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Organisationseinheit der BAM
Weltweit besteht einen hoher, stetig wachsender Bedarf an Natursteininstandsetzung im Bereich des denkmalgeschützten Kulturguts. Das Ausbessem beschädigter Elemente mit sogenannten Steinersatzmassen ist dabei eine etablierte Technik. Hierfür werden Mörtel unterschiedlichster Zusammensetzung verwendet. Die Schwierigkeit für den Restaurator liegt in der Wahl, bzw. der Verfügbarkeit des optimalen Produkts, um im individuellen Fall sowohl den mechanischen und bauphysikalischen Anforderungen als auch den gestalterischen und denkmalpflegerischen Belangen gerecht zu werden. Anhand der im Beitrag an Fallbeispielen erläuterten häufig auftretenden Probleme und der daraus abgeleiteten Anforderungen an Natursteininstandsetzung, lässt sich die Komplexität dieser Aufgabe erkennen. An der BAM wird derzeit im Rahmen eines Forschungsprojekts ein modulares Steinersatzsystem entwickelt. Ziel der Entwicklung ist es dem Restaurator die größtmögliche Freiheit in der Anpassung des Mörtels an die Originalsubstanz zu geben. Erste Ergebnisse aus Parameterstudien zur Bindemittel- und Sandvariation sowie zu Polymermodifikationen werden vorgestellt.
For several years, optical measuring techniques play an ever increasing role in various areas of construction. Applications ränge from simple laser-based distance measurements up to the use of advanced camera Systems to assess shape changes of components. The advantages of such Systems lie in the ränge of non-contact respectively in non-destructive measurement and in the high required accuracy and reproducibility. The continuous improvement and development of sensors and laser sources also opens constantly new applications and areas of applications. Already established measurement methods and technologies can be further developed and adapted to modern requirements. At BAM it is a laser-based measurement System has been developed that is capable to measure the roughness of component surfaces in equal to already established methods.
Since its invention in the early 1990’s, self-consolidating concrete has never become well established in the ready-mix sectors worldwide. The reason for this can be mainly found in the fact that the sophisticated compositions are sensitive against changing environments. This lack of robustness can be attributed to the interaction between cement hydration reaction and high range water reducing agent (HRWRA). Understanding the relevant mechanisms that control the initial flow performance as well as the flow retention helps optimizing SCC mixtures that perform either steadily in one specific environment or that perform largely similarly at steadily changing environments.
This paper depicts how HRWRAs interact with clinker and hydration phases and discusses the important role of the charge density of a polycarboxylic HRWRA in the way the rheology is affected. Based on rheometric results and observations of the Vicat setting times, it is shown that increasing charge densities of the HRWRA and decreasing water to powder ratios (w/p) reduce the flow retention and have lesser retarding effect on the setting. Based on the discussion, optimization procedures for the mixture composition and the HRWRA modification are suggested to achieve optimized performance for varying environmental situations or highest robustness for specific conditions.
The present article gives an insight into the research project BEGLARES. Main topics are the restoration “Dalles de Verre” Windows and the development of repair mortars and techniques. This project is executed in cooperation between Glasmalerei Peters GmbH, the University of York, and the BAM Federal Institute for Materials Research and Testing. It is funded by the Federal Ministry of Economics and Technology. The main mechanism of damage, Standards for protection and repair of concrete structures, and the development of repair mortar and special test specimens are presented.
Repair mortars for the restoration and reprofiling of natural stone elements in cultural heritage
(2011)
For the protection of the world's cultural heritage the restoration of listed buildings and monuments is an important task. In many cases the need to repair and reprofile natural stone elements occurs. Repair mortars for such applications have to match historicocultural interests as well as durability related and constructive interests. Currently a research project dealing with the development and optimisation of such mortars is set up at the BAM. Special focus is laid on the possibility of a modular adaption to match a vast variety of stone properties. Besides the development and lab scale testing of the mortar system, an in-situ application will be planned and executed.
Influence of selected aspects of the mixture proportioning on the performance of repair mortars
(2012)
Whenever the preservation of original substance obtains priority in a restoration task, reprofiling techniques using repair mortars are a welcome solution. For ordinary concrete repair aesthetic aspects are of minor importance whereas for the restoration of natural stone elements they come to the fore. Especially for listed buildings and monuments, historico-cultural and aesthetical interests become the ruling Parameters for planning and execution of restoration tasks. Nevertheless the technical and constructive requirements have to be considered and deterioration processes have to be understood to ensure sustainability and durability of the repair task. Due o differences in the Chemical and mineralogical composition, natural stone provides a vast variety of texture and colour. Also the range of different mechanical and durability related properties is far wider than found with concrete for example. A research project dealing with the development of a modular repair mortar System for natural stone is currently set up at the BAM. To provide the conservator with the best possible options to match colour, texture and technical requirements, the System will be setup on a modular basis. Several different binder Systems on basis of cement, lime and sodium Silicate as well as polymer based Systems are planned, which can be combined with different aggregate compositions and different pigments. To evaluate the mortar performance, test procedures will be defined for tests on mortar samples and on composite specimens. In the paper the experimental Programme will be explained and first results will be presented and discussed.
Many African countries face serious problems associated with the rapid growth of urban Population and the resulting demand for affordable building materials. In search for appropriate Solutions to improve the Situation, the “LightSHIP” project was initiated, whose aims were to identify the required product specifications, to evaluate possible approaches and ultimately to develop new Building materials for East Africa. It was concluded that these materials should be produced in Africa mainiy from local raw materials; prefabricated, easily transportable construction elements are to be preferred. It is therefore reasonable to focus on artificial stones and partition boards. To be Independent of imported cement, it is suggested to make use of volcanic rocks, which are abundant in East African countries, for lime-pozzoian binders and geopolymers in the production of these construction elements. Future research activities should thus concentrate on assessment of the applicability of available volcanic rocks, the influence of their properties on the resulting binders and the design of appropriate binder-reinforcement-filler Systems.
Mörtel für den Neubau und die Instandsetzung sind seit vielen Jahrzehnten im Abwasserbereich für unterschiedliche Bereiche im Einsatz. Zumeist werden diese je nach Anwendungsbereich entsprechend der Vorgaben der Auftraggeber, den Erfahrungen der Hersteller und Verwender sowie den Empfehlungen von Interessenverbänden (z. B. DWA oder DVGW verarbeitet. Zugleich ist eine Reihe von adaptierbaren Regelwerken für ähnliche Produkte aus anderen Anwendungsgebieten verfügbar. Während die Regelwerke zum Schutz und zur Instandsetzung von Betonbauteilen bereits seit ca. 35 Jahren über den Deutschen Ausschuss für Stahlbeton und die Bundesanstalt für Straßenwesen entwickelt und fortgeschrieben werden und seit ca. 20 Jahren auch über ein Mandat der europäischen Kommission im CEN entsprechende Bauproduktnormen im Rahmen der EN 1504 erarbeitet wurden, wurde die Arbeit an einer Produktnorm für zementgebundenen Mörtel für den Bau und die Sanierung von Abwasserkanälen und -leitungen sowie Bauwerken in kommunalen Entwässerungssystemen und Kläranlagen erst im Jahr 2005 aufgenommen. Dieses Regelwerk wurde in Anlehnung an Bauprodukte für andere Anwendungsbereiche erstellt, berücksichtigt darüber hinaus aber die besonderen Anforderungen im Bereich der Abwasserkanäle und -leitungen.
The SPIN project
(2011)
Globally, cement and concrete experts are at the cutting-edge to sustainable, green, healthy but nonetheless high-performance concrete. In the present age, concrete is not yet well established in Africa, which öfters the unique opportunity to build up a cement and concrete market based on the highest available state of technology. As this industry needs high level expertise, a central issue in implementation of skilled technology is cross-linking research institutions and laboratories. It should not be neglected that concrete is a product with comparably low transport ranges, which means that an improved concrete market will mainly support the local economy without exceeding financial drains to the international market, thus fostering the fight against poverty, which is an urgent need in most African countries.
The SPIN project highlights recent developments in the field of cement and concrete research with impact on the local and global economy. Challenges, future developments and opportunities for the African construction industry are in the focus.
The SPIN project is funded by the European Commission (EC) and supported by the African, Caribbean and Pacific (ACP) Group of States under the project body of the ACP Science and Technology Programme. SPIN is acronym for “Spearhead network for Innovative, Clean and Safe Cement and Concrete Technologies”. The project aims to cross-link experts with industry and policy making bodies, aiming to establish sustainable cement and concrete construction in Africa.
As soon as cement is mixed with water, the hydration reaction starts to set of. The progression of the hydration process is governed by the amount and the availability of water and its possibility to access the unhydrated cement grain surfaces. For a total hydration cement theoretically requires water amounting approximately 0.38 of its own mass. Nevertheless, due to the cement’s highly hygroscopic nature, already the moisture in the ambient air can cause first hydration reactions to set in upon the cement grain surfaces. Such pre-hydration processes have an effect on the cement's properties. Dpending on the specific conditions during the storage the significance of the impact on certain properties can vary.
If cement is consumed soon after production and is transported only short distances in a silo wagon to its final destination for immediate use without further stock transfer, the effects are rather negligible. However, if cement is delivered in bags, transported over long distances, shifted serval times and stored for longer time periods until it is finally consumend, these effects can be quite severe. Due to the actual logistical situation with comparably few cement plants, large delivery distances and partially less developed infrastructures, the latter scenario pictures the situation for the most cases in Africa quite well.
In order to verify the relevance of the pre-hydation for practical application, a series of tests was conducted at the German Federal Institute for Materials Research and Testing (BAM). The influence of the cement storage on gresh and hardened concrete properties was investigated for different concrete and mortar types. The investigations show that the impact of the storage conditions is more pronounced for specialized concretes with high sophisticated optimized mixture compositions containing admixtures. Nevertheless, the effects also occur for ordinary concrete and should not be ignored.
This report is based on a three-year experience as coordinator of the ACP-EU funded SPIN project. The project involved eight African and three European partners. Practical and unforeseeable problems are addressed that occurred during the project implementation and ways how they were successfully solved are reported. The major problems in many African institutions were administrations that are not used to work in multi-national consortia and a lack of institutional support for the African researchers. In Europe a misjudgement of the African boundary conditions as well as inflexible administrations caused problems. Finally the funding scheme did not always allow to easily overcome the high number of unexpected practical problems. A major deficit identified during the project was a general trend in Africa to underestimate the role of research for the development of the continent. Most universities focus on teaching applied sciences, which is without doubt important to cover the market need for qualified staff in the rapidly growing African industries. However, this makes it unattractive for highly qualified performers to conduct research on the continent. Furthermore this leads to the situation that the curricula can only contain second hand knowledge. In order to attract international high level researchers, it is suggested to install multi-national regional excellence research centres that only promote PhD and post-doc research on a level that can cope with highest international excellence. High level research is often perceived as not capable of focusing on immediate actual problems that many African economies have to cope with.. However, it is considered to be very sustainable in terms of autonomy and mastering future challenges.
Protection and repair of concrete structures is one of the outstanding topics of the last 20 years of research and development in the concrete research. Reinforced concrete is spread technically relevant for approximate 100 years, as a new construction technology. For decades, concrete as a building material was established and known as a building material of unlimited possibilities and durability, to resist all exposures. The concrete structures were considered untouchable by environmental influences. But at least since the 70s of the 20th Century was obvious due to increased structural damage that concrete components and structures require special protection and rehabilitation measures. Otherwise they will not achieve their planned life time. In this period were also the development of the first regulations for the protection and repair of concrete structures, which were crucially shaped by the former senior public officials in Berlin, Germany. Since that time, for the different application areas: structural engineering, bridge engineering, power plant construction, drinking water construction, wastewater constructions, road and railway constructions, etc partly independent partly closely linked sets of rules were developed.
These national Standards have been superposed by the European harmonization of construction products in the late 90s. CEN as a European Standards Institution has published since 2009 in the EN 1504 series of six product Standards and 4 additional supporting Standards that should govern the repair area. On a world scale the ISO works in TC 71/SC7 on “Maintenance and repair of concrete structures” to develop regulations.
Currently in the whole African subcontinent no binding regulations for concrete repair are available, although a variety of concrete structures are present. There is thus the opportunity to adapt the rules as far as necessary and adapt to African conditions. The contribution would give a brief overview of the Standard techniques and the applicability in Africa.
Rheological optimisation for flowable mixture compositions specified for African boundary conditions
(2013)
To date concrete technology is not yet well established in sub-Saharan Africa but considering the construction technological challenges of the region, without doubt, concrete will play a major role in future. The social, economic, and geographic boundary conditions distinguish greatly from those that can be found in many other regions of the world, where concrete is considerably well established. Düring the last decades, concrete technology underwent a rapid evolution process, but in most countries, where concrete is already well established, innovations are difficult to be brought into practice, Africa, currently has the opportunity and potential, of directly establishing the best available practice in concrete technology.
The conclusion is drawn that self-compacting concrete (SCC) or highly flowable concrete is a reasonable solution for African construction sites. Since on most African construction sites the disadvantageous concreting environment is the most crucial factor for the concrete quality, the outstanding workability properties outweigh any disadvantages of SCC.
Based on this consideration, concepts are developed, how to bring about robust SCC cost-efficiently and reliably into practice as pre-mixed dry compound under consideration of local materials such as rice husk ashes, bagasse ashes, natural pozzolans, cassava starch and lignosulphonate.
For the protection of the world’s cultural heritage the restoration of listed buildings and monuments is an important task. In many cases the need to repair and reprofile natural stone elements occurs. Repair mortars for such applications have to match historico-cultural interests as well as durability related and constructive interests. Currently a research project dealing with the development and optimisation of such mortars is set up at the German Federal Institute of Materials Research and Testing (BAM). To provide the conservatorwith the best possible options to match the colour, texture and technical requirements of the stone, the repair mortar System will be setup on a modular basis. Different binder Systems are planned to be combined with different aggregate compositions and different pigments. By the modular setup the possibility of independent adjustment of mechanical properties and appearance is aimed. In order to guaranty the reversibility and to ensure that the repair mortar does not induce any damage to the original substance, strength and stiffness of the repair mortar have to be well controlled. The use of polymer dispersions is helpful here, as they allow the production of low stiffness mortars with at the same time relatively high flexural strength values. Also investigations on “alternative” modifications known from historical applications such as the use of casein are carried out.
Despite the urgency of seemingly more important building tasks, there is also a great demand for natural stone repair in cultural heritage on the African continent. There is a wide ränge of different objects reaching from prehistoric monuments up to colonial architecture, all in different säte of preservations and subjected to a variety of individual environmental ant climatic conditions, which demand individual and adjustable restoration techniques and materials.
Die Oberflächenrauheit eines Bauteils ist eine wichtige Kenngröße für zahlreiche seiner Eigenschaften. Der im Bauwesen übliche Rauheitsparameter ist die Rautiefe Rt bzw. MTD, die durch volumetrische Verfahren (Sandflächenverfahren) ermittelt wird und in zahlreichen Normen Verwendung findet. Laserbasierte Verfahren müssen deshalb eine Umrechnung der aus Oberflächenprofilen gewonnenen Informationen in Rt bzw. MTD ermöglichen. Hierzu wird i.A. ein empirischer Zusammenhang zwischen Parametern zur Beschreibung des Profils und der Rautiefe der entsprechenden Oberfläche verwendet. Der Aufsatz stellt verschiedene Rauheitsdefinitionen vor und vergleicht sie miteinander. Es wird ferner gezeigt, dass die nach verschiedenen Prüfvorschriften ermittelten Rautiefen voneinander abweichen. Das Vorgehen bei der Ermittlung des Zusammenhangs zwischen Profilparametern und Rautiefen nach einem volumetrischen Verfahren wird demonstriert und der Stand der laufenden Entwicklung eines Prüfgeräts auf Basis eines Linienlasers vorgestellt.
Die Versiegelung von Oberflächen, Bebauung und die Ausweitung städtischer Gebiete führen weltweit besonders in sonnenreichen Regionen zu innerstädtischen Hitzeinseln. Diese Flächen wirken als Wärmespeicher, so dass an Sonnentagen eine Temperaturdifferenz bis zu 10 K zwischen Stadt und umliegendem Land entstehen kann. Verstärkt wird dieser sogenannte Urban Heat Island Effect (UHIE) durch die meist direkte Abführung des anfallenden Regenwassers in die Kanalisation, wodurch eine Kühlung durch stetige Verdunstung unterbunden ist, Mit steigender Urbanisierung wächst auch die Bedeutung dieses Phänomens. Innerstädtische Hitzeinseln ziehen direkte wirtschaftliche und soziale Folgen nach sich, da hohe Temperaturen eine teure Klimatisierung der Städte bedingen. So entsteht ein erhöhter Verbrauch an Ressourcen sowie zusätzliche Abwärme. Das Wohlbefinden und die Gesundheit der Bevölkerung verschlechtern sich bei sehr hohen Temperaturen, was zu sinkender Leistungsfähigkeit und sogar zu einer erhöhten Sterberate führen kann.
The large scale application of self-cooling concrete pavers is a future-oriented approach to reduce the urban heat island effect in inner-city areas. Making use of evaporation enthalpy, these new pavements counterbalance the absorption of solar radiation and the subsequent transfer of heat to the surrounding environment. The concrete pavers consist of a permeable top-layer and a storage layer. As the different requirements of these layers demand different concrete mixtures they are developed and optimised for their respective functions. This paper presents some results of the concrete mixture design and Solutions that combine a sufficient compressive strength as well as good water transportation properties for the face concrete layer.
Todays superplasticizers for self-compacting concrete and high Performance cementitious materials are very versatile. Typically superplasticizers are composed of a polycarboxylic backbone equipped with polyethylene oxide graft chains of variable length and grafting degree. The mode of operation of these admixtures is based on the steric repulsion of the particles upon adsorption. The adsorption is strongly depending upon the charge density of a superplasticizer and the time dependent Adsorption processes control the retention of the flow performance – an important issue particularly for ready-mix and construction site concrete. However, the properties of polycarboxylic superplasticizers typically remain a black box for users. The paper suggests a simple and rapid test method, which can be conducted without sophisticated equipment, to qualitatively distinguish between two types of superplasticizers based on the adsorption mechanism. Interpreting the results in the right way provides a powerful tool to choose the right admixture for individual time dependent flow specifications.
Die Charakterisierung von Oberflächen mittels optischer Technologien wird dank des ständigen Fortschritts bei der Entwicklung von Sensoren und Lichtquellen immer attraktiver. Die kommerziell erhältlichen Systeme werden dabei immer leistungsstarker, empfindlicher und genauer. Mit diesen Systemen ist es möglich, viele hundert Messpunkte innerhalb weniger Sekunden zu erfassen und auszuwerten. Dieser Fortschritt führt auch im Baubereich zu einer ständigen Weiterentwicklung und Verbesserung von Messmethoden und Systemen. So werden bereits standardisierte und angewandte Messprinzipien weiterentwickelt, den neuen Möglichkeiten angepasst und deren Anwendung auf neue Bereiche ausgeweitet. An der BAM ist es gelungen ein Messsystem zu entwickeln, mit dem Rautiefen von Bauteiloberflächen in Anlehnung an bereits standardisierte Verfahren bestimmt werden können. Mit dem Mer vorgestellten System können sowohl horizontale als auch vertikale, gewölbte und geneigte Oberflächen untersucht werden. Dank der Implementierung geeigneter Algorithmen entsprechen die vom System ausgegebenen Ergebnisse denen der seit Jahrzehnten mit den volumetrischen Messverfahren erzielten Ergebnisse. Vor allem bei der Instandsetzung von Bauwerken bringt das an der BAM entwickelte System erhebliche Vorteile, da es zukünftig auch möglich sein wird Wände und Decken genauer zu untersuchen.
Innovative admixture technology has significantly widened up the ränge of possibilities of concrete engineers. For many decades the water to cement ratio (w/c) was the major influencing factor for the performance of concrete. Due to the need to adjust a consistency, which still allowed reasonable workability, the w/c was typically significantly higher than technologically reasonable. Rheology modifying admixtures Support adjusting the concrete consistency largely independent of the w/c. It was only after the invention of the first superplasticizers that modern concrete technology significantly evolved in terms of flowability, strength, and durability, and only due to the steady evolution of the technology modern innovations, such as Self-Compacting Concrete, Ultra-High-Performance Concrete, or Engineered Cementitious Composites were made possible. Today’s superplasticizers are extremely versatile and can be adjusted to individual technological specifications. However, the other side of the coin of versatility is that cementitious Systems incorporating superplasticizers have become more sensitive against environmental influences, such as the environmental temperature, which may cause unwanted effects or demand for supplementary admixture use such as stabilizing admixtures. Hence, concrete mixture composition with admixtures demands for a high level of expertise and offen there is lack of awareness about the mode of Operation of rheology modifying admixtures among concrete technologists. The paper gives a comprehensive overview about rheology modifying admixtures such as superplasticizers or stabilizing agents, and how they can be used depending upon the application in the most favourable way. Based on experiences with the sub-Saharan African concreting boundary conditions, which exhibit many challenges in terms of environmental boundary conditions and construction site logistics, conclusions are finally drawn, how admixtures can be used in the most beneficial way to improve the concrete casting Situation.