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The great recycling mission

The concrete sector aims to become an exemplar of sustainability within the construction industry - and it starts with using more waste products than it produces. NCE reports.

The construction industry generates more than a third of all UK waste and, not surprisingly, the
government wants this halved by 2012 and to hit zero by 2020.

But lurking within this distinctly ungreen state of affairs is a surprising success story.

The concrete sector actually uses and recycles more waste than it produces - it uses just over 5M tonnes of waste, by-products and secondary materials from other industries to make products, and only generates 280,000t of waste.

Sustainability targets

Guy Thompson, head of architecture and sustainability at The Concrete Centre, outlines some of the efforts being made to meet sustainability targets: “Precast concrete uses more waste than it produces with a tonne of precast concrete using 218kg of secondary materials and by-products whilst only producing 6kg of landfill waste.

“Concrete producers and other users of cement are beginning to recognise the value of using environmentally sustainable cements”

Bill Price, Lafarge

 

“UK-produced reinforcement for concrete is manufactured from 100% recycled UK scrap steel. Modern formwork systems and efficient site management minimise ready mixed wastage to less than 2%. Systems are available for re-use of surplus ready-mixed concrete to ensure that it does not go to landfill.”

So convinced is the industry of concrete’s green credentials that sustainability goals are now enshrined in the Concrete Industry Sustainable Construction Strategy (see box).

All very well, but concrete needs cement and cement production has been criticised in the past for its wasteful production process. Happily, things have changed for the better and the cement industry currently replaces 26.5% of virgin fossil fuel with waste-derived material.

“Waste-derived materials are actively sought as cementitious replacements for natural raw materials and fossil fuels. Every tonne of ground granulated blast furnace slag, a by-product of iron production, and fly ash from electricity generation used as cementitious material saves 1.4t of raw material,” says Thompson. “As a proportion of total cementitious materials used in ready-mixed and precast concrete, 31.8% is by-products from other industries which would otherwise go as waste to landfill sites. Cement manufacture uses 1.4M tonnes of waste and produces 45,000t of waste per year.”

Pressure to be sustainable

Bill Price, national commercial technical manager at Lafarge Cement UK, adds: “Specifiers, contractors and end-users are all looking for more sustainable construction materials in a concerted effort to meet ever-tightening environmental targets,” he says. “The carbon footprint of concrete is coming under increasing scrutiny, putting pressure on producers to provide greener alternatives.”

The cement selected for concrete has a major impact on its carbon footprint across its lifecycle. Manufacturers such as Lafarge have responded to their customers’ changing priorities by investing in innovative composite cements that have strong green credentials while offering enhanced durability.

“At the end of a building’s life concrete structures can be adapted for future use, or if demolished recycled as aggregates”

Guy Thompson, TCC

“Composite cements have rapidly increased their share of the UK market - from just 3% in 2002 to more than 30% in 2009,” says Price. “The sales figures speak for themselves - concrete producers and other users of cement are clearly beginning to recognise the value of using environmentally sustainable cements. In 2009 our Phoenix Portland-fly ash cement and Portland-limestone cement comprised over 46% of our total sales and we anticipate continued steady growth this year despite the downturn in the construction industry.”

The development of composite cements with lower embodied CO2 has been central to Lafarge’s drive to reduce the environmental impact of its operations. “As far back as 1979 we launched the first sustainable cement, blended with fly ash (Phoenix), into the UK marketplace. Since then we haven’t looked back,” says Price.

Fly ash

“Today, our leading branded bulk CEM II is still Phoenix, a factory-produced Portland-fly ash cement. As fly ash is a by-product of the energy industry, Phoenix consumes material that might otherwise go to landfill as well as emitting less CO2/tonne during production.”

Price adds that according to recent figures from the British Cement Association (now part of the newly-launched Mineral Products Association) the embodied CO2 in Phoenix cement is typically only 650kg per tonne - a significant reduction from the 930kg per tonne in traditional Portland cement (CEM I).
Thompson believes concrete is a low-waste solution and by optimising its performance characteristics, such as thermal efficiency, sound insulation, fire resistance, robustness and vibration performance, designers can improve the overall material efficiency of a building and lower its associated waste production.

“Designing ‘low waste’ buildings requires a holistic approach through consideration of waste and material resource at each stage,” says Thompson. “Designing the fabric of the building itself to be as versatile as possible can reduce the use of materials by making the structure work harder. For example, by choosing fewer materials for walls and selecting materials that can meet both visual design aspirations and performance requirements.”

The designer has many concrete solutions which can provide efficient designs that avoid over-specification and, therefore, material wastage. Regular plan forms often result in more efficient use of materials, particularly in association with good dimensional co-ordination to avoid off-cuts.

“The omission of downstand beams can provide considerable savings in materials and waste,” says Thompson. “Bends in services are eliminated, and the installation of walls and partitions requires less time, cost and off-cuts. The formwork is also simpler and is well suited to multiple re-use. The adoption of post-tensioned slabs can provide thinner, flat soffits.”

Air voids

The use of slabs that incorporate air voids into the slab can also reduce the weight and use of materials while providing an efficient flooring system with spans up to 14m, he adds. Permanent void formers are an innovative solution where cast insitu concrete is placed over a matrix of recycled plastic balls. Thus the overall thickness of the slab is increased with significantly less concrete. Hybrid systems incorporate a deck of precast concrete permanent shuttering to the soffit side thereby further reducing the need for additional formwork.

The performance benefits of concrete construction can help the designer to reduce or even eliminate the use of additional materials and finishes, reducing waste still further.

Sound insulation, a robust and attractive finish, fire resistance and flood resilience are all provided by exposed structural concrete without the need for extra materials. “Exposed concrete also increases the thermal efficiency of a building which, when used as part of a passive solar design strategy, can significantly reduce the need for heating and air conditioning,” says Thompson. “And at the end of a building’s life concrete structures can be easily adapted for future use, or if demolished can be recycled as aggregates and the reinforcement recycled as scrap metal.”

Thompson believes the concrete sector is wholeheartedly committed to minimising waste and is working with designers on a “less is more” approach to design and construction that exploits the material’s built-in performance benefits.

  • The guide Material Efficiency: optimising performance with low waste design solutions in concrete may be downloaded, free of charge, from www.concretecentre.com

 

2012 sustainability vision

The concrete industry has published its second annual Concrete Sustainability Performance Report.

In 2008 the UK concrete industry agreed a Concrete Industry Sustainable Construction Strategy. This pledge to sustainability objectives was signed by trade associations and companies and included a commitment to publish an annual report on the industry’s sustainability performance.
The report signifies a further milestone towards the fulfilment of the vision that, by 2012, the UK concrete industry will be recognised as being the leader in sustainable construction.
The latest performance report provides 2008 performance data and outlines 12 targets, plus those in development, to be achieved by 2012. Notably these include:
n The reduction by 17% of the level of CO2 emissions as a proportion of concrete output from a 1990 baseline figure of 103.1kg CO2 per tonne to 85kg.
n To further increase the use of material diverted from the waste stream for use as fuel from 17.3% in 2008 to 21% by 2012.
n To increase the percentage of by-products, such as fly ash from power station, used as a proportion of cementitious materials to 33%.
n In addition, by 2012 the percentage of production sites covered by a UKAS Environmental Management System is to increase to 85% and the percentage of production sites covered by a UKAS certified 9001 quality management system is to increase to 90%.
“These are real targets that the concrete industry is committed to achieving and, where possible, to exceeding,” said Andrew Minson, executive director of The Concrete Centre. “The targets are indicative of the industry’s objective to be recognised as the leader in sustainable construction.”

  • To download a copy of the Concrete Industry Sustainability Performance Report visit:

www.sustainableconcrete.com

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