| Popis: |
The construction and demolition wastes (C&DW) frequently are abandoned in private properties, roads, and landfills or collected by non-licensed companies. In Portugal they are few recycling plants operating with this residue, and this work makes the bridge between the mechanical recycling process developed on semi-industrial scale, and the recycling products characterization process developed on laboratorial scale. The main goal of the present work is the quality improvement of the recycled aggregates produced by a construction and demolition waste recycling pilot plant with 50 ton/h located in Montemor-o-Novo. Process operations are the hammer mill comminution, magnetic separation and sieving (bar sieves: 0-4mm, 4-8mm and 8-12mm; and square sieves: 12-22mm, 22-31mm and above 31mm). In order to improve the magnetic separation process, several tests with different distances between the magnet and the conveyor belt were made (21-31cm). On the other hand, to improve the quality of the produced aggregates, the bar screen size fractions were analyzed, according to the Portuguese Standard (NP EN 933-1 2000). The most efficient distances for the magnetic separation process were identified as between 21 and 27cm, with efficiency between 85% and 90% respectively. According to the histograms, the more frequent red aggregate from 0-4mm size fraction are +0.425-0.850; +0.850-1.7 and +1.7-3.35. From the 4-8mm red aggregates, the more frequent size fractions are +4.75-6.7 and +6.7-9.95. Finally, from the 8-12mm red aggregates, the more frequent new size fractions are +6.7-9.50 and +9.50-13.20. Sieving results obtained from cumulative curves for red aggregate showed an decrease in the mass % amount for the size fractions: 0-4mm: 97%, 4-8mm:76% and 8-12mm: 56%. The results from cumulative curves for grey aggregate showed a light decreased in the amount mass % for the size fractions: 0-4mm: 90%, 4-8mm:56% and 8-12mm: 60%. |
