The use of rice husk particles to adjust the rheological properties of 3D printable cementitious composites through water sorption

This work presents an experimental investigation on the use of rice husk fine particles to produce 3D printable cementitious composites. Rice husk was chosen as a potential component for printable composites due to its highwater sorption capacity and its high amount of embodied biogenic carbon. These key features were used to adjust the fresh-state properties of the composites, required for the printing process, while decreasing its environmental impact. In this study, a high-early strength Portland cement was used, and the rice husk content varied from 5 to 15 %, in mass of solids. The hydration kinetics was studied using isothermal calorimetry while the rheology of the composites was evaluated using a viscosimeter equipped with a Vane spindle. The rheological parameters were used to assess the buildability and printability of the concrete mixtures. Results demonstrated that rice husk delays the hydration, but this effect can be mitigated through alkaline treatment of the particles. The rheological tests showed that the water sorption by the particles plays an important role on the fresh properties of the composites. The use of rice husk increased the initial yield stress from 176.5 Pa to 2251.9 Pa, and the structuration rate from 6.03 Pa/min to 23.4 Pa/min, when 15 % of particles were used. Finally, rice husk particles increased the maximum object height and reduced the maximum time between layers, which proved the feasibility of using high water sorption biomass particles to produce 3D printable cementitious composites.