Robust Optimization of Formulation Ratios for the Mechanical, Microstructural and Printing Performance of Cost-Effective 3D Printing Geopolymer (2025-07)¶

The current study conducted a two-stage analysis to examine the impact of different formulation ratios on the characteristics of 3D printing geopolymer (3DP geopolymer). During stage I, the influence of SiO2/Al2O3, and H2O/Na2O molar ratios on the mechanical and 3D printing performance of 3DP geopolymer made with fly ash (FA), and ground granulated blast furnace slag (GGBFS) was examined and optimized using Response Surface Methodology (RSM). With the optimized formulation ratios obtained in stage I, steel fibers were used in stage II to further improve the mechanical performance of 3DP geopolymer. The results of stage I indicated SiO2/Al2O3 and H2O/Na2O ratios had a significant impact on both compressive strength (CS) and shape retention coefficient (SRC). The optimal mix proportion of 70% FA and 30% GGBFS, with molar ratios of SiO2/Al2O3 = 3.22 and H2O/Na2O = 24, achieved CS of 40.1 MPa at 7 days and 42.13 MPa at 28 days, with a SRC of 0.892. The results of stage II suggested that adding 0.5% steel fibers had the highest CS, while adding 0.1% steel fibers provided the best flexural resistance. The combined strength index (CSI) and the cost-effectiveness index (CEI) were further defined and found that adding 0.5% steel fibers was optimal for 3DP geopolymer mortar, offering a 53.6% and 23.25% increase in CS and FS at 28 days over the control mix while maintaining the cost-effectiveness. These findings can be helpful in the fine-tuning of formulations ratios for the development of cost-effective steel fiber-reinforced 3DP geopolymer mortar in future construction projects.