Bond properties and anisotropy performance of 3D-printed construction and demolition waste-based geopolymers: Effect of operational- and material-oriented parameters

This study investigated the bond performance of printed construction and demolition wastes (CDW)-based geopolymer, providing utilization of CDW in green materials through high tech manufacturing methodologies. Considering the requirements of three-dimensional-additive manufacturing (3D-AM), the effects of operational and material-oriented parameters on mechanical performance were examined by conducting compressive strength, triplet shear, direct tensile, and diagonal tension tests. Anisotropy performance (perpendicular, lateral, and parallel), printing time intervals (0, 15, 30, 60-min.) between two consecutive layers, material aging time (0, 30, 60, 120-min.) of CDW-based materials, manufacturing methodologies (cast, horizontal and vertical-printed) were evaluated on the printed specimen. The study showed that the tests conducted on masonry structures could be used on the 3D-printed structure as well. An anisotropic behavior in the compressive strength results was obtained by observing a decreasing trend in results from perpendicular to parallel and, parallel to lateral loading directions. Increasing printing time interval had a negative influence on the compressive strength of CDW-based geopolymers and anisotropy performance was mitigated in a 60-min printing time interval. Although bond strength decreased with raised printing time intervals, similar bond strength values were recorded for 30-min and 60-min printing time intervals. Similarly, increased material aging time caused decrement in bond strength, yet comparable bond strength was obtained for specimen printed with 60-min and 120-min aged mixture. According to the results, printing time intervals showed more prominent effects on bond strength compared to the material aging time. The test results indicate that vertical-printed specimens demonstrated similar mechanical performance with cast specimens, whereas horizontal-printed specimens exhibited slightly weaker performance compared to those.