Additive Manufacturing of Anisotropic Concrete (2020-04)¶

For the tens past years, important development has been achieved on the adaptation of additive manufacturing to the construction industry using concrete. They mostly concerns control rheology at fresh state, setting time, and technology advances. Nevertheless, the reinforcement of 3D printed part remains an open question. Different reinforcement protocols have been proposed in the literature, often based on traditional way of reinforcement. In this context, the aim of this paper is to present an alternative way to reinforce extruded concrete or other pasty materials inspired by the composite industry. The present patented manufacturing methodology is based on extrusion-based additive manufacturing, inspired by pultrusion and co-extrusion process of polymer composites, but taking full advantage of the specific rheological behaviour of cementitious matrix. It consists in the continuous addition of numerous continuous yarn in the extruded mortar before the final extrusion. A comparison between those processes is made. Depending on the number of yarns and their sizes, this process is showed to provide ductility for limited amount of reinforcement and have the potential to be an alternative to passive rebar traditionally used in concrete by providing a true reinforcement in traction to the structure for larger number of yarns, changing extruded concrete in unidirectional composite with brittle matrix. Using appropriate matrix formulation, the mastering of its yield stress during the extrusion is showed to be the most important process parameters.