Emmanuel Keita
Navier Laboratory / University Gustave Eiffel, France
Title:
No formwork, no protection: from early-age drying to curing in 3D printed concrete
Abstract:
In extrusion-based 3D concrete printing, there is no formwork: each deposited filament is exposed to the atmosphere as soon as it leaves the nozzle. With surface-to-volume ratios one to two orders of magnitude higher than in cast elements and high paste volumes, printed materials are intrinsically vulnerable to early-age drying.
This lecture proposes a unified physical framework in which the competition between the evaporative flux at the surface and the capillary supply from the bulk governs the drying regime and the build-up of capillary pressure, hence shrinkage. Recent full-field and in-situ measurement techniques now make it possible to follow this chain from water loss to strain localization. Cracking itself remains less understood, although observations suggest a transition from surface cracklets in the fresh material to propagating macro-cracks as stiffness develops. The effects of early-age drying persist in the hardened state, in particular at the interlayer interface.
Mitigation strategies are then discussed, from evaporation control to crack control. The main message is that curing should be designed into the printing process from the outset, not applied once damage has appeared.
Bio:
Emmanuel Keita is a research director at Laboratoire Navier (CNRS, Université Gustave Eiffel, École des Ponts, Institut Polytechnique de Paris), France. Trained as a physicist, he received his PhD from École des Ponts in 2014 on the drying of porous media and colloidal suspensions.
His research addresses the interactions between construction materials and water: evaporation, imbibition, and the transport of particles and ions in porous media, investigated with imaging techniques such as MRI and X-ray microtomography. He applies this physics-based approach to digital fabrication, in particular early-age drying and cracking in 3D concrete printing, and to earth-based materials.
He chairs a RILEM Technical Committee on the processing of earth-based materials (320-PEM).