The subtitle of the conference on concrete repair refers to the program: ” – not a superficial matter “, because in the case of repair measures on listed reinforced concrete buildings, the characteristic concrete aesthetics come to the fore – but since the surface and building material are made of one piece, it is also important to be aware of the properties and aging of the building material […].
The subtitle of the conference on concrete repair refers to the program: ” – not a superficial matter “, because the characteristic concrete aesthetics come to the fore in the repair measures on listed reinforced concrete buildings – but since the surface and building material are made of one piece, it is also important to take an interest in the properties and ageing of the building material.
The thoroughly well-organized event took place on 27.2.2015 in the training and consulting center for monument preservation, in the BlfD’s building archive in the former Thierhaupten monastery and, with 119 participants, showed the great interest in the above-mentioned topic. The building archive works in an interdisciplinary manner “as an interface between heritage conservation research and practice”, with materials science, building technology and historical construction methods at the heart of its work.
At the beginning, the opening speaker and head of the Thierhaupten building archive, Julia Ludwar, asked the audience whether concrete restoration was a male domain? But with a 3:2 ratio of women among the speakers, the proportion of women in the overall result was visibly enhanced.
The restoration of exposed concrete surfaces is not only a focus of the Thierhaupten building archive. The typical post-war concrete buildings are among the monuments that are growing back; it is important to carry out technology-related preparatory work for the restoration measures that are becoming increasingly necessary.
Photo: BLfD
Although the conference mainly focused on buildings from the 1950s, 1960s and 1970s, there are also older buildings, e.g. two old Bavarian cultural assets, the seven-storey malt house in the Andechs monastery brewery (1906) and the unique reinforced concrete supports of the Predigtstuhl cable car in Bad Reichenhall (1928).
However, the best known are the unpopular concrete buildings in the large cities, such as the Munich GALERIA department store building (1965-1972) on Marienplatz, the large Munich residential complex in Soxhletstraße (1975), the Norishalle in Nuremberg (1965-1967), the theater in Ingolstadt (the polygonal exposed concrete building received Bavaria’s first BDA prize after its completion in 1967) or the Augsburg congress hall (1972).
Together with the hotel tower, the latter forms an urban ensemble from the early 1970s in Augsburg, which is now a listed architectural ensemble, but has been renovated to a modern standard. The exposed concrete building is staged at night with a special lighting concept so that the contrasts between exposed concrete and soft forms, emotions and no-frills buildings, nature and straightforward architecture form a unique and exciting backdrop.
Another very well-known concrete building is the town hall in Bensberg, which has since become an icon of modern construction with its free architectural form in concrete and glass. There, from 1964-1969, the exposed concrete surfaces in a harmonious color context succeeded in creating a connection to the old buildings of the castle complex.
These and other similar buildings have led to a declaration of this architectural style as Brutalism. With the motto “Monuments are not always beautiful”, Dr. Bernd Vollmar from the BlfD acknowledged that the concrete buildings do not always correspond to the usual ideas or ideals of beauty and continue to be the subject of controversial debate. In the meantime, however, there is also said to be local acceptance for the unloved objects, for example through fond memories of exhilarating concerts with Udo Jürgens or Roy Black in Augsburg’s Stadthalle.
The building materials industry has been tackling the problem of concrete restoration since the 1980s: The ZTV-Ing applies to all concrete restoration in Germany, always specifying a surface levelling mortar or filler for the subsequent even application of the final paint coating in order to achieve aCO2-tight surface seal.
As Elke Hamacher, the area consultant for the preservation of architectural and artistic monuments, explained, depending on the age and quality of the concrete, it can be assumed that the carbonation of the concrete is complete after a certain time, which is whyCO2-tight coatings are not always necessary for good old concrete qualities, but this must be determined in advance using various testing methods. It can also be found that the alkalinity of the concrete as a protective medium against corrosion of the iron reinforcement is eliminated, but new corrosion can only occur through the ingress of new moisture, so the old rule “water protection = monument protection” also applies here.
Some listed buildings have been treated with hydrophobic coatings and finally with concrete glazes: first partially for the repair areas and then over the entire surface in order to achieve a uniform surface quality. The preferred use of silicate glazes preserves the mineral character of the concrete surface.
Problem: This special treatment for listed buildings does not comply with the guidelines and the question arose: “Who releases us from the legal requirements?” So far, the contractual chains have worked together to achieve a common goal with a high degree of individual responsibility. The better and safer way for everyone involved came as a suggestion from the audience, namely that standards can be updated according to new findings. For our topic, a supplementary standard for concrete restoration on monuments is clearly missing!
In the practical example of the restoration of the so-called raw material bunker in the area of the UNESCO World Heritage Site Völklingen Ironworks, Dipl.-Geol. Martin Sauder reported on cases of damage with major consequences, where, as a result of massive material and form losses in the form of demolitions, large-scale additions had to be carried out, also in order to restore stability.
In this static-constructive repair, only filling with shotcrete according to DIN 18551 helps as the first supplementary material, after which the surface to be reconstructed is reprofiled with restoration concrete (of the same composition as the original concrete) in the negative imprint of the formwork structure.
The lecture on concrete retouching on listed as well as contemporary modern and even new concrete objects was a real bonus!
Such work to even out undesirable differences in color tone and shape reproduction led to the founding of a specialized company 10 years ago under the partial management of the lecturer Dipl.-Rest. Inga Antony. For her team, too, the aim is to keep interventions to a minimum and to preserve the original as a matter of priority. A great deal of work and skill is expended in order to determine an optimally coordinated selection of materials (mortar production according to the original grading curve) and glaze mixtures in conjunction with effective application techniques for the different initial conditions in order to “… recreate the original surface in terms of color and texture”.
This is where the target-oriented interest groups meet in order to jointly preserve the young architectural monuments with their characteristic formwork pattern as an independent surface aesthetic.
In this context, the possible standardization of previously recognizable restoration/handicraft work steps that can be transferred from object to object was repeatedly discussed. Every restoration object has its own specific characteristics in terms of its history of creation, ageing and treatment, but concrete has an excellent unique selling point: with its hardened surface characteristics – in a flawless mixture and uniform compaction – the artificial stone concrete has clear, manageable material properties (compared to those of the many types of natural stone), which is why the relatively simple development of supplementary regulations that go beyond the applicable DIN regulations would be a good idea for the restoration of exposed concrete buildings.
Conservationists, planners and contractors should be tempted to develop these as models in the near future and apply them successfully in future practical phases.
