Characterization of 3D Printable Geopolymer Mortars (2024-05)¶

In this study, 3D-printable geopolymer mortars were developed, utilizing mine tailings (MT), Class F fly ash (FA), and ground granulated blast furnace slag (GGBFS) as precursors. The precursors were integrated into a binary system, with one consisting of MT and GGBFS (MT/Slag), and the other comprising FA and GGBFS (FA/Slag). Moreover, the mortars were reinforced with basalt fiber (BF) at mass ratios of 0.5% and 1.0% to assess their impact on the fresh and hardened properties. According to the test results, the binder composition and the morphology of the binder significantly impacted the performance of the mortars. In general, the plain MT/Slag mortar exhibited approximately 20% higher workability and 30% higher compressive strength compared to the counterpart FA/Slag mortar. Nevertheless, the FA/Slag mortar outperformed the MT/Slag mortar in terms of buildability, open time, and shape stability. Specifically, the FA/Slag mortar could achieve 14 layers within its 40-minute open time window, whereas the MT/Slag mortar reached 8 layers within a 25-minute open time. Furthermore, the printed MT/Slag mortar showed a shape deformation of approximately 18%, which was notably higher compared to the 4% deformation observed in the FA/Slag mortar. The compressive strength of the FA/Slag mortar exhibited a positive correlation with increasing BF concentration, peaking at 39 MPa with a 1.0% BF content. Conversely, a contrasting trend was noted in the MT/Slag mortars, wherein the compressive strength was reduced to 31 MPa at 1.0% BF. Moreover, the addition of fibers adversely impacted printability, to the extent that the BF-reinforced MT/Slag mortars were unable to be extruded. Based on the findings, the FA/Slag mortar reinforced with 0.5% BF demonstrated the most favorable performance characteristics for 3D printing applications.