RSG and Elite help Hanson Asphalt achieve better sustainability
RSG structures were recently commissioned by Hanson Aggregates to design supply and construct walls for new RAP (Reclaimed Asphalt Pavement) de-watering bays at their Tytherington depot.
The process for recycling RAP material into asphalt works as follows:
RAP material is first crushed and stored, usually with a moisture content of around 8-9%.
Clean stone is heated using large burners which then has the RAP material added to it, the heat from the clean stone meting the existing bitumen on the RAP, before more bitumen is added creating new asphalt to be used.
The more moisture within the RAP, the hotter the clean stone has to be to melt the bitumen and therefore the more energy required for the process.
The introduction of the dewatering bays will reduce the moisture content of the RAP to 2-3% allowing the entire process to be completed using a lot less energy and time, which is good financially and ecologically as it is a much more sustainable way of producing asphalt.
RSG looked at the initial concept which required foundations and walls to be constructed around an internal dewatering “pit” that has a network of pipes within a free draining medium allowing moisture to be “sucked” from the RAP material using a centrifugal pump.
RSG Director Gareth Neale: “Most walling systems suitable to support this type of material would require quite a substantial footing that would then conflict with the pit within the bays. These walls would also be slenderer at the top and trickier to fix roofing structures to. Using the Legato block system, we can use a shallower foundation detail and by utilising a bottom “soldier” and then “spreader” course at the bottom of the walls, we can further reduce bearing pressure and therefore foundation size. With the blocks being 800mm wide, this also gives a lovely size surface to fix roofing structures to.”
The walls are 2.4m high and designed to take the load from the RAP material which has a density of 1.7t/m3 and an internal angle of repose of 300 stored to the full height with an angle of surcharge of 270.
Retractable roofs then sit on top to keep rain off the stored material while the dewatering process takes place. These can be moved back and forward automatically to allow dump trucks and loading shovels to operate in the bays without the need for high roof structures which would require much more substantial walls to support them.
“Whilst the walls aren’t necessarily that high compared to others we construct” continues Gareth, “the RAP material has quite a high-density figure and so we needed a wall design that would be strong, fast to build and economical, which is where the Legato blocks really work. With the 50N strength blocks from Elite, we know what we are working with and so it is a straightforward process for our engineer to produce designs for any type of situation. Another benefit of using this system of construction is that if in the future this plant as required elsewhere, the walls and roofs can be simply de-constructed and moved to another location.”
For more information on the Legato blocks please contact sales@eliteprecast.co.uk or call 01952 588885 / for advice and quotes on all types of walling design, installation roof systems etc. please contact info@rsgstructures.co.uk or call 08452 997597
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