Effect of Vibration on the Rheology of Concrete for 3D Printing

A primary challenge in concrete 3D printing is the need for low yield stress for good flow through the printer and high yield stress for sustaining the self-weight and the weight of subsequent layers. The current 3D printable concrete mixture designs make limited use of aggregates. Aggregates could significantly increase the yield stress of concrete mixtures but are not used since they impede the flow of concrete through a nozzle. A novel idea is presented in this work where vibration is used to control the rheology of concrete. By including coarse aggregate, a high yield stress concrete mixture can be obtained which when vibrated loses its yield stress instantly. Granular suspensions like concrete recover their yield stress immediately after the vibration ceases. The effect of vibration on the yield stress of concrete with varying aggregate content and packing fraction is also described. It is shown that the yield stress of concrete is significantly greater than that of cement mortar and paste and this high yield stress is lost when the concrete is vibrated.