Demolition is the most difficult task when renovating a half-century-old reinforced concrete building

In 1973, the largest residential building in Bács-Kiskun County, the Kecskemét Ribbon House, was inaugurated. The supporting structure of the building was made of prefabricated UNIVÁZ reinforced concrete elements, and a prefabricated reinforced concrete flange beam was placed on site next to the prestressed circular reinforced concrete slab beam for the suspended corridor, and the section between the two was completed with a monolithic reinforced concrete bar. Due to the poorly chosen structural detailing, rainwater infiltration caused significant damage to the structures, while the heterogeneous suspended walkway lacked the necessary bonding of the supporting structural elements, resulting in material quality and construction defects, making the renovation of the building now essential.

The suspended corridor needs a complete reconstruction

The client, the Ribbon House Housing Cooperative, based the design on thorough structural diagnostics during the preparation process, as the aim was to ensure that the rehabilitation of the suspended corridors would provide the supporting structures for another 50 years.

The preservation of the condominium is therefore a major structural engineering task, which the contractor Verticart Kft. is carrying out with great care during the works that started in May 2024 and are expected to be completed by the end of 2024.

Due to the size of the 243.5-metre-long building, construction is taking place in five phases, with durability and the use of high-quality materials being key considerations. This is why they chose Cemix Hungary Kft. products. As we learned from Csongor Kelemen, managing director of Verticart Kft.:

"Cemix was chosen because of its high quality and long-term durability, which was a key requirement during the refurbishment. When selecting the product it was also important to consider that it could be used as a system."

The main advantages of the products used include excellent adhesion, fast curing times and long-term quality assurance. These properties are essential for the durability of the reconstruction of suspended corridors. The customer was particularly concerned about the longevity of the structure, and the Cemix products used in the system proved to be an excellent choice.

Demolition was the biggest challenge

The project is not simple from an organisational and architectural point of view, as the developer expected pedestrian traffic and residential use to be maintained during the demolition and construction processes.

- said Csongor Kelemen. Therefore, only the most critical demolition events were actually restricted. Due to the existing structural conditions, only suspended formwork could be used as a condition for the concreting of the new structural parts.

The biggest challenge was the demolition of the existing structure. Due to its design, construction inaccuracies and deteriorated condition, particular care had to be taken to ensure that no damage was caused to the existing and remaining structures. After several plans, instead of cutting concrete through the initial formwork, the removal of 6.6 m of beams proved to be the safe solution.

"The process," the manager explained, "was particularly spectacular because of the size of the crane, which was used to start the demolition from a height of 25 metres, with the road blocked at half-lane."

Personal participation is important

"Cemix has already had a relationship with the contractor - added István Debreczeni, regional project manager of Cemix Hungary Kft. - because we helped in the renovation of the Reformed Church in Kecskemét a few years ago.

Here too, we have accompanied the project from laboratory testing to the final operation, and we are constantly involved and helping to make decisions.

And Cemix's high quality products are most efficient when installed as a system, which is why the following materials were chosen for the design:

Printing:

•  1645 CTMIX BETONJAV.HABARCS FINOM 25kg - 9625 kg
•  1515 CONTACT CT CONCRETE HANDLE 20kg - 1360 kg
•  1615 CTMAX BETONJAV.HABARCS DURVA 25kg - 2400 kg

Exterior plaster:

•  2023 MP 503 A 40kg - 12480 kg

Coloured plaster:

•  2703 STRUKT.PRIMO R 2 4001 white - 1300 kg

Meshing/planing before colouring:

•  2202 STYROCLEANER 25kg - 4325 kg
•  Glass fabric mesh (50x1m) - 550 m²

The screed layer before the final finish:

• 5232 Screed ZE30

Participants in the project

• Client: Ribbon House Housing Cooperative
• investment promoter: KVALITÁS Kft. - Tibor Sári
• support structure diagnostics: ÉMI Nkft. - Bálint Fekete
• designers: ÉKI TERV Kft. - Tibor Pintér (supporting structure) and Priarch Studio Kft. - Miklós Czikó
• (building structure)
• Contractor: Verticart Kft. Csongor Kelemen
• technical inspector: KVALITÁS Kft. - Tibor Sári
• responsible technical manager: Gergely Bánfi
• work and fire safety adviser: Balázs Fejes
• structural expert: Csaba Holló