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Item type:Publication, Access status: with files , Einfluss der Art grober Gesteinskörnung auf Struktur und Eigenschaften von ultrahochfestem Beton - Abschlussbericht in LangfassungThe addition of coarse aggregate is one possibility to lower the cement content of ultra-high strength concrete (UHPC). Within the research project an UHPC with a maximum grain size of 0.5 mm was varied with 30 vol.-% of coarse aggregate, with a grain size of 5-8 mm. 16 different rock types were added to the fine-grained reference mixture. The rock types cover most of the high strength rocks available in Germany. The rock and the UHPC specimens were examined under different aspects. Both the mechanical behaviour, as the structural and chemical properties were determined. As the main results it can be stated, that not only basalt, but a lot of rock types can be used to produce UHPC, even if the addition of coarse aggregates decrease the strength of all specimens in comparison to the original mixture. Basalt and other fine-grained vulcanic rocks are useful, but also coarse-grained plutonic granite and metamorphic granulite and gneiss. Also with dense sedimentary limestone (Massenkalk), UHPC can be produced. Coarse-grained metamorphic marble, sandstone (also with very high strength), and the sandstone-like greywacke, and metamorphic amphibolite were not successful. Dolomite and the examined quarzite resulted in somehow inconsistent strength values. There is a strong linear correlation of the rock and the UHPC compressive strength. There is no threshod value of the rock strength, resulting in a decrease of the UHPC strength, but the lower the rock strength, the lower is the UHPC strength. A correlation between the typical grain size of the rock and the UHPC strength is not visible. In no case, also with very high spatial analytical resolution, a chemical reaction was visible between the minerals of the rocks and the cement matrix. It seems, that the UHPC ist too dry, after short time, to get chemical reactions between the rock grains and the binder matrix. All rock types were very well embedded in the cement matrix. They are great differences in the coarseness of the grain surfaces. Together with differences in the porosity of the rocks this resulted in effects on UHPC workability.Publicationtype: Report36 9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Micro- and nanostructural investigations of high and ultra-high performance concrete under fatigue(Elsevier, 2025-04-30); ; A fine-grained UHPC, both undamaged and damaged by fatigue loading, was comparatively examined by various microstructural analytical methods, to evaluate the different techniques with respect to their applicability and relevance for the investigation of fatigue damage processes. The fatigue tests were stopped at the transition from phase II to phase III of the s-shaped strain development. The cyclic compression loading was performed with a frequency of ft = 1 Hz, and a stress level between Smin = 0.05 and Smax = 0.75 (fcm = 170.2 MPa). The fatigue process under these loading conditions is dominated by alterations and damages on the nano-scale, that can be observed by transmission electron microscopy. The resulting coarsening of the pore structure was also visible with dynamic vapor sorption. Nanoindentation indicates, that changes of the HD-C-S-H-phase occur. IR spectroscopy also indicates changes of the C-S-H phase and thermal analysis changes of the water content. Dynamic mechanical analysis (DMA) gave insight into the complex Young's modulus and Poisson's ratio changes. The acoustic emission technique gives information on the different processes during the single phases of fatigue and reveal a very different damage behaviour of dry and moist materials. Some microcracks are visible with light microscopy. It appears, that the number of cracks after fatigue is higher than before. With X-ray computed tomography, X-ray powder diffraction, the drying behaviour, the free water uptake, the water uptake under vacuum and by mercury intrusion porosimetry no significant differences between specimens with and without fatigue loading could be observed in this examination.Publicationtype: Journal Article16 13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Effects of Si/Al molar ratio on the microstructure of Metakaolin-based geopolymersPublicationtype: Conference Paper24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Effects of Si/Al molar ratio on the structure and properties of metakaolin-based alkali activated binders(2024-06); Publicationtype: Conference Paper23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Self-organizing systems in the construction industrySelf-organization is found in numerous natural and artificial systems. For the construction industry, self-organizing processes are not only applicable in managing or organizing tasks, they also provide insight into materials or can be implemented into operations on building sites. In this paper, the terms feedback, agents, emergence and self-organization are described to provide an insight into the complex processes relevant to a lot of fields in the construction industry. For this, the principles of adaptive processes are transferred to artificial systems. Besides self-organization in building materials, an outlook is given to describe construction sites as cyber-physical systems. Inside such systems, agents learn to organize work tasks more efficiently, particularly with the help of reinforcement learning. In this regard, a transfer of natural self-organization—which also exist in materials—to building processes is made. A combination of natural and artificial systems is presented to promote self-organization for various fields of application in the construction industry, especially for building sites.Publicationtype: Review Article18 97 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Einfluss der Kristallinität auf die Festigkeit und die Mikrostruktur alkalisch aktivierter MetakaolineBei der Reaktion von Metakaolin mit alkalischen Anregern entstehen eine röntgenamorphe, alumosilikatische Gelmatrix sowie kristalline Natrium- bzw. Calcium-Aluminat-Silikat-Hydratphasen zu unterschiedlichen Anteilen. In dieser Arbeit wurden grundlegende Zusammenhänge zwischen dem Kristallinitätsgrad der alkalisch aktivierten Metakaoline sowie deren mechanischen Eigenschaften untersucht. Dabei wurde insbesondere auf die Porosität, die Druckfestigkeit und thermoanalytische Eigenschaften eingegangen. Die Kristallinität wurde mittels Röntgendiffraktometrie bestimmt. Voraussetzungen für die Ausbildung eines amorphen Gefüges ist die Lösung der reaktiven Ausgangsmaterialien. Nicht vollständige Lösung führt zu inhomogenem Gefüge, in dem sowohl amorphe Matrix als auch kristalline Bereiche vorliegen. Kristalline Reste im Metakaolin dienen als Kristallisationskeim und begünstigen die Bildung weniger stabiler kristalliner Hydratphasen. Es zeigte sich, dass ein höherer Kristallinitätsgrad mit größeren Poren und einem höheren Porenvolumen einherging, das die Druckfestigkeit der erhärteten Bindemittel herabsenkte. Zusätzlich zeigten die thermogravimetrischen Untersuchungen, dass ein dichteres Gefüge gleichzeitig durch den vermehrten Einbau von Kristallwasser gekennzeichnet war.Publicationtype: Conference Paper15 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 38