Deterioration of Outside Walls Made with Concrete Blocks Containing Pyrite


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Title: Deterioration of Outside Walls Made with Concrete Blocks Containing Pyrite

Author(s): J. L. Gallias

Publication: Special Publication

Volume: 212


Appears on pages(s): 607-620

Keywords: concrete block; expansive gypsum; ferrous oxides; oxidation; pyrite

Date: 6/1/2003

The deterioration concerns the outside walls of private houses made with hollow concrete blocks and covered with one-layer of white cement based coating. Six years after construction, the walls presented a random local ejection of the coating leaving in the bottom of the hole a rust coloured deteriorated material. Rust-coloured stains on the surface of the wall was also formed. The field study showed that the bottom of the hole reached systematically the concrete block and that the intensity of the deterioration was panially related with the climatic exposure of the walls. Scanning Electron Microscopy, X-Ray Energy Dispersion Spectroscopy and X-Ray Diffraction investigations on sound and deteriorated samples showed that the deterioration results from the oxidation of pyrite nodules of some millimeters of diameter included in the course aggregate of the concrete mixture of the blocks. The oxidation process of the pyrite occurred in wet conditions and in contact with cement compounds producing expansive gypsum and colloidal ferrous hydroxides. The random cracking and the low permeability of the coating were contributing factors to the deterioration process.