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Nanotechnologie im Bauwesen
(2008)
Zu den Zielen der Nanotechnologie gehört die Entwicklung, Produktion und Anwendung von Materialien und Werkstoffen mit völlig neuartigen Leistungsspektren. Für die Baupraxis und die Materialforschung lassen sich über den Einsatz der Nanotechnologie Ziele wie die Optimierung von Baustoffeigenschaften, Vermeidung von Schäden und neue Funktionalitäten definieren. Der vorliegende Beitrag gibt einen Überblick über mögliche Anwendungsbereiche der Nanotechnologie im Bausektor, wie z. B. zementgebundene Baustoffe, Außen- und Dachfassaden, Fenster und Verglasungen, Brandschutz, Inneneinrichtung und Infrastrukturbau. Zudem werden aktuelle Forschungsarbeiten mit nanowissenschaftlichem und nanotechnologischem Schwerpunkt im Bereich baustoffbezogener Materialien der Bundesanstalt für Materialforschung und -prüfung (BAM) in Berlin vorgestellt. Die Forschungstätigkeiten beziehen sich zum einen auf die Modifikation der Hydratphasen in Ultra-Hochleistungsbeton (UHPC) und zum anderen auf die Weiterentwicklung von Anti-Graffiti-Systemen.
Los contaminantes atmosféricos son con frecuencia responsables
de la aceleración de la degradación de la piedra
en los edificios y monumentos históricos de las zonas
urbanas. Son muchos los factores que influyen de manera
decisiva en el comportamiento de las piedras naturales
ante los contaminantes gaseosos. Dos de esos factores
son la composición de la atmósfera y el tipo de piedra.
Las areniscas en particular son propensas al ataque de
los contaminantes atmosféricos debido a su naturaleza
porosa, pero muchas de las reacciones de las areniscas
no carbonatadas con estos gases no se conocen bien. El
estudio presentado tiene por objeto comprender los procesos
y factores que controlan el distinto comportamiento
de las areniscas respecto al dióxido de azufre. Para el
estudio se investigaron siete areniscas distintas procedentes
del sur y del este de Alemania. Las areniscas mostraban
una diferencia significativa en la composición de
su aglomerado. Por lo que respecta a la absorción de
SO2, las distintas variedades de arenisca mostraron un
comportamiento completamente diferente. Curiosamente,
la cantidad de SO2 depositada no estaba relacionada con
la superficie específica de las areniscas, este parámetro
está relacionado con el contenido en óxidos de hierro.
Air pollutants often accelerate stone deterioration in historical
buildings and monuments in urban areas. Many factors
condition natural stone behaviour with respect to
gaseous pollutants. Two of the more prominent of such
factors are the composition of the atmosphere and the
type of stone. Due to their porosity, sandstones are particularly
vulnerable to air pollutant attack. Many of the reactions
between noncarbonaceous sandstones and these
gases are not well understood, however. The present
study aimed to acquire an understanding of the processes
and factors governing sandstone behaviour when exposed
to sulphur dioxide. Seven different sandstones from southern
and eastern Germany were analyzed for the study.
The binder composition of the stones varied significantly.
They also exhibited completely different behaviour in connection
with SO2 deposition. Interestingly, while the
amount of SO2 deposited was unrelated to the specific surface
area of the sandstones, this parameter was closely
correlated to the iron oxide content.
The interaction of municipal solid waste incinerator bottom ash (MSWI bottom ash), when utilized as an aggregate in concrete, with the cement matrix was investigated. The most prominent reaction observed in lab and field concrete was the formation of aluminium hydroxide and the release of hydrogen gas from aluminium grains reacting in the alkaline environment. The expansive aluminium reaction was identified as a main cause of extensive spalling on the concrete surface. Due to the higher content of bottle glass as part of the ash, in all samples, reaction products of an alkali-silica reaction (ASR) could be observed as well. However, damage due to ASR were less severe than those caused by the aluminium reaction. The expansion rates were low and only a few of the lab samples showed cracking. Microstructural analysis of the samples indicated clearly that a large quantity of the alkali-silica gel which was formed was accommodated in the pores and voids without exerting any strain on the material.
Deciphering the sulfate attack of cementitious materials by high-resolution micro-x-ray diffraction
(2011)
The durability of cementitious materials depends, among others, on their resistance against chemical attack during the service life of a building. Here, we present an approach to analyze changes in the phase composition due to chemical attack in the form of sulfate ingress within the microstructure. Micro-X-ray (µX-ray) diffraction using synchrotron radiation in Debye–Scherrer (transmission) geometry allowed a spatial resolution of 10 µm. Phase transformations in the wake of damaging processes were observed in a detailed high-resolution imaging study. In comparison, samples containing supplementary cementitious materials were investigated and used to reconstruct the influence of different degeneration processes in detail. Additionally, reaction fronts within the bulk were localized by micro-X-ray fluorescence analysis. The experimental setup provided the possibility for analyzing the phase assemblage of a given sample without destroying the microstructure. The specimens for phase analysis are thick sections of the primary material and can be used for further microscopic analysis of the microstructure and microchemistry, e.g., scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDX) or Raman spectroscopy.
Spatially resolved analysis of complex multi-phase systems can be validated through different analytical methods. This study compares investigations by scanning electron microscopy coupled with energy dispersive X-ray fluorescence analysis and high resolution X-ray diffraction. The studied sulfate attacked cement paste containing fly ashes consists of different interacting crystalline and amorphous phases. The complementary methods revealed in detail changes in phase composition due to the chemical attack. The advantages and disadvantages of both methods are discussed and suggestions are given for combining them with additional methods to maximize the information content.
Setting cement: Highly dynamic hydration processes that occur during the first seconds of cement hydration were studied by time-resolved synchrotron X-ray diffraction. Polycarboxylate ether additives were found to influence the formation of the initial crystalline hydration products on a molecular level.
The paper presents the results of a study dealing with the performance of water repellents on hardened blended cement pastes. Since on the European market Portland cement does not play the dominant role anymore and due to the new national and European policies concerning Greenhouse Gases and sustainability, cement manufacturers produce more and more blended cements (CEM IICEM V). Nevertheless, the majority of experience concerning the efficacy of water repellents is gained from Portland cement; therefore knowledge in regard to the interactions of blended cement with water repellent agent is minimal. Two silane-based products were applied on 'fresh' and carbonated cement substrates containing limestone, fly ash, slag and trass, and were investigated in terms of their functionality. The evaluation of the treatments' performance and effectiveness were assessed using various laboratory measurements. Hydrophobicity, water absorption, colour changes and the penetration depth of silanes into the substrate were evaluated before and after artificial aging experiments. Moreover, the outdoor weathering test was performed to shed light on treated surface appearance in a 'real' outdoor environment. The results showed that surface wettability was independent on water ingress or colour variations, especially for cement specimens artificially aged by accelerated carbonation. Cement pastes containing slag and trass seemed to more distinctly affect the water repellents' surface performance.
Ingenieurbauten des Bundesfernstraßenbereichs sind aufgrund ihrer Exposition an vielen Stellen besonders betroffen von Graffiti. Graffitischmierer nehmen hierbei keine Rücksicht auf die Art der Substratmaterialien, und besonders poröse Untergründe bereiten Schwierigkeiten bei der Reinigung. Um Baustoffoberflächen besser zu schützen und von Graffiti leichter reinigen zu können, wurden in den vergangen Jahren spezielle Prophylaxesysteme (Anti-Graffiti-Systeme, AGS) entwickelten. Für die Beurteilung der Funktionalität und Verwendbarkeit dieser Anti-Graffiti-Systeme wurden von der Bundesanstalt für Straßenwesen (BASt) eine neue Technische Prüfvorschrift und Technische Lieferbedingungen (TP/TL AGS-Beton) erarbeitet. Die TP/TL AGS-Beton gilt hierbei nur für die Beurteilung von AGS auf Betonuntergründen. In einer Forschungsstudie wurde untersucht, inwieweit die vorhandene Prüfvorschrift für Betonsubstrate auch auf andere Untergründe, z. B. Naturstein oder Klinker, angewendet werden kann. Weiterhin wurde untersucht, welche Faktoren eine Rolle bei der Reinigung von mit AGS behandelten verschiedenen Substraten spielen.
Cultural Heritage objects are in many cases invaluable and irrecoverable, therefore their protection is a prior goal. One threat arises by intentionally defacing such objects with graffiti. One possibility to face the imminent threat is the application of a surface protection in form of anti-graffiti systems (AGS). However, the knowledge about the performance and durability of AGS on substrates used for historical buildings is still fragmented. The goal of the presented study was to investigate the performance of a newly developed agent in comparison to a selection of commercial anti-graffiti agents on different substrates, which were used for historical buildings. Four commercial anti-graffiti agents with different chemical formulations were selected and tested with the new agent on different stone and brick substrates. The results showed clearly that AGS based on dense, water vapour impermeable coatings are not suitable to porous substrates such as sandstone, brick or porous limestone due to their impair of the hygric properties and the visual appearance of a substrate. The new agent could not completely reach the cleaning efficacy of the dense coatings but exhibited a much lower impact on the properties of the substrate and was therefore better compatible to historical surfaces.