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In the driving seat for motorway aggregates

The £2.5m which was spent to develop an aggregate washing plant at R Collard’s MRF in Eversley was not an insignificant investment, being more than 10%of my company’s annual turnover.

But the decision was not as agonising as one might think when one considers the inexorable rise in demand for recycled or secondary aggregates.

In the late 1990s, recycled products contributed just 14% of the total aggregate market in the UK. By 2012 that figure had increased to 22%, and it is expected to grow significantly in the next few years as worldwide demand for construction products places an ever greater burden on a finite, dwindling natural resource.

Secondary products are unlikely to replace demand for virgin aggregates completely. For high specification and structural concrete applications, such as flyovers, bridges and structural slabs, I suspect that primary aggregate products will always be used. However, a series of developments during the past few years have combined to boost the value and demand for recycled products incrementally.

The environmental lobby and the Government can take credit for the first two of these.

In 2002, the aggregates levy was introduced which, overnight, added £2 to the cost of each tonne of most primary aggregate products. It would be an understatement to suggest that the Government’s intervention in the construction products market was not universally popular, but it was the first, if somewhat crude, step to promote the recycling of construction waste.

At this point, there was still a considerable amount of suspicion about the performance of secondary products which hindered their widespread use, even in low-risk applications such as subbase, pipe-bedding and drainage. But this was addressed in 2004 with the introduction of the quality protocol (QP), developed by WRAP in conjunction with the Quarry Products Association, the Highways Agency and the Environment Agency.

The purpose of the QP was to provide a uniform control process for producers, from which they could reasonably state that their product had been fully recovered and was no longer classified as waste. It provided purchasers with a product to common standards, which increased confidence in its performance.

The QP defined the point at which recycled aggregate was classified as a quality-assured product and was no longer subject to waste management legislation. This removed the regulatory burden and compliance costs for producers and end users of the material. The net effect was that recycled aggregates could now compete with primary sources on a more level playing field – increasing the market value of secondary products.

The introduction of environmental standards for construction and civil engineering products such as BREEAM, Code for Sustainable Homes and CEEQUAL towards the end of the decade served to further encourage the use of recycled products. Up to 12 CEEQUAL points are available for demonstrating that reclaimed or recycled products have been used in civil engineering projects, while a BREEAM credit is specifically available for using recycled aggregates in commercial developments.

A report published in 2009 by WRAP produced data to demonstrate the significant carbon savings in the production of lower grade recycled aggregates compared with virgin aggregate. Lifecycle analysis revealed that the production of recycled aggregate emits a third less CO2 than production of virgin aggregate. This helped to reinforce the environmental benefits of using secondary aggregates.

From 2008, many large utility firms committed to the Utilities Industry Agreement, which sought to promote the transportation of trench excavation waste to recycling locations, where the material could be processed into washed and graded recycled aggregates and transported back to site for use in reinstatement.

More recently, the regional price of virgin aggregate in the south of England has started to increase as many quarries supplying the south-east are starting to come to the end of their life. This, combined with the start-up of a number of major construction and civil engineering projects in the area such as the M3 smart motorway and M4 widening schemes, made us think seriously in 2013 about developing a plant that could process the demolition arisings and excavation spoil discharged at our MRFs to a certifiable standard all year round.

Developing a wash plant which could process construction and civil engineering wastes into a clean, homogenous recycled product would enable us to work even during the winter months when added moisture causes the wastes to bind more than usual.

We researched the market and were pleased to learn that a new generation of aggregate processing technology had been developed to enhance the efficiency of the process. We were impressed by the Aggresand 165/Aggrescrub 150 modular system, manufactured by Terex Washing Systems and distributed by Duo Equipment, which offers excellent accessibility to all components (see box for details).

The planning process for the aggregates plant was complex and delayed the development significantly but, by April this year, we were ready to start the installation. Carried out by Duo, it took just six weeks and the plant was then officially opened by local MP Gerald Howarth at a special event in June.

The facility will process up to 250,000 tonnes a year of certified high-grade aggregates from waste products brought to our MRF, in the creation of a circular economy for the construction and civil engineering sectors in the south of England. Clients, developers and contractors will now have a local source of five recycled products that will help them to reduce costs while enhancing the environmental performance of projects in the area.

We are obviously proud of our involvement in this closed-loop system and of being part of a drive towards a sustainable product. But we have an additional reason for developing a quality source of course and fine aggregates because next year we plan to introduce a ready mixed concrete batching plant at Eversley.  

New generation wash plant

The Aggresand 165/Aggrescrub 150 modular system, manufactured by Terex Washing Systems, has a number of innovative features.

At its core is a dual cyclone system, which enables two sand products to be produced: a fine sand and a high-grade coarse sand with <2% silt content. The two can be blended to maximise the grading.

A number of sorting systems have been integrated to remove clay, ferrous metals and contaminates such as plastics and organics. This enables more wastes, which would previously have been sent to landfill, to be used as feedstock for the plant.

The wash plant operates year-round due to its electric drive feeder system which screens cohesive material aggressively, even when its moisture content changes. A vibrating trash screen removes and dewaters <5mm floating trash before the thickener to prevent the spray bar nozzles getting blocked as the water is reused.

An automatic flocculent mixing and dosing system minimises the use of flocculent by sampling the feed to the thickener every minute. This measures the quantity of silt entering and adjusts the dose rate of the flocculent solution accordingly.

Its modular design allows the plant to be configured specifically to each user and fully adjustable components enable bespoke products to be generated. 

Robert Collard is founder of Hampshire-based construction recycling specialist R Collard

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