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- 2.1 Sicherheit von Energieträgern (42)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (42)
- 7.6 Korrosion und Korrosionsschutz (35)
Eingeladener Vortrag
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In this work, a probabilistic framework for identification of traffic loads on concrete Bridge structures is presented using data from a FE structural model in combination with a finite volume approach for traffic load modelling. The identification approach uses Bayesian Inference to identify traffic loads from measured sensor data from travelling load experiments performed at BAM. The work focuses on the load identification part of the Framework utilizing global structural response measurements only. The obtained information on traffic loads can be forwarded to further analysis such as fatigue and structure state estimation or model updating.
Elastomers are usually mechanically reinforced with high loadings of carbon black (CB) to achieve the properties demanded; high amounts of mineral flame retardants are used to fulfill fire safety requirements. In this study, multilayer graphene (MLG), a nanoparticle made of only 10 graphene sheets, is applied in low loadings, 3 parts per hundred rubber (phr) to reduce the total amount of filler or boost performance in hydrogenated acrylonitrilebutadiene rubber (HNBR). In the HNBR/MLG nanocomposites, 3 phr MLG replaced 15 phr CB, 3 phr aluminum trihydroxide (ATH), or 15 phr CB + 3 phr ATH. The nanocomposites were prepared via master batch by ultrasonically assisted solution mixing and subsequent conventional two-roll milling. A comprehensive study is presented, illustrating the impact of MLG on curing and mechanical properties; e.g. replacing 2.5 phr ATH with 3 phr MLG increased the Young's modulus by over 60% and hardness by 10%, while improving flame retardancy, and reducing the total heat evolved by 10%. MLG is a multifunctional filler, as demonstrated by various enhancements in terms of the mechanical and flame retardancy properties of the rubber composites.
Elastomers, such as hydrogenated acrylonitrile-butadiene rubber (HNBR) are usually mechanically reinforced with high loadings of carbon black (CB) to achieve the properties demanded; high amounts of mineral flame retardants are used to fulfill fire safety requirements. These high filler loadings sometimes cause deterioration of the physical properties of the material. In this study, multilayer graphene (MLG), a nanoparticle made of only 10 graphene sheets, is applied in low loadings (3 phr) to reduce the total amount of filler or boost performance.1,2,3 In former studies nanofiller achieved increased flame retardancy at very low lowdings.4,5,6 The dispersion of the nanofiller is essential for the properties of the nanocomposites.7 The nanocomposites were prepared via master batch by an ultrasonically assisted solution mixing and subsequent conventional two-roll milling.
SEM and TEM micrographs and rheological measurements revealed that the MLG nanoparticles were well dispersed in the HNBR matrix. In the HNBR nanocomposites, 3 phr MLG replaced 15 phr CB, 3 phr ATH or 15 phr CB + 3 phr ATH and achieved large consistent improvement in curing, rheological and mechanical properties of the HNBR. The nanocomposites with partial replaced CB reduced the filler loading up to 60% without any deterioration of the properties. The HNBR/MLG nanocomposites achieved an even higher Young’s modulus, hardness and thermal conductivity. MLG achieved advanced flame retardancy by improving the protection layer. The layer is created during the burning phase and acted as an afterglow suppressor. This study proposed the combination of ATH with MLG as a promising approach to reduce the amount of filler, in addition to improving the mechanical properties and fire performance of HNBR rubbers.
Elastomers are used in a wide range of automotive and railway applications. However, a severe drawback of most rubbers are their high flammability. Therefore, flame retardants (FRs) are added to improve the performance in fire. Generally, rubber composites are filled with high amounts of mineral fillers such as aluminium trihydroxide (ATH) to fulfil fire safety regulations. These high loadings may cause deterioration of the physical properties of the material. This work shows the implementation of two new strategies to achieve the modern demands on non-toxic FRs and the reduction of fillers.
The first approach was the implementation of multilayer graphene (MLG), acting as a multifunctional filler, reinforcing agent and FR. The study presents filler combinations with a systematic variation of the fillers carbon black (CB), MLG and ATH. The nanocomposites were prepared via master batch by an ultrasonically assisted solution mixing. Afterwards the master batch was compounded into the rubber in a two-roll milling. MLG substituted high amounts of the conventional filler CB, leading to reduced filler loadings and a consistent improvement in curing, mechanical and FR properties.
The second strategy was the combination of phosphorous-containing FRs with a potential new polymeric char promoting agent polyaniline (PANI). Char promoting additives such as pentaerythritol (PER) improve the effectiveness of the FR system. The combination of ammonium polyphosphate (APP) with PER was successfully investigated for natural and styrene-butadiene rubber composites. This work investigates the flame retardancy of the combination of FRs with PANI and its capability to act as a char/barrier promoter in EPDM.
The morphology of the rubbers and homogenously dispersion of MLG was investigated via scanning/transmission electron microscope (SEM/TEM) micrographs. Rheological and mechanical measurements assessed the influence of the fillers on the physical properties of the rubber composites. Characterization via thermogravimetric analysis (TGA) led to a broader understanding of the decomposition. In order to determine the flame retardancy effect of these materials, a multi-methodical approach was selected. Limiting oxygen index (LOI) and UL-94 were used to quantify the flammability of the rubber composites. The cone calorimeter provided information about the fire behaviour in forced flaming conditions. Residues were investigated via elementary analysis and XPS to clarify the composition of the remaining material. Glow-Wire and FMVSS 302 tests revealed significant results in terms of flame retardancy. The flame retardancy investigation of rubber composites, combinations of ATH with MLG and ATH with phosphorous-containing FRs, broaden the horizons of rubber flame retardancy solutions. By examining alternate FR formulations and their effect on mechanical and physical properties of the rubber, new insight into the range of applicable additives for rubber composites may be won.
Derzeit gibt es intensive Diskussionen über die Entlassung von Deponien aus der Nachsorgephase. Die Deponie müsste dafür nach der Deponieverordnung (DepV) u. a. „insgesamt dauerhaft standsicher" sein. Geokunststoffe erfüllten ihre Funktion über einen Zeitrahmen von lediglich mindestens hundert Jahren. Dies stehe somit im Widerspruch wird argumentiert. Das neue LANUV-Arbeitsblatt 33 schließt daher im Moment eine Entlassung aus der Nachsorge von Deponien faktisch aus, wenn in den Böschungen Geokunststoffprodukte eingesetzt wurden. Auch der Fachbeirat der BAM zur Zulassung von Geokunststoffen, Polymeren und Dichtungskontrollsystemen hat sich daher mit der Thematik beschäftigt. Die aktuelle Situation soll daher auf dieser Grundlage diskutiert werden.
To examine the capability to detect and localise damage using the Measurement- and Model-based Structural Analysis (MeMoS), a small-scale truss bridge (1520 mm × 720 mm × 720 mm) made of aluminium profiles is built as a test specimen for this purpose. The truss frame of the test bridge is made of aluminium profiles with a sophisticated design of the cross-sectional area. In comparison, with solid profiles, only a fraction of the material is needed to produce the profiles, while their bending resistance decreases slightly. The profiles are built into a truss frame by connecting them by means of fastening sets made of steel. The bridge model is mounted on four steel bearings which each of them consist of a cylinder arranged between two plates. Fixed bearings are made by holding onto one end of the bridge. The bridge is subjected by an external load by placing a heavy object beneath it. At the same time, measurements can be conducted below the bridge. Therefore, the bridge specimen is elevated by attaching it on a pedestal with four columns. Damages can be induced by loosening the fastening pieces.
To examine the capability to detect and localise damage using the Measurement- and Model-based Structural Analysis (MeMoS), a small-scale truss bridge (1520 mm × 720 mm × 720 mm) made of aluminium profiles is built as a test specimen for this purpose. The truss frame of the test bridge is made of aluminium profiles with a sophisticated design of the cross-sectional area. In comparison, with solid profiles, only a fraction of the material is needed to produce the profiles, while their bending resistance decreases slightly. The profiles are built into a truss frame by connecting them by means of fastening sets made of steel. The bridge model is mounted on four steel bearings which each of them consist of a cylinder arranged between two plates. Fixed bearings are made by holding onto one end of the bridge. The bridge is subjected by an external load by placing a heavy object beneath it. At the same time, measurements can be conducted below the bridge. Therefore, the bridge specimen is elevated by attaching it on a pedestal with four columns. Damages can be induced by loosening the
fastening pieces.
The substantial progresses in fiber-optic communications in combination with the increasing economic and political interest in structural health monitoring have led to a commercial establishment of distributed Brillouin sensing. The sensor systems, mainly based on the time-domain techniques, have been successfully implemented in the areas such as pipeline leak detection, geohazard effects, and ground movement detection.
This chapter introduces a further advancement in the area of Brillouin sensing in the frequency domain. The so-called Brillouin optical frequency-domain analysis (BOFDA) offers crucial perspectives in terms of dynamic range and cost efficiency.
The main principle of the frequency-domain approach takes advantage of the reversibility between the time and frequency domain given by a Fourier transform in the analysis of linear systems. The hereby presented overview gives a summary of the benefits and challenges of frequency-domain measurements closely tied to the narrowband recording of the complex transfer function. This function relates the counterpropagating pump and probe laser light along the sensor fiber providing the pulse response of the measurement system by applying the inverse Fourier transform (IFT). The strain or temperature distribution can be then determined from the retrieved Brillouin frequency shift (BFS) profile along the fiber.
Die Laserinduzierte Plasmaspektroskopie (engl.: Laser-induced Breakdown Spectroscopy, kurz: LIBS) ist eine Kombination aus Laserablation mittels eines energiereichen Laser-Pulses, der Erzeugung eines Plasmas auf der zu untersuchenden Oberfläche und dem quantitativen Nachweis der Elementzusammensetzung durch spektroskopische Untersuchung der vom Plasma emittierten Strahlung. Ein LIBS-Gerät liefert dem sachkundigen Planer Daten für die Bewertung des Ist-Zustandes von Bauwerken unserer Infrastruktur durch die zweidimensionale Erfassung von Elementverteilungen. Typische Anwendungen sind die Erfassung von Chlor, Schwefel, Kohlenstoff, Natrium, Kalium und Lithium in Beton oder als – Qualitätssicherung – der Nachweis der mit einem Marker versehenen Tiefenhydrophobierung.
In Zusammenarbeit zwischen Industriepartnern und der BAM wurden ein Labor und ein mobiles LIBS-System für die Vor-Ort-Messungen entwickelt. Die Analyse erfolgt vollautomatisch. Die Ortsauflösung beträgt bis zu 0,1 mm x 0,1 mm. Es können Messflächen von 140 mm x 170 mm gescannt werden. Die Erstellung von 2D-Elementverteilungen im Beispiel unten benötigt weniger als 10 Minuten.
A big part of the infrastructure is made of concrete, which is a multiphase system made of cement, aggregates, water and pores. Concrete is often used in combination with steel as reinforced concrete. Environmental influences, especially the ingress of harmful ions in combination with the ingress of water, trigger different damage processes which reduce the designed lifetime of a structure. The ingress of chlorides from de-icing salt or sea water leads to corrosion of the reinforcement. In addition, the carbonation of the concrete may trigger the corrosion of the reinforcement. The ingress of alkalis from deicing salts may cause the expansion of the amorphous silica aggregates (alkali-silica reaction) through
formation of a swelling gel of calcium silicate hydrate if water is present. The ingress of sulphates may cause spalling of the concrete surface due to ettringite formation.
For the standard procedure in civil engineering cores are taken, cut in slices, grinded and the obtained homogenized powder is solved in acid and investigated by standard procedures.
BAM has developed the LIBS technique for the 2D evaluation of the chemical composition of concrete. The technique is established for automated laboratory use with high numbers of samples to investigate transport processes of harmful species (Cl-, CO2 , SO4 2-and alkalis) in concrete. Information about ingress depth and the quantitative values are important to estimate the remaining lifetime of the infrastructure. LIBS is a surface technique. To get information about the ingress depth, a drill core has to be taken and cut in the middle. The measurements are carried out at the cross section. The main advantages of LIBS are the direct measurement on the surface of the concrete, fast analysis (sample rate 100 Hz) with a spatial resolution of up to 100 µm, the consideration of the heterogeneity of the concrete and the possibility of automated measurements which save a lot of manpower and time. As an example the investigation of ingress profiles for standard diffusion and migration tests in civil engineering takes hours in comparison to just a few minutes using LIBS. At the same time a 2D-evaluation provides information about hot spots of elemental concentration which may not be found by standard methods.
The state of the art of LIBS technique for applications in civil engineering will be presented, including typical results of 2D investigation of concrete in laboratory. The performance is also demonstrated by examples for onsite applications using a mobile LIBS system. The road map to standardization is presented as well.