Development of Cementitious Mortars for Aerial Additive Manufacturing

Abstract

Additive Manufacturing (AM) methods in the construction industry typically employ ground-based deposition methods. An alternative to transform the role of AM in construction is to introduce an aerial capability. A recent project titled Aerial Additive Manufacturing (AAM), the first AM system to use untethered, unmanned aerial vehicles (or ‘drones’), has demonstrated the 3D-printing of cementitious materials during flight. An autonomous aerial system would minimise requirements for working at height, thus reducing safety risks and release AM from ground-based constraints. This study investigates viscous cementitious mortars for AAM. To assess workability and buildability, a robotic arm representing UAV movement in three-dimensional space moved a lightweight deposition device to extrude multiple layers. Constituents such as Pulverised Fuel-Ash, Silica fume, polyol resin, limeX70 and Polypropylene fibres were added to cement-based material mixes. Sand:binder ratios were a maximum of 1.00 and Water:binder ratios ranged from 0.33–0.47. Workability and buildability of mixes were evaluated using performance parameters such as power required for extrusion, number of layers successfully extruded, the extent of deformation of extruded layers and evaluation of mechanical and rheological properties. Rheology tests revealed mortars with a suitable workability-buildability balance possessed a Complex modulus of 3–6 MPa. Mechanical tests showed that resistance to deformation and buildability positively correlate and indicate compressive strengths in excess of 25 MPa. This study has demonstrated that structural cementitious material can be processed by a device light enough to be carried by a UAV to produce an unsupported, coherent multiple-layered object and further demonstrated the feasibility of untethered AAM as an alternative to ground-based AM applications in construction.