Leaching of hazardous substances from additives and admixtures in concrete

Artikel i vetenskaplig tidskrift, 2006

The aim of this work was to study the leaching of hazardous substances in additives and admixtures that are commonly contained in concrete. Time-dependent leaching has been analyzed for three types of metal containing concretes: with ordinary Portland cement (OPC), fly ash, and slag. The concretes had uniform leaching patterns, clearly above detection limits. The prolonged diffusion test of 1,700 days showed a substantial decline in metal release. There was no significant difference between the concretes with byproducts and the concrete with Portland cement. This study proposes an alternative availability test to NEN 7341, for generation of data for use in models of leaching during the service life of concrete as a monolithic material. The results of the two different availability tests are compared for naturally carbonated and noncarbonated materials and for different particle sizes. The leaching of concrete with admixtures containing thiocyanate, resin acids, or nonylphenol ethoxylate was also studied, because of their toxic character. The thiocyanate was leached with an initial fast dissolution process followed by a slower continuous diffusion process. The leached amount thiocyanate in the availability test was very high, 71%, due to its high solubility. Resin acids from tall oil-based air-entraining agents in concrete had a continuous diffusional leaching that is proportional to the square root of time. The fraction available for leaching was 17% of the added amount of oil and ∼20-30% of the added amount of nonylphenol ethoxylates. In addition to nonylphenol ethoxylate, nonylphenol was determined-a more toxic, genotoxic and low-degradable substance.