Study on Preparation and Rheological Properties of 3D Printed Pre-Foaming Concrete

Abstract

The high fluidity and low yield stress of fresh foam concrete affect the shape stability and buildability of foam concrete in the printing process, which is quite a challenge to its application in digital construction. Therefore, this article proposes the preparation and characteristics of 3D printed pre-foaming concrete (3DFC). The rheological properties proved that the addition of 0.1 wt.% Hydroxypropyl methyl cellulose (HPMC) to 3DFCs weakens the fluidity but increases the static yield stress and apparent viscosity, thus enhancing the buildability. More importantly, the influences of surfactant on the rheological property, compressive strength, pore structure and thermal conductivity of 3DFCs were evaluated. Analysis results show that the static yield stress of 3DFCs decreases from 1735 to 687 Pa with surfactant dosage from 0 to 2 wt.%. Moreover, the addition of surfactant significantly reduced the apparent viscosity of 3DFCs (especially at low shear rates), but its viscosity recovery rate was basically unchanged, which is good for buildability. Thanks to the increase of porosity, the volume density of 3DFCs decreased from 2211 to 1159 kg/m3, but the compressive strength of 3DFCs also decreased slightly. The thermal conductivity of 3DFCs shows good thermal insulation performance in the range of 0.2254–0.2879 W/m·K, which is also due to the increase in porosity of 3DFCs. Finally, in order to verify the practical application value of 3DFCs, an industrial printing product with more than 30 layers during the field application is displayed.