WRAP (The Waste & Resources Action Programme)

Testing of concrete to determine the effects on groundwater

The need for a more sustainable construction industry, as well as increasing pressures on landfill space, have led to an increasing use of recycled and secondary materials as aggregates in concrete1,2. However, if users are to have full confidence in these materials, it is important that they are shown to have neither an adverse impact on the properties of concrete, nor on the environment, through leaching of hazardous materials. However, only limited data regarding the potential for leaching from concrete containing such materials into controlled water (groundwater and drinking water) are currently available.

It is widely accepted that the leaching behaviour of potential recycled and secondary aggregate materials needs to be assessed. However, a universally accepted method to assess this is not yet established. Several test methods to assess leaching behaviour for different situations are available. However, very different leaching conditions are adopted in each and the choice of a test methodology to represent the in-service leaching characteristics of the material is not straightforward. Some methods may appear too severe, while others may seem too conservative. There is concern that the results from a severe test, together with the use of acceptance criteria that are too restrictive, may be unrealistic and could preclude the use of suitable materials. On the other hand, if the criteria or the test method are too lenient, there is a risk that potentially dangerous substances could find their way into the environment. It is therefore not surprising that standard methods and assessment criteria have not yet been agreed among stakeholders to assess the leaching performance of aggregates in concrete. The objective of the project was to assess the leaching characteristics of concrete containing recycled and secondary aggregates using several of the standard tests already practiced in the UK or specifically proposed for aggregate materials3, 4 ,5. These results are compared with results for primary aggregates. Results produced by different laboratories testing the same materials have also been assessed.

This report summarises the results of leaching tests on a range of recycled and secondary aggregates used in concrete. Otherwise equivalent concretes made using primary aggregates have been included to provide a basis for comparison. The results were compared with a series of leaching acceptance criteria developed for various purposes, including waste acceptance.

It must be stressed that the leaching from different sources of the same type of material could vary considerably, and any specific material should be considered on a case-by-case basis, rather than solely relying on the results obtained during this study. Further information on the leaching characteristics of generic material types is given on the AggRegain website.

This work was carried out for WRAP by the Building Research Establishment (BRE) and Scott Wilson (SW).

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