Research on the mechanical properties and frost resistance of aeolian sand 3D printed mortar

The purpose of this study is to use aeolian sand obtained from Inner Mongolia to partially replace quartz sand as fine aggregate to prepare 3D printed mortar to solve the scarcity problems of quartz sand resources in northwestern China. The mechanical properties tests (including flexural strength, compressive strength, tensile bond strength and axial compression tests) and frost resistance tests of cast specimens and printed mortar specimens in the X, Y and Z directions (abbreviated as CS, PS-X, PS-Y and PS-Z) were investigated. Furthermore, their microscopic morphology and pore structure parameters were compared and analyzed using scanning electron microscopy (SEM) and low field nuclear magnetic resonance (NMR), respectively. The results showed that the flexural strength and compressive strength of the samples following the inclined cross-path were superior to those following the Z-shaped path specimens. The tensile bonding strength of the CS, PS-X, PS-Y and PS-Z exhibited that F-3 > F-3X > F-3Z > F-3Y, and the peak stress was observed as F-4X > F-4 > F-4Z > F-4Y. This was attributed to the cement hydration of CS and PS-X being more sufficient than those of PS-Y and PS-Z. Furthermore, freezing-thawing cycles accelerated the degradation of aeolian sand 3D printed mortar specimens, increased their weight loss rate and porosities, as well as reduced relative dynamic modulus of elasticity. The porosities of specimens were as follows: PS-Y > PS-Z > PS-X > CS, and the porosity of PS-Y was 97.62 %, 36.07 % and 10.67 % higher than those of CS, PS-X and PS-Z, respectively. The significance of this research is to provide technical guidance and basis for the application of aeolian sand in 3D printed mortar in the future.