In contrast to upcycling in an open loop, there is a form of recycling that is called downcycling. At each recycling loop, the functional material quality is degrading, so the value of the material is cascading down. The modelling of downcycling in LCA needs therefor some extra explanation, especially since most of the recycling in practice is still downcycling, e.g. the recycling of paper, crushed concrete aggregate, and the mechanical recycling of plastics (= shredding and re-melting). The consequence of the degradation of the material in each step is that the material will, in the end, end-up in land-fill (or under roads), in the sewer, or in a municipal waste incinerator.
An example is crushed concrete, shown in Fig 5.6c: Product A is concrete with natural gravel, Product B is concrete is with aggregate of crushed concrete. Product C is crushed concrete under a road.
In LCA, the issue is how to model the calculation. The only practical way is “cut-off” at each time the materials ends up in a waste stockpile (as we do in the upcycling examples for open and closed loop in Fig 5.6b). But how to deal with the end-of-life debits or credits of the total chain?