Leaching of Hazardous Substances from Concrete Constituents and Painted Wood Panels

Doktorsavhandling, 2004

At a time of increased concern about environmental issues in the building sector, it is essential to know the environmental performance of different building materials. Knowledge of the possible release of hazardous substances in building materials is scarce, and these aspects have often been neglected in environmental assessment methods. This research has studied the content and leaching behaviour of hazardous substances in concrete constituents and paints on wooden facades. The leaching tests for both materials were diffusion tests to study the time-dependent leaching, and availability tests to find the fraction that is available for leaching in the long term. The first part presents studies of concrete with additives of admixtures and industrial by-products such as slag and fly ash. The complex leaching process is studied both theoretically and in laboratory experiments. There was no significant difference in leaching of metals between the concretes with by-products and concrete with Portland cement. Each of the studied metals showed a unique leaching pattern. A new availability test instead of commonly used standard tests is proposed, when the purpose is to estimate the leaching during the service life of monolithic concrete. A different view of the leaching process and its changes over time is also presented. The leaching of concrete with admixtures containing thiocyanate, resin acids or nonylphenol ethoxylate was also studied, because of their toxic character. Both the diffusion test and the availability test showed relatively high leached fractions. Two thirds of the total amount were leached from crushed concrete containing thiocyanate. Not only nonylphenol ethoxylate but also nonylphenol was found in the leachate water – a more toxic, genotoxic and low-degradable substance. The results imply risks of using unspecified, crushed concrete in landfills. Part Two of this thesis presents leaching studies of biocides in wooden fa¸ade paint. Painted wood panels is a common fa¸ade cladding in Sweden, and microbiological growth in the paint is hampered by means of biocides. Panels in the field were exposed to natural rain, and both the run-off water and the surface analysis showed that considerable leaching from paint might occur Time-dependent leaching tests in laboratory environment gave lower leached amounts and a different behaviour than in the field study, which could be due to different climatic conditions and paint systems. A more aggressive, long-term availability test yielded profiles of the paint film with a non-steady-state condition, and clear signs of leaching about 30-50% when comparing profiles before and after leaching. The profiles reveal that the biocide IPBC migrates not only towards the surface, but also into the wood.