Mix suitable for concrete 3D printing: A review

The potential application of 3D printing technology is envisioned to create a third industrial revolution creating disruption in the economy, providing personalization and adaptation of the design. The construction field is quickly catching up with this new technology using the aid of a concrete 3D printer, the development of which is aimed at providing safer working conditions, economy and architectural freedom. The process of extrusion-based concrete printing requires the printable mix to flow through the distribution network and be deposited layer-by-layer on the build substrate or directly on-site analogous to the ink-jet printing process. In this case, for the mix to be printable, it should be capable of being pumped, extruded and deposited in layers within an optimized duration of time. The printing time-gap between layers is complicated by the scale and complexity of the geometry. The rheological behavior of the fresh mix will have a significant influence on the ability of the mix to be pumped and extruded while the mechanical response of the fresh concrete will influence the ability of the concrete printer to build layers with bonded interfaces. The design mixes are formulated to provide the maximum compressive and tensile strengths to the printed specimen which are influenced by the print parameters like time gap between layers, size of the nozzle in relation to the aggregate size. This paper aims at reviewing the concrete-mixes including fiber-reinforced, Geopolymer mixes suitable for the 3D printing process looking at both the fresh and hardened properties of the mix while simultaneously shedding light on appropriate printing parameters. The strategies used by researchers, in selecting appropriate material mix to tune the fresh properties of concrete and to improve the interfacial bond strength are discussed. Recommendations are provided to improve the quality of 3D printing process. (C) 2019 Elsevier Ltd. All rights reserved.