This study explores the use of commonly utilized materials (sulphoaluminate cement, fly ash, expanding agent) in the creation of three inorganic coatings (C-coating, F-coating, E-coating) to improve the interlayer bonding properties of 3D printed mortar. The mechanical properties of mortar with/without coating were characterized by compressive test and flexural test. The bonding properties of the coatings were assessed through splitting tests and micron indentation tests. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the characteristics of hydration products and pore structure. The findings demonstrate that both F-coating and E-coating significantly enhance the mechanical properties of 3D printed mortar. Specifically, F-coating led to a 42% increase in flexural strength and a 71% increase in bond strength. The XRD and SEM analyses revealed that the fly ash contained in F-coating has a pozzolanic effect by reducing the content of Ca(OH)2 (CH), promoting the formation of calcium silicate hydrate (C-S-H) gel, and enhancing microscopic morphology. The expansion agent contained in the E-coating could significantly increase the content of AFt, and the needle-like AFt plays a good bonding performance between the interfaces. In this manuscript, two kinds of cheap and easy-to-obtain interlayer coatings for 3D printing mortar are found.
Keywords:
3D printed mortar; weakness zone; inorganic coating; interlayer bonding properties