Summary:

Geosynthetics, materials that are broadly used in civil engineering and en-vironmental protection, have certain initial characteristics, which are obtained while testing new products. However, with time, these values change as a result of the influence of degrading factors. Getting to know the scope of these changes enables improving products or designing structures with the appropriate safety factor.
Power industry in Poland uses mainly hard and brown coal in processes of energy generation. Fly ashes raised by the exhaust fumes and separated by elec-trofilters and ash-slag removed from furnace chamber are combustion by-products. Nowadays, the ash-slag mixtures are valuable anthropogenic soils, used for building embankments, where the geotextiles are also built in.
The taken up research aimed at the determination of the influence of the ash-slag chemistry on the changes of chosen strength parameters of geotextiles. The main degrading agent in the period of the research, which could influence the structure and thus the strength of geotextiles, was pH of the ash-slag. The mixture was taken from the dumping ground of the Steelworks Arcelor Mittal Poland S.A. in Kraków, from several places of the holding pond of the surface of 15 ha, from depths 0.5 to 2.0 m. The carried out chemical tests revealed strongly alkaline pH, which can destructively influence the structure of fibres of the adhering geotextile, and as a result the strength parameters of the product.
The static punch strength of the samples prepared according to the standard PN-EN ISO 12236 was checked, and the "fresh" material was compared with the one subjected to the strongly alkaline reaction and the atmospheric factors.
Stitched geotextiles were used for the tests, two of them made of polypro-pylene (PP), two - of recycled fibres of polypropylene and one - two-ply, made of synthetic staple fibres PP/PES.
To execute the research assumptions, a 1.0 m high experimental embank-ment was built up of the ash-slag mixture, in which the geotextiles were built in. The structure of the embankment ensured protection of the geosynthetics from the solar radiation and permeating groundwater. The samples were buried at the depth of 0.5 m and left for 8 and 24 months. Natural atmospheric factors could directly influence the embankment. Samples of geotextiles were placed in a way so that both sides of the product were in a direct contact with the ash-slag mixture, and the upper surface was marked.
After getting out the geotextiles from the embankment, they were subjected to the static puncture and the obtained test results allowed to make two basic conclu-sions:
- 8-months period of resting the geotextiles in the embankment did not es-sentially influenced their puncture strength. For none of types of the geotextiles were noticed any decrease of the value of the puncture force.
After 24 months of resting in the embankment made of the ash-slag mixture, the geotextiles GRK 151 and 401 made of the polypropylene fibres lost 15-16% of their puncture strength. The geotextiles R 404, 1024 and Terrafix made of the re-cycled polypropylene fibres lost 17-19% of their puncture strength.