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    Bligh Tanner, Wagners & HASSELL - Suspended Geopolymer Concrete Floor Panels

    Geraldine Chua

    The University of Queensland’s Global Change Institute (GCI), designed by HASSELL in conjunction with Bligh Tanner and Wagners, is the world’s first building to successfully use cement-free concrete for structural purposes. The only prior use has been for footpaths by local authorities as a test case.  

    Piloted by the team in its bid to achieve a 5 Star Green Star Education Design and As-Built ratings for the Institute, the suspended geopolymer concrete floor panels are made from Earth Friendly Concrete (EFC), a Wagners brand name for their commercial form of geopolymer concrete.

    With less embodied energy, the geopolymer precast concrete contains no normal Portland cement, comprising sand, aggregate and a binder that is made from the chemical activation of two commonly recycled materials – ground granulated blast furnace slag (GGBS), a waste product from steel production, and fly ash, a waste product from coal-fired power generation.

    It also has extremely low CO2 emissions as compared to normal Portland cement-based concrete, as no new manufactured cement is required when replacing normal concrete with EFC.

    Numerically, utilising EFC instead of normal 40MPa strength grade concrete can lead to CO2 savings of 220kg p/m3. With regards to the 33 precast EFC beams used in the GCI building, this is a 6908 kg reduction in C02 emissions.

    In a world where eight per cent of global carbon emissions are generated during the manufacture of cement, the suspended geopolymer panels demonstrate a new structural use which can benefit and contribute to a reduced carbon footprint in the construction industry worldwide.

    Closer to home, the precast geopolymer concrete floor panels application has allowed the GCI building to be sustainably constructed, minimising the toll it could otherwise have taken on the environment.

    INITIATIVES

    • The panels include cast-in pipes for hydronic cooling/heat transfer and were shaped with a vaulted soffit to maximize surface area of concrete-to-air contact for efficiency of heat transfer. Combined with the thermal mass of the concrete, this has assisted with the low energy cooling of the 6 star Green Star building
    • Very low shrinkage, typically 350 microstrains when tested to the Australian Standard drying shrinkage test
    • Low heat of reaction which avoids the possibility of thermal cracking in large element concrete pours
    • 30% higher flexural tensile strength than normal concrete
    • Higher durability than normal concrete – higher acid resistance, higher resistance to sulphate attack and the ingress of chloride ions, which are responsible for the corrosion of the reinforcing steel contained within the concrete
    • Apart from the structural performance properties, EFC has a natural off white appearance which is a desirable architectural feature
    • Geopolymer concrete can be crushed up at the end of its economic life like normal GP based concrete, and used as aggregate in either road base materials or to make new concrete
    • The pioneering use of geopolymer concrete on the GCI project has been awarded 2 Innovation points in the Green Building Council assessment for Green Star rating

    Images: Wagners and Bligh Tanner

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