Mechanical performance of extrusion-based two-part 3D-printed geopolymer concrete: A review of advances in laboratory and real-scale construction projects

3D printing of geopolymer is considered an alternative to cement-based concrete due to its sustainability and novel manufacturing techniques. Comparisons have been drawn between one-part and two-part 3D-printed geopolymer concrete (OP3DPGPC and TP3DPGPC, respectively). Some articles have projected OP3DPGPC to be user-friendly since it is excited with powdered activators. However, the embodied energy and the carbon emissions of liquid silicate reactants in TP3DPGPC are 70 % and 50 %, respectively, less than the solid silicate used in OP3DPGPC. Also, studies show that TP3DPGPC exhibits superior mechanical performance compared to OP3DPGPC. This study comprehensively reviews the advances in the laboratory-scale and real-scale development of extrusion-based TP3DPGPC, their material composition, constituents’ proportion, and mechanical performance. Data were collected from articles published on TP3DPGPC across renowned journals from 2017 to 2024 and internet sources to identify real-scale TP3DPGPC structures. The mechanical properties of TP3DPGPC available in the literature include compression, flexure, interlayer bond, tensile bond, direct tensile, and splitting tensile strength. These studies show that the mechanical performance of TP3DPGPC depends on the type and proportion of precursor(s), type and composition of the reactants, aggregate type, aggregate-to-binder ratio, activator-to-binder ratio, the molarity of NaOH, SiO₂/Na₂O ratio, water-to-binder ratio, water-to-solid ratio, liquid-to-solid ratio, additive types, fibre (type, content, and aspect ratio), and curing (type and conditions). Similarly, the mechanical performance of TP3DPGPC is dependent on the printer parameters, the configuration, and the loading direction. The data generated will serve as the basis for future studies and the prediction of mechanical performance. Finally, a review of the microstructure properties is conducted to justify the mechanical performance.