Alkali-Activated Binder Requirements for Extrusion and 3d-Printing of Carbon Reinforced Concrete

The development of new building materials with a low CO footprint is the subject of current global research. Continuous and additive manufacturing methods such as extrusion and 3D printing of concrete can be used to produce lightweight and material-minimized components e. g. made of carbon textile reinforced concrete (TRC). For successful use of these manufacturing processes, high demands are placed on the rheological properties in order to ensure formwork-free production. During extrusion, the concrete must be soft enough to be transported by the extruder and stiff enough so that the concrete does not change its geometric shape after leaving the extruder. The requirements for 3D printing are even higher, since a layer structure must also be ensured, which means that the reaction speed of the concrete must be precisely matched to the manufacturing process. In order to develop sustainable concretes for the production of carbon TRC structures, alkali-activated materials (AAM) offer a high potential to substitute the high cement content in concrete. The development of these AAM is much more demanding compared to conventional concretes with cement, as the rheological and hardening properties are strongly dependent on the choice of raw materials and activators. In the investigations performed as part of the CRC/TRR280 project at RWTH Aachen University and TU Dresden, rheological test methods have been developed to predict the suitability of AAM for the manufacturing process. Based on a suitability testing program for AAM, the opportunities and challenges for the use of AAM for extrusion as well as 3D concrete printing are highlighted. Furthermore, an outlook for the construction of carbon TRC structures made of AAM is given.