Rheological Modifiers in Optimizing Quick Nozzle Mixing Technology for 3D Concrete Printing

Quickly mixing concrete at or near the printing nozzle is a new technique developed by the authors to improve 3D concrete printing technology. Quick nozzle mixing (QNM) solves the inherent problem in 3D concrete printing due to the opposing rheological demands for buildability and pumpability. 3D printing requires the concrete to be pumpable, which requires the concrete to be flowable without segregation, while the same concrete should be buildable once printed, which requires the concrete to be stiff and not flowable. The same concrete cannot satisfy both demands. Transporting the concrete to dry materials and mixing the dry materials will not only solve this problem but also allow the printing process to be stopped anytime and start again when needed without having to clean all the equipment (pump, hoses, etc.). The main issue with mixing at the nozzle is that the duration allowed for mixing is relatively short, depending on the nozzle's print speed and the mixer size.
To accomplish this technique, the quality improvement of concrete experiencing a short mix (less than 70 s) was studied. The effects of rheological modifiers on the mixing process of concrete were investigated. Results show that the mixing duration can be shortened by increasing the mixing intensity and optimizing raw materials. Furthermore, the type of rheological modifiers can significantly influence the mixing power.