[This article is in response to our previous report: UK standards inhibit green building progress]
It鈥檚 holiday season and for many a trip to a foreign country can raise the question, 鈥渨hy don鈥檛 we do it like this at home?鈥�.
You might have thought this when reading some recent media reports about concrete recycling in Europe and an alleged missed opportunity to recycle concrete from tall buildings in London.
While there are times in life when we might look at some countries with envy, the reality in this case is different and one where we should not view the UK as a recycling laggard compared to its European neighbours.
The UK has an excellent track record of recycling construction and demolition waste (CDW) and is currently providing a valuable contribution to the UK circular economy by reducing the need to extract natural aggregate.
The volumes are significant. Around 90% of hard construction and demolition waste is recycled as aggregates ensuring that the UK successfully utilises 70 million tonnes of recycled and secondary materials in its aggregates market. This is three times higher than the European average and highlights that the use of recycled and secondary materials in Britain is close to full potential.
This use tends to be in unbound applications and there is undoubtedly an opportunity to use more recycled aggregate in the manufacture of concrete. However, contrary to some media stories, which focused on the opportunity to use recycled concrete from the demolition of tall buildings in the City of London, UK concrete standards do not constrain this recycling opportunity.
It was suggested that BS 8500 prescribes that only 20% of recycled concrete aggregate (RCA) can be used in reinforced concrete and that standards in Switzerland and France provide more opportunity.
This is incorrect and our UK standards are not a barrier to such innovation. BS 8500 differentiates recycled aggregates into two types: crushed concrete aggregates (CCA) and recycled aggregate (RA). There are no limits on the proportion of coarse CCA that can be used in designed concrete and they can be used in most exposure conditions up to strength class C40/50.
In addition, there are no limits at all if the CCA is of a known composition and has not been previously used such as returned concrete.
When thinking about concrete recycling, we should take a holistic view to inform circular economic strategies.聽 Using a large percentage of recycled aggregate in concrete is arguably not always the best use for this resource from a sustainability perspective. This is because almost all CDW is utilised in the UK so its use back into concrete is not solving a waste to landfill problem.
Also natural aggregate in the UK typically has very a low embodied carbon and CCA therefore does not need to travel very far before resulting in a higher carbon solution.聽聽
This, coupled with the technical reality that a high percentage CCA in concrete, tends to lead towards an increase in equivalent CO2 (eCO2) as the resultant concrete requires more water which in turn will require more cementitious content.
Given the UK鈥檚 significant economic and social infrastructure pipeline, there is not enough potential CCA in the UK to completely replace the need for natural aggregates in concrete production.
Despite these considerations, there is undoubtedly scope to continue to embrace more use of recycled aggregate in concrete. Good progress is being made to increase the uptake.
Changes in demolition practice to yield more higher quality recycled content combined with digital platforms and innovation are creating promising alternative high value uses for crushed concrete aggregate.
These include utilising the recarbonation performance of CCA to suck up and lock in CO2. A variety of technologies are in development that can accelerate this natural recarbonisation process to lock in the CO2 more quickly. They also have the added benefit of often not needing extra water content and therefore reduce carbon in concrete 尘补苍耻蹿补肠迟耻谤别.听
Another innovation is in 鈥榙eep cleaning鈥� the aggregate to use the powdered surround of the natural aggregate to create a recycled concrete paste with a high recarbonation capability.聽
The Mineral Products Association is part of a research team looking into the technical potential of this powder (known as recycled concrete fines or RCF), which includes for use in the manufacture of new lower carbon cement and use as a supplementary cementitious material (SCM) in the manufacture of lower carbon concrete.
One benefit of the deep clean is that resulting aggregate is closer in composition to natural aggregate, and may be able to be renamed as 鈥榬eused aggregate鈥� rather than recycled.
A greater percentage of reused content in buildings is preferable from a circular economic perspective under current evolving metrics, compared to recycled content.聽 This terminology is yet to be determined but it is the direction that I personally would like standards to take. In this way, these small pieces of stone have more opportunity to stay in perpetual use in construction for potentially centuries
British Standards for concrete have continued to evolve and advancing the circular economy remains a key area of focus for the UK Concrete industry Sustainable Construction Strategy.聽 We are actively seeking to enable greater circularity and advance the retention of concrete in the supply chain at its highest value and in end-of-life scenarios.
While our industry will always continue to look at the very best construction, recycling and manufacturing approaches from around the globe, we must also appreciate the opportunities to drive change using new innovation and current British policy.
About the author: 聽Elaine Toogood is senior director of concrete & The Concrete Centre at the Mineral Products Association
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