Quality Improvement of Recycled Aggregates From a Constrution and Demolition Waste Recycling Pilot Plant

摘要

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,22-3 lmm 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 (21-3 lcm).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%.