Page 60 - Hub-4 Magazine ISsue 64

Quarrying
Stockpiled material
Stockpiled material
Raw material
Material falling from conveyor
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, 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. 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. Approximately 75% of all concrete used globally is non-structural which
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www.hub-4.com Sept/October 2020 - Issue 64