Source: Materials Recycling Word (MRC)
A start-up in Scotland has been developing a solution that reduces the carbon impact of concrete and uses incinerator bottom ash in the process.
Andrea Lockerbie finds out more .
We are surrounded by concrete – it is the most widely used building material in the world. Concrete is made using cement mixed with aggregate and that cement is carbon-intensive – believed to contribute 8% of the worldwide global emissions caused by humans.
Recycl8 wants to tap into the carbon reduction goals of concrete manufacturers, alongside the ambition of energy-from-waste (EfW) operators to increase their recycling rates. Founder and managing director Ian Skene has a background in the waste sector, as a founder/ director of an EfW plant in the north-east of Scotland.
After burning the waste, EfW plants are left with incinerator bottom ash (IBA) which requires disposal – mostly it is landfilled. Skene has been working with a catalyst provider for the past two to three years to find a way to stabilise IBA.
“We have taken that IBA residue and developed a system to utilise it and turn it into a low-carbon concrete,” he explains.
Recycl8 claims its process cuts the embodied CO2e content of concrete by more than 60%, leading to a reduction in CO2e of 240kg for every cubic metre of concrete used. It replaces some of the aggregates in concrete, be it virgin or recycled, and uses that in combination with the catalyst – which keeps the material stable – to form the low-carbon concrete.
Testing has included ensuring that the material does not leach into the environment. Part of the front-end process is to reduce the potential for leachable heavy metals coming out of the IBA, prior to making the concrete. Its tests to date have found it can reduce the potential leachate by 96%: “Once it is combined with the cement to make a concrete, that then ties [the IBA] up completely.”
Skene explains that Recylc8 is now at the end of a nine-month programme of testing. The company was started in 2019 and got finance together in 2020. It has received grants from Scottish Enterprise’s high-growth ventures fund and a fairly significant grant from Innovate UK to supplement its testing programme.
Carrying out the testing during the most part of a year and using IBA from six incinerators should allow for full exposure to the seasonal variations in the composition of residual waste as well as differences in collection systems. Testing has been to verify the strength of the concrete product and achieve end-of-waste classification.
Skene says: “We know we can make concrete with it – that was the first primary test. Early on, we managed to produce a concrete that met C60 standard [a grade referring to the material’s compressive strength], which is suitable for bridge-building and for precast. So, we got a far better result than we were targeting.
“We expect to be able to produce concretes around the C30 and C35 grades. C30 is a lower strength commercial grade mostly used in pavement construction, reinforced bases, outside paved areas or lighter external applications. C35 offers greater strength and can be used on larger commercial buildings and foundations for added support.”
A next step for Recycl8 would be to set up a demonstration plant, where potential customers can visit.
“We will start off that way, but we are intending licensing the process to concrete manufacturers. We are not intent on being in opposition to concrete manufacturers, we will work with them and supply the admix, as we call it,” he says.
As IBA currently goes to landfill at a cost, the vision is that this material would be diverted to the Recycl8 solution at the same cost but with the added benefit of pushing IBA up the waste hierarchy, so helping EfW plants to improve their recycling rates and concrete manufacturers reduce their carbon.
The business has applied for UK and international patents, and is hoping to achieve Best Available Techniques for the process from the relevant environment agencies.
According to Skene, the recycled product has enhanced qualities compared with the current standard.
“It is a higher quality product. There may be potential difficulties getting a British Standards (BS) mark for the material because it is actually better than [the BS] minimum standards. So we may need to convince them that we have got a unique product and [needs] a BS standard of either some equivalent or a new one.”
Tests have found that the finished product shows resistance to sea water and is classified as an acid-resistant cement – a quality that was not by design, but rather happy accident.
“If you compare standard concrete to a Malteser, say, it is very porous. It allows water to ingress, and sea water then erodes and corrodes the concrete itself. If water goes into areas where the material will freeze or heat up, then there is a likelihood that the concrete will fail. “Whereas we are very tight-knit in molecular structure. I demonstrate sometimes with Stickle Bricks – it is a tighter binding mix and that means there are no air spaces inside the concrete. At the surface it is very non-porous – it is impermeable – so that makes it very resistant to sea water, which lends itself to flood protection systems.”
Recycl8’s first target sector is the global renewable energy market and offshore windfarm projects – an industry set for growth, with proposed projects including floating wind farms which potentially require concrete solutions that can withstand the sea.
Skene says: “For the past two to three years, I have been looking at the south harbour in Aberdeen – there has been a huge development there – and just wishing I had been five years
earlier and able to sell that product, because we are absolutely certain we could have given them a better concrete mix with longer life expectations with the materials we are using.”
Recycl8 has been having discussions with the offshore wind sector, and Skene has had “a number of discussions with international cement and concrete manufacturers which are all very interested and want to do their own testing and trials”. The latter cannot be progressed until it receives the end-of-waste status.
Skene believes the cost-effectiveness of his solution should make it a straightforward choice for concrete manufacturers: “It won’t mean them paying additional cost, we believe, at this stage, for a green concrete. Normally, when you are increasing the quality and standard and improving the carbon footprint, there is a cost that comes with that, but we are assuming it will be fairly well matched to current cement/concrete financial solutions.”
He does not fear any future issues with supply of IBA, believing there will always be an element of waste that cannot be recycled and will become residual waste, with limits to the recovery of material for recycling.
“Because I have come from the waste industry, I know people simplify these sort of things and say, well, there is 6% plastic in that waste type, you should be able to pull that out and recycle all that material. But if you are in the back of a 10 or 20-tonne waste compactor vehicle collecting these things, I’m sorry, but there is no way you can recover that material with the current collection systems.”
He sees the solution working on with IBA from incinerators used by nearby cement manufacturers, and says there are lots of synergies. For example, incinerators in areas of high population density will map to the need for cement in such areas. The testing phase produced results that were above expectation, so Skene is confident that Recycl8 will get the necessary end-of-waste classification, and this will pave the way for the next steps in getting the low-carbon concrete solution out to market.