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Eingeladener Vortrag
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Reinforced concrete buildings are frequently damaged by cracks, spalling and corroded
reinforcement bars. The present article focuses on the damage analysis of one of the first
buildings in Berlin that was constructed using reinforced lightweight concrete, which makes it
historically important. The compressive strength, carbonation depth, location and diameter of
reinforcement bars as well as moisture and salt profiles were determined. The carbonationinduced corrosion of the reinforcement bars represented the main damage of the building.
Certified repair mortars with lightweight aggregates (LWA) do not exist on the German
market. Therefore, an appropriate repair mortar was developed in accordance with DIN EN
1504 and the German guideline for the repair and protection of concrete structures (RL-SIB).
On the one hand, historic preservation requirements, such as: colour of the mortar,
possibilities of surface patterning, maximum preservation of the original substance and
reversibility of any Intervention must be met. On the other hand, technical requirements of the
relevant Standards must be achieved. The developed mix was designed to resist the identified
causes of deterioration. Thermal strains within the repair mortar and between the repair
mortar and the Substrate influence the crack formation and thus the durability. Therefore,
special attention was paid to the bonding and shrinking behaviour of the concrete repair
System. By using polymers, both hardened mortar properties and durability were influenced
positively.
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.