Fabrice Toussaint

Estimating Measurement Artifacts in Concrete Rheometers from MRI Measurement on Model Materials

Measurement artifacts in concrete or mortar rheometers often prevent the user from having access to absolute correct values of the rheological parameters of the tested material. As there does not exist any rheometer giving access to the “correct” or “real” values of these parameters, it is even not possible to estimate the order of magnitude of the error induced by these artifacts. It is however possible to have access to the local and real rheological behavior law by measuring local velocities and local concentrations of particles through Magnetic Resonance Imaging (MRI) techniques. In this paper, we compare macroscopic measurements and local MRI measurements of the behavior of suspensions of natural sand particles and bi-disperse spherical particles in model yield stress fluids (emulsions). In doing so, we seek to illustrate the potential consequences of artifacts on the measurements of the flow curve of cementitious materials. We reach the conclusions that particle migration is at the origin of the discrepancy between concrete rheometers.

Experience in Online Modification of Rheology and Strength Acquisition of 3D Printable Mortars

This study focus on the early age properties of two mortar formulations designed for a 3D printing extrusion process. They follow a new design and process strategy, which consists in formulating a mortar to be self-levelling, to optimize pumpability, and then incorporating an additive in the extrusion nozzle to modify rheology properties and setting properties to adapt it to the requirement of the printing process (self-sustaining as soon as the material exits the nozzle, and fast strength acquisition). Two types of additives are considered: an alkali-free shotcrete accelerator and a starch ether based VMA. Compression and shear strength measurements from 2 min to 4 h after the incorporation of the additive demonstrate the capacity of the method to create mortars with strength acquisition vastly superior to results from the literature. Lab-scale extrusion and operational feedback from 3D printing customers demonstrate the feasibility at operational scale. The variety of properties obtainable by playing with different types of additives is also discussed.