Lehrstuhl Werkstoffe des Bauwesens

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Characterization of the alkali and hydrolysis resistance of polymer-impregnated, alkali-resistant glass filaments
(2024-09-02) Kempis, Florian; Orlowsky, Jeanette
The aim of this series of tests was to characterize the alkali and water resistance of alkaliresistant (durability) glass filaments, which were optimized with two non-vulcanized formulations based on co-polymerizing styrene-butadiene rubbers (CemFil-SBR1 and CemFil-SBR2). Furthermore, it was assessed which of the two polymer-impregnated multifilament yarns is the better alternative for use in cementitious binders. For this purpose, the impregnated multifilament yarns were chemically conditioned for up to twelve months at temperatures of 23 and 50 ◦C in 2.5 percent sodium hydroxide solution and 2.5 percent potassium hydroxide solution as well as in 3 percent salt and distilled water. The samples were then subjected to material science tests. The liquid absorption capacities and the changes in the mass of the composite materials were determined at different times during conditioning. The load-bearing capacity of the samples was also tested using uniaxial fiber strand tensile tests. The durability of the polymer-impregnated multifilament yarns was described in detail in conjunction with scanning electron microscopy images and nominal cross-section determinations. The test liquids caused a reduction in strength during the storage period, which was accelerated by increased temperatures. The reduction in strength is mainly due to glass corrosion of the filaments. Glass corrosion is delayed due to the good impregnation quality, which fundamentally improves the durability of the yarns. The results of the durability tests show that the polymer-impregnated multifilament yarns CemFil-SBR2 are probably more suitable for use in cementitious binders, as they have better alkali and hydrolysis resistance.
Characterization of the chemical resistance of two non-vulcanized styrene–butadiene rubbers (SBR)
(2024-06-14) Kempis, Florian; Orlowsky, Jeanette
The objective of this series of tests is to characterize the alkali and water resistance of two non-vulcanized formulations based on co-polymerizing styrene–butadiene rubbers (SBR1 and SBR2). The relative merits of the two polymer systems as impregnating agents for alkali-resistant glass reinforcement in cementitious binders are assessed. For this purpose, polymer films were synthesized and then chemically conditioned for up to half a year at temperatures of 23 °C and 50 °C in sodium hydroxide and potassium hydroxide solutions as well as in salt and distilled water. Changes in mass, tensile strength, and material hardness were evaluated to assess the chemical resistance of the two polymer systems. The different test liquids generally led to swelling (increase in mass) and degradation (reduction in mass) of the polymer structures. These two processes occurred simultaneously. The liquid absorption capacity of the SBR1 impregnation system was between 25.05% and 51.60% by weight, depending on the test liquids. In contrast, the SBR2 impregnation system exhibited a lower liquid absorption capacity, with a weight increase from 21.19% to 42.90%. The chemical conditioning resulted in a maximum mass reduction of the polymer structure SBR1 of 8.82% by weight. The polymer SBR2, on the other hand, only lost up to 2.88% by weight. The tensile strengths of the unconditioned samples of the polymer systems SBR1 and SBR2 were 55.49 ± 7.47 N and 80.87 ± 15.96 N, respectively. The test liquids caused a reduction in strength over the storage period which was accelerated by increased temperatures. The loss of strength of the polymer structure SBR2 was lower over the entire conditioning period. In this context, a correlation was found between strength and material hardness. Overall, the polymeric impregnation system SBR2 had a lower liquid absorption capacity and a lower degree of damage caused by the degrading test liquids. Furthermore, the tensile strength was generally higher and more robust over the entire conditioning period. The results of the durability tests indicate that the SBR2 polymer system is more suitable for use in cementitious binders, as it exhibits less degradation of the polymer structure in response to chemical aging processes.
Self-compacting high-strength textile-reinforced concrete using sea sand and sea water
(2023-07-10) Kryzhanovskyi, Vitalii; Avramidou, Athanasia; Orlowsky, Jeanette; Spyridis, Panagiotis
In this study, a self-compacting high-strength concrete based on ordinary and sulfate-resistant cements was developed for use in textile-reinforced structural elements. The control concrete was made from quartz sand and tap water, and the sea concrete was made from sea water and sea sand for the purpose of applying local building materials to construction sites in the coastal area. The properties of a self-compacting concrete mixture, as well as concrete and textile-reinforced concrete based on it, were determined. It was found that at the age of 28 days, the compressive strength of the sea concrete was 72 MPa, and the flexural strength was 9.2 MPa. The compressive strength of the control concrete was 69.4 MPa at the age of 28 days, and the flexural strength was 11.1 MPa. The drying shrinkage of the sea concrete at 28 days exceeded the drying shrinkage of the control concrete by 18%. The uniaxial tensile test showed the same behavior of the control and marine textile-reinforced concrete; after the formation of five cracks, only the carbon textile reinforcement came into operation. Accordingly, the use of sea water and sea sand in combination with a cement with reduced CO2 emissions and textile reinforcement for load-bearing concrete structures is a promising, sustainable approach.
Untersuchungen zu mineralischen Tränkungen von technischen Textilien für die flächige Instandsetzung von gerissenen Bauwerken mit Textilbeton
(2023) Lenting, Martin; Orlowsky, Jeanette; Raupach, Michael; Willems, Wolfgang M.
In dieser Arbeit wurden mineralische Tränkungen von technischen Textilien für die flächige Instandsetzung von gerissenen Bauwerken mit Textilbeton untersucht. Der Schwerpunkt lag auf der Entwicklung einer mineralischen Tränkung in Kombination mit einem einfachen Textiltränkungsverfahren und der anschließenden Untersuchung und Bewertung der Materialeigenschaften am Textil und im Verbundprobekörper. Auf Basis von Kieselsäureester konnte ein Instandsetzungsystem für z. B. temperaturbedingte Rissbewegungen gerissener Bauwerke entwickelt werden, welches die Rissbewegung in viele feine Risse im Textilbeton verteilt. Neben standardisierten Prüfmethoden wurde das mineralische Tränkungsmaterial auch mittels Mikroskopie, REM-EDX-Analysen sowie TGA-Analysen hinsichtlich des allgemeinen Tragverhaltens und hinsichtlich besonderer Beanspruchungen durch Temperatur und Alterung auf Eignung geprüft. Dazu wurden verschiedene technische Textilien, Tränkungsmaterialien mit unterschiedlicher Verkieselung und Mehrfachtränkungen betrachtet. Abschließende Untersuchungen zur Rissheilungs- und Rissüberbrückungsfähigkeit dienten der Überprüfung des Instandsetzungssystems hinsichtlich praxisnaher Randbedingungen. Die Tastversuche an zwei Rissüberbrückungsprobekörpern in Anlehnung an die Systemprüfung nach dem BAW-Merkblatt MITEX zeigten, dass ein Instandsetzungssystem aus Textilbeton mit Textilgelegen aus zweifach getränkten Carbonrovings mit dem entwickelten Tränkungsmaterial Kieselsäureester 100 ohne Lösemittel eine Rissbewegung im Grundkörper (Bestandsbauwerk) von bis zu 0,6 mm aufnehmen kann und in ausreichend viele Risse mit geringen Rissbreiten verteilt.
About the effectiveness of a hydrophobic surface treatment of Baumberger Sandstones
(2022-01-31) Orlowsky, Jeanette; Groh, Melanie; Braun, Franziska
The Baumberger Sandstone, a sandy limestone, is used since the Middle Ages as a building material not only in the surrounding Münster region of North Rhine-Westphalia (Germany), where it is quarried since to date. To prevent the ingress of water and reduce weathering processes conservation methods, mostly in form of organosilicon compounds, were used. This study deals with the performance of applied hydrophobing agents on Baumberger Sandstone samples and their influence on the weathering processes during long-term exposure. The samples were exposed at several locations in Germany to different climatic conditions for up to 24 years. Afterwards, investigations concerning the water absorption behaviour and the degree of superficial damages were carried out. With an evaluation method on basis of NMR measurements, a very low and uneven distributed effective hydrophobic zone could be detected. This caused an ingress of water in the uppermost part and a progressive weathering of investigated natural stones. Thus the hydrophobic surface treatment did not lead to a significant decrease of weathering or damaging processes. Based on these results a hydrophobic surface treatment of Baumberger Sandstone seems not to be suitable.
Quantification of the influence of concrete width per fiber strand on the splitting crack failure of textile reinforced concrete (TRC)
(2022-01-26) Beßling, Markus; Orlowsky, Jeanette
The composite material textile reinforced concrete (TRC) requires a high bond performance between the fiber strand and the concrete matrix. While the influence of the textile on bond behavior is well known, in this publication the influence of the concrete matrix is investigated by means of single-sided pull-out tests. The results of the presented study show dependence between the concrete strength and bond performance of the composite material. When a concrete of a higher-strength class is used, the bond-flow–pull-out distance curve shifts upward independent of the textile geometry and the yarn impregnation. A simplified model is presented to predict the occurrence of a crack along the fiber strand. This model serves as a basis to investigate the correlation between concrete width per fiber strand and resistance against a splitting crack. The effective concrete tensile strength decreases to about 35% when the concrete width is increased from 10 mm to 50 mm. To quantify the decrease, a mathematical relationship, which describes the test results independent of textile and concrete type, is proposed.
Zur Ermittlung des Langzeitverhaltens hydrophobierter Natursteinoberflächen unter dem Einfluss der natürlichen Verwitterung
(2021) Braun, Franziska; Orlowsky, Jeanette; Middendorf, Bernhard
In dieser Arbeit wurde das Verwitterungsverhalten unbehandelter und mit Steinschutzstoffen imprägnierter Baumberger, Schleeriether und Obernkirchener Sandsteine über einen Zeitraum von bis zu 30 Jahren analysiert. Ziel war es zu prüfen, ob eine hydrophobe Oberflächenausstattung im Vergleich zu nicht-behandelten Oberflächen auch auf lange Sicht in der Lage ist, Verwitterungseinflüsse deutlich zu verlangsamen und das Verwitterungspotential auf ein Minimum zu reduzieren. Ebenso erfolgte eine Eignungsprüfung der unterschiedlichen Stoffgruppen (Silane, Siloxane und Silikonharze), wodurch mittelspezifische sowie stoffgruppenabhängige Aussagen hinsichtlich der Verwendung sowie zur Langzeitwirkung getroffen werden konnten. Zur Bestimmung der Leistungsfähigkeit wurden zerstörungsarme und zerstörungsfreie Untersuchungsmethoden herangezogen. Neben den standardisierten und genormten Prüfmethoden konnte anhand unilateraler NMR-Messungen, bestehend aus NMR-Saugversuchen und NMR-Tiefenprofilen, die Langzeitwirkung von Hydrophobierungen bewertet werden. Der Fokus lag auf dem zerstörungsfreien Nachweis der verbliebenen Hydrophobie sowie auf der Analyse der sich in Folge der Tränkungsmaßnahme und Verwitterungseinflüsse ändernden feuchtetechnischen Eigenschaften. Hieraus konnten wesentliche Einflussgrößen bezüglich der Dauerwirksamkeit definiert werden. Die ausgehend davon entwickelten Bewertungskriterien stellen eine praxisorientierte Handlungsempfehlung für die Planung, Ausführung und Kontrolle von Hydrophobierungsmaßnahmen dar.
Prestressing effect of shape memory alloy reinforcements under serviceability tensile loads
(2021-03-06) Beßling, Markus; Czaderski, Christoph; Orlowsky, Jeanette
Repairing and strengthening of existing aged steel-reinforced concrete structures is a major challenge. Today, much of the repair work completed is insufficient and brittle. A promising new solution for repair and strengthening tasks is the use of iron-based shape memory alloy (Fe-SMA). The pre-strained Fe-SMA components enable the pre-stressing of existing building components due to the heat-triggered contraction of the steel. Thus, deflections can be reduced or even recovered. In addition, the cracking process can be adapted, and an improvement in the load, under which the first crack appears, is possible. In this paper, the effects of pre-stress generated by activated Fe-SMA rebars, which were centrally embedded inside of a concrete specimen, are shown. The objective of the study is to quantify the improvement in the loads of the first crack and show the influences of the pre-stressing on the load-bearing behavior and the cracking process. For this purpose, axial tensile tests were performed on concrete bars with height, width, and length of 50 mm, 70 mm, and 900 mm, respectively. These were compared to usual construction steel rebars, pre-strained but nonactivated Fe-SMA rebars, and activated Fe-SMA steel rebars. The evaluation of crack patterns and openings was done using digital image correlation (DIC). The pre-stressing of the concrete causes an increase in the first crack loads of more than 150%, which indicates a clear improvement in the state of serviceability limit.
Analyzing surface near regions of hydrophobic and long-term weathered natural stones at microscopic scale
(2020-06-12) Braun, Franziska; Orlowsky, Jeanette; Brüggerhoff, Stefan
The visual appearance of building structures is an important attribute which reflects the character and identity of a region. Due to the influence of weathering, the surfaces of building stones alter, leading to aesthetic changes of the material surface such as discoloration or darkening. In this study, near-surface regions of weathered Baumberger (BST), Schleeriether (SST), and Obernkirchener Sandstones (OKS) have been analyzed at the microscopic scale in order to investigate the intensity and the extent of visual as well as structural changes and how both can be a ected due to the presence of surface treatments with hydrophobing agents. It could be detected that aesthetic changes appeared already after 2 years of outdoor exposure, with the slightest variations on BST surfaces, followed by SST and OKS. The use of hydrophobing agents leads to a reduction in surface darkening in the short term. After long-term weathering, no significant changes are visible, as similar values in total color di erence (DE*) were measured. Biogenic growth and the formation of black weathering crusts are the main reasons for color alterations in the case of the examined stones. The surface damages occur especially on calcareous (BST) followed by clayey (SST) and quartzitic (OKS) stone surfaces.
The influence of 30 years outdoor weathering on the durability of hydrophobic agents applied on Obernkirchener Sandstones
(2020-01-20) Orlowsky, Jeanette; Braun, Franziska; Groh, Melanie
The durability of eleven different water repellents applied on one sandstone type was studied after a long-term weathering at seven different locations in Germany. By measuring colour changes, it could be shown that the formation of black crusts, the deposition of particles and biogenic growth caused a gradual darkening as well as significant changes in total colour over time. Additionally, the water absorption behaviour was investigated with two different methods: applying a low pressure using the pipe method and capillary water absorption measurements from a wet underlay. Afterwards, the test results were analysed with four different evaluation methods: calculation of the protection degree from pipe method and capillary water absorption, determination of the velocity of water uptake during capillary water absorption and calculation of the damaged depth of the stone surface using single-sided NMR technique. The growing damaged depth leads to an increase of the water uptake velocity and to a decrease of the protection degree of the applied hydrophobing agents. Three protective agents based on isobutyltrimethoxysilane showed already after two years of outdoor weathering a clear loss of performance, which significantly increased after 30 years of exposure.
Zur Dauerhaftigkeit von AR-Glasbewehrung in Textilbeton
(Beuth, 2004) Orlowsky, Jeanette; Raupach, Michael; Reinhardt, Hans-Wolf
AR-Glasbewehrungen in Betonen, die zum Beispiel im Verbundwerkstoff Textilbeton zum Einsatz kommen, verlieren infolge Bewitterungen langfristig an Festigkeit. Die Kenntnis der zeitabhängigen Entwicklung des Festigkeitsverlustes ist ein wesentlicher Aspekt bei der Anwendung textilbewehrter Bauteile in statisch relevanten Bereichen. Im Rahmen dieser Arbeit wird die Entwicklung eines Dauerhaftigkeitsmodells beschrieben, welches den Verlauf des Festigkeitsverlustes von AR-Glasbewehrungen in Textilbetonen infolge beliebig komplexer Bewitterungen, wie sie z. B. bei Außenbauteilen auftreten, abbildet. Zur Realisierung dieses Ziels wurde zunächst die maßgebende Ursache für den Festigkeitsverlust von AR-Glas im Beton ermittelt. Darauf basierend erfolgte eine modellhafte Beschreibung des Festigkeitsverlustes bei konstanten Klimabedingungen sowie die Verifikation des Modells mit einer Vielzahl an Untersuchungsergebnissen, die auch mit unterschiedlichen Versuchsmethoden bestimmt wurden. Die Einflüsse Feuchte, Temperatur, pH-Wert, Glasart und Dauerlast auf den Festigkeitsverlust der AR-Glasbewehrung wurden untersucht. Zusätzlich wurden auch kombinierte Beanspruchungen analysiert, um abschließend ein Dauerhaftigkeitsmodell herzuleiten, welches die Berücksichtigung beliebig komplexer Bewitterungen erlaubt. Mit dieser Arbeit wurde somit die Grundlage für eine quantitative, auf die jeweiligen Material- und Bewitterungsbedingungen abgestimmte Prognose des Festigkeitsverlustes von ARGlasbewehrung in Textilbeton geschaffen.
Analyzing of coatings on steel - reinforced concrete elements by mobile NMR
(de Gruyter, 2016) Orlowsky, Jeanette
A large number of infrastructural concrete buildings are protected against aggressive environments by coating systems. The functionality of these coating systems is mainly affected by the composition and thickness of the individual polymeric layers. For the first ti me ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive delermination of these irnportanl paramelers on the building sile. However, before lhis technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i .e. the NMR signal, needs to be studied. The results show a shift of the NMR profile as weil as an increase of the signals amplitude in the case of the reinforced samples, while calculating the thickness of concrete coating leading to identical results.
Zur Dauerhaftigkeit von Oberflächenschutzsystemen für die Erhaltung von Betonbauwerken
(2012) Orlowsky, Jeanette
Characterization of natural and consolidated stones from Jordan with non-destructive ultrasonic technique and physico-mechanical methods
(2012-01-05) Ahmad, Abdelraheem; Middendorf, Bernhard; Simon, Stefan; Snethlage, Rolf
The purpose of this dissertation was to investigate different stone samples (limestone, basalt and marble) from five important archaeological sites in north and northeast Jordan for the purpose of their conservation. This research focused on the use of non-destructive ultrasonic technique as validated by traditional physico-mechanical methods for the study of the weathering of the selected stones and their durability and the evaluation of the effectiveness of consolidation treatments. The selected stones were characterized and the changes in their properties after artificial weathering and consolidation were studied. It was found that the susceptibility of the studied stone samples to salt damage is determined by their petrophysical rather than mechanical properties. In terms of loss of stone material, the damage induced by the crystallization of salt in the stones seems to be dependent on their proportion of micropores and free porosity. Durability estimators for the evaluation of the weathering resistance of stone were consequently developed. The study provided additional evidence that ultrasonic technique is an effective method for estimating the degree of cracking and evaluating the effectiveness of stone consolidation treatments. Ultrasonic velocity seemed to correlate well with the degree of cracking in the stones. This implies that weathering classification schemes, such as those already existed for marble, based on correlation between ultrasonic velocity and increasing porosity can be developed for the studied stones. However, it is necessary to study these correlations for the particular stones in fresh and different weathering conditions. This dissertation recommends the in situ application of ultrasonic technique for the assessment of the weathering condition of Jordanian archaeological stones and for the evaluation and control of consolidation treatments.
Schutz und Instandsetzung von Waschbetonoberflächen
(Universität Dortmund, 2002-07-03) Katschke, Silke; Neisecke, Jürgen; Schäfer, Horst Georg
Waschbeton unterscheidet sich von üblichen Stahlbetonoberflächen nur durch die Oberflächenstruktur. Folglich treten auch hier die bekannten Abplatzschäden über korrodierenden Bewehrungsstählen bei unzureichender Betonüberdeckung oder Betonqualität infolge Karbonatisierung auf. Für Schutz und Instandsetzung von Schäden an Stahlbetonoberflächen gelten die Vorgaben und Anforderungen der ZTV-SIB des BMV bzw. der Rili-Sib des DAfStb derzeit als Stand der Technik. In beiden Regelwerken finden sich jedoch keine Vorgaben oder Hinweise für Schutz und Instandsetzung von Waschbetonoberflächen. Unter Berücksichtigung der Verfahren und Werkstoffe der Regelwerke wurden drei im Erscheinungsbild unterschiedliche Verfahrensweisen zur Instandsetzung von Waschbetonoberflächen in umfangreichen Untersuchungen im Labor und am Bauwerk untersucht. Ein weiterer Schwerpunkt lag auf der Messung und statistischen Auswertung der Schichtdicken der OS-Beschichtung zur Sicherstellung der erforderlichen systemspezifischen Mindestschichtdicke. Aufgrund der Ergebnisse der vorliegenden Arbeit kann davon ausgegangen werden, daß Schutz und Instandsetzung von Waschbetonoberflächen auch unter Erhalt bzw. Wiederherstellung der ursprünglichen Oberflächenstruktur mit den hier ermittelten Werkstoffen und Verfahrensweisen unter Anwendung der erforderlichen Sorgfalt entsprechend dem Stand der Technik möglich ist, wobei das Anlegen von Probeflächen am Bauwerk in jedem Falle unerläßlich ist.
Über ein bildgebendes Ultraschallecho-Verfahren für die zerstörungsfreie Prüfung von Betonbauteilen
(Universität Dortmund, 2002-04-22) Wollbold, Frithjof; Neisecke, Jürgen; Diederichs, U.
Die vorliegende Dissertation befasst sich mit dem Aufbau und der Weiterentwicklung eines neuartigen Prüfsystems zur Prüfung von Beton und mineralischen Bauteilen nach dem Ultraschallecho-Prinzip. Prüfungen im Bereich der Betonwerkstoffe nach dieser Methodik waren i.W. auch aus technischen Gründen bis ca. 1990 nur im Labor, nicht jedoch in der Baustellenpraxis möglich. Durch den Einsatz neuentwickelter Prüfköpfe und die Integration moderner Computerkomponeten in das Prüfsystem wurde es erreicht, dass auch direkt vor Ort ("in-situ") eine signifikante Interpretation der gewonnenen Messdaten wesentlich durch eine schnelle bildgebende B-Bild-Darstellung möglich ist. Die vorliegende Dissertation beschreibt die Schritte zum Aufbau und zur Erweiterung der Prüfeinrichtung sowie die im Labor und mit dieser Technik erstmals auch an praktischen Bauwerken durchgeführten Untersuchungen. Ein Teil der Arbeit befasst sich zudem mit einem speziellen Forschungsprojekt, welches die Möglichkeiten zur Ankopplungsverbesserung der Prüfköpfe mittels einer sog. "Elektro-Viskosen Flüssigkeit" untersucht.

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