by optimised environmental, economic, mechanical, durability, and insulating properties.
