Multi-physics modelling of 3D-printed concrete evolution in environmental conditions

Extrusion-based 3D-printed cementitious structures have high water loss after printing provoking significant plastic shrinkage. In this study, we propose a thermo-poro-mechanical model of printed cementitious materials, driven by the experimental observation of a positive correlation between the printed wall thickness and compressive strength at the hardened state. The model is developed to represent evaporation at free surfaces, water consumption associated to the cement hydration and water flow within the material, accounting for their effect on temperature variations, strains and on the evolution of stiffness and compressive strength. Comparisons of compressive strength and plastic shrinkage with experiments are presented, demonstrating the validity of the proposed model. In the absence of protective measures, wall thickness is positively correlated with compressive strength and negatively correlated with shrinkage. When preventing evaporation by putting printed specimens in water, plastic shrinkage is significantly reduced and the compressive strength is increased, reaching similar values as cast samples.