The new headquarters of the building materials manufacturer HeidelbergCement consists of three interconnected building sections of different heights. The atrium of each building section provides plenty of light and luminance. The building was opened in June 2020 and provides up to 1,000 employees with a state-of-the-art work environment. The architectural firm AS+P Albert Speer + Partner based in Frankfurt was responsible for the project as a general planner, and carried out the design in collaboration with W+Architektur, with the latter providing the consulting office for the client’s project manager.
PERI, one of the leading formwork and scaffolding manufacturers worldwide - and the building materials manufacturer HeidelbergCement - combined their architectural and concrete expertise for the execution of this project. In doing so, the existing limits of PERI’s concrete construction offerings were pushed. The architectural highlights of the project were successfully realized using special PERI formwork elements.
Customized PERI formwork in use
The project as a whole was a massive undertaking. “A total of around 31,500 m3 of concrete, 97,500 m2 of formwork, 7,500 t of reinforcing steel, and 250 m3 of masonry were used over the 16-month construction period," says Thomas Mehl. Thomas, the project manager, was responsible for the project as a whole and carried it out successfully with his team from the PERI Frankfurt branch office and the Free-Form Concrete technical office under the management of Johann Bergmiller.
Twisted Supports in SB 4 Architectural Concrete
The focal point of the newly built atrium are three spectacular X-shaped supports which serve as the structural root of the building, and also take on the form of a tree. Thomas Mehl and Johann Bergmiller agree: the highlight of the project was the formwork and concreting process for these supports in SB 4 architectural concrete quality, which hold up the 1,200 t and 700 m2 ceilings of the approximately 11-m-high atrium. Each of these supports consists of three square cross-sections inclined towards each other, crossing over at about a third of the total height.
To achieve the required formwork design for the tree-like supports, the engineers at PERI pushed the limits of what is technically feasible. Due to the special geometry of the supports - the three-dimensional characteristics of the three pillars, and the fact that they overlap - creativity was essential. The very high architectural concrete requirements, the structurally essential fresh concrete pressure of 200 kN/m2, and the tough space limitations in the atrium made it impossible to use conventional special-purpose timber formwork.
The formwork beneath the point of the intersection had to be entirely non-destructive so that it could be subsequently reused for the other supports, which provided another layer of complication to the construction process. "So, following discussions with the client, we decided to use a highly complex type of 3D formwork consisting of steel elements with a construction height of 150 mm," says Bergmiller, who was responsible for the planning process for this special-purpose formwork.
At two and a half months, the time frame allotted for the planning process through to the delivery of materials in Heidelberg was extremely demanding. The basis for the three-dimensional planning - carried out using CAD systems PERI CAD and RHINO - was a 3D model of the tree-like supports, which took the subsequent element separation points into account. These separation points posed another challenge for the planners of the formwork construction, as they had to blend seamlessly into the architectural concrete of the building. No more than a one-panel joint was allowed to be visible over the entire height of the support. In addition, visible fixing screws, tie holes and formlining joints were to be avoided.
Sophisticated Honeycomb Structure
"You can picture the supporting structure of the completed pillar formwork as a kind of honeycomb structure consisting of no fewer than 63 CNC laser-cut individual components," says Bergmiller. "The individual components were assembled as a plug-in system, so we could do away with time-consuming welding in rigs," he explains.
Each individual component had to be newly constructed and statically dimensioned. A total of around 12.7 t of steel was used during the construction process. 5-mm-thick steel formlining was then attached to the supporting structure to withstand the high level of fresh concrete pressure. "The biggest challenge was the formwork solution at the point where the arms of the three tree-like supports intersect," says Bergmiller. Additional external rigging constructions were fitted with the specific aim of counteracting the deformation of the steel.
Due to the large volume of materials required for the overall project, the bulk of the structure was pre-assembled in the factory and delivered to Heidelberg at the precise time it was required. The tree-like supports were assembled step by step on site. The reinforcement was installed at the same time and the formwork was easily integrated into the PERI UP Flex falsework, which was already in place. Incidentally, the compatibility of the systems was one of the key reasons why the customer decided to work with PERI.
Pushing the Envelope
Even before construction began, it was clear to those responsible for the project that erecting the tree-like supports would be an exceptional challenge. With this in mind, the engineers from PERI collaborated with HeidelbergCement's lead architectural concrete coordinator Ingo Lothmann to develop a technological solution for an unprecedented scenario. In addition to the concrete technology requirements regarding the colour and structure of the architectural concrete surfaces, placing the concrete would also be an extraordinary undertaking. Unlike most other cases, the concrete was introduced from below instead of from above.
A concrete distribution system conveyed a total of 30 m3 of concrete into three-pillar sections simultaneously and forced the concrete upwards by up to 11 m using three pump hoses in the formwork. The slide gate valves used for injecting the concrete were positioned in such a way that they were no longer visible upon completion. PERI sensors integrated into the formwork made it possible to measure the fresh concrete pressure in real-time during the concreting process and to monitor it on a mobile phone using PERI InSite Construction Web Application. The characteristic data determined for the formwork pressure provided an accurate overview of the concreting process for the pillars.
In the end, those responsible for the project were more than satisfied with the outcome. "With this project, we have once again broadened the horizons of what is technically feasible in special-purpose formwork construction," says Johann Bergmiller, in summary.
Feature Wall in SB 4 Quality
In addition to the tree supports, the new headquarters also features other architectural highlights. The so-called feature wall in the building’s foyer is characterised by its recessed radial pattern, which consists of several prefabricated concrete elements that were retrofitted to the in-situ concrete wall. In addition to the highest architectural concrete quality of SB 4 standard in white, an additional requirement was that no visible fastening points or tension holes should be visible as this would negatively impact the appearance. There are no visible vertical joints and a maximum of two visible horizontal joints at the height of the galleries. The butt joints were concealed by an overcut. In order to be able to realise the 8 cm thick prefabricated concrete elements (4 cm in the recesses), project-specific PERI special formwork was used.
Uneven Cross Vault in SB 4 Grey Concrete
Another challenge was the domed ceiling, which consists of an uneven cross vault with a circumferential edge upstand in SB 4 grey concrete. This was expected to be formed at a height of up to 7 m and a slab thickness of 25 cm. The desired result: a joint and butt-free appearance without visible fixing points on the formwork facing. The formwork solution that PERI developed for the implementation of the cross vault consisted of a total of 82 3D-designed architectural concrete timber formers.
Diamond-Shaped Recesses in the Casino
The casino on the ground floor of the new headquarters also features an eye-catching design. It offers HeidelbergCement employees ample seating and a commercial kitchen. This room features a special reinforced concrete ceiling with radial sharp-edged beams. In SB 4 white concrete from the underlying ceiling in SB 2 grey concrete, these interventions stand out due to the striking use of shapes and colours. Here too, no visible fixing points of the formlining or bracing points of the beam formwork are visible.
For the slab, PERI special formwork developed especially for the project was used, which was later implemented with a total of 64 different diamond-shaped box outs pre-assembled in the factory. The load was transferred on four diamond-shaped supports with different cross-sections in the facade area.