An approach to develop printable strain hardening cementitious composites

TLDR

Additive manufacturing of cementitious materials promises greater construction automation, but requires new materials that meet process‑specific performance criteria and whose characterization methods remain debated. The study aims to develop a printable strain‑hardening cementitious composite mix design through a systematic rheology investigation. The authors used two existing mixtures, varied water‑to‑solid ratio, fibre volume, and chemical admixtures, measured rheology with a ram extruder and Benbow‑Bridgwater equation, correlated bulk and shear yield stresses with printing quality, and confirmed strain‑hardening behavior via four‑point bending, tensile, and compressive tests. Printing trials showed that bulk and shear yield stresses correlate with printing quality, enabling prediction of supported layer count, and the framework demonstrates that bulk yield stress predicts buildability while shear yield stress indicates a pumpability threshold.

Abstract

New additive manufacturing methods for cementitious materials hold a high potential to increase automation in the construction industry. However, these methods require new materials to be developed that meet performance requirements related to specific characteristics of the manufacturing process. The appropriate characterization methods of these materials are still a matter of debate. This study proposes a rheology investigation to systematically develop a printable strain hardening cementitious composite mix design. Two known mixtures were employed and the influence of several parameters, such as the water-to-solid ratio, fibre volume percentage and employment of chemical admixtures, were investigated using a ram extruder and Benbow-Bridgwater equation. Through printing trials, rheology parameters as the initial bulk and shear yield stress were correlated with variables commonly employed to assess printing quality of cementitious materials. The rheology properties measured were used to predict the number of layers a developed mixture could support. Selected mixtures had their mechanical performance assessed through four-point bending, uni-axial tensile and compressive strength tests, to confirm that strain hardening behaviour was obtained. It was concluded that the presented experimental and theoretical framework are promising tools, as the bulk yield stress seems to predict buildability, while shear yield stress may indicate a threshold for pumpability.