Method of enhancing interlayer bond strength in 3D concrete printing

Abstract

Additive manufacturing is predicted to revolutionize the way in which we construct our cities and structures. These technologies can create a big potential for freeform design whilst also providing reductions in cost, materials wastage and workplace injuries. 3D concrete printing (3DCP) is one technique that is being investigated. Although many benefits are evident, there are many technological issues that have yet to be explored, particularly that of the bonding strength in extrusion based 3DCP. Extrusion based 3DCP works on a layer by layer deposition of a stiff cementitious mix, forming a material interface. This interface essentially becomes a position of weakness, forming a weak bond. Currently the interlayer bond is assumed to be related to either mechanical anchorage effects or chemical hydration effects. This paper hypothesis that the mechanical effects are predominant and to prove the hypothesis presents a series of experiments that were carried out to analyse and enhance the bond at this interface. The methodology employed in this study will focus on applying a cement paste to the top of an extruded substrate layer before the secondary layer is deposited. We demonstrated that the application of a paste at the interlayer does show an increase in bond strength. The greatest bond strength was found in pastes mixed with additives to sustain flow characteristics, over a time gap. The increase in contact area on both layers is now verified to be a crucial factor in bond strength development.