An Eco-Friendly Ultra-High-Performance Geopolymer Concrete with Quaternary Binders for 3D Printing (2024-12)¶

Ultra-high performance geopolymer concrete (UHPGC) offers a sustainable solution for high-shape-flexible structures, while has barely been applied in 3D-printing construction (3DP) due to its challenging issues of high viscosity and low extrudability. This study aims to develop a 3D-printable "one-part" UHPGC (3DP-UHPGC) by using fly ash (FA), ground blast furnace slag (GBFS), steel slag (SS), and silica fume (SF), along with citric acid (CA) as a retarder. A multi-scale investigation was conducted to understand the modification mechanisms of SS, SF and CA on the printability and mechanical properties of 3DP-UHPGC. The results indicated that SS and SF improved the buildability of 3DP-UHPGC by raising the polymerization/hydration rate, and CA prolonged the flowable time and decreased viscosity by complexing with the extra Ca2+ introduced by GBFS and SS, which realized the 3D-printing of UHPGC. The microstructural compactness of UHPGC matrix was densified and the steel fiber-matrix bonding was strengthened by the increasingly formed C-S-H gels and C(N)-A-S-H gels through the pozzolanic reaction and extended geopolymerization between SF and the alkali ions provided by SS. Thanks to the synergistic effect of SS and SF, the 3D-printed UHPGC achieved the highest compressive strength of 123.03 MPa and flexural strength of 17.0 MPa.