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The sustainable way to use aggregates

July 21th, 2009
The sustainable way to use aggregates

The UK has an abundant supply of aggregates for use in building materials and construction projects but as the shift towards sustainability gathers pace, interest in recycled sources has increased.

Across the UK the demand for aggregates stands at approximately 275 million tonnes per year. Most of this is used in the manufacture of concrete or concrete products, such as blocks and railway sleepers and for asphalt. Other uses include drainage, bedding for pipework and decorative landscaping as well as bases for roads, paths and other surfaced areas.

Primary aggregates are drawn from 1,300 extraction sites on land or from offshore dredging. In many cases the haulages distances are thus relatively short. Nevertheless, recycled aggregate often has a double advantage of being processed close to the building site where it can be used and its re-use avoids the need for landfill, with its attendant transport cost and environmental impact.

In addition to recycled aggregate, secondary aggregates are also widely used, especially in concrete manufacture. These resources include waste materials such as slag from the steel industry and pulverised fuel ash (PFA) from coal fired power stations. CEMEX, the leading building materials provider, is in the forefront of these developments, creating carefully formulated blends for high performance concrete.
The company is also pioneering the regular use of recycled concrete in its full range of concrete mixes. For example, at the Gorton plant in Manchester, 10% of crushed, recycled concrete is used on a routine basis and customers are increasingly requesting details on this significant saving in primary aggregates. Indeed, it was an important factor in the supply of concrete to G & J Seddon for the construction of the new Glendining Primary School for Salford City Council. In this case 800m3 of concrete was supplied; the recycled element representing the equivalent of 13 concrete mixer trucks worth of material.

CEMEX is actively involved in increasing the supply of all forms of recycled aggregate, from china clay waste in Cornwall to crushed glass and construction and demolition waste across the UK. At quarries in the Bristol area, for instance, CEMEX produces high quality recycled aggregate (Type 1) - which can be used in creating the base layer for roads and concrete surfaces - along with a range of other recycled aggregates for use as a ‘Fill Material’.

At present 25% of the demand for aggregate is met through the use of recycled and secondary materials. The Waste and Resources Action Programme (WRAP) estimates that the proportion of recycled aggregates can be increased to 30% by 2011 and the government gave this target further impetus in the 2009 budget with an annual increase in the landfill tax of £8 per tonne from 2011 to 2013. In addition, the levy on primary aggregates was increased to £2 per tonne.

Increasingly, public projects require a set percentage of recycled material to be used. In some instances this can be a substantial proportion, such as the in the ‘Church Village Bypass’ in South Wales where the Welsh Assembly has imposed a requirement for 45% recycled aggregate.

Despite the excellent progress being made, barriers to using sustainable aggregates remain.  For example, the quality of crushed and graded rubble from building sites can vary between samples, making engineers cautious about using any form of recycled material where defined standards must be met. Confusion or inadequate understanding of cements produced from recycled materials can also restrict uptake of secondary aggregates. 

Research into the use of recycled aggregates for use in making concrete, concrete blocks and as a sub base is ongoing around the World.  In the UK, pressure to develop more sustainable forms of construction is helping to accelerate the process and is creating a demand for more detailed information.

Industry initiatives, such as those led by WRAP, support ongoing research and commercial development The Aggregates Programme aims to increase the availability of sustainable aggregates by helping companies invest in reprocessing infrastructure to produce higher quality recycled aggregates to meet market demand.

Quality protocols have also been introduced to help users of recycled aggregates demonstrate that aggregate products have been fully recovered and are no longer a waste. The programme also aims to provide agreement on defined standards and specifications, thus increasing confidence in performance and providing a clear ‘duty of care’ audit trail to ensure compliance with waste management legislation.
Many of these measures are designed to break down barriers to using recycled aggregates and to encourage a positive position when tenders are drawn up and contracts assigned.

However, in order to ensure the carbon footprint for construction materials really is minimized on the building site, suitable materials must be available locally. For example, recent initiatives have made increased quantities of high quality recycled aggregate available in the London area but on rural sites, far from urban areas, primary aggregates may still be the ‘greener’ option.

Another way in which many major producers of sand, gravel, stone and other aggregates can make the industry more sustainable is through increased efficiency and improved technology. Reduction in dust during the processing stages is one area under investigation and on its many quarries and extraction sites across the UK, CEMEX is playing its part in raising standards.

Overall the UK therefore has a good track record in the use of sustainable aggregates as well as in the drive towards developing new opportunities.

Building the Future
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