Concrete 3D printing of lightweight elements using hollow-core extrusion of filaments

This paper investigates an approach of 3D printing lightweight concrete elements using extrusion of hollow-core filaments. Two different filament shapes of rectangular hollow shape and U-shape were printed by using customised nozzles. The primary challenge in hollow-core 3D printing is the extrudability and the stability of the overhang of the filament at fresh state. The stability of the overhang was assessed by determining the viscosity recovery rate and yield strength growth rate of the mix with nanoclay as a thixotropic additive. The mix containing 0.2 wt% of nanoclay has shown good extrudability and enhanced stability of the overhang. The hollow-core 3D printed elements have shown a reduced density of 1369.6 kg/m3 and 1701.7 kg/m3, compared to 2114.1 kg/m3 obtained for solid-core printing. The compressive strength and the Modulus of Rupture (MoR) of hollow-core filaments evaluated at different directions reveal a significant strength loss in perpendicular and lateral directions due to the effective bond area reduction between filaments. The thermal performance of 3D printed panels assessed using simulated test room experiments reports that the hollow-core panels have high thermal inertia due to increased insulation capacity. However, the lack of thermal energy storage has resulted in high indoor temperature in these test rooms.