Optimizing cement-based material formulation for 3D printing: Integrating carbon nanotubes and silica fume

This study aims to determine the optimal mix designs of cementitious composites and compare various properties by adding carbon nanotubes (CNTs) and silica fume to the 3D printing system. Adding 0.2 % CNTs and 20 % silica fume in the mixture significantly improved printing quality, buildability, open-time, and rheology. Compared to the control mix, the layer's width and height error reduced from 140 % and 6 % to less than 1.5 %, while buildability and open-time increased by 210 % and 263 %, respectively. Furthermore, the compressive and flexural strengths were enhanced with the addition of CNTs and silica fume for both cast and 3D-printed samples. Specifically, at 28 days, the compressive and flexural strengths of 3D-printed samples increased by 78 % and 498 %, respectively, compared to the control mix. The compressive strength of 3D-printed samples was lower than that of cast samples. However, at later ages, the variation was reduced to less than 2 % with the addition of 0.2 % CNTs and 20 % silica fume. On the other hand, 3D-printed beams showed 8 % higher flexural strength than cast beams. Microstructural examination revealed that the addition of silica fume fills gaps in the cement matrix. Moreover, CNTs act as nanoscale linkages within the cement matrix, resulting in enhancements in the buildability and mechanical characteristics of 3D-printed cement-based materials.