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- Carbonation (2)
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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.
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.
Despite the numerous possibilities to influence the properties of repair mortars by modifications of the mixture proportioning, it is almost impossible to change an individual property without influencing other mortar properties. When optimising a mixture, it has to be decided for each individual case, which of the mortar properties needs to be treated with the highest priority. Most properties can be altered by several different measures, which may vary in effectiveness, side effects and cost efficiency. As the prevention of shrinkage induced constraining cracks is crucial for the durability and Service life of a concrete repair task, in the presented paper special attention is paid to the influences on the mortar’s shrinkage behaviour. On the basis of parameter studies it is shown, how it may be beneficial in certain cases to accept the worsening of some general properties if by this measure another property, which is essential for the individual application task, can be enhanced significantly. In general a tailor-made approach for the mixture proportioning seems beneficial but due to the complexity of the constituents’ interactions in repair mortars, it bears a high risk of unexpected malfunctions.
Main topics of the research project BEGLARES are the restoration of "dalle de verre" concrete Windows and the development of repair techniques and mortars. 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 damages, the development of repair mortar and special test specimens are presented.
The cement and concrete market in East, Central and Southern Africa is highly fragmented. The concrete industry in this area consists of multiple parties, including producers and suppliers of construction materials, formal and informal contractors, engineers and architects, unions of trades persons and workmen, governmental bodies and formal institutions of research and education. All these institutions mostly do not interact adequately, which makes building with cementitious materials susceptible to damage and failures. Completely opposed to the situation in Europe or North America, cement in Africa is often unaffordable, while manpower is cheap, which results in a questionable economisation of cement. Typically, there is not sufficient awareness of methods to sensibly reducing the cement content in concrete or replace Ordinary Portland Cement by adequate alternative materials. Research activities in this field of technology are often missing completely. Only few countries in the area, such as South Africa, are exempted from these issues.
This paper presents the SPIN project, which is a joint project of a consortium of 8 African and 3 European partners within the ACP Science and Technology Programme. The project is funded by the EC and ACP Secretariat is the project body. The main objective of the current project is to strengthen the cement and concrete industry in the East and Central African regions. The project shall generate reasonable solution strategies to implement clean, safe and sustainable cement and concrete technology on the African continent, including general and specific guidelines for sensible application. Furthermore it shall be the kick-off for future projects, research activities and the world-wide expansion of a European-African network.
The paper addresses special problems the cement and concrete market in Eastern, Central and Southern African countries has to face. Several options are presented in detail, which shall help overcoming the current situation. Customized solutions for the African market include rational methods for reducing the amount of cement used and the replacement of Ordinary Portland Cement with cheaper alternatives. The use of recycled concrete through a new and economically effective method, as well as the opportunity of using locally available resources is also discussed.
Today polycarboxylate ether based superplasticizer (PCE) is commonly used in concrete technology when high flow properties and water reduction are specified. The ionic strength of the polymers’ backbones determines the adsorption behaviour of polymers on clinker and early hydration products. The amount of required polymers for specified flow properties and the performance over the time of casting is thus determined by the molecular structure of the superplasticizer. The time depending consumption of polycarboxylate ether polymers strongly affects the reaction of aluminates and sulphate ions as well as the hydration process in general. Hence, the choice of polymers for particular flow properties greatly affects the very early properties of cementitious materials such as setting, heat evolution and autogenous deformations.
In order to better understand how PCEs influence the early properties, mixes from cement, limestone filler, viscosity modifying agent and water were varied with a high and a low charge density superplasticizer in differing amounts. Results are presented from measurements with an automatic Vicat device, an isothermal heat flow calorimeter, and shrinkage cones. Tests were conducted at 5, 20, and 30 °C.
It is shown that in presence of PCE the final set correlates well with the inflexion point of the heat flow curve, which emphasises the interrelation between C-S-H formation and setting. No such clear correlation can be found for the initial set, which is attributed to the fact that the initial set is rather a rheological than a structural phenomenon, so that other effects overlap with C-S-H formation. The results demonstrate that for a given polymer concentration low charge density polymers yield earlier setting than high charge polymers. However, this influence is overridden by the influence of the total amount of polymers in a cementitious system. Since PCE is typically added according to rheological specifications, and low charge PCE typically requires higher amounts of polymers than high charge PCE for comparable flow performance, low charge PCE retards setting more than high charge PCE.
The paper furthermore points out that there is no significant influence of the polymer type or amount on the early deformations. Since type and amount strongly affect the hydration, it is demonstrated that early setting causes higher strain after the final set. It is hence concluded that higher PCE solid contents reduce the risk of early cracks that occur at time of setting, when a solid structure has already been formed but without resistance against cracks yet.
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.