The Neuenheim district of Heidelberg is filled with large buildings: university departments, research institutes and company head offices. They look solid, imposing, and rather dour. Heidelberg Materials’ recently opened headquarters is the new kid on this block, and it could hardly be more different.
Though itself a fairly massive 50,000m2, its fluid lines impart an admirable lightness. And the facade shines, not just architecturally, but actually: it is made from sparkling white concrete.
Attracting attention is the aim here, for while the building had to provide a modern, high-performing environment in which to gather some 1,000 of Heidelberg Materials’ staff, it also stands as an unashamed advertisement for concrete. As the company (known until recently as Heidelberg Cement) puts it: “It is a sample project for sustainability, and demonstrates what concrete is capable of nowadays, both technically and aesthetically.”
“Yes, we are absolutely trying to show what concrete can do,” agrees Kathrin Gallus, associate partner at architect and general planner Albert Speer + Partner (AS+P). “To demonstrate how it can be shaped, and how it can be part of a building that performs extremely well environmentally.” Heidelberg Materials’ new HQ does this in a number of ways. Its stunning white facades, for example, are made from concrete containing a proprietary additive that removes pollution from the air it comes into contact with.
The building is powered by solar panels that cover approximately 1,000m2 of the roof, and heated and cooled by a ground-source heat pump sunk into the earth below. These and other measures, such as 28 electric car charging points, enabled it to achieve the DNGB Platinum standard – the German Sustainable Building Council’s highest rating. (It also won the innovative architecture category at the German Design Council’s 2022 Iconic Awards.)
Comprising three connected blocks arranged around courtyards, the building’s in-situ concrete frame sits on a 0.8m-thick foundation slab, with 250mm-deep floor slabs. “Energy from the heat pump and the thermal mass effect of all the exposed concrete is a great combination,” says Gallus. “The concrete floors are actively heated and cooled by warm or cold water from the ground, run through pipes set in the slabs.” This works in conjunction with the passive effect of the exposed concrete soffits, which absorb excess heat in summer and store it in winter.
“There is also local control, so users can still open windows if they want. For all this to work, of course, the concrete must be exposed to the air inside the building. But that’s great for us because we want people to see the concrete anyway.”
Mighty white: the precast facade
Approximately 1,000 precast elements make up the building’s facades, and they needed to be as homogenous and dense as possible, says Koen van Tartwijk, head of projects for Byldis,
the Eindhoven-based manufacturer. “This meant as few pores as possible in the concrete, so we thought carefully about the interplay between water, cement and additives. We found the right balance by lowering the water-cement factor, and achieved better workability by using additives.
The bright white colour comes from white cement and Norwegian White gravel aggregate, which we used in sizes up to 15mm.”
Because elements made months apart might end up next to each other on the facade, quality control was paramount: “It was agreed with the client that the clarity of the concrete surface would not drop below a set value. This was checked by measuring the surface clarity after an element had dried, using a specialist camera.”
The moulds for the facade elements were precision-made from 3,800m2 of ply boards using a combination of CNC routing and traditional joinery. To ensure a smooth finish, the sanded and oiled internal surfaces were protected with foil until the moment the concrete was poured.
Most of the exterior facade panels were identical: 3.5m high, 5.8m long, and weighing 3.13 tonnes. Similar panels, but with straight rather than curving verticals, were made for the internal courtyard facades.
“So around 40% were identical exterior panels, 30% identical courtyard panels and for the rest, smaller numbers of corner elements and the slightly different panels below roof level,” says van Tartwijk. “All were made from precision, heavy-duty plywood moulds which yielded up to 70 uses each. We considered making them from other materials, such as fibreglass, but timber gave us the finish we wanted.”
He adds that although the Byldis factory is highly automated, most of the reinforcement had to be made by hand: “So while we can easily make a rectangular cage automatically, these delicate, curved shapes were quite labour-intensive.”
Most challenging of all were the three, curving canopies that grace the building’s entrance: “These were massive, 9m x 4.7m elements, each weighing 29 tonnes. The reinforcement was so complex that we found we couldn’t print a drawing that the rebar workers could make sense of. In the end they worked directly from 3D computer models – a technique born out of necessity, but one we have taken forward since.”
And it is the visuals that really set this building apart – notably its astonishing facades (see box, right), assembled from some 1,000 precast concrete panels, most weighing around three tonnes. “We have taken inspiration from nature, which is present all around us, even in a city,” says Gallus. “The site is close to the river Neckar, and that is reflected in the moulded lines of the facade.”
Ensuring that the panels would achieve the desired “sparkling wave” effect involved some serious research and preparation, however. “It was challenging,” concedes Gallus. “We worked hard to achieve the surface – so that it would look right, and also not be too porous, so it would perform well against pollution. “We made sample blocks, to help us choose the finish and the type of whiteness. Then we made whole panels and left them exposed outside for a year to verify the durability.”
In this, the facade is helped by a specialist cement containing titanium dioxide, which reacts with sunlight to remove nitrogen oxide from air. “It not only cleans the air, the photocatalytic effect also helps a little to keep the surfaces clean,” says Gallus. Once completed, the precast elements required special measures to ensure the bright finish was not compromised: “We wanted them to stay really white,” says Koen van Tartwijk of Eindhoven-based manufacturer Byldis. “So we literally handled them with white gloves and there were notices saying ‘Ornamental Concrete. Do not touch’ all over the yard.”
Inside the building, more concrete spectacles await. In particular, the triple-height reception area features three impressive “trees” – actually nine tall columns supporting an 880m2 ceiling. “To support this ceiling traditionally would have involved many columns or very thick columns,” says Gallus. “There is a lot of weight above, as the building is at its highest point here, with four storeys above the reception area.
Casting the twisted ‘trees’
Probably the most technically demanding part of the building to construct were the three in-situ concrete “trees” that adorn its 10.5m-high foyer. Reflecting Heidelberg Materials’ desire to show concrete at its very best, these elements had to be as visually perfect as possible – resulting in the columns being “poured” from below to help ensure a smooth, blemish-free, almost glassy finish.
This unusual process involved injecting concrete into the (non-visual) base of the heavily reinforced column forms from the basement floor below.
A self-compacting SB4 fine mix with a maximum aggregate size of 8mm was used. In order to rise 10.5m, the fresh concrete needed to be pumped at pressures of up to 200kN.
To withstand this, bespoke steel moulds were built. These comprised 63 individual parts that could be assembled on site as a plug-in system to avoid time-consuming welding. A 150mm-deep steel honeycomb structure on the exterior lent extra strength to the moulds, which were also lined with a 5mm-thick steel formlining.
For each tree, concrete was injected into all three columns simultaneously. To guard against blockages or formwork deformation, the pour pressure was monitored in real time via embedded sensors and a mobile phone app.
“So again we are taking inspiration from the nature around us to find a more refined solution. There are trees outside, lining Berliner Strasse and the parks by the Neckar, so we have arranged nine columns in three ‘trees’, each comprising three angled concrete ‘trunks’. The result is more elegant and interesting than just thick vertical columns.” Each of the nine tree columns is 500mm square, 11m high and, although made from similar pale concrete to the facade, was constructed in situ (see box).
“Because the columns are set at an angle, and connect about a third of the way up, this was very challenging – both for the engineer to calculate and for the contractor to construct. The connection plates with the floor are quite complex, there is a lot of reinforcement, and the finish had to be perfect.”
Also in the foyer is a stunning triple-height feature wall. Slim white precast panels have been attached to the in-situ wall, each with a unique cast-in geometric pattern, echoing the lines of the angled tree columns. “We considered making this feature in-situ,” says Gallus. “But precast was best to achieve the precision and finish we wanted over that kind of height.”
There is more to admire elsewhere in the building too. In the staff restaurant, for example, the ceiling has been created from in-situ concrete by pouring reinforced beams around 64 large diamond- shaped formers. Each beam is 300mm across and 500mm deep, creating a deeply textured and eye- catching diamond pattern. Like the facade and the foyer, it serves to remind diners and their guests of the artistry that can be wrought with concrete.
