Filtern
Erscheinungsjahr
Dokumenttyp
- Beitrag zu einem Tagungsband (31)
- Zeitschriftenartikel (15)
- Vortrag (12)
- Forschungsbericht (6)
- Beitrag zu einem Sammelband (1)
Schlagworte
- Acoustic emission analysis (6)
- Cracks (5)
- Durability (5)
- Digital image correlation (4)
- Grout (4)
- Grouted connection (4)
- Nano-silica (4)
- Spaltzugfestigkeit (4)
- Tensile strength (4)
- Concrete (3)
Organisationseinheit der BAM
- 7 Bauwerkssicherheit (26)
- 7.4 Baustofftechnologie (24)
- 7.2 Ingenieurbau (12)
- 7.1 Baustoffe (8)
- 8 Zerstörungsfreie Prüfung (7)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (4)
- 8.6 Faseroptische Sensorik (4)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (3)
- 2 Prozess- und Anlagensicherheit (2)
- 2.4 Prüfung und Bewertung von Explosivstoffen/Pyrotechnik (2)
Eingeladener Vortrag
- nein (12)
This paper presents experimental investigations and analyses on the early-age-behavior of zero-slump concrete, such as compaction behavior and green-strength. First, the influence of the granulometric properties of the fines is discussed in detail. For this purpose, the early-age behavior of two different fines (quartz flour and fly ash) is investigated by means of the intensive compaction test (IC-test). The tests on the influence of the fines focus on effects caused by differences in the particle shape and the use of a plasticizing admixture. The conducted tests on the compaction behavior of the fines and their corresponding green-strength are extended to continuously graded granular mixes. Here, the influence of optimized particle packing on the early-age behavior is presented and a comparison on the basis of the aforementioned quartz flour and fly ash is made. In this consideration, experimental investigations on the early-age behavior of a zero-slump concrete mix and possible effects on the hardened concrete properties are included.
This paper addresses the characterization of six different amorphous silica samples with respect to their application in cement paste. Different mixes are compared and analyzed using the mini spread-flow test. Also the granular properties, different void fraction states of packing and distribution moduli q are analyzed and compared using a mix design tool. A deformation coefficient is derived from the spread-flow test, which correlates with the value of specific surface area computed from the particle size distribution, and intrinsic density of the samples. Finally, the thickness of a constant water layer of 25 nm around the particles is computed at the onset of flowing. The granular analysis demonstrated that it is possible to decrease the water demand of the cement paste when nanoparticles are added and the resulting grading follows the modified Andreasen and Andersen curve (q = 0.5), and the concentration of nano silica is less than 5% bwoc.
Für die rechnerische Dimensionierung der Betondecken im Oberbau von Verkehrsflächen für den Neubau sowie die Erneuerung nach RDO-Beton 09 ist die statische Spaltzugfestigkeit an der unteren und oberen Bohrkernscheibe entsprechend der Vorgaben der AL Sp-Beton zu bestimmen. Aufgrund der unzureichenden Kenntnis der Präzision dieses Prüfverfahrens wurden, basierend auf dem Entwurf des FGSV-Merkblatts zur statistischen Auswertung von Prüfergebnissen, mit einem breit aufgestellten Ringversuch die statistischen Kennwerte an Labor- und Bestandsbetonen unter Vergleich- und Wiederholbedingungen ermittelt. Zur möglichst guten statistischen Absicherung nahmen an dem Ringversuch dreizehn erfahrene Prüfstellen teil, die vorab einem Audit unterzogen wurden. Zur Abdeckung des vielschichtigen Einsatzes des Prüfverfahrens erfolgte der Ringversuch an acht Prüflosen, die sowohl die Erst-/ Eignungsprüfung und Übereinstimmungskontrolle bei Neubaumaßnahmen, als auch die Restsubstanzbewertung von Betonfahrbahnplatten berücksichtigen. Zur Bewertung des Materialeinflusses wurde zusätzlich ein Prüflos mit Labormörtel untersucht.
Die Probenvorbereitung erfolgte zentral an der BAM. Zur Sicherstellung einheitlicher Prüfbedingungen bei den Prüfstellen wurde zusätzlich eine detaillierte Standardarbeitsanweisung erarbeitet, die partiell bereits Eingang in das Normenwerk gefunden hat. Bei der Plausibilitätsprüfung aller prüflosspezifischen Einzelwerte der Spaltzug- und Druckfestigkeit wurden vereinzelt sowohl Ausführungsfehler als auch Übertragungs- und Tippfehler festgestellt. Der sich anschließende Lilliefors-Test zeigt, dass die ermittelten Einzelwerte bis auf wenige Aus-nahmen normalverteilt sind und damit die Voraussetzungen für die statistische Auswertung gegeben sind.
Mittels grafischer Darstellung der Mandel’s h- und k-Werte wurden die Auffälligkeiten hinsichtlich der Mittelwerte und Varianzen prüflosspezifisch für die einzelnen Prüfstellen visualisiert und anschließend einige von ihnen mittels Grubbs- und Cochran-Test als Ausreißer identifiziert. Nach Ausreißerelimination wurde mit dem klassischen Verfahren bei der Spaltzugfestigkeit der geringste Variationskoeffizient unter Vergleich- und Wiederholbedingungen bei der Erst-/Eignungsprüfung mit 6,2 und 6,4 Prozent ermittelt. Bei einer Verminderung des Materialeinflusses durch die Verwendung eines Labormörtels verbessern sich die statistischen Kennwerte auf 4,5 und 5,3 Prozent. Mit 8,2 und 9,5 Prozent beziehungsweise 8,6 und 9,5 Prozent werden bei der Restsubstanzbewertung von Wasch- und Unterbetonen die höchsten Werte bestimmt.
Das robuste Auswerteverfahren (ohne Eliminierung der Ausreißer) nach dem Entwurf des FGSV-Merkblatts zur statistischen Auswertung von Prüfergebnissen erwies sich in der Form als ungeeignet und bedurfte einer Überarbeitung. Bezüglich der vergleichend mit klassischen und robusten Verfahren gewonnenen Kennwerte ist festzustellen, dass bei sehr homogenen Messergebnissen eines Prüfloses beide Verfahren nahezu die gleichen statistischen Kennwerte liefern. Bei der Eliminierung von Ausreißern sind die Ergebnisse des robusten Verfahrens in der Regel etwas größer als die des klassischen Verfahrens.
Die begleitenden vertiefenden Untersuchungen bei der Spaltzugprüfung mit innovativen Prüftechniken lieferten wertvolle Erkenntnisse zur Bewertung der Prüfeinflüsse.
Am Ende des 19. und zu Beginn des 20. Jahrhunderts wurden auch in Berlin vermehrt Bauwerke mit einer Fassadenverblendung aus Eifeler Tuffsteinen errichtet. Die Eifeler Tuffsteine zeichnen sich aufgrund ihrer hohen Porosität einerseits durch eine gute Verarbeitbarkeit aus. Andererseits sind sie nur schwach gebunden und besitzen deshalb eine geringe Verwitterungsbeständigkeit.
Concrete-glass windows or commonly referred to as “Dalle de Verre” windows are prevalent in historical monuments across Europe. “Dalle de Verre” windows were made by placing cut stained glasses, of various shapes and sizes, into a steel reinforced concrete frame. In addition to the steel reinforcement, a few steel wires run across the concrete elements to hold the glass windows into place. Much of these structures have been damaged due to carbonation of the thin concrete covers and consequent corrosion of the steel reinforcement; and exhibit several cracks due to the expansive nature of corrosion products formed at the steel–concrete interface. This study focussed on understanding the efficacy of electrochemical realkalisation in reinstating the passive state of the steel reinforcement embedded in such concrete glass windows. Simulant “Dalle de Verre” windows (representative of windows at Kaiser-Wilhelm Gedächtniskirche) were produced using different cements with a water/cement ratio of 0.6 and carbonated under accelerated conditions. Post carbonation, the concrete glass windows were electrochemically realkalised using a sacrificial anode. The influence of highly alkaline conditions due to electrochemical realkalisation on the glass-concrete interface has also been investigated. This study shows that the passive state of the steel reinforcement in “Dalle de Verre” windows, particularly at the Kaiser-Wilhelm Gedächtniskirche (memorial church) in Berlin, can be reinstated using the electrochemical realkalisation method.
Introduction of a monitoring system for Bingham fluids in additive manufacturing with concrete
(2022)
Freeform additive manufacturing of concrete structures is a rising technology in civil engineering with several fascinating advantages. Nonetheless, to ensure reliability and structural integrity, standards and quality control are required in the future to bring this technology into the market. As the concrete is manufactured continuously, continuous quality control of the printing process is also required, i.e. comprehensive process monitoring. At BAM, a test rig will be installed, enabling the printing of concrete structures with a maximum size of 2 m x 1 m x 1 m (l x w x h). Here, process monitoring is the focus of the test rig. In this study, we show the results of the first pump tests, including the measurement of several parameters such as temperature and pressure along the supply system, i.e. from the concrete pump to the printer head.
Die Kaiser-Wilhelm-Gedächtniskirche (KWG) gilt als eine der wichtigsten Sehenswürdigkeiten Berlins in der City West und als ein herausragendes Beispiel für die „Dalle de Verre“ Verglasungen in sakralen Gebäuden. Der vorliegende Beitrag widmet sich der Fassade und den Glasfenstern des neuen Glockenturms, wobei die beschriebenen Szenarien aufgrund der annähernd gleichen Bauweise der restlichen neuen Baukörper in weiten Teilen starke Analogien aufweisen und insofern übertragbar sind.
The determination of the blast protection level of laminated glass windows and facades is of crucial importance, and it is normally done by using experimental investigations. In recent years numericalmethods have becomemuch more powerful also with respect to this kind of application. This paper attempts to give a first idea of a possible standardization concerning such numerical simulations. Attention is drawn to the representation of the blast loading and to the proper description of the behaviour of the material of the mentioned products, to the geometrical meshing, and to the modelling of the connections of the glass components to the main structure.The need to validate the numerical models against reliable experimental data, some of which are indicated, is underlined.
It is important to protect critical buildings (shopping centres, government buildings and embassies), infrastructure and utilities, train and underground stations against being damaged, destroyed or disrupted by deliberate acts of terrorism, criminal activity and malicious behaviour. Normal regulations and building guidelines do not generally take into account these threats. The introduction of appropriate regulations or guidelines, where deemed necessary, should enhance the resilience of buildings and infrastructure against explosion incidents. In order to protect the built infrastructure, methods are required to quantify the resistance of structural components against explosive loading and to assess the hazards resulting from the failure of an element. The applicable state-of-the-art techniques may include either experimental or numerical methods, or a combination of both. Therefore, the thematic group (TG) on the resistance of structures to explosion effects was formed in order to bring the required expertise together, make it commonly available and to find and define harmonised methods and solutions which can be provided to the decision-makers responsible for critical infrastructure protection. This report discusses the differences between the existing standards for testing blast-resistant glazing and windows and it presents basic recommendations for the future development of the suite of European standards in this area.
It is important to protect critical buildings (shopping centres, government buildings and embassies), infrastructure and utilities, train and underground stations against being damaged, destroyed or disrupted by deliberate acts of terrorism, criminal activity and malicious behaviour. Normal regulations and building guidelines do not generally take into account these threats. The introduction of appropriate regulations or guidelines, where deemed necessary, should, enhance the resilience of buildings and infrastructure against explosion incidents. In order to protect the built infrastructure, methods are required to quantify the resistance of structural components against explosive loading and to assess the hazards resulting from the failure of an element. The applicable state-of-the-art techniques may include either experimental or numerical methods, or a combination of both. Therefore, the thematic group (TG) on the resistance of structures to explosion effects was formed in order to bring the required expertise together, make it commonly available and to find and define harmonised methods and solutions which can be provided to the decision-makers responsible for critical infrastructure protection. The current report summarizes existing best practices for the numerical finite element modelling of blast loading, including the important topics of domain discretisation, implicit/explicit formulation, Lagrangian/Eulerian solvers, the mathematical description of the material behaviour etc. Furthermore recommendations for the modelling of laminated glass elements are formulated and knowledge gaps in this application area are pointed out. Hence the report builds the basis for an actual evaluation of the different numerical methods, their suitability to certain problems, and their capability to support/complement the experimental testing of glass components. It thus provides helpful information to design architects and engineers, and more generally to critical infrastructure stakeholders, responsible for the structural integrity and security of the infrastructure in case of an explosion.
The determination of the blast protection level of laminated glass windows and facades is of crucial importance, and it is normally done by using experimental investigations. In recent years numerical methods have become much more powerful also with respect to this kind of application. This report attempts to give a first idea of a possible standardisation concerning such numerical simulations. Attention is drawn to the representation of the blast loading and of the behaviour of the material of the mentioned products, to the geometrical meshing, as well as to the modelling of the connections of the glass components to the main structure. The need to validate the numerical models against reliable experimental data, some of which are indicated, is underlined.
It is important to protect critical buildings (shopping centres, government buildings and embassies), infrastructure and utilities, train and underground stations from being damaged, destroyed or disrupted by deliberate acts of terrorism, criminal activity and malicious behaviour. Normal regulations and building guidelines do not generally take into account these threats. The introduction of appropriate regulations or guidelines, where deemed necessary, should enhance the resilience of buildings and infrastructures against explosion incidents. In order to protect the built infrastructure, testing methods are required which can answer the question whether certain building elements can withstand certain loading conditions created by an explosive event. The applicable state-of-the-art techniques may include either experimental or numerical methods, or a combination of both. Therefore, the thematic group (TG) on the resistance of structures to explosion effects was formed in order to bring the required expertise together, to make it commonly available and to find and define harmonised methods and solutions which can be provided to the decision-makers responsible for critical infrastructure protection. The TG described in a fist report JPC87202 the physical phenomena which have to be understood in order to ensure a proper testing of the elements and a correct interpretation of the results. In a second step, the differences between the existing standards for testing blast-resistant glazing and windows have been derived, and a basis for fundamental recommendations for the future development of the suite of European standards has been addressed JRC94930. Based on the prior findings, this report now formulates the proper enhancements of the existing standards in terms of actual recommendations for the improvement of the test standards.
During the past 20 years, innovative developments in concrete technology have enabled the production of ultra-high performance fibre reinforced concretes (UHPFC) for the protection and preservation of concrete structures. The main characteristics of UHPFC comprise high compressive and flexural strength as well as high ductility compared to normal strength, normal weight concrete (NSC). This paper focuses on the analysis of crack formation and crack propagation in UHPFC under tensile loading under quasistatic conditions by using acoustic emission (AE) and optical deformation analysis (ODA).
AE is a non-destructive technique to monitor the development of micro structural damage processes caused by external forces. In this context, AE allows for a continuous monitoring of changes in the microstructure (cracks) over time and the corresponding localisation by appropriate algorithms. The AE measurements were performed along with ODA at the surface of the samples in order to analyse the deformation behaviour of the samples and the crack propagation.
For the tests, a UHPFC reference mixture was developed and tested with three different volume percentages of steel fibres (1.0 V.-%, 2.0 V.-%, and 3.0 V.-%). This paper shows that the application of AE is a suitable method to analyse the crack propagation in UHPFC specimens under tensile loading and to localise the crack initiation. Furthermore, insights into the failure mechanism of the fibres are offered by the analysis of the signals of the AE measurements, which allows for a better understanding of UHPFC and its general performance.
Waste sludge, a solid recovered from wastewater of photovoltaic-industries, composes of agglomerates of nano-particles like SiO2 and CaCO3. This sludge deflocculates in aqueous solutions into nano-particles smaller than 1 µm. Thus, this sludge constitutes a potentially hazardous waste when it is improperly disposed. Due to its high content of amorphous SiO2, this sludge has a potential use as supplementary cementitious material (SCM) in concrete. In this study the main properties of three different samples of photovoltaic's silica-rich waste sludge (nSS) were physically and chemically characterized. The characterization techniques included: scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), nitrogen physical adsorption isotherm (BET method), density by Helium pycnometry, particle size distribution determined by laser light scattering (LLS) and zeta-potential measurements by dynamic light scattering (DLS). In addition, a dispersability study was performed to design stable slurries to be used as liquid additives for the concrete production on site. The effects on the hydration kinetics of cement pastes by the incorporation of nSS in the designed slurries were determined using an isothermal calorimeter. A compressive strength test of standard mortars with 7% of cement replacement was performed to determine the pozzolanic activity of the waste nano-silica sludge. Finally, the hardened system was fully characterized to determine the phase composition. The results demonstrate that the nSS can be utilized as SCM to replace portion of cement in mortars, thereby decreasing the CO2 footprint and the environmental impact of concrete.
In this study two different types of nano-silica (nS) were applied in self-compacting concrete (SCC), both having similar particle size distributions (PSD), but produced through two different processes: fumed powder silica and precipitated silica in colloidal suspension. The influence of nano-silica on SCC was investigated with respect to the properties of concrete in fresh (workability) and hardened state (mechanical properties and durability). Additionally, the densification of the microstructure of the hardened concrete was verified by SEM and EDS analyses. The obtained results demonstrate that nano-silica efficiently used in SCC can improve its mechanical properties and durability. Considering the reactivity of the two applied nano-silicas, the colloidal type showed a higher reactivity at early age, which influenced the final SCC properties.
Die Forderung, für repräsentative Bauwerke wie Botschaften und Flughäfen auch außergewöhnliche Lasten aus Explosion zu berücksichtigen, wurde in jüngerer Vergangenheit zunehmend gestellt. Das aufgrund dieser Lasten zu erwartende Schadensausmaß kann durch den Einsatz von energiedissipierenden Schutzbauteilen in der Fassadenbefestigung begrenzt werden. Die Dissipation der Explosionsenergie in den Schutzbauteilen kann beispielsweise über ein Crashmaterial erfolgen. In diesem Aufsatz werden Untersuchungen an zementgebundenen Materialien, die diesem Zweck dienen sollen, vorgestellt. Der Einfluss unterschiedlicher Zusätze auf die für ein Crashmaterial maßgebenden Eigenschaften wird in einer Parameterstudie untersucht. Als besonders geeignet wird ein Material identifiziert, bei dem die Zugabe eines Gasbildners das Matrixgefüge im Hinblick auf das gewünschte Kraft-Verformungs-Verhalten positiv verändert. Dynamische Versuche mit diesem Material geben Aufschluss über dessen Komprimierungsverhalten bei hohen Stauchraten.-----------------------------------------------------------------------------------------------------------------------------------------------
In the past few years public awareness of the need to protect structures against blast effects has risen. Energy dissipating protective components placed at the façade connectors allow protecting people in the building as well as the primary building structure from damage due to blast loads. One possibility to dissipate the blast energy is using protective components with crash material. This paper presents tests on cementitious crash materials studying the effect of different additives to the compression-behavior of the material. Additional experiments enable analyzing the material behavior under static and dynamic test conditions.
Im Rahmen einer Bachelorarbeit und in Kooperation mit der Bundesanstalt für Materialforschung und -prüfung (BAM) wurden die eintretenden Schädigungsprozesse während des Spaltzugversuche mittels innovativer Prüfverfahren untersucht. Ziel war es, in Untersuchungen Erkenntnisse über das Versagensverhalten unter statischer und dynamischer Spaltzugbeanspruchung bei der Variation verschiedener Einflussfaktoren zu gewinnen. Hierfür wurde die Aussagekraft innerer und äußerer Schädigungsindikatoren zur Charakterisierung der auftretenden Bruchmechanismen analysiert.