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Die Wechselwirkung von hoher Alkalität und feuerverzinktem Betonstahl in der Frischbetonphase generiert einen Störung in der Verbundzone. diese Störung basiert sowohl auf der Wasserstoffentwicklung in der Frischbetonphase bis zur diffusionskontrollierten Decksschichtbildung als auch auf die erstarrungsverzögernde Wirkung von Zinkionen auf die CSH-Phasenbildung. Diese werden zwangsläufig infolge anfänglicher starker Korrosionsprozesse frei, und reichern sich in der Verbundzone an. Hier kann es beim normgerechten Ausschalen nach 24h zu weiteren Störungen des Haftverbundes kommen das davon Auszugehen ist das die Erstarrung der CSH-Phasen in der Verbundzone noch nicht begonnen hat.
Kurzvorstellung zu einem DFG-Antrag. Themengebiet sind alterative Bindemittel für die Herstellung von Stahlbetonbauwerken in Kombination mit feuerverzinktem Betonstahl. Die Möglichkeit Bindemittel zu verwenden die keine Alkalitätsreserve vorhalten müssen lässt sich mit feuerverzinktem Betonstahl generieren. Hierbei können die pH-Werte um 8 mit einer Reduktion der Korrosionsgeschwindigkeit einhergehen, sofern man den direkten Vergleich mit hochalkalischen Betonen anstrebt.
Reshapeable magnetic field sensors fabricated on flexible substrates by thin-film deposition or printing have recently emerged with promising applications in different field. In this study, flexible anisotropic magneto-resistive (AMR) sensors were used for the scanning of a curved and flat sample with reference defects, to prove the capability of this method for curved surface scanning, and to benchmark the performance when compared to a more stand-ard method using rigid giant magneto-resistive (GMR) sensors. Defects with depths ranging from 110 μm up to 2240 μm were detected with a signal-to-noise ratio (SNR) of 2.7 up to 27.9 employing flexible AMR sensors.
Flexible electronics is an emerging field that has been gaining a lot of attention in recent years, with the appearance of flexible solar panels, screens and other such novel devices. Recent developments in this area have lead to the appearance of flexible magnetic field sensors which are produced by thin-film deposition on flexible substrates. These devices show promising capabilities for several applications such spatial navigation, micro-fluidic particle detection, biomedical applications and intelligent textiles [1]. One possible field of interest is the application of these devices for electromagnetic (EM) non-destructive testing (NDT), since it would enable in-contact scanning of surfaces with arbitrary shapes.
Flexible anisotropic magnetoresistive (AMR) sensors mounted on a rotative mechanical holder were used to scan a semi-circular ferromagnetic sample with 3 reference defects via magnetic ux leakage (MFL) testing, thus demonstrating the applicability of this method for the scanning of curved surfaces.
Application of Elastic Reverse Time Migration to Ultrasonic Echo Data from Concrete Structures
(2025)
To enhance ultrasonic imaging of concrete structures, we adapted the geophysical migration method, Reverse Time Migration (RTM), for non-destructive testing (NDT) in civil engineering. First, two 2D elastic RTM algorithms, each considering different wave types, were implemented and evaluated with synthetic ultrasonic data. The algorithm that best resolved numerical concrete structures was subsequently applied to real ultrasonic data from a concrete specimen. Compared with conventional synthetic aperture focusing technique (SAFT) imaging, elastic RTM reproduced a greater number of structural features in both the numerical model and the concrete specimen. In particular, elastic RTM reconstructed vertical interfaces as well as hidden lower edges of modeled cavities and tendon ducts. Notably, imaging the full cross-sections of tendon ducts, which enables direct diameter estimation, represents a novel achievement for ultrasonic NDT.
This research seeks to understand and identify the most promising approaches to enhance the flame resistance of poly(limonene carbonate) (PLimC). Furthermore, the goal is to develop a PLimC-based material that incorporates halogen-free flame retardants (FRs) that are not only highly effective but also environmentally sustainable, contributing to the advancement of greener materials for safer use.
The plastic industry depends on fossil-based materials, causing environmental concerns. PLimC, a sustainable polymer derived from limonene and CO₂, offers a promising alternative. Its use in fire-safe applications underscores the need to optimize its performance. This study evaluates halogen-free FRs to identify and understand the most promising approaches to enhance PLimC’s flame resistance, aiming to improve fire safety and support eco-friendly material development.
This study has as its main task to conduct experimental evaluations to analyze the thermal properties, flammability, and fire behavior of each system. Pyrolysis, together with the evolved gases of the samples, were analyzed by thermogravimetric analysis coupled with a FTIR spectrometer. The energy content was determined by using a bomb calorimeter. The flammability of the samples was assessed by the reaction to small flame tests such as the UL 94 burning chamber and limiting oxygen index (LOI). The burning behavior in forced flamed conditions was evaluated using the cone calorimeter.
Thermal properties were first evaluated to gain a deeper understanding of the pure PLimC thermal stability and fire behavior. This analysis builds on PLimC's structural similarity to polycarbonate (PC), due to its carbonate group, and to polyolefins (PO), due to its aliphatic limonene-derived segment, providing insights into optimizing PLimC for sustainable, fire-safe applications.
The initial results, which defined our starting point, showed that the LOI of PLimC was 17.2%, very close to that of PO such as polyethylene (PE) and polypropylene (PP) (~18%). In contrast, PC has a higher LOI of ~24%. Additionally, PLimC did not produce any char (0 wt.-%), similar to PO, whereas PC forms char due to its phenolic structures. The effective heat of combustion of PLimC, measured using bomb calorimetry, was determined to be 31.1 MJ/kg. This value is comparable to that of PC (~30 MJ/kg) but significantly lower than PO (~44 MJ/kg). These findings, which demonstrated similarities to both PO and PC, prompted the evaluation of various commercially available FRs at standard market concentrations.
Four halogen-free FR systems were chosen for evaluation: 1. mixture of APP (20 wt.-%) + pentaerythritol (10 wt.-%) as an intumescent system [PLimC / APP / Penta], 2. mixture of the phosphorus compound PX200® (16 wt.-%) + PTFE (0.4 wt.-%) as antidripping [PLimC / PhosC / PTFE], 3. aluminum trihydroxide ATH (50 wt.-%) [PLimC / ATH], and the potassium sulfonate salt Bayowet® (0.4 wt.-%) [PLimC / SulfS]. The concentrations were decided according to the standards used in the industry.
Cone calorimeter results show that PLimC has the usual behavior of a non-charring specimen (fast burning and high peak of heat release). ATH proved to be the most effective flame retardant, achieving the biggest reductions in the effective heat of combustion (EHC) and total heat evolved (THE). Additionally, ATH achieved the highest increase in the LOI (17.1% to 26.0%). With these results, we understood that the FRs commonly used with polyolefins (at concentrations standard in the industry) exhibit similar behavior in terms of flammability and flame retardancy when applied to PLimC.
Additionally, we aim to investigate bio-based flame retardants to further improve the sustainability of the material. Given that phytic acid salts and lignin have demonstrated effective flame-retardant performance in polyolefins, we consider these compounds promising candidates for application in our system.
In combination with new types of drive technologies, more and more flammable gases could be introduced into the traffic area “road tunnel” in future. If these vehicles have an accident and the gases are subsequently released, there is the possibility that the mentioned substances show a heavy gas behavior due to their storage conditions. From a safety point of view, this scenario has to be assessed with regard to its effects on the tunnel structure and the people involved. The aim of the experimental investigations carried out in this work is to create the basis for such an analysis by investigating the spreading behavior of the gases after they have been released in the tunnel and determining the influence of individual geometric and operational parameters on this behavior. Specifically, this work is based on the scenario of a continuous, momentum-free release of propane within a vaulted road tunnel with active longitudinal ventilation. The tunnel-specific boundary conditions that are relevant to this scenario are first worked out by a theoretical analysis. The basis of the subsequent experimental part is formed by two test rigs built as part of the work, which are similar in their essential features, but differ in scale. In both facilities, the aforementioned release scenario was simulated under various boundary conditions based on an idealized tunnel segment. The dispersion behavior is primarily assessed by the averaged concentration distribution near the ground, which results from a large number of detectors arranged in the experimental area. The detectors operate on the principle of weakening infrared light in the presence of hydrocarbons. Measurements of the flow field properties accompany the concentration measurements. The conception of the test rig on a scale of 1:12 is based on dimensional analysis. The actual release campaign comprises a large number of individual experiments in which selected parameters were varied over the tunnel-relevant range. The predicted heavy gas behavior for propane emerged clearly in the experiments. In cases in which the cloud laterally reaches the tunnel walls, the gases are channeled, which is accompanied by reduced longitudinal dilution. It was possible to identify the release rate and the flow velocity as the factors that have the greatest influence. The former basically increased the concentration, while the latter decreased it. All other tested parameters resulted in more complex propagation situations, which force a differentiated consideration of the influence. Lifting the source from the ground also reduced the concentration. In the case of an eccentrically arranged source and a transverse slope of the roadway, the influence is largely limited to the lateral concentration distribution in the immediate vicinity of the source. Nevertheless, both parameters plus a possible longitudinal slope of the roadway only showed a slight effect on the area far-downstream from the source. In addition, the phenomenon of backlayering, which is known from the spreading of fire smoke in the tunnel, could be demonstrated with a steep longitudinal slope. Obstacles increased the complexity of the situation. While globally the dilution of the cloud is partly invariant to obstacles, locally an increase as well as a decrease in concentration can be observed under certain conditions. For the unobstructed tunnel, it was finally possible to define a dimensionless parameter that describes the curve of the longitudinal dilution on the ground within the heavy gas cloud. From this, a simple graphical nomogram is derived for the continuous release of heavy gases in an unobstructed tunnel environment, which can be used to estimate the concentration in relation of a dimensionless source distance. For exploring the real, undistorted behavior experiments were also carried out in original scale. Due to the similarity of both test rigs in terms of scale, the test results can also be used to check the scalability of the spreading situations. For that, two configurations that have already been examined in small scale were selected. The main limitation for test execution and regarding the scalability comparison was the dependence of the flow conditions within the test rig from external wind conditions which occurred despite of taken countermeasures. The large-scale release was associated with pronounced fog formation. The near-ground spreading corresponding to the heavy gas behavior could be confirmed. However, in detail the spread was far more unsteady. Looking at the time-averaged concentrations, the processes already known from the small-scale test were qualitatively well approximated. Remaining quantitative differences, however, require critical consideration. This discrepancy is more likely a consequence of the experimental compromises have to be made in the specific case. From the observed gas behavior, the development of a surface fire initiated by ignition of the re-leased gases is considered to be the most likely subsequent scenario for the release of heavy, flam-mable gases in tunnel-like enclosures. The thesis concludes with recommendations on the methodological approach to be favored in the future.
The presentation summarizes the 1H NMR relaxation pinciple for the nondestructive material characterization of building materials. We explain the basic principle of NMR and showcase 3 application cases: 1) Moisture transport and 2) In-situ pore size characteriztaion of buildiing materials and 3) Hydration characteristics of new, more climate friendly cementitious binders and mortars.