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Abstract :
[en] Globally, half of all generated waste is produced by the building sector. The finer fraction of this construction and demolition waste (C&DW) is often polluted with substances harmful for the durability of concrete, which is why their incorporation into a new structure is generally avoided.
The most important contamination present in these materials consists of gypsum (CaSO4.2H2O) residues from the construction or demolition site. The presence of sulfates from this gypsum may complicate and accelerate the sulfate attack reaction, which is a deteriorating process that causes the expansive formation of the mineral ettringite. The high volume of this ettringite will cause an expansive stress within the concrete, with degradation and cracking of the structure as a result. Additionally, the leaching of sulfates can give rise to environmental problems.
In this project, the fine fraction of C&DW from different industrial sources was investigated, to establish the gypsum contamination of actual recycled materials. Ion chromatography was used to determine the concentration of water soluble sulfates.
Results showed a variable sulfate content, depending heavily on the source of the materials. Nevertheless, the total amounts surpassed the acceptable sulfate contents specified in the European standard EN 206. The obtained information about the concentration and size distribution of sulfate contamination in fine recycled materials (FRA) will help the development of a testing protocol for the effects of internal sulfate attack caused by gypsum residues.
