Effect of Microwave Heating on Inter-Layer Bonding and Build-Ability of Geo-Polymer 3D Concrete Printing

The emerging concept of 3D concrete printing (3DCP) by the laminate stacking of layers without form-work has major issues of poor inter-layer bond adhesion and inadequate build-ability of printed layers. This paper explores microwave heating technique as a set-on-demand method to increase the structuration rate of geo-polymer concrete for 3DCP applications. The microwave heating was applied just before the placement of layers (i.e. at the nozzle head) and the effect of heating duration on the inter-layer bond strength and build-ability were assessed. Moreover, the loss of surface and bulk moisture and the bond strength enhancing mechanism were also investigated. The results demonstrated that the optimum microwaving duration of 10s has increased the inter-layer bond strength by 132%. The inter-layer temperature and surface moisture loss has shown an increasing trend with the heating duration. Despite the increased surface moisture loss with microwave heating, the observed increment in inter-layer bond strength (for up to 10s of heating) was due to the acceleration in poly-condensation reaction between the filaments having adequate stiffness for maximum mechanical interlocking with minimum deformation after stacking. On the other hand, the build-ability of printed filaments, as measured from the rate of particle re-flocculation and structuration, has showed a major improvement. Findings from this study propose incorporating “set-on demand” technique using electromagnetic radiations in construction 3D printing. This initiates a new era of print heads, designed to solve problems faced by current concrete printing industry.