15 September 2020
Strength and quality are attributes measurable on a scale. High quality and low, strong, and weak. So too are the quality and structural integrity of recycled sand and aggregates, writes Eunan Kelly, Head of C&D Waste Recycling at CDE. We recently caught up with Eunan to learn more about the importance of the right technology, and the right processes to unlock the concrete potential in recycled sand & aggregates.
When supported with the appropriate processing practices and technology, sand and stone resources recovered from CD&E activities are suitable for high-value construction and infrastructure projects.
UK Statistics on Waste, published by the Department for Environment, Food & Rural Affairs, estimates the UK generated 221 million tonnes of total waste in 2016, with CD&E activities accounting for 62% of that total. This is over 3/5 of total waste in the UK!
The industry is the single largest contributor to waste generation in the UK by some margin, accounting for more than five times that of household waste which is 12% of total waste generated. These waste resources can be recovered to a high specification and returned to the construction sector to further the UK’s circular economy.
A Time for Change
In the materials processing industry, we’re having to speak out in defence of recycled sand and aggregates and lobby for attitudinal change to encourage greater acceptance and adoption of recycled materials.
We’re often told it’s not possible to produce structurally sound concrete from recycled sand and aggregates or it’s unfeasible to replicate the water-to-cement ratio with recycled products to produce a durable concrete. Some people have even suggested that concrete produced from recycled aggregates has more embodied carbon than concrete produced from natural materials. These are arguments our industry is faced with regularly, and misconceptions that we at CDE move to challenge.
Today, research is on-going to identify alternatives to sand and aggregates in concrete production. Some of the research centres around the use of woods, shredded up vehicle components, and other unnatural concrete constituents. Such research seemingly disregards our largest waste stream, construction, demolition & excavation waste (CD&E), and fails to recognise the fact that much of the material in this stream originates from the natural constituents of concrete and therefore lending itself perfectly to producing concrete.
Though a huge social issue, the volume of plastic waste does not represent anywhere near the same as that of CD&E waste. Unlike plastic waste, a product that has been heavily processed for its original use, sand, and stone recovered from CD&E waste shares the same or similar geological make-up to that of virgin materials.
The Logical Answer
To combat depleting natural sand and aggregate resources we should better utilise the abundant incoming CD&E waste stream.
In its appraisal, concrete produced from recycled sand and aggregates is unfairly pitted against higher-strength concrete produced using virgin aggregate, such as granite or basalt, and natural sand. It is fair to say that not all granite or sandstone deposits display the same strength characteristics and therefore selective end-use logic is applied.
The same is true for sand and aggregates recovered from CD&E waste. Given the variability of rock geologies and other man-made aggregates, such as brick and bound concrete, we must also apply the same end-use logic.
This should not, however, undermine the potential of concrete produced from recycled materials. It is a case of identifying the strength of concrete that can be produced from recycled sand and aggregates and then pinpointing suitable applications for the product. It should also be pointed out that current wet processing technologies deployed by CDE around the world can produce washed sand and aggregates that when used in the production of similar strength concrete are comparable in cement consumption.
Low strength granite or gritstone would not be used to construct a multi-storey building, but we can identify suitable concrete strength applications for their use. Similarly, with CD&E material, we may never use it to construct that same multi-storey building, but there are still many applications for which it is suitable.
The C&D Pioneers
For example, Thompson Recycling, based in Scotland, produces a wide range of products for the construction sector using C&D waste. With the support of CDE technology, the company is able to replicate the grading of local virgin sand deposits to provide the local construction market with a viable and creditable alternative to natural resources. Such is the quality of the recycled sand and aggregates it extracts from C&D waste, its 100% recycled sand is BSI-approved for structural concrete.
Current concrete strength specifications allow for recycled aggregates to be used in the appropriate proportions to produce the required strength. It’s probably fair to say that the majority of concrete produced is C40 or below.