Investigating the Poisson Ratio of 3D Printed Concrete

Poisson’s ratio, defining the lateral to longitudinal strain of a material under uniaxial load, is an extensively used material property in engineering analysis and design. For conventionally cast concrete, an isotropic static Poisson ratio typically ranges between 0.15 to 0.25. However, no ratio has been established for 3D printed concrete, and is currently widely assumed to be 0.2 and isotropic in computational modelling applications. This layer-wise additive manufacturing technology is notorious for yielding orthotropic mechanical properties due to the presence of weak interlayer regions at the structural level and elongated oblate voids at the material level. This study therefore aims to characterise the static Poisson ratio of printed concrete. Specimens were prepared from a printed element and uniaxially tested both parallel and perpendicular to the printing direction. Digital image correlation technology was employed to facilitate the capturing of specimen strains, followed by micro-computed tomography scans to determine void topography. The results indicate larger Poisson ratios apply for 3D printed concrete compared to its cast counterpart; up to 17 and 33% increases were obtained when printed specimens were tested perpendicular and parallel to the printing direction, respectively. This orthotropic behaviour is ascribed to the oblate voids present in the printed specimens.