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- Author or Editor: Nadezda Stevulova x
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The activity of microorganisms plays a very important function in the whole spectrum of degradation processes such as corrosion of metals and concrete, the plugging of the pipeline and filters in consequence of the biofilms creation or the efficiency reduction of heat exchangers. The microorganisms that cause microbiologically influenced corrosion of concrete are ubiquitous in the environment and they produce either organic or inorganic acids that can dissolve and disintegrate the concrete matrix. This paper is focused on the concrete biocorrosion’s study in real sulfuretum conditions — in a sewer pipe with wastewater in Košice city. Concrete samples with addition of 5 and 10% of coal fly ash respectively as well as reference samples without coal fly ash addition were used for the experiment. The weight changes and surface changes of concrete samples were valuated after 4-month exposition to the real sulfuretum influence. The concrete biodeterioration studies in sewer pipes suggest the analogical biodegradation processes for all samples, whereby the composition of concrete and duration of aggressive environment influence are also important.
In this paper, the effect of mean particle length of hemp hurds on compressive strength and other parameters of fibrous-composites is studied. Hemp hurds of various origin (Hungarohemp LTd, Nagylak, Hungary; Hempflax, Netherlands) with a wide particle size distribution were used in the experiments. Six samples of hemp hurds with various mean particle length (from 7.3 mm to 39.9 mm) were used for the preparation of fibrous composites based on MgO-cement as a binder. Bulk density, compressive strength, thermal conductivity and water absorbability of fibrous composites after 28 days of hardening were tested. The impact of men particle length of hemp hurds slices on values of bulk density, compressive strength and water absorbability of hardened composites was confirmed.
Development of lightweight composite materials based on organic binder is oriented on conventional inorganic binders replacement by alternative materials such as MgO cement. The objective of this paper is lightweight composites preparing with hemp shives and conventional binders (hydrated lime, cement) replacement by MgO cement. The achieved experimental results of compressive strength and thermal conductivity of hardened composites indicate that the use MgO cement based on the milled caustic magnesite is suitable conventional binders replacement in hemp concrete.
This paper is focused on utilization of coal fly ash, steelmaking slag and glass bottle fragment in concrete production. Each of these wastes was mixed into concrete, and compressive strength was tested.The first part of this paper is focused on Portland cement replacement by mechanochemical activated coal fly ash and the second part is aimed to natural aggregate replacement by steelmaking slag and glass bottle fragment in concrete mixture. The results showed that coal fly ash has a positive influence on compressive strength development, and steelmaking slag and glass waste can be successfully used as a natural aggregate replacement.
All composites based on natural fibers absorb moisture in humid atmosphere and when immersed in water or capillary action. Therefore, one of the major drawbacks of polymer fibers is their high availability to moisture sorption and their heterogeneity, which leads to a weak interface between the fibers and matrix and a poor transfer of the applied stress between the materials, resulting to reduction of physico-mechanical properties. An experimental investigation was conducted to testing the water absorption of hemp composites with MgO-cement binder and its influence on the physico-mechanical and thermal characteristics of composites. The achieved results of composites indicate that water absorption test has deteriorative influence on observed properties due to the degradation of the fibre-matrix interface.
Nowadays, color concrete pigments are used to revive space in the construction of new buildings, reconstruction existing buildings and squares. Color pigments represent a partial weight replacement of the binder. Color pigmented concrete also has properties like traditional concrete namely high strength, good durability and weather resistance for its variable use. In this paper, characterization and classification of color pigments, using and their influence on the properties of concrete is given. The experimental part of concrete composites studying (with color pigments) includes testing of physical and mechanical properties in comparison to reference sample (without color pigments).
Nowadays, the use of natural fibers as reinforcements for composite is attractive. Plant fibers from hemp, jute, sisal and others are used for the purposes of the construction. In this paper the attention is given to the preparation of composites based on hemp hurds. Hemp hurds is obtained from hemp stem in the fibers processing. Lightweight composites based on alternative binder MgO-cement and unmodified and chemically modified hemp hurds as filler were prepared. Their water absorption behavior was observed in time dependence.
The current annual worldwide production of by-products is estimated about 700 million tons of which 70 % is fly ash at least. Large quantities of fly ash are available at low costs around the world and its use in concrete seems to offer the best solution to reduce its consumption. With regard to these facts and Slovak needs, the chemical and mechanical properties of hardened concrete composites with various share of fly ash were studied. Other focus of this study is the investigation of the influence of different chemical admixtures on development of the concrete properties, their environmental and economic impacts.
Biocorrosion of natural and synthetic materials is an irreversible biochemical process, where a significant participation of bacteria societies takes place. The biocorrosion of concrete sewer pipes is caused mainly by the sulphuric bacteria and sulphate-reducing bacteria (SRB) forming a part of the biological circulation of sulphur and its compounds in biosphere. The aim of this work was to simulate a biocorrosion and to study the effect of simultaneous action of Acidithiobacillus thiooxidans ( A.t. ) and sulfate-reducing bacteria on concrete samples under model conditions. The biocorrosion effect has been proved and a further study is planed.
Biodeterioration can be seen as a process, which decreases value of materials and constructions and has been defined as the deterioration of materials of economic importance by organisms. Since the discovery bacterial genus Acidithiobacillus caused rapid corrosion of concrete especially Acidithiobacillus thiooxidans .This paper presents the results of concrete specimens’ biodeterioration study by bacteria Acidithiobacillus thiooxidans and Desulfovibrio genera under model conditions. Biodeterioration was carried out in laboratory reactor, where simultaneous effect of Acidithiobacillus thiooxidans and Desulfovibrio genera happened. The pH values of leachate, mass of concrete specimens change, Ca and Fe content in leachate were evaluated. After experiment the morphology of corroded surface were observed by scanning electron microscopy.
