Influence of Pumping/Extrusion on the Air-Void System of 3D Printed Concrete

3D printing with concrete offers many advantages over conventional construction methods and interest in this field of research has seen a rapid rise in recent years. While there have been large number of cases of successful fabrication of 3D printed structures, ensuring the long-term durability performance of the fabricated structures is equally important. Freeze-thaw damage is one such deterioration issue, especially in cold places like Switzerland. This study investigated the effect of the different processing conditions encountered in 3D printing, namely pumping, acceleration/mixing and extrusion on the air void system of a standard 3D printable mortar mix. The 3D void size distribution of the air voids obtained using a recently developed stereological model, along with the ASTM C457 results showed that pumping had the major impact on the void structure as both air content and spacing factor decreased significantly. The effect of acceleration/change in rheology and extrusion on the void structure was also prominent from the obtained results. The 3D protected paste volume (PPV) curves showed that pumping and acceleration processes could enhance the freeze-thaw performance.