Mechanisms of rheological modifiers for quick mixing method in 3D concrete printing

Quick mixing technology at the nozzle is a potential approach to avoiding the opposing requirements for pumpability and buildability and improving productivity in 3D concrete printing. However, the addition of rheological modifiers poses a challenge in quickly achieving a uniform mix while minimizing mixing energy. This study investigated two common rheological modifiers, including polymeric carboxymethylcellulose (CMC) and nano-clay. Their effects on the liquid bridge of mixing water and the mixing evolution and yield stress of concrete were investigated. Results show that the resistance of mixing concrete with CMC reduced with mixing time after a peak whereas that with nano-clay exhibited an opposite trend. An increase in modifier dosages enhanced the liquid bridge force and rupture energy, increasing mixing resistance; the CMC was more influential than nano -clay. Furthermore, the quick mixing method resulted in better dissolution (or dispersion) of these modifiers and higher yield stress but cost more mixing energy.