Construction and demolition waste-based geopolymers suited for use in 3-dimensional additive manufacturing

This paper focuses on the evaluation of ambient-cured 100% construction and demolition waste (CDW)-based geopolymers in terms of rheological properties for 3-dimensional additive manufacturing (3D-AM). The CDWbased precursors used for geopolymer production were hollow brick (HB), red clay brick (RCB), roof tile (RT) and glass (G) activated by different combinations of sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2) and sodium silicate (Na2SiO3). Rheological properties were evaluated via empirical tests such as flow table, vane shear test, modified mini-slump test and compressive strength test for mechanical characterization. Based on these results, the extrudability performance of selected CDW-based geopolymer mixtures was analyzed with a ram extruder, and finally, a single mixture was selected to be used in laboratory-scale 3D-printing. The geopolymer mixture activated by 6.25 M NaOH and 10%-Ca(OH)2 exhibited the best performance in terms of rheology and compressive strength, and it was therefore selected for use in laboratory-scale 3D-printing. 3D-AM application at the laboratory scale showed that ambient-cured 100% CDW-based geopolymers can be successfully used for 3D-printing, with adequate rheological and mechanical properties and without any additional chemical admixtures, and that the empirical test methods used are effective in assessing the suitability of CDWbased geopolymers for 3D-AM applications. The outcomes of this work are believed to contribute to the current literature significantly, as they combine the advantages of green material development, waste upcycling, reduced raw materials and easy/fast/accurate producibility.