Rheological and pumping behaviour of 3D printable cementitious materials with varying aggregate content

3D printing with cementitious materials is an emerging technology and provides an active area of research. Despite this, there are only limited studies that examine the pumping behaviour of high yield stress fluids such as printable concrete. We present a study on the rheological behaviour of 3D printable cementitious materials with different aggregate-to-binder ratios (a/b) and analyse the pumping and printing characteristics with the measured rheological parameters. We observed that an increase in a/b resulted in a significant increase of plastic viscosity, and a nominal increase in yield stress and storage modulus. The variation in plastic viscosity and yield stress with increasing aggregate content was analysed with the Krieger-Dougherty and Chateau-Ovarlez-Trung model, respectively. Also, the rheological properties of the paste rich lubrication layer during pumping were determined with the help of a tribometer. The yield stress and viscous constant of the lubrication layer increase with the increase in a/b. The pumping pressure predictions were carried out by a suitable theoretical model by considering appropriate flow conditions for different mixtures. The variation in critical height of printed elements with an increase in a/b was correlated with the observed rheological parameters.