Stiffening controllable concrete modified with redispersible polymer powder for twin-pipe printing

Abstract

To achieve stiffening control in 3D concrete printing, a twin-pipe pumping (TPP) system has been developed, where two streams of cementitious materials are pumped separately via two pumps and blended over a helical static mixer right before extrusion. However, in addition to the interlayer region, the presence of striations consisting of unmixed limestone-based regions reduces the mechanical integrity of printed elements in earlier research on TPP strategy making use of a cement-based mixture and a limestone-based mixture. In this work, we examined the use of redispersible polymer powder (RDP) as a means to improve the mechanical performance of such 3D printed elements. Limestone powder in the limestone-based mixture was partially substituted by different dosages of redispersible polymer powder (5, 10, and 15 %). Rheological behavior of the cement-based mixture and the limestone-based mixture was evaluated. Further, we studied the effect of RDP addition on the hydration and the early age mechanical behavior of the combined mixtures. In the hardened state, specimens extracted from 3D printed wall elements were tested for flexural, compressive, and tensile strength. Its microstructure was examined using scanning electron microscopy. From the results of various studies conducted, although adding redispersible polymer powder would slightly reduce the very early age mechanical strength, it enhances the mechanical integrity in the hardened state due to film formation in the limestone-based mixture.