Building site waste sorting
The initial step in the recycling of construction site waste after collection, the sorting done by Paprec Group on its specialist sites, allows the material destined for landfill and re-use to be separated, cleaned and prepared, with not everything going to the same outlets. To gain a better understanding of the subtleties of re-using construction waste, we should examine the techniques used today in group waste sorting centres and, step-by-step, follow the journey taken by public works waste in Paprec’s specialist recycling factories.
Although Paprec uses ultra-efficient automated sorting lines to do most of the work, not all construction waste containers received by the group go through the same process.
Thus, 10 to 15% of the tonnage of materials from waste collections made by the group are pre-sorted by the construction site waste management company's customers and therefore do not need to pass along the sorting line.
Among the tonnages, there are skips filled entirely with wood, scrap metal, inert waste or plaster. That is to say the opposite of the majority of recyclable waste, that comprises skips of mixed rubble. Once this selection, the most basic, has been carried out and the rubble skips have been emptied, the separation and waste sorting operations themselves can begin
SORTING BY SIZE
To start with, the waste is placed in a rotary screen (a rotating cylindrical device used to separate public works waste by size) and this performs an initial separation of the wood, cardboard, metals, plaster, concrete blocks and inert rubble into three categories: fines (earth, sand, dust), medium size rubble (5 to 15 cm diameter) and larger demolition, deconstruction and construction waste.
The last category is then sent directly to the manual waste sorting cabin, which we will come back to later, without going through the other stages in the chain, designed for the effective separation of smaller fragments that are more difficult to isolate.
BLOWER AND OVERBAND
Once the largest items of rubble and materials have been removed, two separate systems then allow Paprec’s professionals to eliminate a certain quantity of final waste (also known as “sorting refuse”, it amounts to 20 to 25% of a waste skip) and capture any ferrous metals contained in the rubble.
Automatically routed by conveyor belts, medium-size waste passes into the heart of the blowing system, which removes light-weight materials from the rubble, such as rock-wool and polystyrene residues (both final waste).
It is then sent to a magnetic conveyor (the famous Overband), whose magnetised lower part captures any ferrous material contained in the waste. Under the effect of centrifugal force and because of the throats in the Overband, these fragments are then ejected into a waiting container and the remainder of the waste continues along conveyors towards the flotation pond.
Also known as densimetric separation, flotation sorting isolates heavy and light fractions in the public works waste flow. Dropped into a pond, the rubble and plaster sinks, while wood, for example, floats.
This method separates some types of material but Paprec also uses this sorting method to separate inert and non-inert waste (i.e. types of waste that disintegrate on contact with water and/or release a gas, such as plaster made of schist, modified by various chemical processes).
Separated, washed and captured in the pond by special conveyors, deconstruction and construction waste is then removed to manual sorting cabins, the final links in the chain, in both the real and the figurative sense.
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