| The role of superplasticizer in extruding cement-based materials was analyzed. Theoretical analysis shows that superplasticizer makes paste less extrudable by deflocculating particles, which was corroborated by rheological experiments. Observation of microstructure shows that superplasticizer does not help fiber dispersion in extruding fiber-reinforced paste. However, superplasticizers can reduce the water demand of extrudable paste at constant total extrusion pressure, or can decrease the total extrusion pressure at constant water to cementitious materials ratio.;Co-extrusion, simultaneous extrusion of multiple layers, and rheology were studied to produce functionally graded materials. It is found that rheological control is vital for successful co-extrusion of layered materials. During extrusion, the paste flow in the barrel and the die land in a ram extruder should be plug-like, while the paste should be sheared and uniformly elongated in the die entry region. In the barrel of the extruder, evidence for plug flow in the barrel was seen only at low extrudate velocities. In the die land, plug flow was achieved due to a thin liquid layer adjacent to the wall being sheared. For co-extrusion, a simple method using thin-walled tubes was found to be effective to prepare layered feedrods. Functionally graded cellular structures of cement-based materials were successfully co-extruded by using a low extrudate velocity when the paste had decreasingly shear viscosity from inner layers to outer layer. The extensional rheology parameters were calculated from the die-entry pressure and shear parameters, using the entrance flow theory. The die-entry term in the Benbow equation was modified to better describe the flow mechanism of extrusion. It was found that the flow in die-entry region was dominated by elongation. To ensure successful co-extrusion, a model was proposed: the extensional viscosity of the inner layer should be less than that of the outer layer, but still at least one-third that of the outer layer.;Clay was explored to replace commonly used cellulose plasticizer in order to solve the problem of air voids associated with cellulose. The effect of clays on plasticizing cementitious pastes was evaluated by rheological and zeta potential measurements. Only zeta potential was found to be valuable to assess the effectiveness of clay as a plasticizer. The PGN clay, which had high amount of montmorillonite, with combination of silica fume, polyethylene glycol and superplasticizer was found to be efficient to reduce air voids in extrudates. |
