Climate-friendly social housing with geopolymer concrete

• Name

  Geopolymer concrete for climate-compatible residential building

• Country

  Germany, 2024

• Fields of Expertise

  Readymix

• Categories

  Admixtures & Additives

The “4HÖFE” new-build project is one of Norderstedt’s largest and most important construction undertakings. Around 300 apartments, including owner-occupied, rental and retirement flats, are being built on four construction sites in the town centre. A special pilot project is being launched on one of the four construction sites. Under the project name UBS4, the company blu, a subsidiary of the Hamburg construction company AUG. PRIEN, is building 71 climate-friendly social housing units there as the future owner and landlord. Three four- to five-storey buildings are to be erected on an area of 4,000 m². The neighbourhood will also have an underground car park with space for 40 cars, 142 bicycles and 71 storage rooms.

Sustainable energy supply

Through the construction project, blu wants to find out how much CO₂ can be saved in subsidised residential building. In order to construct the apartment blocks as sustainably as possible, the project team is focusing on various environmentally friendly measures. For example, in contrast to the other housing complexes in the “4HÖFE” project, electricity and heat are to be supplied by roof-mounted photovoltaic systems and a large heat pump per building. The façades of the three apartment blocks in the UBS4 construction project will also be made of recycled clinker brick, and environmentally friendly cellulose will be used as insulation. Many of the building elements are standardised and will be delivered ready-made. Moreover, the houses will be built as a timber-frame construction on a reinforced foundation slab made of cement-free geopolymer concrete.

Sustainable construction

Geopolymer concrete is an environmentally friendly, cement-free alternative to conventional cementitious concrete. It contains binders based on industrial by-products such as granulated blast furnace slag or fly ash. Together with the Australian company Wagners, MC has developed the first cement-free concrete, known as Earth Friendly Concrete (EFC). The required German building authority (DIBt) approval for the concrete was granted for the first time in September 2019. EFC and MC’s extensive expertise were also used for the UBS4 builds. Compared to reference concretes made from cement, EFC enables CO₂ savings of up to 75 %.

Building with geopolymer concrete

In the project, a powdered activator compound from MC was used to activate the binder in EFC. In order to maintain a working time of 90 minutes, the high-performance superplasticiser MC-PowerFlow 4100 was also used. This enabled the application properties to be precisely adjusted and optimised, both for the precast concrete parts, which were produced by element manufacturer fdu GmbH & Co. KG, and for the ready-mixed concrete, which was produced in a collaboration between Betonlift GmbH & Co. KG and ROBA-Neuland Beton GmbH & Co. KG.

With its unique construction method, UBS4 is a future-oriented project that, quite rightly, was given the status of a state-wide model project by the state of Schleswig-Holstein. Construction work began in July 2023 and the apartments should be ready for occupancy as early as October 2024.