Effect of microwave heating under varying exposure conditions on rheological properties, interlayer bond and buildability performance of 3D-printed geopolymer

This study investigates the novel application of microwave heating to optimize the rheology, interlayer bond, and buildability of 3D-printed geopolymers at various printing stages. Unlike conventional methods, microwave heating significantly enhances stacking performance (buildability) while reducing flowability, addressing critical challenges in 3D printing. The findings also indicate that deformation resistance coefficients for fiber-free and fiber-reinforced geopolymers reaches 0.933–1.00 after 30 and 45 seconds of microwave exposure, respectively, demonstrating superior shape retention ability after microwave heating. Notably, microwave heating improves ultra-early (i.e., 2 h and 4 h) interfacial strength proportionally to power and duration, offering a breakthrough for rapid construction. In addition, drying shrinkage decreases by 0.096–0.226 % (fiber-free), 0.054–0.166 % (PE fiber), and 0.067–0.17 % (steel fiber), highlighting the efficacy of microwave heating in mitigating cracking of 3D-printed geopolymers. The optimized microwave processing parameters establish in this study serve as a foundation for in-line, large-scale 3D printing applications, offering a scalable solution in printability and structural integrity.