Filtern
Dokumenttyp
- Vortrag (23)
- Beitrag zu einem Tagungsband (18)
- Zeitschriftenartikel (5)
- Beitrag zu einem Sammelband (4)
- Posterpräsentation (3)
- Buchkapitel (1)
Sprache
- Deutsch (37)
- Englisch (15)
- Mehrsprachig (2)
Schlagworte
- Repair mortar (10)
- Instandsetzungsmörtel (6)
- Betoninstandsetzung (5)
- Concrete rehabilitation (4)
- Cultural heritage (4)
- Modulare Systeme (4)
- Natural stone (4)
- Polymer cement mortar (PCC) (4)
- Repair systems (4)
- Stone reprofiling (4)
Eingeladener Vortrag
- nein (23)
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.
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.
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.