Use of Waste Materials to Reduce Cement and Natural Aggregates in 3D Printing Mortars

3D printing (3DP) is an example of a sustainable technology capable of replacing traditional manufacturing processes. One of its advantages is the use of optimized production processes, even for customized products, as well as the almost non-existence of waste. 3DP mortars (3DPM), therefore, rely heavily on Portland cement (PC), a material with high carbon emissions and energy consumption related to its manufacture. In order to comply with the growing environmental regulations and concerns, it is imperative that its use becomes more moderate and, as such, alternatives to PC or additives to reduce its percentage are being sought. At the Faculty of Engineering of University of Porto, research has been conducted to produce 3DPM with different waste materials. This study has the following objectives: (i) reduce PC by adding sugarcane bagasse ash (SCBA), with a strong emphasis on performance; (ii) substitute natural sand with recycled brick sand (RBS), aiming at replacing a natural aggregate while exploring new aesthetic possibilities. As to assess their viability as 3DPM, several mortars with different amounts of SCBA and RBS were formulated, taking into account some of its fresh and hardened properties as well as exploring different colours and textures. In the end, the best compositions were printed using material extrusion equipment.