Use of Ultralow Dosages of Graphene to Enhance the Microstructural and Mechanical Properties of 3D-Printed Cementitious Mortars

Abstract Three-dimensional (3D) concrete printing offers an economical and sustainable option for rapid, formwork-free construction of geometrically unique structures. However, 3D-printed concrete elements often suffer from print-induced anisotropy and reduced mechanical performance. This study investigates the use of two novel graphene derivatives—fractal graphene (FG) and reactive graphene (RG)—as multifunctional nano-modifiers to overcome the aforementioned limitations associated with 3D-printed concrete. The influence of ultralow dosages (0.02% by mass of binder) of FG and RG on early-age heat release in graphene-modified pastes and the porosity and direction-dependent mechanical properties of 3D-printed elements are reported. FG and RG accelerate early hydration kinetics, with RG inducing a more pronounced shift in the acceleration peak due to its functionalized surfaces. Significant reductions in total porosity and critical pore diameter are noticed. Enhancements of up to 25% in compressive and flexural strengths are observed. The anisotropy in compressive strength is shown to be reduced by up to 50% through the use of FG or RG, indicating improved structural homogeneity. The graphene-modified specimens also exhibit enhanced strain capacity and improved crack-bridging behavior. These findings demonstrate the ability of ultralow dosages of FG and RG to simultaneously enhance hydration, refine microstructure, and improve mechanical properties of 3D-printed cementitious materials.