Elaine Toogood, Director, Architecture & Sustainable Design at MPA The Concrete Centre, explores the opportunities and benefits of MMC concrete to support a more circular economy.
The construction industry is developing a much greater understanding of carbon impacts across the entire lifecycle of buildings and materials, from embodied carbon at construction, to operational energy efficiency, to what happens at end-oflife. There is also a growing recognition among government, industry and the public that we urgently need to transform our linear take-make-dispose economic model into a circular one and that this can also offer significant carbon reductions. Applying this to construction with shifts in behaviour, innovative design and developments in concrete based MMC, we can ensure we build more sustainably with longevity, efficiency and waste reduction in mind.
Material efficiency
At the core of circular economy thinking is material efficiency and waste avoidance. Offsite construction, in all its forms, offers benefits in this regard and precast concrete is no exception – with factory-based production and just-in-time delivery, site wastage rates can be dramatically reduced. Offsite concrete benefits particularly from low factory wastage thanks to reusable forms and volumes of batched concrete matched to need. In addition, its robustness and resilience mean less packaging is needed with large panels simply lifted straight off the delivery vehicle, ready for assembly on-site.
Reuse
The benefits of concrete's robustness and durability extend far beyond materials delivery. Retaining and reusing a structure can help extend a building's life for as long as possible and extract the maximum value from it. These benefits are increasingly recognised by designers, developers and planners and there are numerous examples of precast concrete structures being given a new lease of life. This is often categorised as retrofit which belies its very real circular economy benefits, especially if the building is already over 50-60 years old, the current accepted design life for most contemporary buildings.
The conversion of Centrepoint from office to residential is one well known example. As is ORMS' conversion of Camden council's old offices into a boutique hotel chain – The Standard. In each of these, both the precast concrete facades and internal structures were retained, requiring little more than a clean to be reused.
This is testament to concrete's durability. According to the design standards for a concrete frame located internally (a 'low exposure' environment) no additional measures are required to achieve a service life of over 100 years compared to 50. The inherent low maintenance requirements of a concrete structure, and its resilience to fire and the impacts of water, mean that it can remain serviceable over a long period, with the potential for multiple reuses during its lifetime.
The key to optimising this inherent longevity therefore lies in the way that it is designed. The 'long life loose fit' approach to design is well established and can ensure future functionality of structures through consideration of spans, optimum loads, regular grids and generous floor-to-ceiling heights. The many lessons being learned through current retrofit projects will also help inform the futureproofing of today's new buildings.
Design for disassembly
We can also maximise the lifespan of components by designing them to be disassembled and reused elsewhere. This is commonly applied to elements likely to be replaced more frequently, such as fixtures and fittings, but is being increasingly considered for more substantial elements such as cladding. Designing the less permanent layers or parts of a building to be easily removed and replaced serves not only to reduce waste but helps extend the longevity of the underlying structure by making it easier to upgrade it.
Structural precast concrete elements can also be designed for disassembly and reuse. Today, this tends to be limited to elements that are expected to be in place for relatively short periods of time, such as stairs and stadium seating, fencing, barriers and paving. The upper tiers of London's 2012 Olympic stadium, for example, were designed so that they can be reused elsewhere, though for now they continue to fulfil their original function.
Since offsite solutions are designed for site assembly, the leap towards enabling their disassembly seems straightforward. Interesting recent examples of prefabricated concrete structures designed specifically to be disassembled for reuse elsewhere include the Circle House, Denmark's first circular housing scheme using precast concrete components, and the 'D-Frame' structural system developed by Laing O'Rourke. Greater standardisation of construction elements can also be seen as unlocking the potential of this approach.
Deconstruction, instead of demolition is likely to become more commonplace, when a structure does reach end-of-life. Buildings will be dismantled with more consideration given to maintaining materials at their highest value for potential reuse. In Norway there is already a draft standard for the reuse of hollow core concrete planks.
Recycling and concrete
When concrete does reach the end of its life, it can be, and generally is, recycled. Most of concrete's mass is aggregates, and when recycled, it becomes aggregate again. Some of this makes its way back into new concrete, but most recycled aggregate, which comes from reprocessing of various inorganic material previously used in construction, such as masonry rubble, is used 'unbound' as sub-base materials, fill and hardcore. Already, over 90% of the UK's hard construction, demolition, and excavation waste, is diverted from landfill for use elsewhere in construction.
In fact, most concrete currently contains some recycled material, and often upcycling materials from other industries such as GGBS and fly ash as cementitious content, and China Clay waste, which has similar properties to primary aggregates and is commonly used as an alternative in some parts of the country. Here, one part of the industry's waste is another's raw material. On top of this, there are many exciting research projects that seek to use local waste resources in concrete – from coffee grounds to oyster shells – further promoting the reuse of local, secondary materials in construction. Offsite concrete construction already enables long life buildings, structures and elements to provide immediate value and well into the future. As industry starts to embrace a more circular economy, we can expect yet more exciting innovations and examples of good practice to help keep those wheels in motion.
For more information visit: www.concretecentre.com
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