Extrusion of ECC: Recent Developments and Applications

Extrusion of particulate pastes and suspensions in general is difficult and the rheological parameters play a central role in the process when using conventional extruders. More important – the rheological properties of the paste or suspension are subjected to conflicting demands in an extrusion process. Extrusion of cementitious (fiber reinforced) materials has proven particularly difficult due to the high inter-particle friction combined with the disastrous effect of static zones in the flow pattern, and to the ease of phase migration or separation. In order to deal with these conflicting demands on the rheological properties of cementitious particulate materials, various methods have been suggested to dewater the particle suspension during extrusion, however practical extrusion of thin-walled cementitious large-scale elements has not been possible until the discovery of the “dewatering extrusion principle” which enabled the contradictory requirements on rheological properties to be accommodated. The present paper describes the fundamentals of the process and preferred embodiments of the extruder principle. Further the paper describes the current understanding of the dewatering process and how it can be utilized to control the extrusion process. Finally, an application of the extrusion principle is described in the shape of a thin-walled, semiflexible ECC pipe.