Concrete recycling – turning rubble into a valuable building material
Our soil contains an important resource, and that is gravel for making concrete. But gravel mining is strictly regulated for ecological and landscape conservation reasons. This is why it is important for building rubble and other demolition material to re-enter the life cycle of materials. Close to 54% of the concrete that goes into Swiss Re Next is from recycled material, which is used wherever it is smart and feasible to do so.
Did you know that Switzerland leads Europe in per-capita consumption of concrete? Concrete mostly consists of gravel and sand that gets mixed with cement and water. Switzerland's soil is rich in gravel. In fact, it is the only resource it contains in major quantities. In Switzerland, 60 million tonnes of gravel are mined every year. The bulk is mined from the roughly 900 pits and quarries in our country; the rest is dredged from close to 100 sites in lakes and rivers.
Despite the stony soil, gravel mining in Switzerland is reaching its limits. Can we afford to continue stripping away more and more of the natural gravel filtration system for our groundwater, day after day? Another concern is that many gravel deposits occur in protected landscapes or are off limits because they lie under valuable arable land or in built-up areas. "It is becoming harder and harder to mine gravel in the closest possible vicinity of urban agglomerations, even though doing so would have the least impact on the environment", laments Martin Weder, who is the director of the association for the Swiss gravel and concrete industry (FSKB)1.
54% of concrete used for Swiss Re Next is recycled from demolition projects
Materials from demolished buildings are far too valuable to be dumped in landfills rather than recycled. When we demolished the old office building, we hauled a total of six thousand tonnes of concrete and mixed rubble and asphalt to the nearby recycling centre in Rümlang. There, the rubble is run through a breaking and sorting system, crushed by an impact crusher and stripped of any metals by a powerful magnet. The salvaged concrete is sent on conveyors to different storage silos according to its grade. Any non-recyclable matter left over is taken to a landfill.
Much of the concrete used in Swiss Re Next was recycled from demolition material sourced from within 25 kilometres and reprocessed in regional recycling centres. This meets the requirements for Minergie Eco and LEED Platinum certification which Swiss Re Next aims to achieve. According to civil engineer Marcel Zimmermann of Ernst Basler + Partner, recycled concrete is produced and quality-tested to meet the standards of the Swiss Association of Engineers and Architects (SIA), just like new concrete. In the Swiss Re Next project, we use recycled concrete both for load-bearing and non-structural interior walls, as well as for above-ground ceilings. New concrete is used for the foundation slab, exterior walls that come into contact with soil, and ceilings underground.
Demolition projects are the mines of the future
With the volume of building rubble set to continue growing, the construction industry is called on to aim for a near-100% recycling rate using creative, sustainable and economic solutions. The time has come for what is known as urban mining, and the City of Zurich, too, has committed itself to it. According to estimates by Heinrich Gugerli of the local government's centre for sustainable building (Fachstelle Nachhaltiges Bauen), the city by 2050 will rely entirely on its built infrastructure for resources to use in urban renewal projects. "By then we'll be quarrying our existing buildings for gravel."
- Worldwide, some 30 billion tonnes of concrete were used in 2012, or roughly four tonnes per capita per year. In other words, concrete is the second most consumed product in the world after potable water. For comparison, oil consumption per capita per year is approximately 500 kg.
1 Federal Office for the Environment (Bafu), magazine "environment", issue no. 4/2011