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Recycling and roadworks – what does this mean?

Have you ever driven through a stretch of roadworks, seen signs telling you about how much material has been recycled and wondered: “What does that mean - what has been recycled?” David Walker from Hanson, contractors for the Leigh Road Transforming Cities Fund (TCF) project, tells us what is going on behind the scenes.

Spoil CropSpoil as it arrives at Allasso Recycling 

In road improvement projects such as the one on Leigh Road/Wimborne Road West, a lot of ‘spoil’ material, such as old road surface and road-base concrete, gets produced as a by-product of the work. Nowadays, we prefer to recycle this spoil into new road building material rather than sending it to landfill. It is crushed, mixed with a binder material and turned into what road builders call CBGM.

CBGM stands for Cement Bound Granular Material and is a mixture of crushed up spoil, water and cement-based binders. The main benefit of this is that virtually any ‘spoil’ can be utilised to create the CBGM, thus recycling the old construction materials as opposed to sending them to landfill. CBGM is an HBM (Hydraulically Bound Material) which is a material that hardens under the presence of water, creating interlocking bonds which allows the material to gain strength over time; particularly useful in the British climate!

Hanson has been working with supply chain partner Allasso Recycling since 2017, who have a dedicated facility for taking in the spoil from our Dorset construction projects, processing them and then returning them as new CBGM for use on the new building projects.

Large grade aggregate ready for useAllasso’s recycling plant crushes the spoil into smaller pieces, which we now refer to as aggregate. Different CBGM materials require larger or smaller sizes of aggregate depending on their eventual use. The different sizes of aggregate are sorted or ‘graded’ using screening machines, which are large vibrating sieves with different sizes of grid. Once graded, the different-sized aggregates are then washed and stored on site, ready for use. (Right) 

As soon as some new CBGM is required at a work site, the correct size aggregate is selected and fed into an automated mixing plant (Below). This mixes the aggregate with the cement binders and water, at the correct proportion for the material being produced, and then feeds the new CBGM directly into a waiting lorry ready for transportation to the site. This process can literally be turned round in an hour, making it an efficient, on-demand service.

Allasso's CBGM mixing plant

Although this may sound like an energy and cost intensive process, it is in fact a lot more environmentally friendly and cost efficient than quarrying new aggregate, mixing and transporting virgin concrete and sending the old spoil to specialist landfill sites. With high materials, transport and landfill costs, plus the environmental damage of emissions and landfill, recycling spoil actually makes strong economic and environmental sense! 

By recycling the old spoil, a new, safe and hardwearing building material is produced locally. Most of the CBGM that is used for Hanson construction contracts in Dorset is now salvaged and recycled from other construction and maintenance works within the county, significantly reducing carbon emissions, landfill impact and material costs.

Since Allasso’s Dorset plant was established, we estimate that approximately 23,000 tons of materials have been recycled for use on Dorset’s road network. We use their CBGM mostly in the lower layers of roads, cycleways and pavements, and to strengthen the edges of carriageways.

This process gives significant cost savings for us at Hanson, as well as to BCP and Dorset council tax payers. It also has a significant and positive environmental impact; good news not only for Dorset but for our planet too!


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