Complete Utilisation of the Sand Fraction from Dem.. (Recdemo)
Complete Utilisation of the Sand Fraction from Demolition Waste Recycling
Date du début: 1 déc. 2001,
Date de fin: 31 mai 2004
Sand and gravel are important natural resources, used extensively in the production of concrete. In Germany alone an estimated 8 tons of mineral building material per capita was produced in 2000. Waste from demolition of buildings amounts to 500-800 kg (per capita/year). In Germany, approximately 70 percent of this rubble is recycled. However, large quantities of the recycled material are used for pavements and road construction, landfill site constructions and other low grade uses. For the production of concrete, only the coarse fraction (> 2 mm) is used.
The use of the sand fraction, amounting to approximately 30 percent of demolition waste, for producing concrete is not yet common practice, though this offers the potential to replace consumption of natural sand as an aggregate. Demolition material has some disadvantageous properties compared to natural sand, such as a high quantity of the finest material, high water demand and sometimes high contaminant content.
Demolition waste is mainly treated using a dry process. However, the finest material cannot be separated out from the sand fraction sufficiently using dry methods only. Therefore, this project set out to demonstrate wet processing of the sand fraction.
The project aimed to demonstrate that with proper source selection and wet processing using a jig, the sand fraction from demolition waste can be utilised as an aggregate for concrete. The residues from the wet treatment, i.e. the finest fraction and the light fraction from jigging, contain the substances that impair concrete quality. These residues are rich in lime and organic matter, which can be used in the production of compost. The project will also demonstrate that composting offers a suitable use for such materials, thus reducing landfilling.
The input material for the demonstration project was demolition rubble which is one of the most important waste streams in terms of mass and volume. In a commercial treatment plant for construction waste a pre-selection was performed to ensure that the amount of contaminants was small enough to obtain recycable products. The material was to be crushed during pre-treatment to less than 32mm, and separated using a 4mm sieve. In the pilot plant for wet treatment a fraction between 0.1 and 4 mm suitable as aggregate was to be produced from the undersize material. The innovative step in handling the sand fraction is use of an optimised jig.
The applicability of the fraction as aggregate was investigated by standard testing procedures for mortar and concrete. These tests included strength tests and investigations of the manufacturing behaviour. Utilisation of the residues from the wet treatment was demonstrated. From the residues, i.e. the finest and lightest fraction, together with other waste materials a compost was, which could be utilised for the reclamation of areas formerly used for sand and gravel exploitation.
The results of the project are as follows:
â¢ The wet processing technique investigated can improve the material properties of crushed concrete fines in comparison to the dry-treated input material. Laboratory tests showed a clear reduction of the content of binder matrix and a significant reduction of the water absorption in the heavy fraction thus obtained.
â¢ The results of the tests for building materials on mortar specimen made with the heavy fraction e.g. compressive strength, flexural strength and dynamic modulus of elasticity, show an improvement of the material properties. However, depending on the settings of the pilot plant and the quality of the input materials the results may vary.
â¢ The correlation between the strength properties, acid-insoluble and loss by washing was low.
â¢ Material properties of mortar with recycled aggregates did not compare so well with those of mortar with natural sand. The results of previous tests on mortar with wet-treated crusted concrete fines obtained from a different source were also better than the results obtained in this study.
â¢ Strength tests on concrete showed that the replacement of natural aggregate by wet-treated crushed concrete fines at levels up to 50% had little effect on the compressive strength. These results contrast clearly with the lower compressive strength of concrete made with dry treated crushed concrete fines.
â¢ Natural sand can be replaced by wet-treated crushed concrete fines up to a certain level. To ensure that â depending on the material source â the variable quality of the crushed concrete fines does not affect the concrete quality, a safety factor needs to be defined. The study shows that wet-treated concrete fines can be recycled on a higher level.
This project has been selected as one of the 24 "Best" LIFE Environment projects in 2004-2005
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