Penetration of Cement Pastes into Particle-Beds: A Comparison of Penetration Models

Abstract

For the selective paste intrusion (SPI) method, thin layers of aggregate are locally bound by cement paste where the structure shall arise. After completion of the printing process, the structure is excavated from the particle-bed and the unbound particles are removed. However, for a sufficient layer bonding and shape accuracy, the rheology of the cement paste must be adapted to the flow resistance of the particle-bed. For practical application, that means mostly time and material consuming “trial and error” tests. To prevent that, analytical models can help to predict the penetration of the cement paste. This paper presents four analytical models to calculate the penetration depth of a cement paste into a particle packing. Based on Darcy’s law, an already existing model is slightly modified (model A+) and a generalized (model C), an advanced generalized (model D) as well as a simplified model (model B/B+) are developed. Compared to conducted tests on the penetration depth, model B showed good accuracy (deviation <1.5 mm) for pastes with a yield stress ≥8.2 Pa, model A+/B+/C for ≥ 5.4 Pa and model D even for <5.4 Pa. Finally, an application guide for each model for practical use will be given.

Combining Wire and Arc Additive Manufacturing and Selective Paste Intrusion for Additively Manu-factured Structural Concrete

“…The penetration depth of the cement paste into the particle bed depends on the rheological properties of the cement paste and the flow resistance of the particle bed. To avoid the effort of "trial and error" tests, Pierre et al [7,29] and Weger et al [2] developed calculation and simulation models to predict the penetration depth of cement pastes in the SPI process.…”

“…Under the assumption of a particle bed with an average aggregate diameter d 50 of 1.0 mm, 1.6 mm as well as 2.6 mm and the measured rheological parameters of the investigated cement pastes, see Table 4 the penetration depth of the cement paste can be calculated using Eq. 1 [2].…”

“…In this way, concrete elements with complex geometries and structures can be produced. To meet the optimum between required layer bonding and sufficient shape accuracy, the rheological properties of the cement paste, i.e., its yield stress and dynamic viscosity, are crucial [1,2]. The combination of the SPI process and the Wire and Arc Additive Manufacturing (WAAM) process enables the production of free-formed, high-strength reinforced concrete elements, which opens up a wide range of applications.…”

Large Particle 3D Concrete Printing—A Green and Viable Solution

“…With the selective paste intrusion process described above, strengths in the range of normal concrete up to 78 MPa were achieved so far [ 10 , 35 , 37 , 38 , 39 ]. The mechanical properties depend largely on the bond quality between the individual layers and the degree of filling of the cavities between the aggregates [ 35 ].…”

Digitaler Betonbau durch additive Verfahren – Sachstand und Forschungsbedarf

“…. Mit der Kenntnis der rheolo gischen Eigenschaften -wie Fließgrenze, Viskosität oder Thixotropie -zu verschiedenen Zeiten nach dem Mischen, lassen sich die Teilprozesse analytisch und/oder numerisch modellieren und optimieren[12,[38][39][40][41].Die rheologischen Eigenschaften sind eng mit der Mischungszusammensetzung und der zeitlich veränderlichen Eines der neuesten Anwendungsbeispiele ist das erste 3Dgedruckte, bewohnbare Haus in Deutschland, das Mitte 2021 in Beckum fertiggestellt wurde[34], Bild 3. Das zweigeschossige Haus mit einer Grundfläche von 80 m 2 wurde direkt auf der Baustelle gedruckt[34].Das derzeit rasante Voranschreiten der additiven Fertigung im Betonbau und die stetig zunehmende Zahl der Bauwerksrealisierungen sind ein Indikator dafür, dass eine Vielzahl der Baubeteiligten die mit der Anwendung dieser Technologie verknüpften Vorteile bereits erkannt hat[35].…”