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.