Filtern
Dokumenttyp
- Vortrag (3)
Sprache
- Englisch (3)
Referierte Publikation
- nein (3)
Schlagworte
- Rheology (3) (entfernen)
Organisationseinheit der BAM
- 7 Bauwerkssicherheit (3) (entfernen)
Eingeladener Vortrag
- nein (3) (entfernen)
Additive manufacturing of concrete structures is a novel and emerging technology. Free contouring in civil engineering, which allows for entirely new designs, is a significant advantage. In the future, lower construction costs are expected with increased construction speeds and decreasing required materials and workers. However, architects and civil engineers rely on a certain quality of execution to fulfil construction standards. Although several techniques and approaches demonstrate the advantages, quality control during printing is highly challenging and rarely applied. Due to the continuous mixing process commonly used in 3D concrete printing, it is impossible to exclude variations in the dry mixture or water content, and a test sample cannot be taken as a representative sample for the whole structure. Although mortar properties vary only locally, a defect in one layer during printing could affect the entire integrity of the whole structure . Therefore, real-time process monitoring is required to record and document the printing process. At the Bundesanstalt für Materialforschung und -prüfung (BAM) a new test rig for the additive manufacturing of concrete is built. The primary purpose is measuring and monitoring the properties of a mortar during the printing process. The following study investigates an approach for calculating yield stress and plastic viscosity based on experimentally recorded pressure data. The calculations assume that fresh mortar behaves as a Bingham fluid and that the Buckingham-Reiner-equation is applicable. A test setup consisting of rigid pipes with integrated pressure sensors at different positions is utilized. Monitoring the printing process with different sensors is crucial for the quality control of an ongoing process.
While today, engineers can choose from a wide range of rheology modifying admixtures, in some parts of the world, these are difficult to access, due to their complex processing. However, alternatives can be bio-based polymers such as polysaccharides from various sources. These are easily accessible all over the world, do not demand for complicated processing, and typically they are more sustainable than many established materials, which are crude oil-based.
The paper presents the effects of acacia gum, cassava starch and the gum of triumfetta pendrata A. Rich on the rheological performance of cementitious systems. It is shown that acacia gum can be as efficient as polycarboxylate based superplasticisers, cassava starch can reduce the yield stress slightly with little effect on the plastic viscosity, and the gum of triumfetta pendrata A. Rich increases the thixotropy of cement pastes with plasticizing polymers significantly.
In the last years flowable concrete has become increasingly important in applications such as, for systems with highly reinforced concrete with a complicated formwork, or sprayed concrete and 3D-printing of concrete. For all these applications it is necessary to have tailored rheological properties. Rheology can be described by values of yield stress and plastic viscosity, which can be determined for example by evaluation of rheometer measurements. But for different materials various rheometers with different geometries and stirrers are being used. To see the effects from paste in concrete, it is necessary to investigate mixes of paste, mortar and concrete, stepwise. But currently there exists no device, which is calibrated for these different systems at once. Due to this fact, conventional tests such as V-funnel efflux-time and flow diameter were determined, as well as rheometer data in different cell sizes and geometries.
In this study the assessment of rheological effects in the binder on the rheology of mortar was investigated by using combination of two rheometers.