Study of the leaching behaviour of paving concretes: quantification of heavy metal content in leachates issued from tank test using demineralized water

Abstract

The leaching behaviour of concretes made from porphyry aggregate, river sand and Portland cement or blast furnace slag cement has been studied by means of a tank test using demineralized water in accordance with NEN 7345. The results show that the amount of heavy metals leached is small, much lower than the parametric values specified by the European Directive defining the quality of drinking water, and becomes negligible after prolonged immersion. At the end of the tank test, the fraction of heavy metals leached by the concrete represents less than 1% of the total heavy metal content of the cement. To refer to the bulk content as a criterion of environmental quality is therefore unjustified and unduly restrictive. The results suggest that the controlled use of alternative fuels and raw materials to replace natural materials does not in any way alter the leaching behaviour. Similarly, the replacement of a defined fraction of the clinker with blast furnace slag does not compromise the environmental compatibility of the concrete in terms of the heavy metals it releases. A second finding of these experiments is that the risk of contamination due to release of heavy metals from concrete on-site appears small. The total heavy metal content of concrete is of the same order of magnitude as (or even smaller than) that of a soil considered as being unpolluted in Belgium. Moreover, the fraction of heavy metals released by the concrete as a proportion of this total heavy metal content is nonsignificant.