The Importance Of Recycled Aggregates In Sustainable Development
With a growing population, building new housing and infrastructure, and doing it in a sustainably conscious way, is vitally important.
From caves, to mud huts, timber-framed buildings to concrete, humans have long made their abodes by utilising naturally available materials. Traveling around you notice how older buildings reflect the area’s geology; Scottish granite, Cotswold sandstone, Yorkshire gritstone, Welsh slate, South Downs flint.
Locally quarried materials still offer a more carbon-savvy source than imported aggregate by cutting out shipping and reducing road/rail transport requirements. Yet, new quarries and extensions to old ones are often contested over concerns of traffic, environmental factors, and alternative use for land such as farming or recreation.
Can We Sensibly Reduce The Amount Of Quarrying?
Even if we wanted to return to the cave age, there aren’t enough caves to serve today’s population, sorry!
One thing we can do to make a big difference is to recycle what has already been extracted.
Due to the durability and stability of many minerals, over 90% of construction and demolition (C&D) waste can be recycled back into new material. Most demolition waste can be split into its original components of clay, sharp sand, builder’s sand, graded aggregate, ferrous and non-ferrous metal, and wood fibre.
How Is C&D Waste Recycled, And What Are Recycled Aggregates Used For?
Central to this recycling process is a washplant, which is ‘simple’ according to Darren Grace, technical lead at NWH Group’s C&D recycling plant at Dalkeith.
Like many recycling operations involving mixed materials it can take many ‘simple’ processes before the final products are output, but this is something that is developing across the industry at pace.
Mixed C&D waste is brought onto site and is tipped onto pre-screeding equipment. This removes very large pieces that are taken for further breaking down or use as is. The remaining material is transferred around the plant via conveyors, with numerous stacker conveyors radiating out from the plant. These stockpilers take clean and graded material from the plant into separate product bins for customer collection.
Separation technologies take advantage of the different masses and sizes from one material to another, and often include a series of vibrating screens, hydro-cyclones and spirals, and filter presses. These systems generally use a lot of water, but in line with the circular concept, most aggregate washing and separating plants recycle the same water repeatedly in a closed-loop system.
Some recycled aggregates can have more water absorption properties than their raw source, due to cement residues. In many applications this isn’t a problem and may even be beneficial, such as in permeable surfacing for water runoff absorption. Cement residue can be removed through additional scrubbing or acid application, although these methods come with their own processing implications.
Another factor with recycled aggregates is that the density is usually reduced – lighter but with less compressive strength.
Usually the last product to be removed is the finest particles of all – clay. Filter presses are capable of turning high volumes of clay slurry into clear water and hard, dewatered slabs which are useful for lining lagoons, canals and other geotechnical purposes.
This used process water is, if necessary clarified or pH corrected before being pumped back to the start of the system.
Will We See A Day When There’s No Need For Quarrying Or Mining?
It should be noted that many building materials still require a certain amount of virgin material for structural reasons, to the density reduction referenced earlier.
So, although 90% of C&D waste can be recycled, much of it is used for landscaping, geotechnical applications, and non-structural purposes such as back-fill.
By using recycled C&D waste for what we can, it much reduces the pressure to mine so much. This in theory makes the case for essential quarrying easier to define, especially when the materials are needed locally or for their contribution to carbon-neutral buildings in an energy-efficient way.
Something of note is that the shift from fossil-fuel extraction to green energy is a huge increase in demand for quarried minerals such as silica, lithium, copper, chromium, manganese, molybdenum, nickel and others. With price and supply pressures mounting, there is a big risk that extraction of these could tip toward countries that lack protections for (or even exploit for pricing advantage) the environment, workers, or local communities.
In conclusion, there will be a need for further advancement in recycling technologies and techniques along with responsible quarrying. This should ideally all be done within the country or regional market that they serve, in order to shorten the supply chain and reduce transportation emissions.
Atlantic Pumps are passionate about helping aggregate processing and recycling sites optimise their operations by cutting energy use, extending equipment lifespan and recycling process water on-site.
Together, we can all make a big difference in reducing waste, cutting unnecessary transport, and refining quarrying techniques and outcomes.
