An all-round success using TTK circular trapezoidal girder formwork from PASCHAL for the general modernisation of the wastewater treatment plant.

The Walpershofen wastewater treatment plant has been in continuous operation for 40 years and was designed to serve 36,000 inhabitants.

The complete renovation and expansion for treating wastewater from 58,000 inhabitants, including stormwater treatment, is being carried out in four major construction phases. Transitioning between these phases needs to be smooth in some areas, because the general renovation is being carried out during ongoing operations.

OBG Tiefbau GmbH & Co KG, a company with 50 years of tradition, is able to guarantee its clients reliable as well as economical installation. The company, which is part of the OBG Group from Ottweiler, therefore uses formwork systems from PASCHAL for in-situ concrete constructions, and is also doing so in the total renovation of the wastewater treatment plant, which involves 4 construction phases over 6 years. HSB Schalung GmbH has supported OBG Tiefbau for many years. This PASCHAL trading partner, based in Ensdorf in Saarland, is a specialist for formwork solutions in civil engineering.

Construction phase one includes the aeration tank for nitrification

The cylindrical concrete tank structure was built as a “3-lane" concrete tank on the old secondary settlement system. To ensure that everything ran smoothly during the renovation of the wastewater treatment plant in Walpershofen, OBG Tiefbau relied on TTK circular trapezoidal girder formwork with clamp connection. The use of TTK circular formwork in Saarland once again worked wonders: once set, the segments were a perfect fit and did not have to be repeatedly reset. This and the quick clamp connection are significant factors that reduce the construction time greatly. Similarly, when dismantling the formwork, the quick clamp connection can be easily released and the connecting clamps are stored on the panel for the next use. This keeps them immediately available for reconnecting.

Three perfect circles using TTK circular trapezoidal girder formwork with clamp connection

The aeration tank structure consists of three cylindrical concrete tanks, each 9.00 m high and 40 cm thick.

The outside diameter is 38 m. The outside diameters of the two inner tanks are 30.8 m and 21.6 m respectively. This provides a volume of approx. 2,800 m³ for all three tanks. The outflow of the secondary sedimentation is separate for each tank and has a diameter of 60 cm. The plate aerators connected to the blower station are located at the bottom of the tank.

Effective PASCHAL service

In accordance with the formwork concept designed for the circular structures in Steinach, pre-formed and height-extended TTK segments for a diameter of 21.6 m were delivered to the construction site. Thanks to the robust and torsion-resistant formwork segments, the formwork panels delivered were erected directly from the truck by crane. The segments were quickly connected to each other using clamp connections. The section for the first concreting work was then finished. The dismantling, moving and connecting for the next phase went just as quickly. The inside diameter was completed in 4 phases. The precisely rounded segments retained their settings during all phases and did not need to be dismantled. This shows how stable and robust the formwork system is constructed.

The TTK formwork panel elements were “dismantled” for the two larger diameters on site.

To dismantle the first segment, the PASCHAL foreman Martin Ketterer was on site and assisted the steel-reinforced concrete specialists from OBG with an initial briefing. The remaining segments were dismantled by the building workers themselves.

Manuel La Greca, foreman at OBG added: “The clear instructions and the simple circular system enabled us to adapt the elements for the other two diameters quickly and easily”.

After dismantling, the two larger concrete circles were created according to the same pattern.

The middle ring was constructed in 5 phases and the outer ring in 6 phases using waterproof concrete.

The reinforced concrete column in the centre of the aeration tanks was formed with circular column steel formwork with a diameter of 60 cm. It acts as a support for the steel path structure.

After the basic reinforced concrete structures were completed, site manager Detlef Lenschow was highly satisfied with the installation time and quality of work. During the interview, he emphasised that this was greatly helped by the dimensional accuracy, robustness and easy handling of the TTK system.

The next 3 construction phases in sight

As in the past, the subsequent construction phases will be continuously managed by Johannes Werth from HSB Schalung. Manuel La Greca, foreman at OBG Tiefbau, is certain: “The next formwork tasks, this time with the LOGO.3 wall formwork system, will also run just as smoothly and swiftly as the installations of the first construction phase”.