Abstract
Extrusion is a process that consists in forcing a formable material to pass through a die having the cross-section of the part to be obtained. This way of processing is used with conventional and fibre-reinforced cement-based materials to fabricate various construction elements such as panels, pipes and roadside curbs. Recently, with the development of digital fabrication methods and especially 3D concrete printing by selective deposition, the extrusion techniques have experienced a significant increase in interest.
 This letter describes the screw and ram extrusion techniques and their applications in construction industry. Furthermore, the underlying mechanisms involved during extrusion flow are delineated and the roles of rheological and hydro-mechanical behaviours (the latter one in a soil mechanics sense) in defining the extrudability – ability of being extruded – of the cementitious materials are highlighted. Finally, specific points such as flow-induced anisotropy of fibre reinforced cementitious materials or surface defects are addressed.
Highlights
Extrusion is a common manufacturing process used in many industrial sectors
The application of extrusion to concrete and other cementitious materials has been mostly limited to specific cases, such as roadside kerbs or slender elements made of high‐performance engineering composites [1, 2]
This “engineering” characteristic is commonly associated with the ability of the concrete to remain homogeneous during flow, meaning that no water drainage occurs during extrusion
Summary
Extrusion is a common manufacturing process used in many industrial sectors. When utilizing mineral materials in the construction industry, the process is widely used to form fired, unfired or stabilized clay bricks at a highly productive rate. One important aspect with respect to the extrusion of cement‐based materials is the definition of the term itself This “engineering” characteristic is commonly associated with the ability of the concrete to remain homogeneous during flow, meaning that no water drainage occurs during extrusion. Extrusion flow is used to estimate the flow properties of stiff cement‐based materials whose rheological and tribological behaviour could not be evaluated using rotational rheometers [16]. Despite their having been already applied to cement‐based materials, these methods and techniques have been inspired by the literature on ceramics, especially the works of Benbow and Bridgewater [8]. Different ram extruder designs allow studying the load necessary to change the cross‐section of cement‐based materials [12, 18] or to measure the friction acting at the extruder wall [13, 19]; see Figure 1
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