Publication

T. Juraschek, O. Weichold
J. Phys. Org. Chem. 2017; e3739
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Development of an electrochromic device triggered by the macrocell current in chloride-induced corrosion of steel-reinforced concrete

ABSTRACT: This article presents the development and characterisation of an electrochromic device and its application to detect steel corrosion in reinforced concrete. Steel corrosion inflicts an enormous annual economic damage, which could be reduced by the installation of appropriate monitoring devices. These should be simple, reliable, long lasting, and should not require service or maintenance. The present electrochromic device is constructed in such a way that it uses the macrocell current in an active, chloride‐induced corrosion element as power supply to trigger the colour change. This way, the system stays inactive until corrosion occurs. The device consists of diheptyl viologen in a liquid polymer electrolyte made from LiClO4 and poly(ethylene glycol) with Mw = 400 g mol−1. The addition of viologen lowers the resistance but causes no further changes in the electrochemical properties of the polymer electrolyte. Impedance spectra indicate ion transport rather than capacitance effects to dominate the electrochemical properties. Experiments using direct current in the microampere range show electrochromic switching times of several minutes, which is sufficient for the intended monitoring application.

Lecture

M. Brenner
Tagung der GDCh-Fachgruppe Bauchemie, Weimar, 19. September 2017

Functionalisation of fibre surfaces for textile-reinforced elastomers

ABSTRACT: Decisive for the load-bearing capacity of textile-reinforced structures is the performance of the interface. In cementitious systems, this is usually achieved by form-fit joints (e.g. carbon textiles impregnated with epoxy resin and sanded). In polymeric materials, such a stiff bond is often undesirable due to the smaller modulus of elasticity, and in elastomers it is even counterproductive. The presentation reports on an investigation into the targeted chemical functionalisation of glass, basalt and carbon fibres to reinforce chloroprene and EPDM. The fibres were modified with bis[3-(triethoxysilyl)propyl]tetrasulphide (TESPT) and 3-(mercaptopropyl)trimethoxysilane (3-MPTMS). For application, the substances were mixed with dissolved elastomer and applied to the fibres by hand. The modified fibres were then vulcanised into the elastomer in a specially manufactured mould and the fibre-matrix adhesion was tested in a pull-out test. With glass and basalt fibres, an improvement in the bond of up to approx. 100 % could be achieved; with the modification of carbon fibres, the bond can be improved by approx. 50 %.

Lecture

O. Weichold

Tagung der GDCh-Fachgruppe Bauchemie, Weimar, 19. September 2017

Polymere im Bauwesen – weiche Materialien in einer harten Welt

Publication

O. Weichold, U. Antons
J. Infrastruct. Syst. 2017, 23, 04017010
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Assessing the Performance of Hydrophobing Agents on Concrete using Non-Destructive Single-Sided Nuclear Magnetic Resonance

ABSTRACT: Single-sided nuclear magnetic resonance is a nondestructive analytical technique by which the ingress behavior of hydrophobing agents as well as the properties and performance of the resulting hydrophobic layers can be assessed quantitatively. The method is used to compare the behavior of two low-molecular-weight hydrophobing agents, n-octyltriethoxysilane and i-butyltriethoxysilane, on concrete and to assess the properties of the resulting hydrophobic layers. For the octyl derivative, ingress appears to be a simple transport process without pronounced polycondensation in the liquid phase or reaction with the pore walls because the detectable amount stays rather constant during the first day of observation. In addition, the thickness of the resulting hydrophobic layer correlates well with the endpoint of the transport process. In contrast, the detectable amount of the butyl derivative is reduced to half during the first 18 h, indicating either substantial polycondensation or anchoring to the pore walls, and the hydrophobic layer is approximately 25% thicker than indicated by the ingress profiles. The different behavior could originate in differences in the molecular structure, particularly the steric demand of the alkyl substituents, although this requires a more detailed study. Both compounds proved to be excellent hydrophobing agents since the layers were found to be impermeable when kept in a shallow water bath (unidirectional transport through the layer) for more than 1 year. The results demonstrate that single-sided nuclear magnetic resonance is an excellent nondestructive tool for quality assurance when applying such protective layers.

Lecture

T. Juraschek
EUROCORR 2017, Prag, 3. September 2017

Chemical, Non-Electronic Corrosion Indication Systems

ABSTRACT: Corrosion of the steel reinforcement in concrete causes an enormous economic damage. In particular, chloride-induced macroelement corrosion of the reinforcement is one of the bottlenecks in the service life time design of a majority of infrastructure buildings with a significant exposition to chloride. Corrosion monitoring offers a possibility to detect the onset of corrosion events and start independent restoration actions at a point, where costs can be kept at a minimum.
The presentation focusses on the testing procedure and verification of the prototype, under conditions simulating real-life corrosion events. Color change is not observed when applying zero-load currents, but occurs within minutes after raising either the potential or current to levels typical for corrosion events. The color change is persistent even after turning the power source off. We applied potential controlled current profiles as well as voltage controlled current profiles to the device, also with respect to peak current profiles to show the response of the system under realistic circumstances. Also, we investigate the influence of zero-load current and voltage events during the passive state of the reinforcement steel after passivation. Furthermore, experiments on reinforcement steel and reinforced concrete samples are shown as a proof-of-principle experiment.

Career

Our alumna Elena Heß starts a job at HeidelbergCement on 1 July 2017.

Publication

R. Schulte Holthausen, O. Weichold
J. Infrastruct. Syst. 2017, 23, B4016006.
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Non-destructive Evaluation of Thermal Damage in Concrete by Single-Sided Nuclear Magnetic Resonance

ABSTRACT: A new technology to coat concrete with coherent layers of glass by flame-spraying is currently developed at the Institutes of Building Materials Research and Mineral Engineering of RWTH Aachen University in Germany through a joint program. A major factor influencing the pull-off strength of the flame-sprayed glass coating is thermally induced damage in the underlying concrete substrate. In this article, the authors present a nondestructive test method using single-sided 1H nuclear magnetic resonance (NMR) to evaluate the thermally induced damage in concrete specimens. The particular NMR device used in this project primarily detects water and can qualitatively assess the water content as well as the relative size of water-filled voids such as pores and cracks. To do so, the specimens are water saturated and subsequently analyzed by NMR. Changes in the NMR-signal are interpreted in terms of change in porosity and development of cracks inside the cement stone as a function of depth from the concrete surface.

Bachelor thesis

Iva Rroshi

Congratulations on the successful completion of the bachelor thesis
Zur Untersuchung der Genauigkeit bei der Ermittlung des Bindemittelgehalts an Betonproben durch Methoden der chemischen Analytik
Investigation of the accuracy conerning the determination of the binder content of concrete samples by methods of analytical chemistry

Master thesis

Markus Brenner

Congratulations on the successful completion of the Master's thesis
Funktionalisierung von Faseroberflächen für textilbewehrte Elastomerlager
Functionalization of Fiber Surfaces for Textile-Reinforced Elastomeric Bearings

Konferenzbeitrag

T. Juraschek, O. Weichold
6th International Conference on Concrete Repair (Concrete Solutions), Thessaloniki, 2017, S. 207–211.

In-situ methods of detecting steel corrosion using permanent and non-electronic systems

ABSTRACT: Current systems for detecting corrosion of the reinforcement in concrete are realized via highly specialized systems that are commercially not available. Thus, these systems require complete technical support by the installing company. This report shows a cheap, efficient, independent, and reliable method to detect corrosion events in concrete. The detection system is based on an electrochromic device, which changes its colour upon the change of electrochemical potential caused by the corrosion process. The device is realized by a layer-by-layer setup of a transparent electrode, e. g. indium-doped tin oxide (ITO), followed by an electrochromic layer. The system is closed by a metal counter electrode. The electrochromic layer can consist of an electrochromic compound in a conducting polymer system. By connecting such elements to a series of sensors, e. g. an anode ladder, it is possible to monitor the corrosion progress and to verify the service life design of a structure.

Konferenzbeitrag

P. B. Sassmann, O. Weichold
6th International Conference on Concrete Repair (Concrete Solutions), Thessaloniki, 2017, S. 235–238.

Development of Electrically Conductive Resins for the On-Site Fabrication of Sensors for Corrosion Detection and Risk Assessment in Reinforced Concrete

ABSTRACT: Assessing the risk of corrosion in steel-reinforced concrete can be accomplished using different types of sensors such as anode ladders or multi-ring electrodes. The former are unsuitable for retrofit installations, while the latter require the use of embedding mortars to achieve conductive connections with the surrounding concrete. However, the porosity of the embedding mortar differs from that of the concrete and the retrofitting action introduces additional moisture. This interferes with resistivity and/or potential measurements and makes interpretations of the actual situation problematic. To circumvent these disadvantages, we have developed a liquid reactive polymer resin with high electrical conductivity that can be used to fabricate sensors directly inside drill holes. The mixture solidifies in a short time and its adhesive properties provide an excellent conductive connection to the concrete walls. The resin contains no water so that reliable values can be obtained immediately after solidification. By changing the additives both resistivity and potential sensors can be obtained. The mixture is cheap so that large sensor networks can be installed at reasonable costs. Such networks are ideal for the precise localization of corrosion events and more importantly for risk assessment in steel-reinforced structures.