Rheological and mechanical properties of 3D printable alkali-activated slag mixtures with addition of nano clay

Abstract

Alkali-activated slag mixture (AAS) is seen as a prospective option to replace Portland cement for three-dimensional (3D) printing to reduce carbon emission. This paper investigates the use of nano clay and adjusting SiO2/Na2O (Ms value) of an alkaline solution to meet the demands for the additive manufacturing process, such as pumpability and buildability. Results showed that the use of nano clay can considerably improve the structural build-up of AAS mixtures. The dynamic and static yield stress of AAS mixtures declined as Ms value of the activator increased. In terms of mechanical properties, the compressive strength increased with an increase of Ms value, while the flexural strength decreased slightly as Ms value increased. A higher Ms value can result in a lower porosity, but more micro-cracks. The mixture with Ms value of 0.8 and 1% nano clay addition was found to be the most suitable for 3D printing as it had greater buildability during printing with less bottom deformation, and had higher strength and lower porosity in the later stages. The main reaction product for the AAS mixture is found to be the C-A-S-H gel with a chain-like structure.