Understanding and mitigating plastic shrinkage in 3D-printed concrete elements

In recent years, 3D concrete printing (3DCP) has evolved from a bold vision to a promising construction technique. 3DCP offers multiple advantages in cost savings, increased productivity and design freedom. However, alongside its promise, the 3D printing of concrete elements and structures brings substantial challenges. One among them is the early-age cracking of printed concrete elements due to shrinkage-induced deformations. Damages caused by plastic shrinkage and related cracking can severely compromise the durability, serviceability, aesthetics and structural stability of 3D-printed concrete elements. The ability to control and mitigate plastic shrinkage and related cracking is an unavoidable step towards the wide application of 3D-printing technology in the construction practice. This dissertation focuses on the mechanisms of plastic shrinkage, related cracking of 3D-printed concrete elements, and studying appropriate mitigating approaches. Affordable and easy-to-apply experimental setups were developed for measuring unrestrained and restrained shrinkage-induced deformations and relevant material properties of 3D-printed concretes. The findings of this study contribute to establishing a unified testing framework for studying the shrinkage and related cracking of 3D printable concretes. Based on the developed experimental methodology, specifics of the mechanisms involved in the plastic shrinkage and related cracking of the 3D-printed elements were studied. The numerical simulation of the evolution of capillary pressure in 3D-printed elements supplemented experimental investigations. Special attention was paid to the analysis of the effect of the layer width and the influence of the surface area exposed to desiccation on the extent of the plastic shrinkage and cracking in 3D-printed concrete elements. Also, the deformation behaviour of 3D-printed concrete elements due to shrinkage-induced stresses is analysed. Finally, various approaches for mitigating plastic shrinkage and cracking are examined, and practical solutions for reducing the damages caused by shrinkage-induced deformations are suggested.