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Krom i krossad återvunnen betong
RISE Research Institutes of Sweden, Built Environment. (CBI Betonginstitutet)
2019 (Swedish)Report (Other academic)
Abstract [en]

For environmental reasons there is a demand to use less amounts of natural stone and gravel as aggregate, which leads to an increasing use of recycled materials, for example construction demolition waste (CDW), when new civil engineering structures and buildings are constructed. Cement and concrete contain a certain amount of soluble hexavalent chromium which may cause health problems and can be leached to the environment and influence it negatively. From a concrete structure the leaching is minimal, but when the concrete is crushed and the specific surface increase, leaching also increases and may reach levels where it may influence the environment.

This report gives an overview and background to:

·       existence of chromium in CDW and particularly the hexavalent chromium,  

·       requirements as regard chromium on CDW for different applications or as landfill and

·       what happens with the chromium when the CDW is incorporated in new concrete or asphalt.

Chromium is generally present in the earth surface in the non-toxic form of three valent chromium. When cement is produced, a part of this chromium is converted into hexavalent chromium, which is toxic and very soluble in water. It may cause contact allergies. Because of this EU limited the amount of hexavalent chromium in cement put on the market to 2 ppm in 2013. The same limitation was introduced in Sweden already in the 1980's. In old concrete, which is often the type of concrete that will be demolished, crushed and used for recycling, cement with much higher hexavalent chromium content may have been used.

Through a EU decision and regulations from the Swedish Environmental Protection Agency the leaching amount of dangerous substances, for example soluble chromium is limited in materials which shall be put into landfill. Generally, two values are needed, the initial leaching value which describes the concentration of the compound in the leaching water initially, and an accumulated leaching value which is supposed to describe the total amount of chromium that will be leached from the material. The Agency has also published a handbook on the use of recycled materials in civil engineering structures, where limiting values on total amount and leached amounts are given for two applications; for general use (non-bound) in for instance road structures and when used to cover landfills. In this case there is also a demand on total amount of chromium, in addition to the two leaching values.

When using CDW as aggregate in new concrete and in asphalt there are now limiting values as regards chromium.

The test methods used, element analysis, shake tests (bulktests) and percolations tests, are briefly described. Results from tests on CDW with these methods reported in the literature are given. Normally, the values on leaching lie around the limit value for inert landfill, sometimes they are higher and sometimes lower.

A description of a couple of long-time field tests where the leaching has been measured on road structures with CDW are included.

The results indicate that : 

  • crushed new uncarbonated concrete normally has values of initial and accumulated leaching which are lower than the limiting values for inert landfill and for civil engineering structures,
  • carbonation of Portland cement concrete gives increases the amount of leached chromium,

§  crushed concrete, even a carbonated one, fabricated with a cement with maximum soluble chromium = 2 ppm generally exhibit test values for initial and accumulated leaching which are below the limiting values for inert landfill and for civil engineering structures,

 

§  slag in the concrete binds the chromium and makes it more insoluble, both in new and carbonated concrete and  

  • for old concrete, where high chromium cements have probably been used, special measures may be necessary in order to fulfil the requirements for inert landfill and for civil engineering structures.

Examples of special measures:

  • A good sorting of the CDW at the demolition site. The CDW shall preferable come from only concrete and stone. Bricks, gypsym etc. gives higher leaching values.
  • Good knowledge about the original demolished structure gives a possibility to be freed from testing.
  • To use a wet process to sort the demolished material. Some of the soluble chromium will then be leached already at this stage. This leads to a higher probability to pass the requirement on initial leaching on the resulting material. The process water will then contain soluble chrome and must be taken care of in end environmentally friendly way and.   

§  To let the CDW carbonate and the wash it and take care of the wash water in end environmentally friendly way. This will lower the initial leaching value, which is the most problematic requirement to fulfil.   

Place, publisher, year, edition, pages
Borås, 2019. , p. 35
Series
RISE Rapport ; 2019:102
Keywords [en]
Chromium, hexavalent chromium, recycled concrete, construction demolition waste
Keywords [sv]
Krom, sexvärt krom, återvunnen betong, bygg- och rivningsavfall
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:ri:diva-44773ISBN: 978-91-89049-33-8 (electronic)OAI: oai:DiVA.org:ri-44773DiVA, id: diva2:1426957
Projects
Swerock InnovationspartnerskapAvailable from: 2020-04-28 Created: 2020-04-28 Last updated: 2020-04-29Bibliographically approved

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