Cement is very widely used concrete raw material due to its easy availability, good usability and because of its low price. In 2019, cement production was estimated to reach 4.2 billion tonnes whose environmental impact is large: about 4-8% worldwide carbon dioxide emissions. Therefore, low carbon alternatives for cement industry are actively sought after. The industrial side streams of process and mining industry such as ash, slag and tailings, offer an enormous and heavily underutilised local low carbon secondary raw material source In a 3 year project “Urban Infra Revolution” (2017-2020) funded by EU initiative Urban Innovative Actions, we developed local industrial side stream based 3D printable geopolymer composites for the use in urban infrastructures. During the project more than 20 industrial side streams were characterised and necessary pretreatment processes were developed for them. Five different geopolymer composite recipes where the circular material content varied between 68 to 99.6 %, were developed. Their mechanical properties were comparable to those of ordinary cement. It was seen that the environmental impact of geopolymer composites was highly recipe dependant and thus, the Global Warming Potential of different recipes varied between +40 to -98 %. The higher impact was mainly due to the activator used in the geopolymer composite recipe. As a pilot product a 100 m long noise wall was built out of 3D printed geopolymer composite elements in Lappeenranta, Finland. The 3D printable geopolymer composites offer a low carbon alternative option for applications where fast setting time and free form are a value adding factor, and where unnecessarily landfilled local secondary raw materials are available thus promoting transformation into circular economy.
 

side streams, circular economy, cement industry, 3D printing