Links:
[1] http://coac.arquitectes.cat/ca/suport/actualitat/normativa-us-materials-naturals-excavats
[2] http://www.boe.es/diario_boe/txt.php?id=BOE-A-2017-12043
[3] https://www.arquitectes.cat/ca/system/files/2017-10-23_residus_materials_naturals.pdf
[4] http://coac.arquitectes.cat/ca/javascript%3Ahistory.back%281%29