Effect of Water-to-Binder, Aggregate-to-Binder-Ratio and Admixtures on Printability and Mechanical Properties of 3D Printable Mortar Mixtures (2024-12)¶

Formwork free technology such as 3D-printing of concrete improves the project productivity and provides higher geometric flexibility in building design. However, most 3D-printable mixtures are rich in binders which pose shrinkage, economic and sustainability issues. Hence, there is a need to develop 3D-printable mixtures with increased aggregate to binder (a/b) ratio. In this study, the effect of water to binder ratio (w/b), admixtures and increasing a/b ratio (1.0, 1.5 and 2.0) on extrudability, buildability and mechanical properties were investigated. The extrudability was assessed through flow table test and surface characteristics of printed filaments (measured through image analysis) while buildability was assessed through buildable height test, layer slope index test (based on geometrical dimensions of printed object) and unconfined compressive strength test. The increase in w/b ratio of mixtures improved extrudability but reduced buildability. The addition of fly ash was found to be beneficial in improving the extrudability. With increasing a/b ratio, the surface irregularities and extrudability reduced while the buildable height increased. The static yield stress of the extrudable and buildable mixtures, determined through stress growth test, was in the range of 2.1-2.6 kPa. The printed specimens had lower compressive strength than mould cast specimens. The anisotropic index of the printed specimens was less than 0.30 which infers that the printed specimens are not anisotropic in compression. Also, in the considered printing protocol, there were no weak joint formed between 2 successively printed layers. This work is likely to contribute to the development of mixture design guidelines for 3D-printable mixtures.