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Rydon closes the loop on concrete recycling

When Rydon was left with 14,000 tonnes of concrete following initial demolition on a project, the team looked for ways to reuse all the crushed concrete so it didn’t have to go offsite.

While working on the redevelopment and regeneration of the Durand Estate in Carshalton, Surrey, Rydon found that the demolition of the existing blocks of flats resulted in a substantial amount of leftover crushed concrete.

Although this could be recycled offsite, Rydon contracts manager Richard Whitby and his team decided to see if there was another way to reuse the concrete, perhaps a little closer to home.

14,000 tonnes of concrete to recycle

“We’re working on the redevelopment of an old estate in Sutton,” he explains. “We’re totally demolishing the old 1960s precast concrete blocks of flats to create a new development which is a mixture of houses and flats.”

The regeneration is split into four phases and Rydon is working as part of the Lavender Partnership, which is made up of Sutton Borough Council, Affinity Sutton and Rydon.

“We asked how we could make best use of the crushed concrete which was leftover from the demolition process”

Richard Whitby, Rydon

“We’ve completed phase one, which had 95 units in total, and have started on phase two, which will have 116 units,” Mr Whitby says. “The groundworks of phase two have recently been completed.”

The demolition of the flats for phase two resulted in 14,000 tonnes of crushed concrete. “The team and I wanted to look at how we could recycle the material,” he says. “We knew we could use the concrete during the remaining phases, but not all in phase two, and the subsequent phases would then result in more concrete.”

Replacing CFA with ground improvement

Conscious of reducing the scheme’s carbon footprint and wanting to reuse as much of the material as possible directly onsite, Mr Whitby and his team looked at the construction process to see where the concrete could be used.

“We asked how we could make best use of the crushed concrete which was leftover from the demolition process,” Mr Whitby says. “The structural engineer suggested using vibro stone columns instead of the more traditional CFA piling. So we asked Keller to come in and discuss if it was an option, and we were delighted when it turned out it was.”

It was at that meeting that Mr Whitby also suggested that, rather than importing the stone for the stone columns, they could reuse the crushed concrete that was already onsite. So the team changed the original foundations design to ground improvements using vibro stone columns with ground beams instead of Continuous Flight Auger piling.

“Although the material onsite needed to be graded before we could use it, this decision led us to be able to use a large proportion of the crushed concrete in the piling process,” Mr Whitby says. After crushing the old buildings, Maldon Demolition put the material through a grading and validation process to produce 40-75 mm stone for use in both the vibro columns and the working platform.

Grading the concrete to use around the site

The grading process from the recycled buildings also created MOT Type 1 and 6F2 for the bases of the new roads serving the estate. Groundworkers Hague Construction made use of 10 mm stone for the drainage surrounds.

“Through doing this we were able to make use of the full 14,000 tonnes of waste concrete”

Richard Whitby, Rydon

“The remainder of the crushed concrete was certified and used for building the base for new roads on the estate, and as filling around storm culverts under the road,” Mr Whitby says.

“Through doing this we were able to make use of the full 14,000 tonnes of waste concrete created in phase two demolition within phase two of the project. This also means we can do the same thing in subsequent phases and we don’t have to send any of the concrete to be used offsite.”

Reducing lorry movements

The vibro process uses a depth vibrator which compacts the surrounding soil, removing the need to dispose of the spoil created by bored piling methods. “The process has several benefits over traditional piling methods,” explains Keller Foundations director Derek Taylor.

“It doesn’t generate any excess soil, which would need to be removed; it’s a simpler construction technique; it’s quicker and cheaper than traditional CFA piling; and in this instance it also means we can reuse the crushed concrete.”

Reusing the concrete means there is no need to bring to site any stone for the columns and this, coupled with the lack of excess soil needing to be removed from site, has resulted in an overall saving of 1,340 lorry movements so far across the project.

“While it is a more cost-effective process when compared with other methods, Rydon paid to have the concrete certified so it was cost neutral,” Mr Whitby says.

“The environmental benefits make it completely worthwhile though; it saved a huge amount of soil from going to landfill when compared with using CFA and it also saved on the crushed concrete going to landfill.”

Six storeys and counting

Although the technology used in vibro stone columns has been around for some time, it is rarely used on a project as tall as this development.

“Rydon was quite progressive in even asking to use this technique on this project,” Mr Taylor says. “As one of the blocks is six storeys, we would not normally have asked the question, but Rydon challenged the obvious.”

Vibro stone columns are normally used on buildings of up to four storeys, and as one of the blocks on this site was six storeys, a full-scale loading test was undertaken to prove the ground treatment was able to support the building. “Choosing CFA would have been the easy option – we use it all the time and are very familiar with the system – but we wanted to challenge the process,” Mr Whitby explains.

“Rydon were quite progressive even asking to use this technique on this project”

Derek Taylor, Keller Foundations

“We worked with the National Housebuilding Council, who were very helpful. Normally you only build up to four storeys when using this ground treatment, but because they are timber-frame buildings they’re much lighter so can take up to six storeys.

“Initially we were slightly nervous about using the system, but working with Keller, the NHBC and others gave us the confidence to move forward.” Stone columns are also easier to remove in any future redevelopment, again adding to the system’s sustainability.

Closed-loop recycling is the future

Using this closed-loop recycling of the crushed concrete has many environmental benefits, not least the carbon savings due to the fact no new concrete is used in the foundations.

Mr Whitby believes that schemes and technologies such as this mean future regeneration projects are more likely to succeed as they make logistical, economic and environmental sense.

“It’s technology like this that is making regeneration jobs more feasible going forward,” Mr Whitby says. “The economy is going through difficult times, so any ideas like this which make regeneration schemes more likely to succeed are important.”

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