Major concrete rehabilitation project for the Predigtstuhl cable car system

Extensive concrete renovation works were carried out between summer 2018 and autumn 2020 on the top station and the supporting pillars of the famous Predigtstuhl cable car system in Bad Reichenhall, Germany. And the project was an all-round success, as evidenced by the award of the 2020 Bavarian Heritage Preservation Prize in the Private Buildings category.

Built in 1928, the Predigtstuhl cable car system in Bad Reichenhall is the oldest original large-cabin funicular in the world. The steep ropeway section of 2,400 metres in length consists of three supports with heights between 9 and 32 metres and a maximum rope span of almost 1,000 metres. Serious damage was found on the three ropeway support pillars, which dated from the time the funicular was first constructed. These were designed as reinforced concrete hollow chamber structures and are anchored either in reinforced concrete foundations or in solid underlying rock. In addition to major defects in the concrete structure and the covering, areas of exposed reinforcement were also found at the support heads.

 

Heritage-compatible repairs required

Extensive repair work had become a matter of urgency. As requested by the client, Predigtstuhlseilbahn GmbH & Co. KG, the renovation measures needed to preserve the original formwork board structure yet greatly improve structural and aesthetic durability. Dr. Schütz Ing.-Büro from Kempten in Allgäu, Bavaria, was entrusted with overall responsibility for the large-scale project.

To meet the specifications of the client and the heritage agency, the construction contractor selected for the task, Heiko Schupp Beschichtungen (coating systems) from Stödtlen, Germany, collaborated with MC’s technical sales consultant Andreas Supp in putting together an appropriate rehabilitation proposal. A sample area was prepared directly on site in Bad Reichenhall, and this served to convince all involved of the viability of the system devised – and, in particular, its suitability for recreating the formwork board pattern required on the visible faces.

For the renovation work, the supports had to be completely scaffolded, with additional working and storage platforms needing to be erected in the alpine terrain. Not just the weather but also the logistics of the undertaking proved to be quite a challenge. As the renovation work had to be carried out during ongoing cable car operations – during the day outside the danger zone around the ropeway cantilevers, at night in the danger zone – deliveries could only be made by helicopter with a maximum payload of 900 kg.

 

Extensive rehab of the ropeway supports

As the cantilevers of the ropeway supports had numerous cracks, the injection resins MC-Injekt 1264 compact and MC-Injekt 1264 TF were used for initial stabilisation. Holes were drilled in a 10 × 10 cm grid and these were then grouted with the injection material. These two low-viscosity epoxy-based duromer resins enable rigid filling of cracks, joints and cavities in dry buildings and civil engineering structures. They exhibit fast strength development, cure even under dynamic loading and offer high tensile and compressive strength values. MC-Injekt 1264 TF can also be applied at ambient temperature down to +5 ° C.

 

Once the cracks had been grouted, the actual rehabilitation of the concrete around the supports could begin. For this, Nafufill KMH was used both as a corrosion inhibitor and as a bond coat. This MC corrosion protection covering for reinforcing steels used as part of a concrete repair programme has been tested according to German code ZTV-ING, TL/TP PCC BE and the DAfStb repair guidelines for stress classes M2/M3, and is certified according to EN 1504 Part 3.

Durable concrete repairs with Nafufill KM 250

The next stage in the repair of the concrete components involved application of Nafufill KM 250, the fire-resistant, fibre-reinforced PCC concrete replacement for both structural and non-structural components. Nafufill KM 250 offers high carbonation resistance as well as being resistant to de-icing salts and chloride-proof. The product is formulated as a concrete replacement compound compliant with German code ZTV-ING, Part 3 Solid Construction, Section 4 for SPCC and PCC II concrete repairs of dynamically and non-dynamically stressed surfaces.

 

Modern concrete cosmetics to restore that old look

In order to restore the board structure of the exterior, the surfaces were reprofiled with a polymer-modified fine filler from MC-Bauchemie designed for both the localised and the wide-area cosmetic patching of standard and fair-faced concrete. This allows layer thicknesses of up to 6 mm to be applied in a single pass. The MC fine filler is resistant to temperature swings according to EN 13687-3 and certified according to EN 1504-3, Class R1 for non-structural building components. It is also classified as a non-combustible construction material according to EN 13501, Euroclass A1.

 

Effective surface and concrete protection

The surface protection regime involved an initial deep hydrophobic treatment with the single-component impregnation agent Emcephob WM. Emcephob WM is certified and approved in accordance with DIN V 18026 as an OS 1 surface protection system with an OS 2 structure. It reduces chloride absorption, is resistant to alkalis and further improves resistance to freeze-thaw cycling and de-icing salts.

Finally, a preventive transparent concrete protection glaze for outdoor weathered surfaces was applied in the form of MC-Color Proof pro. This two-component polyurethane-polymer combination is open to water vapour diffusion and inhibits carbonation. It is also UV-stable and resistant to weathering, temperature swings, frost and de-icing salts. Its integrated Easy-to-Clean Technology has provided test evidence of cleanability in accordance with German code ZTV-ING, TL/TP AGS-Beton.

 

The rehabilitation of Bad Reichenhall’s Predigtstuhl cable car system required a high degree of ingenuity in every respect in the development of detailed solutions, especially when it came to the reconstruction of the original concrete surfaces. The results achieved with the keenly tailored solutions adopted can only be described as exemplary, with new standards being set in terms of heritage conservation.