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ln most of the ASR-test procedures, the expansion of concrete or mortar specimens is used as an indicator to assess the ASR-potential of an aggregate or a specific concrete mix. For these tests, the specimens are stored in an ASR-provoking environment, where the reaction is accelerated by elevated temperature and humidity. To measure the length change, the storage must be interrupted for at least a few minutes. Düring the 60 °C Concrete Prism Test (60 °C-CPT), the specimens are cooled down to 20 °C for 24 hours, to ensure the same hygrothermal conditions for every measurement. This limits the number of measurements during the test period and may lead to additional effects, that probably influence the expansion development.
With a recently developed device, it is possible to continuously monitor the expansion ofprisms without interrupting the ASR-provoking storage. Due to the dense database of this automated test, the results can contribute to a better understanding of the ASR-process. This study compares results of the automated and conventional 60 °C-CPT. Tests of different aggregates showed, that the results of the automated and conventional test are consistent, but the expansions during the conventional test are generally higher. Preliminary results led to the conclusion, that the cooling for the measurements leads to additional expansions. Therefore, a modified threshold should be discussed for the automated 60 °C-CPT.
During the service life of structural sealant glazing (SSG) facades, the loadbearing capacity of the silicone bonds needs to be guaranteed. Laboratory Tests can assess the durability of SSG-systems based on mechanical characteristics of the bond after simultaneous exposure to both climatic and mechanical loads.
This article studies how the material characteristics of two common structural sealants are affected by laboratory and field exposure. Dynamic mechanical Analysis (DMA) confirms a reduction in the dynamic modulus of exposed Silicone samples. Results from thermogravimetric analysis, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and small-angle X-ray scattering/wide-angle X-ray scattering show differences between the two sealants and indicate no/minor changes in the composition and morphology of the laboratory and field exposed sealants. Mechanical characterization methods, such as DMA, and tensile and shear testing of the structural bond, are shown to be sensitive toward the combined climatic and mechanical loadings, and are hence suitable for studying degradation mechanisms of structural sealants.
Durability Assessment of Structural Sealant Glazing Systems applying a Performance Test Method
(2020)
During the service life of a Structural Sealant Glazing (SSG) facade, its silicone bond is exposed to climatic, chemical, and mechanical loads. While current durability assessment methods schedule separate test programmes for accelerated weathering and fatigue, the presented test applies mechanical loading and weather cycling simultaneously to simulate 50 years of use. Specifically designed medium-scale system specimens resemble a common SSG-bond. Displacement-controlled sinusoidal load cycles in two load directions subject these specimens to tensile, compression and shear loads. Weathering comprises temperature and humidity cycles, UV-radiation, and application of water and detergent. During testing, the forces transmitted by the system specimens are continuously measured for performance assessment. The resulting system response reveals mechanical performance characteristics like elastic moduli and dissipated energies which decrease during exposure, indicating stress relaxation and degradation. Two common structural sealants were tested. After testing, sections of the system specimens were subjected to tensile and shear tests for mechanical characterisation. Strengths and moduli are notably reduced by combined loading compared to those of reference and weathered specimens. Hardness and visual inspections of the bond correlate with the performance and bond characteristics. The approach introduced in this article provides a basis for life cycle assessment of SSG-systems.
Der 60 °C-Betonversuch ist eine in Deutschland und international verbreitete Methode um die Empfindlichkeit von Gesteinskörnungen und Betonen hinsichtlich einer Alkali-Kieselsäure Reaktion (AKR) zu prüfen. Dieser Beitrag stellt eine neuentwickelte automatisierte Variante der Prüfmethode in einem Minireaktor vor. Dabei werden die Dehnungen von Betonprismen nicht, wie beim konventionellen Test manuell, sondern automatisch in entsprechend ausgerüsteten Prüfbehältern gemessen. Neben einer Reduzierung des Messaufwands bringt die automatisierte Prüfung im Minireaktor weitere Vorteile. Die Dehnungssignale werden, anders als bei der konventionellen Messung, quasi-kontinuierlich aufgezeichnet und bilden das Expansionsverhalten der Prismen detailliert ab. Außerdem bleiben Unterbrechungen der AKR-provozierenden Lagerung aus, die bei der konventionellen Prüfung notwendig sind. Im Beitrag werden die automatisierte und konventionelle Prüfung anhand der Dehnungen von Prismen zweier Gesteinskörnungen verglichen. In Übereinstimmung mit vorhergehenden Untersuchungen sind im Minireaktor gemessene Dehnungen systematisch kleiner als manuell gemessene. Als mögliche Ursache werden Unterschiede im Auslaugverhalten experimentell untersucht. Zur Überprüfung der Einstufung der zwei Gesteinskörnungen erfolgen außerdem Referenzprüfungen in der Nebelkammerlagerung bei 40 °C.
Reliable performance of structural sealant glazing (SSG) systems is necessary to utilise advantages of SSG in glass facades. Conventional durability assessment of structural sealant joints is based on separated weathering tests and empirical fatigue testing. This work presents a new test methodology for performance assessment of SSGjoints at simultaneous weathering and two-dimensional mechanical loading. The climatic and mechanical load function were derived from common loading scenarios according to a worst case approach. A System test specimen, resembling a common SSG-joint, was exposed to 24 h of combined loading in a custom-designed test facility. From the recorded mechanical system response, characteristic parameters were evaluated to assess the performance of the system at varying climatic and mechanical conditions. These experimental results reveal effects of ambient conditions, previous loading and deformation Amplitude peaks on the system response. The proposed test methodology opens up for new performance-related approaches in durability testing.
Zur Vermeidung der schädigenden Alkali-Kieselsäure-Reaktion (AKR) in Betonbauwerken wird die Alkalireaktivität von Gesteinskörnungen getestet. Der 60°C-Betonversuch ermöglicht eine vergleichsweise schnelle Einschätzung nach fünf-monatiger Testdauer. Dazu wird die Dehnung von Betonprüfkörpern, die mit der zu testenden Gesteinskörnung hergestellt wurden, manuell alle 28 Tage gemessen. Ein alternatives, an der BAM in den vergangen Jahren entwickeltes Verfahren setzt Dehnungssensoren ein, um kontinuierlich und online zu messen. Ziel dieses MNPQ-Projektes war es ein Messmodul zu entwickeln, welches eine kontinuierliche Dehnungsmessung leicht handhabbar umsetzt. Das von der Firma Schleibinger Geräte Teubert und Greim GmbH und der BAM in Kooperation entwickelte Messmodul lässt sich entweder in die herkömmliche AKR-Prüftruhe, in einen Wärmeschrank oder einen eigens entwickelten Minireaktor einlagern. Die kontinuierliche berührungslose Dehnungsmessung mittels Wirbelstromsensoren hat sich als robust und leicht handhabbar herausgestellt. Im Rahmen des Projektes ausgeführte Messungen untersuchen Einflüsse von gegenüber dem konventionellen Test variierten Testparametern, wie u.a. der Prüfkörperzahl je Behälter und dem ausbleibenden Drehen der Prüfkörper während des Tests. Die kontinuierliche Erfassung von Schallemissionen und Ultraschallgeschwindigkeit erweist sich als interessante Option um ein umfassendes Bild der Schädigungs-, Expansions-, und Hydratationsvorgänge zu gewinnen. Der eingefügte Erfolgskontrollbericht stellt den Projektverlauf dar und zeigt Chancen des entwickelten Gerätes auf.
The susceptibility of concrete structures due to alkali–silica reaction (ASR) can be assessed by means of ASR concrete prism testing at 60 °C, according to RILEM AAR 4.1. There, expansion of concrete prisms indicates alkali-reactivity of the examined concrete mix. This work applies in situ expansion measurement to accelerated concrete prism testing. Automated measuring facilitates both storage without the usually necessary interruptions for manual measurement and acquisition of quasi-continuousexpansion data. A comparative experimental programme showed that conventional testing resulted in stronger expansion and leaching of alkalis than automated testing. Experimental simulation of interruptions, typically associated with manual measurements in conventional testing, could prove the influence of these cooling–heating cycles. Two phenomenological approaches, frequently used for describing reaction kinetics of ASR by linking it to expansion results from ASR-testing, were validated with continuous expansion data of three types of aggregate. Experimental expansion depicted s-shaped curves similar to them of the modelling approaches. However, strong swelling recorded in the beginning of the test was not covered by the model curves. Auxiliary measurement of acoustic emissions and ultrasonic velocity helped characterising mechanisms such as hydration and cracking, which also influence prism expansion. The proposed modification of the measurement procedure provides an extended basis to analyse expansion mechanisms. Regarding data for validation of ASR-expansion models, continuous expansion results are preferable to conventional test results.
The accelerated concrete prism test (ACPT-60 °C) facilitates testing of alkali-silica reactivity of aggregates within five months. Manual measurement is usually conducted to determine expansion of test specimen every 28 days. This conventional procedure gives only limited insight to expansion behaviour of ASR-affected prisms. Due to the large time intervals, expansion exceeding the critical value of 0.3 mm/m is likely to be noticed late. Continuous recording resolves this problem and delivers beneficial information on the shape of the expansion curve.
Displacement transducers integrated into a special testing equipment developed at BAM put continuous measurement into practice. Additionally, ultrasonic velocity and acoustic emissions are measured in-situ and provide deeper insights into hydration and crack formation processes during the test.
Aiming for an automated testing method close to the German guideline, the following technical and methodical challenges arise. Changing of the vertical orientation of the prisms with every manual measurement as standardised cannot be implemented. Furthermore, preliminary results already proved true that cooling and heating cycles, as necessarily associated with each manual measurement, can evoke additional expansion. Therefore, interrupted and continuously measured expansions reveal systematic differences, indicating the necessity to adjust the threshold expansion value for automated testing.
Results presented in the paper: Different types of reactive aggregate have been tested applying continuous and manual expansion measurement to the concrete specimens. Development of continuously measured ultrasonic velocity and acoustic emissions of the aggregates tested diverge significantly while the expansion curves vary in shape and maximum strain. Prisms produced from a slowly reacting aggregate do not exhibit noticeable crack formation. It shows that comprehensive measuring helps describing and distinguishing ASR-damage mechanisms.
Models of ASR-induced expansion, available in the open literature, so far are validated with discontinuous data hardly tracing the modelled curve. Continuous measurement improves validation and further model development.
The accelerated concrete prism test (ACPT-60 °C) facilitates testing of alkali-silica reactivity of aggregates within five months. Manual measurement is usually conducted to determine expansion of test specimen every 28 days. This conventional procedure gives only limited insight to expansion behaviour of ASR-affected prisms. Due to the large time intervals, expansion exceeding the critical value of 0.3 mm/m is likely to be noticed late. Continuous recording resolves this problem and delivers beneficial information on the shape of the expansion curve.
Displacement transducers integrated into a special testing equipment developed at BAM put continuous measurement into practice. Additionally, ultrasonic velocity and acoustic emissions are measured in-situ and provide deeper insights into hydration and crack formation processes during the test.
Aiming for an automated testing method close to the German guideline, the following technical and methodical challenges arise. Changing of the vertical orientation of the prisms with every manual measurement as standardised cannot be implemented. Furthermore, preliminary results already proved true that cooling and heating cycles, as necessarily associated with each manual measurement, can evoke additional expansion. Therefore, interrupted and continuously measured expansions reveal systematic differences, indicating the necessity to adjust the threshold expansion value for automated testing.
Results presented in the paper: Different types of reactive aggregate have been tested applying continuous and manual expansion measurement to the concrete specimens. Development of continuously measured ultrasonic velocity and acoustic emissions of the aggregates tested diverge significantly while the expansion curves vary in shape and maximum strain. Prisms produced from a slowly reacting aggregate do not exhibit noticeable crack formation. It shows that comprehensive measuring helps describing and distinguishing ASR-damage mechanisms.
Models of ASR-induced expansion, available in the open literature, so far are validated with discontinuous data hardly tracing the modelled curve. Continuous measurement improves validation and further model development.
Zur Vermeidung der schädigenden Alkali-Kieselsäure-Reaktion in Betonbauwerken wird die Alkalireaktivität von Gesteinskörnungen im Vorhinein getestet. Der 60°C-Betonversuch ermöglicht eine vergleichsweise schnelle Einschätzung nach fünf-monatiger Testzeit. Dazu wird die Dehnung von Betonprüfkörpern, die mit der zu testenden Gesteinskörnung hergestellt wurden, manuell alle 28 Tage gemessen. Ein alternatives, an der BAM in den vergangen Jahren entwickeltes Verfahren setzt Dehnungssensoren ein, um kontinuierlich und online zu messen. Die Dehnungskurven sind eine gute Grundlage sowohl für die Prognose vom Expansionsverhalten während des Tests als auch für die Validierung von Expansionsmodellen.
The concrete prism test at 60°C facilitates accelerated testing of alkali-silica reactivity of aggregates within five months. Manual measurement is usually conducted to determine expansion of test specimen every 28 days. This conventional procedure gives only limited insight to expansion behaviour of ASR-affected prisms. Due to the large time intervals, expansion exceeding the critical value of 0.3 mm/m is likely to be noticed late. Continuous recording applied in this work resolves this problem and delivers beneficial information on the shape of the expansion curve.
Different types of aggregate have been tested applying continuous and manual measurement to the concrete specimens.
Models of ASR-induced expansion, available in the open literature, so far are validated with discontinuous data hardly tracing the modelled curve. Continuous measurement improves validation and further model development.
Electrocoalescence of aqueous droplets in oil emulsions is commonly contemplated for enhancing separation.
High voltage electric fields can induce charges to Drops evoking merging of adjacent droplets. The newly formed larger Drops then sink faster in gravitational common settlers. Therefore, separation performance of an electrostatic coalescer is strictly linked to characteristics of the electric field and properties of the liquid−liquid system. In this work, the coalescence Performance of water droplets sinking in dodecane at a pulsed DC electric field is investigated. An experimental setup allowing the simultaneous injection of similar sized drops, setting of voltage and pulsation frequency, and particle tracking at high frame rate and resolution is designed. The generated data are used to check the validity of modeling approaches for drag, dipole−dipole forces, and film-thinning. Furthermore, CFD simulations are carried out using a volume of fluid method tracking the interfaces between the two phases.