Restoration of bridges or buildings with carbon concrete massively conserves resources, reduces construction time – and can save structures facing demolition
In conventional restoration methods of existing concrete components, the required amount of concrete is an essential aspect in the sustainability assessment. For example, when using steel-reinforced shotcrete, a layer of concrete at least 70 mm thick must usually be applied to ensure corrosion protection of the reinforcement. Here, carbon concrete is an alternative with enormous potential.
With this method, instead of reinforcing steel, high-strength and at the same time filigree carbon fibre grids (carbon grids) are embedded in one or more layers in a thin matrix of special mortar and applied to the concrete component to be rehabilitated. Carbon grids are much lighter than steel, have a significantly higher tensile strength and are insensitive to corrosion. Much less concrete is required for rehabilitation measures and to ensure durability than with standard methods. A total thickness of the new layer of 10 to 20 mm is sufficient in building construction. The repair method is approved by the general building authorities in Germany, making the application easy.
Positive effects
The resulting effects include not only significant savings of concrete and steel – combined with the conservation of the necessary resources. As a secondary effect, a faster return to service can have positive impacts. And fundamentally: thanks to its mechanical properties, carbon concrete can enable the renovation and upgrading of structures that would otherwise have to be demolished and rebuilt – with good economic and ecological effects.
Comparative studies confirmed the enormous potential of carbon concrete. When only considering the material consumption of different restoration methods, the savings amounted to up to 85 % of resources such as cement and aggregate as well as 52 % of CO2 emissions. If the preservation of buildings through carbon concrete reinforcement is compared to a new construction of a building (replacement), even a material saving of 93 % and a CO2 reduction of 62 % are achieved.
In practice
Projects that have already been successfully completed include, for example, the so-called "Hyparschale" in Magdeburg. It was only possible to preserve the geometrically complex, unique hall building because its roof structure could be strengthened with a carbon concrete layer of 10 mm without adding too much extra weight to the supporting structure.
And the method has already been successfully used in the first reinforcement of a motorway bridge. At the Frankfurt west intersection of the A648 over the Nidda river, repairs had to be carried out due to the risk of stress corrosion cracking. Thanks to carbon concrete, a reinforcement layer only 3.5 cm thick was sufficient to extend the service life by a further 15 years without affecting the cycle paths underneath and the course of the Nidda.
Conclusion
The composite material carbon concrete offers great potential for the restoration and upgrading of existing buildings. In addition to static and economic aspects, it brings enormous advantages in terms of CO2 savings and resource conservation.
Sources
Schumann, A.; Schladitz, F.; Schöffel, J.; May, S.; Curbach, M.: Ressourceneinsparung mit Carbonbeton – Am Beispiel der Verstärkung der Hyparschale in Magdeburg. In: Hauke, B. (Hrsg.): Nachhaltigkeit, Ressourceneffizienz und Klimaschutz, Konstruktive Lösungen für das Planen und Bauen – Aktueller Stand der Technik, Berlin: Ernst & Sohn, 2021
Riegelmann, P.; May, S.; Schumann, A.: Das Potential von Carbonbeton für den Brückenbestand – das ist heute schon möglich! In: 30. Dresdner Brückenbausymposium – Ergänzungsband 2021. Planung, Bauausführung, Instandsetzung und Ertüchtigung von Brücken, 8./09. März 2021; Dresdner Brückenbausymposium, Seiten: 79-90, 2021
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