New building forms a “gateway” to the politically and historically significant Dutch metropolis – with CO₂-reduced concrete from Dyckerhoff Basal

KJ Den Haag is a building in the green heart of the city, consisting of a new reception hall for the renovated main railway station with various commercial units covering 1,200 m², with apartments above and two directly connected, striking residential towers, each approximately 90 m high.  

The architects at Powerhouse Company are responsible for the design, which they created to blend in perfectly with the neighborhood. The notched, straight columns that form part of the lightweight concrete façade of the two residential towers are inspired by the formal classicism of The Hague's administrative architecture. In turn, the dynamic station concourse on the ground floor, with its curved wooden ceiling and large, curved glass surfaces, forms a striking contrast. It forms, so to speak, the valley between the two towers. The curved elements of the concourse, reminiscent of dunes, are reflected in the stepped U-shaped silhouette of the central valley area. In addition, the formerly dreary Queen Juliana Square in front of the new complex is to be transformed by the experts at DELVA Landscape Architecture into an emotive green space with dune vegetation, connecting to the adjacent De Koekamp park. The greenery of the park is echoed in the roof gardens and green terraces of KJ Den Haag.

The project phase began in 2015, construction work started at the end of 2023, and the work is scheduled to be completed by the end of 2025. The Dutch companies Synchroon from Utrecht and Amvest from Amsterdam are working together as a consortium under the name “KJ-Plein” as project developers. The supporting structures were designed by IMd Raadgevende Ingenieurs (consulting engineers), and construction is being carried out by the Gouda-based company J.P. van Eesteren. The construction will not only create space for restaurants and shops, but also nearly 400 residential units.

In addition to a total of approx. 17,000 m³ of reinforced concrete, wood is also being used for the curved roof of the station entrance hall, as well as glass, concrete, and aluminum for the façade. The in-situ concrete is being supplied by Dyckerhoff Basal from its plant in The Hague. Dyckerhoff Basal is a subsidiary of Dyckerhoff GmbH and belongs to the Italian Buzzi Group.

The KJ Den Haag project is not only challenging in terms of its architecture, but also in terms of concrete technology. Concrete in a wide range of strength classes and consistencies was required, while at the same time minimizing CO₂ emissions from building materials and making optimal use of the available raw materials.  

Model – Concrete formulations in various strengths (graphic: J.P. van Eesteren)

The cement used was mainly CEM III/B 42.5 N-LH/SR from Neuss. To further reduce CO₂ emissions, the strength verification for the higher-strength concretes was not carried out until they were 56 days old. This made it possible to exploit the post-hardening potential of the blast furnace cement and reduce the cement content in the concrete. For concretes in consistency class F5, the proportion of fine particles was increased to improve flowability by adding limestone powder instead of cement.  

In all concretes, part of the natural aggregate was replaced by RC aggregate, which helps to conserve primary resources. Optimizations in the construction processes also improve the ecological footprint of the building, e.g., the construction of walls and ceilings in different thicknesses. In addition, alternative, lighter reinforcements such as basalt reinforcement were used, particularly in the penthouses.

The use of experimental concrete containing biochar was completely new. Biochar is produced in a process known as pyrolysis from plant biomass such as wood residues, tree cuttings, or agricultural waste. This is a process in which biomass is carbonized in the absence of oxygen at temperatures between 400°C and 800°C to form a carbon-rich, porous substance. The synthesis gas and pyrolysis oil produced during this process can be used for heat generation, for example. Biochar has a wide range of uses, particularly in agriculture and water treatment. Due to its ability to store CO₂ over the long term, it is also attracting increasing public interest in the field of building materials.

Tested here was the use of biochar as an additive in concrete. It is currently still under discussion whether the CO₂ bound in biochar can be credited towards reducing the carbon footprint of concrete. 

Since this application was completely new territory, the construction was preceded by extensive testing in Dyckerhoff Basal's concrete laboratory to determine the optimal formulations for pouring the innovative concrete. It was used for the construction of the penthouses at the top of the residential towers. The required strength and hardening time could be guaranteed with the use of biochar.

Good workability was also important. The dark color of the freshly poured concrete with biochar fades after a few days as the concrete surfaces dry (see photos 6 and 7 in the slideshow).

A total of 90 m³ of this experimental concrete was used. The individual concreting operations were closely monitored by the Dyckerhoff Basal concrete laboratory to ensure consistent, high quality.

The new complex is easily accessible from anywhere. Local and long-distance public transport and taxis are available throughout the day. By car, you can quickly reach Utrechtsebaan, the feeder road to the A12 highway. However, there is no underground car park under the new building complex, but one of the largest bicycle parking garages in Europe with approximately 8,000 parking spaces and modern facilities. KJ Den Haag is only a few minutes' walk from the historic city center, the Malieveld fairground and event venue, and the Haagse Bos forest.

The seriousness with which the city, where many nationalities meet every day, takes its role as the seat of various courts and institutions for the protection of people and their rights is also demonstrated by the fact that the Declaration of Human Rights will be displayed for all to see on the wooden ceiling of the entrance hall.

Photos: title – Visualization /Powerhouse Company; 1, 2, 5 to 8 – Dyckerhoff Basal; 3, 4, 9,10 – J.P. van Eesteren

For further information, please contact:
Iris Weise-Rosch, Tel.: +49 611 676-1187
marketing@dyckerhoff.com