Formulating printable concrete mixtures based on paste rheology and aggregate content: Application to alkali-activated binders

The printability of concrete mixtures is evaluated for varying aggregate content using binder pastes of different compositions. The inter-relations between the binder paste rheology and the aggregate content are explored for printable concrete mixtures made with pastes of alkali-activated binders and cement. Concrete printability depends on the paste content for coating aggregate and filling spaces between the aggregate. The paste coating thickness around the aggregate under pressurized flow conditions is identified with the boundary layer at the aggregate surface, and it depends on the paste viscosity. Pressurized concrete flow in extrusion-based printing requires excess paste content beyond filling spaces in compacted aggregate with coating layer. There is a linear relationship between the excess paste content in printable concrete mixture and the yield stress of the paste. Printable concrete mixtures made with pastes of higher yield stress require larger excess paste content and accommodate smaller aggregate fractions.