Die beiden Schwerpunkte dieses Berichtes liegen in der Entwicklung eines numerischen Verfahrens zur quantitativen Beurteilung rissbehafteter Proben oder Bauteile nach Warmvorbelastung und in der Durchführung von, auf die numerischen Arbeiten abgestimmten, experimentellen Untersuchungen zum Einfluss der Art der Vorbelastung und des Spannungszustands (Constraint) im Rissspitzenbereich auf die Bruchzähigkeitserhöhung.
Hochfeste und ultrahochfeste Stahlfaserbetone eignen sich aufgrund ihrer Eigenschaften für den Einsatz bei extremen mechanischen Beanspruchungen. Das für diesen Einsatz erforderliche duktile Bruchverhalten unter Zugbeanspruchung wird ausschließlich durch die Zugabe von geeigneten Stahlfasern und deren Wirkung in der Zementsteinmatrix erreicht. Für eine gezielte stoffliche Optimierung des Systems sind fundierte Kenntnisse zur Wirkungsweise der Stahlfasern notwendig, die bei bisherigen Untersuchungen lediglich auf Basis von klassischen Messverfahren zerstörender Prüfungen gewonnen wurden. Durch das Einbeziehen von Methoden der zerstörungsfreien Materialcharakterisierung können das Bruchverhalten hochfester und ultrahochfester Stahlfaserbetone orts- und zeitaufgelöst untersucht und die einzelnen Phasen des Schädigungsprozesses identifiziert werden. Anhand der vorliegenden Ergebnisse von Zugversuchen eines ultrahochfesten Stahlfaserbetons wird der kombinierte Einsatz von Methoden der zerstörungsfreien Materialprüfung gezeigt und deren Anwendbarkeit in der Analyse des Bruchverhaltens diskutiert. Das Hauptaugenmerk liegt dabei auf der Charakterisierung der ausschlaggebenden Versagensmodi unter Zugbelastung durch die einzelnen Verfahren und dem Vergleich zu klassischen Messmethoden (z. B. Extensometer). Die Zugversuche wurden dazu parallel durch optische Verformungsanalyse mittels Bildkorrelation (DIC), Schallemissionsanalyse (SEA) und 3-D-Computertomografie (CT) begleitet.
Ultra-high performance fiber-reinforced concretes (UHPFRCs) are most suitable for applications with extreme mechanical loads. These extreme conditions require ductile behavior under tensile loading, which is obtained solely by the working mechanism of steel fibers. Profound knowledge on the working mechanism of the steel fibers is necessary to optimize this material. Usually, this knowledge is obtained by means of classical destructive measuring techniques. Adopting measuring techniques from non-destructive material testing helps to analyze and to identify the different stages of the fracture mechanism of UHPFRC in detail. The application of different non-destructive measuring techniques is shown exemplary on tensile tests conducted on an UHPFRC mix and its applicability for analyzing the fracture behavior of such concretes is discussed. The main focus is on the characterization of the relevant failure modes under tensile loading by the different measuring techniques and the comparison with classical measuring techniques (e.g. extensometer). The tensile tests have been analyzed by optical deformation measurements using digital image correlation (DIC), acoustic emission analysis (AE), and 3D computed tomography (CT).
This paper presents a novel approach for developing sustainable building materials through Sequential Learning. Data sets with a total of 1367 formulations of different types of alkali-activated building materials, including fly ash and blast furnace slag-based concrete and their respective compressive strength and CO2-footprint, were compiled from the literature to develop and evaluate this approach. Utilizing this data, a comprehensive computational study was undertaken to evaluate the efficacy of the proposed material design methodologies, simulating laboratory conditions reflective of real-world scenarios. The results indicate a significant reduction in development time and lower research costs enabled through predictions with machine learning. This work challenges common practices in data-driven materials development for building materials. Our results show, training data required for data-driven design may be much less than commonly suggested. Further, it is more important to establish a practical design framework than to choose more accurate models. This approach can be immediately implemented into practical applications and can be translated into significant advances in sustainable building materials development.
In recent decades, the number of components in concrete has grown, particularly in formulations aimed at reducing carbon footprints. Innovations include diverse binders, supplementary cementitious materials, activators, concrete admixtures, and recycled aggregates. These developments target not only the enhancement of material properties but also the mitigation of the ecological and economic impacts of concrete — the most extensively used material by humankind. However, these advancements also introduce a greater variability in the composition of raw materials. The material’s behavior is significantly influenced by its nanoscale properties, which can pose challenges in accurate characterization. Consequently, there’s an increasing need for experimental tuning of formulations. This is accompanied by a more inconsistent composition of raw materials, which makes an experimental tuning of formulations more and more necessary. However, the increased complexity in composition presents a challenge in finding the ideal formulation through trial and error. Inverse design (ID) techniques offer a solution to this challenge by allowing for a comprehensive search of the entire design space to create new and improved concrete formulations. In this publication, we introduce the concept of ID and demonstrate how our open-source app “SLAMD” provides all necessary steps of the workflow to adapt it in the laboratory, lowering the application barriers. The intelligent screening process, guided by a predictive model, leads to a more efficient and effective data-driven material design process resulting in reduced carbon footprint and improved material quality while considering socio-economic factors in the materials design.
Fused cement clinker can be produced from molten basic oxygen furnace slag (BOFS) by way of a reductive thermochemical treatment. During the thermochemical treatment, oxidic iron is reduced to metallic iron and separated. The resulting low-iron slag has a chemical and mineralogical composition similar to ordinary Portland cement (OPC) clinker. In this study, the hydraulic reactivity of the fused clinker from BOFS with and without gypsum was investigated using isothermal calorimetry, differential scanning calorimetry, in situ X-ray diffraction and powder X-ray diffraction. Furthermore, a synthetic fused clinker without foreign ions and fused clinker produced by a mixture of both materials was studied. The hydraulic reaction of the fused clinker from BOFS was considerably slower than that of OPC. However, the reaction can be accelerated by adding gypsum as a sulfate carrier. Furthermore, the results showed an increased reaction rate with decreasing content of foreign ions such as Fe, P or Mn.