Vlasta Ondrejka Harbulakova

Performance of Fiber-cement Boards in Biogenic Sulphate Environment

The paper presents the results of the study of selected fiber-cement boards parameters influenced by sulphur-oxidising (Acidithiobacillus thiooxidans) and sulphur-reducing bacteria (Desulfovibrio desulfuricans) attack. The experiments proceeded during 80 days under laboratory model conditions. The surface changes, chemical composition and pH of leachates as well as weight changes were investigated. The more extensive leaching of silicon and calcium ions from the cement matrix was confirmed under bacteria influence. The pH of liquid media has been settled to 7 and 9 for Acidithiobacillus thiooxidans and Desulfovibrio desulfuricans, respectively after initial increasing. Very small decrease in weight of samples in range 0.001 - 0.93 % was measured after the experiments.

Fly Ash Incorporation into the Concrete Composites in Order to Improve their Environmental Performance

Fly ash, representing the fine particulate matter, can be widely used in concrete production in order to improve the concrete properties and its environmental performance. The paper is aimed at applying a statistical approach to evaluate the results of the chemical sulphate corrosion of cement composites with and without fly ash addition. Two aggressive media simulating a sulphate corrosion: 0.5 wt.% solution of H2SO4 and 0.5 wt.% solution of Al2(SO4)3 were used. The deterioration process was evaluated by dissolution of the basic components of cement composites due to the aggressive media ́ exposure. The concentrations of dissolved Ca, Si, Al, Fe, Mn and Cu ions in leachates were measured and used as input data in a correlation analysis.Significant and up to very high correlation coefficients have been calculated for all analysed ions leachability excepting cuprum. The findings revealed the similar leaching mechanisms of analysed ions from the concrete samples with 5 and 10 wt. % of fly ash addition. The addition of coal fly ash was not definitely confirmed to increase the environmental resistance of concrete samples in terms of calcium and silicon leaching.