Rheological properties and compressive strength of construction and demolition waste-based geopolymer mortars for 3D-Printing

Abstract

Entirely construction and demolition waste (CDW)-based ambient-cured geopolymer mortars with rheological properties fitted for 3-dimensional additive manufacturing (3D-AM) were developed in an effort to combine the advantages of improved waste minimization, development of green materials and easy/fast/accurate materials production/processing. CDW-based hollow brick (HB), red clay brick (RCB), roof tile (RT), concrete rubble (C), and glass (G) were used for the development of geopolymer binders while C was used solely as fine aggregates. Mixtures were activated by different combinations of sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2), and sodium silicate (Na2SiO3) as the alkaline activators. Rheological assessments were made based on the empirical test methods including flow table, vane shear and modified mini-slump tests. Compressive strength measurements were also made. Finally, two representative mortar mixtures with low and high viscosity were printed via a laboratory-scale 3D printer and the rheological properties were correlated with printing behavior of geopolymer mortars. Overall, the study showed that entirely CDW-based geopolymer mortars without any chemical admixtures having suitable rheological properties for 3D-AM can be manufactured successfully. The empirical test methods utilized are adequate in determining the rheological properties of CDW-based geopolymer mortars suited for use in 3D-AM. The designed entirely CDW-based geopolymer mortars with adequate compressive strengths were shown to be capable of extrusion via 3D-AM free of any defects/discontinuity, capable of maintaining its initial shape under the effect of the weight of consecutive upper layers and fully matched with the designed printed structure.