Since aluminium’s commercialisation in the 1880’s with the advent of the Hall-Héroult process, aluminium’s recyclability has been well documented. In fact, it has always been encouraged as the material is valued highly with its ability to be virtually 100% recycled. With the advent of portable handheld XRF analysers (X-Ray Fluorescence) the ability outside the laboratory to identify the various aluminium alloys now allows easier recycling of various alloys back into their original grades.
There are currently eight ‘series’ of ‘grades’ used to identify the different types of aluminium alloy available. An alloy is created by mixing other types of materials into the pure aluminium to offer desirable features such as greater strength or a higher melting temperature. These ‘mixes’ are recognised as ‘series’ or ‘grades’ of aluminium that offer different properties, each having a specific application and use. Grades are identified using four-digit numbers with the first number denoting the ‘series’ or ‘grade’ which also indicates the primary alloying elements. This grading system is known as the International ‘Alloy Designation System’. Extrusion grade aluminium used in fenestration is normally a 6061 or 6063 grade of alloy both of which use magnesium and silicon as the alloying elements to create magnesium silicide.
Quickly identifying the alloy enables a closed loop recycling opportunity where there is no loss of quality through cross contamination with other alloys. This has been something that CAB have been pioneering for some time with their own ‘Closed Loop Recycling Scheme’ where members report their recycling within the scheme.
One CAB recycler member, Alutrade in the Midlands, has perfected a separation process for aluminium fenestration products where thermal breaks and hardware are removed, resulting in a ‘clean’ aluminium alloy presented in a chipped form for easy handling and transport. This chipped alloy is then shipped directly to a re-melter where the recycled aluminium is formed back into billet or logs for the extrusion process. So, from aluminium extruded windows back into 6061 or 6063 extrusions which are very likely to be window profiles once again.
Main contractors, their clients and specifiers of fenestration systems are now becoming aware of this short, economic, closed loop recycling ability of aluminium fenestration known as a ‘cradle to cradle’ approach. Aluminium is a valuable commodity, so to adopt a remove, recycle and reuse approach realising its value can significantly contribute to the cost of a replacement facade.
A couple of years ago, Camden Council awarded McLaren Construction a £100m contract to re-clad four towers on Camden’s Chalcots Estate. Re-clad in 2008, the high-rise estate located in Swiss Cottage was one of the the first projects to be found fitted with defective cladding following the Grenfell disaster. The work to remove the cladding and windows is currently underway at this time.
As the defective cladding is removed the aluminium windows located within the cladding are also de-glazed, gaskets removed and placed into skips for transport to Midlands based Alutrade where they are separated and processed using XRF analysers, then sent onto Hydro for recasting into billet or logs. This operation is a two stage shred process, whilst the aluminium is XRF analysed on arrival at Alutrade, the final chipped material is also further XRF analysed to ensure zinc levels, which is a residue material from fitted hardware, are below 0.03%. The ease of XRF analysis is therefore crucial to the recycling process.
The Camden project in total consists of four tower blocks containing approximately 3,500 windows and once processed the chipped aluminium is being shipped to Hydro at Deeside for recasting into low-carbon Circal billet for Hydro Building Systems.
All scrap metal from the process, zinc and stainless steel items are sent for recycling. Residue from resin thermal breaks in older windows is sent away for incineration. In more modern windows, as on the Camden project, expensive engineering plastics such as polyamide, also known as ‘PA6’ or ‘Nylon 6’, is used to form high strength thermal insulation within the aluminium profile. The recycling process also collects this material in the form of chip material. These chips can be used as a filler in other areas of construction or infrastructure projects, or sent for incineration, a process which is known as ‘energy recovery’ or ‘thermal recycling’. As more polyamide thermal breaks are now entering the recycling arena, work is now underway to recycle this material back into product or back into its constituent parts by the manufacturers.
With more recycling companies dismantling fenestration systems and separating them into various materials for recycling, the specification of aluminium in various construction projects, commercial and residential will continue to grow. A specification of aluminium today, offers a good residual value in the future when the facade is to be replaced. Our cities now become material resources or ‘urban mines’ where we are able to recycle much of the material that already exists.
Should you wish to learn more about the use of aluminium used in construction, please contact CAB directly, or why not consider joining the Association and be recognised as being involved in supporting your Industry and helping to shape its future. More information on our website at c-a-b.org.uk