Influence of Multi-Walled Nanotubes on the Fresh and Hardened Properties of a 3D Printing PVA Mortar Ink (2020-03)¶

3D printing concrete has been accepted as a promising construction material which can realise formless construction and digital design. The fresh properties and the hardened strength of concrete ink are crucial for structural applications. In this study, different volume fractions of multi-walled carbon nanotubes (MWCNTs) were added to a 3D printing PVA fibre-reinforced mortar ink to modify its mechanical properties. To evaluate the effect ofMWCNTs on the workability of 3D printing mortar, the buildability, shape stability, flowability and setting time of fresh mortar were tested. The improvement efficiency of MWCNTs on the mechanical properties of 3D printing PVA mortar ink was also experimentally studied. The test results indicate that a small amount of MWCNTs has almost no effect on the ink’s workability. The early age compressive and flexural strength of printing mortars with MWCNTs can be effectively improved, which benefits the requirements of 3D printing. The 3-d compressive strength of mortar with addition of 0.1 wt% of MWCNTs can be enhanced by 33.6%, while the 28-d strength was hardly affected. Agglomeration and poor dispersion of MWCNTs can generally be detected by SEM images as volume content of carbon nanotubes increases. Considering the influence of MWCNTs on the fresh and hardened properties of mortar and on the requirements of 3D printing, the optimum volume fraction of carbon nanotubes for 3D printing PVA fibre-reinforced mortar should be 0.02–0.05 wt%.