Interlayer bonding properties of 3D printed mortar with three types of inorganic coatings

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