Cementitious materials are the most important kinds of building materials, which are usually produced by cast moulding. Recently, automatic producing methods are so strongly required for improving industrial efficiency that extrusion moulding is predicted to be a typical method for producing cementitious building materials for precast concrete.Extrusion moulding has been adopted for forming clay bricks and some kinds of plastics. For cementitious materials, special types of extruders were developed on the extension of extruders for burnt clay bricks in Japan. Since high strength and durability of cementitious materials and components can be improved by continuous pressing by extruders, specific flexural strength (per unit density) is comparatively higher than precast ones.Both good properties and automation-oriented manufacture of extrusion moulding will make the market share expand and take the change of precast concrete. However, in order to perform the extrusion moulding, a compatible combination between material technologies and machinery ones is correctly required. The latter aspects have been studied in the field of clay extrusion procedures. The former aspects have not been studied to make any scientific consensus, and are still on the initiating stage of study.This paper proposes a method for predicting the actual operating points and clarifying prerequisite conditions to perform the extrusion procedures. First, a unique relationship is proposed between conveying amount per a rotation of extruders and extruding pressure which is primarily independent of rotational frequency and the kinds of materials and their mix proportions. The relationship is dependent on machinery factors and die geometries. Secondly, actual extruding velocity under any rotational frequency can be determined on the basis of extruding pressure and a series of single shear tests of materials.The predictive method is verified by a series of experiments on extruding standard cement mortar with various mix proportions of silica sand by a standard extruder.
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