Twin-pipe pumping strategy for stiffening control of 3D printable concrete: From transportation to fabrication

Resolving the contradictions between the pumping and deposition process still remain as a bottleneck in 3D concrete printing. Fluidity retention is beneficial for pumping operations, while fast stiffening after extrusion is indispensable for a high construction rate. To overcome this drawback, an inline mixing strategy, named twin -pipe pumping, using a motionless static mixer and two pumps is proposed. During the printing process, two distinct mixtures are premixed, including a Portland cement-based mixture (without accelerator) and a limestone powder-based mixture (with a high dosage of accelerator). Both mixtures come with a long open time and a high fluidity to optimize the pumping performance. These mixtures are pumped from two separate pipes and merged by the static mixer before extrusion. The stiffening rate of the mixture is then drastically modified inside the static mixer and the combined mixture can reach a high construction rate with good shape stability.