Valorization of a low-quality coal ash, in the preparation of alkali activated inks for applications in 3D additive manufacturing

This paper explores the potential of coal ash-based alkali-activated materials (AAM) for additive manufacturing (AM), coal ash with a high loss on ignition, which is traditionally discarded in landfills. This research evaluated the effect of mineral additions such as metakaolin, CaCO3, and glass residues in AAM. The fresh stage properties were examined by extrudability, shape retention factor (SRF), and buildability. In addition, the microstructure was analyzed by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical tests such as compression and flexural strength were conducted on the casted and printed AAM. The AAM optimized was employed to print layer-by-layer directly from Crealty Ender 3 with a ceramic extrusion 3D printer kit. The experimental results found that AAM elaborated with alkali activators based on NaOH/Na-sulfate solutions show the best characteristics to be printed: shape retention of 80%, initial setting time of 125 min, extrusion pressure between 160 and 240 kPa, compressive strength of 12.5 MPa, and 5.2 MPa of flexural strength.