Extrusion Criterion for Firm Cement-Based Materials

Abstract

Abstract:The stability of the flow induced by the extrusion forming process of a cement based material is largely influenced by the relative migration between the lubricating liquid phase and the granular skeleton. In the present work, we propose linking rheological concepts and soil mechanics (consolidation theory, Darcy's law) to reach a simple criterion which predicts the extrusion ability of a mortar. Extrusion tests on studied mortar are performed at different ram velocities for criterion validation. Résumé :La stabilité de l'écoulement du procédé de mise en forme par extrusion de matériaux à base cimentaire est largement influencée par la migration relative entre la phase liquide et le squelette granulaire. Dans ce travail, nous proposons de lier les concepts de rhéologie et de mécanique des sols (théorie de la consolidation, loi de Darcy) pour définir un critère simple qui prédit l'aptitude à l'extrusion d'un mortier. Des essais d'extrusion à différentes vitesses de piston sont ensuite réalisés pour valider le critère. Zusammenfassung :Die Stabilität des durch Ausstoßungsformen-Prozeß eines Zements veranlassten Flusses stützte Material ist in hohem Maße unter Einfluß der Verhältnismigration zwischen Schmieren der flüssigen Phase und granulierten Skelettes. In der gegenwärtigen Arbeit haben wir vor, rheology und Boden-Mechanik-Begriffe (Verdichtungstheorie, Gesetz von Darcy) zu verbinden, um ein einfaches Kriterium zu reichen(erreichen), das die Ausstoßungsfähigkeit des Mörsers(Mörtels) voraussagt. Ausstoßungstests auf an verschiedenem Widder durchgeführten Zementteigen.

Linking fresh paste microstructure, rheology and extrusion characteristics of cementitious binders for 3D printing

“…This substantiates the parameter values extracted from the model. If an extrusion yield stress of 20 kPa is required of the binder leaving the extruder to be printed in shape stable manner as suggested in Ref, then all the mixtures except the plain OPC and OPC‐fly ash pastes chosen in this study satisfy that criterion.…”

“…This requires appropriate particle size distributions at multiple scales—at the paste level, particle sizes capable of retaining paste cohesion to enable flow as well as provide enough yield stress to the mixture, and at the concrete level, aggregates that can provide shape stability and green strength. Size distribution is also a contributing factor to liquid phase migration under extrusion pressure, leading to flow‐induced heterogeneities in the printed structure . The time‐and‐pressure dependence of cement paste rheology adds another level of complexity to the printing process.…”

Extrusion of cement-based materials - an overview

“…The homogeneity condition can be studied from the point of view of soil mechanics [9][10][11][46][47][48]. Perrot et al [12] considered a competition between the velocity of the extrusion flow with the velocity of water drainage.…”

“…However, these two groups of materials also exhibit some critical differences, mainly resulting from the size and shape of their particles. Cement-based materials are more sensitive to water drainage, in a sense that they are prone to exhibit a behaviour similar to that of granular materials, unlike platelet-shaped clay particles, which makes them difficult to extrude [9,10]. The article at hand presents a state-of-the-art review on the extrusion of cement-based materials with a special focus on their flow characteristics and rheological properties.…”

Manufacturing cement-based materials and building products via extrusion: from laboratory to factory

“…The constitutive model was successfully employed in simulating the monotonic upsetting process (Zhou and Li, 2007) and the ram extrusion process (Zhou and Li, 2009) of semi-solid, dough-like fibre-reinforced fresh cement-based materials tailored for extrusion. On the other hand, Perrot et al (2009) proposed linking the rheological concepts of firm cement-based materials and soil mechanics and established a simple criterion to predict the extrusion ability of a mortar.…”