Jeanette Orlowsky

Recommendation of RILEM TC 232-TDT: test methods and design of textile reinforced concrete: Uniaxial tensile test: test method to determine the load bearing behavior of tensile specimens made of textile reinforced concrete

Textile reinforced concrete (TRC) is a high performance cementitious composite using straight and parallel aligned fibers of suitable materials, e.g. ARglass and carbon, as continuous reinforcement in form of textiles. Textile reinforced concrete is usually used for thin concrete elements or as strengthening layers for concrete structures. Textile reinforced concrete shows a multi linear stress-strain-behavior with three distinct stages (uncracked, multiple cracking, cracking completed). The crack formation in textile reinforced concrete is significantly finer than in customary reinforced concrete. Therefore, not only the tensile strength of the concrete but also the total tensile load bearing behavior of the composite material textile reinforced concrete is of importance. The uniaxial tensile test presented here is a test method to determine the load bearing behavior of tensile specimens made of TRC. Bond characteristics of textile reinforcement can not be derived from this tensile test since this information could only be derived indirectly from cracking patterns. However, in textile reinforced concrete cracking is mainly controlled by transverse fibers which are typically present in textile reinforcement. For bond properties reference is given to the RILEM recommendation TDT A.2 (pull-out).

Behavior of Textile-Reinforced Concrete in Fire

Textile-reinforced concrete has great potential for use in lightweight, thin-walled structural components. Since such elements participate directly in load transmission in the structural framework, satisfactory fire resistance is often desirable. Experience until now, however, has been limited with respect to the behavior of textile concrete elements subjected to fire. In this investigation, four fire tests have been performed on textile-reinforced concrete sections (I-profiles), in which one side of the sections was exposed to fire. The textiles tested were AR glass, carbon, and carbon coated with styrene butadiene. These experiments demonstrated that the load-bearing behavior of textile-reinforced structural components in fire greatly depends on the textile used, their bond to the concrete, and the behavior of the concrete under high temperatures.

Impact of Silane and Siloxane Based Hydrophobic Powder on Cement-Based Mortar

Impact of the addition of silane and siloxane based hydrophobic powders on cement based mortar was studied. Effect of powder addition on mechanical properties and water absorption of cement based mortar is described. Impact of accelerated ageing, including UV radiation, and rain-sun cycles on hydrophobic performance was assessed, demonstrating excellent durability of silane-based hydrophobic performance.

Durability models for GRC: uncertainties on strength predictions

Abstract Even though several models exist in the literature to predict the strength durability of glass fibre (textile) reinforced concrete (GRC), a considerable gap still exists between theory and practice. No real guidelines are available for testing, model calibration and model selection. This work analyses all the uncertainties in the GRC strength durability determination process. The paper addresses the determination of the best approximating model by applying a statistical model selection method (Akaike’s information criterion) on an extensive series of accelerated aging tests; a theoretical approach is presented which enables the user to check the reliability of the model selection. A method is presented for the determination of the uncertainty in the strength prediction, taking into account both the statistical distribution present on the (tensile) strength of the GRC material as well as the effect of model calibration based on a limited set of accelerated aging tests.

Durability aspects of AR-glass-reinforcement in textile reinforced concrete, Part 1: Material behaviour

Textile reinforced concrete (TRC) is an innovative material for thin-walled, structural elements with a high load-bearing capacity. For a safe design of TRC load bearing structures ambitious investigations were carried out to predict the time-dependent loss of strength of the AR-glass reinforcement embedded in fine grained concrete as a consequence of weathering. In the present paper possible reasons for the loss of strength of state-of-the art AR-glass reinforcement in nowadays cementitious mixtures are described and their relative importance is discussed, based on new results. In the accompanying paper (part 2), these results are used to present a durability model under complex weathering conditions.

Textile reinforced concrete : Durability issues: Changes of the bond and tensile strength due to ageing

Textile reinforced concrete (TRC) is one promising possibility to produce thin-walled high load bearing structural elements. Besides the maximum load bearing capacity, the durability under various conditions is one major issue for future applications. Usually AR-(Alkali-Resistant)-Glass is used as reinforcement. Even if it is AR-Glass, the high alkaline environment in concrete leads to a loss of the tensile strength.

Durability aspects of AR-glass-reinforcement in textile reinforced concrete, Part 2: Modelling and exposure to outdoor weathering

For a safe design of TRC (Textile reinforced concrete) load bearing structures the loss of strength of TRC as a consequence of weathering should be modelled. In part 1, possible reasons for the loss of strength of a state-of-the art AR-glass textile reinforced concrete were discussed. These findings are first used in this paper as a base for a corrosion model, describing the loss of strength in lab conditions. Subsequently, temperature and humidity were continuously measured during outdoor weathering and implemented into the model.

Textilbewehrte Spritzmörtelschichten zur Instandsetzung von Wasserbauwerken / Shotcrete Layers with Textile Reinforcement for Repair of Hydraulic Constructions

Water engineering structures build out of concrete are often massive and older than five decades. The concrete substrate of these structures shows often a low strength, cracked joints as well as cracks which are moving due to temperature changes. Using non reinforced sprayed mortar to repair these structures leads to cracks in the repair mortar due to the alteration of crack widths in the ordinary structure. The bond between old concrete and repair mortar as well as the durability of the sprayed mortar will be reduced due to the described cracks. The following paper describes a solution for this problem. The use of textiles as reinforcement in sprayed mortars results in a fine distributed crack image which is not critical for the durability of the repair mortar. Different kind of textiles combined with one type of sprayed mortar, available on the market, where tested in the laboratory during a research project. At the end of the project the new composite material was applied on a column at a dam in Horkheim.

Zerstoerungsfreie Bestimmung der oberflaechennahen Betonfeuchte mittels NMR / Non-destructive determination of the surface near moisture content of concrete by means of NMR

Die Dauerhaftigkeit von Bauwerken im Freien wird stark von der Betonfeuchte beeinflusst, insbesondere hinsichtlich des Entstehens von Korrosion. Bei Massnahmen zum Schutz des Betons gegen eindringende Stoffe (Wasser, Chloride, Kohlendioxid), zum Beispiel durch Oberflaechenschutzsysteme, kommt der Bestimmung der Betonfeuchte darueber hinaus eine zentrale Bedeutung zu. Die oberflaechennahe Betonfeuchte kann im Labor zerstoerungsfrei zum Beispiel mit der an der RWTH Aachen University entwickelten NMR-MOUSE (Nuclear Magnetic Resonance Mobile Universal Surface Explorer) bestimmt werden. Eine baustellentaugliche Untersuchungsmethode gibt es derzeit noch nicht. Die Technik der Bestimmung der Feuchte mit der NMR-Mouse unter Laborbedingungen wird beschrieben. Die Einsatzmoeglichkeiten der Technik werden an drei Anwendungsbeispielen vorgestellt: Bestimmung des Wassergehalts in einer Betonrandzone, Wasseraufnahme- und Wasserabgabeverhalten von Feinbetonen und Nachweis der Austrocknung des Betons durch eine aufgebrachte Hydrophobierung (OS 1). Die Bestimmung des Wassergehalts in der Betonrandzone erfolgte an einem Bohrkern eines Betons C 20/24 mit einem hohen W/Z-Wert von 0,75 ueber eine Tiefe von 5 mm in Schrittweiten von 0,5 mm. Das aufgenommene Tiefenprofil und die daraus zu ziehenden Schluesse werden im Einzelnen schriftlich und bildlich dargestellt. Im zweiten Beispiel wurde der zeitabhaengige Wassertransport in der Betonrandzone an verschiedenen Feinbetonen, die man speziell fuer die Anwendung bei Textilbetonen entwickelte, im Rahmen von kapillaren Saugversuchen beobachtet. Dieser Beton aus CEM II mit einem W/Z-Wert von 0,43 und einem Groesstkorn von 4 mm war mit einer Acrylatdispersion polymermodifiziert, um die Dauerhaftigkeit des Textilbetons zu verbessern. Parallel untersucht wurde auch eine Betonprobe mit der gleichen Betonmischung wie der polymermodifizierte Beton jedoch ohne Polymerzugabe. Die aufgenommenen Tiefenprofile der Betonfeuchte bis in eine Tiefe von 5 mm werden wiederum bildlich dargestellt und textlich beschrieben. Es zeigt sich, dass der Wassergehalt mit zunehmender Messtiefe abnimmt und dass sich mit zunehmender Saugzeit im vorderen Probenbereich ein Saettigungszustand einstellt. Festzustellen ist auch, dass die Eindringgeschwindigkeit des Wassers bei dem Beton mit Polymerzugabe deutlich verringert wird. Das dritte Beispiel zeigt die austrocknende Wirkung des Aufbringens einer Hydrophobierung auf den Betonuntergrund. ABSTRACT IN ENGLISH: In the field of restoration of concrete structures, the moisture content in the surface zone of concrete is of particular importance. To measure this in a non-destructive way and with a high depth-resolution, the NMR-MOUSE (Nuclear Magnetic Resonance Mobile Universal Surface Explorer) has been developed at the RWTH Aachen University. Due to the low weight and the simple handling of the NMR-MOUSE, this technique is suitable for on-site investigations of buildings. However, before this method can be applied to real life structures, a correlation between the measured NMR signal and moisture content in the concrete needs to be established in model investigations. This report exemplifies the correlation between NMR signal and moisture content of a concrete C 20/25. The progress of capillary water uptake and drying was followed by NMR investigations in the surface zone of concrete. Furthermore the progress of drying was observed by NMR through a hydrophobic layer (OSI) of a water saturated concrete specimen. (A)