Impact of Very Early Age Drying on Printed Concrete Microstructures

In this work, the microstructure of concrete elements printed in an industrial printing facility is assessed using Scanning Electron Microscopy (SEM), Mercury Intrusion Porosimetry (MIP) and X-ray micro-tomography. All printing parameters and curing conditions are chosen to create extreme and detrimental printing conditions in an industrial production factory.
The studied elements are printed in various exposure conditions in terms of external desiccation. In our measurements, we make a distinction between the microstructural modifications of the interface between layers, which may be at the origin of preferred propagation paths for ionic species in the liquid phase, and the microstructural modifications of the bulk material linked to the absence of a protective mold.
Our results suggest that material drying on time scales between tens of minutes and couple hours drives the changes in the material microstructure, porosity and pore size distribution. Many features are similar to the ones typically observed for the well-known self-desiccation of hydrating cement-based materials. The ones observed here are however fully driven by the water exchange with the environment and happen before hydration starts to leave the induction period.