Effects of viscosity modifying admixture and nanoclay on fresh and rheo-viscoelastic properties and printability characteristics of cementitious composites

Abstract

This study explores the effects of a viscosity modifying admixture (VMA) and attapulgite nanoclay (ANC) on rheological and viscoelastic properties as well as printability characteristics of mortar mixtures used for 3D printing. A total of sixteen mortar mixtures with varying dosages of VMA and ANC are prepared using a factorial design of experiments. Rheological properties of each mixture including static yield stress, plastic viscosity, and dynamic yield stress are evaluated through rotational rheometry tests such as ramp test and stress growth test. Then, the viscoelastic properties such as storage modulus, loss modulus and linear viscoelastic range are determined using oscillatory rheology tests. A thermogravimetric analysis (TGA) is conducted to assess the effects of VMA and ANC on hydration characteristics of mortar mixtures. A statistical analysis is performed to further evaluate the individual and joint effects of VMA and ANC on key performance parameters. An unsupervised clustering algorithm is used to group the mixtures into three clusters based on the obtained rheological and viscoelastic properties. A direct printing test using a screw type 3D concrete printing is conducted to assess the printability and buildability of the mortar mixtures selected from each cluster. Results indicate that the ANC can more effectively alter both rheological and viscoelastic properties of mortar composites for 3D printing compared with VMA. However, the combined use of VMA and ANC in printable mortar mixtures leads to a high static yield stress and storage modulus and the resulted mixture exhibits good buildability without any plastic collapse.