Adriana Estokova

Properties Characterization of Chemically Modified Hemp Hurds

The effect of chemical treatment of hemp hurds slices in three solutions (EDTA (Ethylenediaminetetraacetic acid), NaOH and Ca(OH)2) on the properties of natural material was discussed in this paper. Changes in the morphology, chemical composition and structure as well as thermal stability of hemp hurds before and after their modification were investigated by using FTIR (Fourier transform infrared spectroscopy), XRD (X-ray powder diffraction analysis) and TG (thermogravimetry)/DSC (differential scanning calorimetry). Size exclusion chromatography (SEC) measurements were used for determination of degree of cellulose polymerization of hemp hurd samples. Chemical modification is related to the partial removal of non-cellulosic components of lignin, hemicellulose and pectin as well as waxes from the surface of hemp hurd slices. Another effect of the chemical treatment applied is connected with increasing the crystallinity index of cellulose determined by FTIR and XRD methods. Decrease in degree of cellulose polymerization and polydispersity index in chemically modified hemp hurds compared to the original sample was observed. Increase in thermal stability of treated hemp hurd was found. The most significant changes were observed in alkaline treated hemp hurds by NaOH.

Assessment of natural radioactivity levels of cements and cement composites in the Slovak Republic.

The radionuclide activities of 226Ra, 232Th and 40K and radiological parameters (radium equivalent activity, gamma and alpha indices, the absorbed gamma dose rate and external and internal hazard indices) of cements and cement composites commonly used in the Slovak Republic have been studied in this paper. The cement samples of 8 types of cements from Slovak cement plants and five types of composites made from cement type CEM I were analyzed in the experiment. The radionuclide activities in the cements ranged from 8.58–19.1 Bq·kg−1, 9.78–26.3 Bq·kg−1 and 156.5–489.4 Bq·kg−1 for 226Ra, 232Th and 40K, respectively. The radiological parameters in cement samples were calculated as follows: mean radium equivalent activity Raeq = 67.87 Bq·kg−1, gamma index Iγ = 0.256, alpha index Iα = 0.067, the absorbed gamma dose rate D = 60.76 nGy·h−1, external hazard index Hex = 0.182 and internal hazard index Hin was 0.218. The radionuclide activity in composites ranged from 6.84–10.8 Bq·kg−1 for 226Ra, 13.1–20.5 Bq·kg−1 for 232Th and 250.4–494.4 Bq·kg−1 for 40K. The calculated radiological parameters of cements were lower than calculated radiological parameters of cement composites.

Testing Silica Fume-Based Concrete Composites under Chemical and Microbiological Sulfate Attacks

Current design practices based on descriptive approaches to concrete specification may not be appropriate for the management of aggressive environments. In this study, the durability of cement-based materials with and without the addition of silica fume, subjected to conditions that leach calcium and silicon, were investigated. Chemical corrosion was simulated by employing various H2SO4 and MgSO4 solutions, and biological corrosion was simulated using Acidithiobacillus sp. bacterial inoculation, leading to disrupted and damaged surfaces; the samples’ mass changes were studied following both chemical and biological attacks. Different leaching trends were observed via X-ray fluorescence when comparing chemical with biological leaching. Lower leaching rates were found for concrete samples fortified with silica fume than those without silica fume. X-ray diffraction and scanning electron microscopy confirmed a massive sulfate precipitate formation on the concrete surface due to bacterial exposure.

Application of Granulated Blast Furnace Slag in Cement Composites Exposed to Biogenic Acid Attack

The deterioration of cement-based materials used for the civil infrastructure has led to the realization that cement-based materials, such as concrete, must be improved in terms of their properties and durability. Leaching of calcium ions increases the porosity of cement- based materials, consequently resulting in a negative effect on durability since it provides an entry for aggressive harmful ions, causing corrosion of concrete. The use supplementary cementing composite materials have been reported to improve the resistance of concrete to deterioration by aggressive chemicals. The paper is focused on the investigation of the influence of biogenic acid attack on the cement composites affected by bacteria Acidithiobacillus thiooxidans. The concrete specimens with 65 wt. % addition of antimicrobial activated granulated blast furnace slag as durability increasing factor as well as without any addition were studied. The experiments proceeded during 150 days under model laboratory conditions. The pH values and chemical composition of leachates were measured after each 30- day cycle. The calcium and silicon contents in leachates were evaluated using X - ray fluorescence method (XRF). Summarizing the results, the 65% wt. addition of antimicrobial activated granulated blast furnace slag was not confirmed to be more resistant.

Investigation of Suspended and Settled Particulate Matter in Indoor Air

Particulate matter is a natural part of the atmosphere, where the solid or liquid particles are suspended in the air. These suspended particles, also known as suspended particulate matter represents a dispersion aerosol system. In the air there are many types of microscopic airborne particles originated from both natural and anthropogenic processes, such as atmospheric clouds of water droplets, photochemically generated particles, re-suspended particulates, fumes arising from the production of energy, etc. They are present in various forms, eg. mists, fumes, dust. The atmosphere contains particles of the size ranging from slightly larger than molecules up to hundreds of micrometers, which consists of a variety of chemical compounds [1]. Depending of their lifetime, the particulates observed at a location can be both of local origin or the product of the transport over distances of hundreds to thousands kilometres.

Thermal degradation of natural and treated hemp hurds under air and nitrogen atmosphere

Sustainability goals are essential driving principles for the development of innovative materials in the construction industry. Natural fibers represent an attractive alternative as reinforcing material due to good mechanical properties and sustainability prerequisites. The study has been focused on the comparative investigation of chemical and physical treatments of hemp hurds and their influence on the thermal behavior of main hemp constituents in air and nitrogen atmosphere. Thermal decomposition of hemp hurds involves several parallel reactions related to heat and mass transfer processes. A comparison of DSC and TG/DTG results of hemp hurds samples before and after treatments demonstrates a better thermal stability for treated samples. It is caused by changes in chemical composition due to a partial removal of non-cellulosic components from hemp hurds structure, an increase in cellulose content and decrease in its degree of polymerization. The results show different thermal behavior of the hurds samples heated under nitrogen and air atmosphere. Based on DTG records, several-stage process of mass loss has been found for the samples under air, whereas only two-stage process under nitrogen.

Bio-Corrosion Resistance of Concretes Containing Antimicrobial Ground Granulated Blastfurnace Slag BIOLANOVA and Novel Hybrid H-CEMENT

The article deals with the study of biocorrosion of concretes by sulphuric acid induced by oxidizing bacteria Acidithiobacillus thiooxidans. The concretes were prepared from reference cement CEM I 42,5 N, the mixtures of CEM I 42,5 N and antimicrobial ground granulated blastfurnace slag BIOLANOVA (GGBS) (with amount of GGBS 65 mass % - CEM III/A 32,5 N, 75 mass % - CEM III/B 32,5 N, 85 mass % - CEM III/C 32,5 N a 95 mass % - CEM III/C 32,5 N) and novel hybrid cement H-CEMENT (HC). The experiments were carried out in model laboratory conditions at 30 °C during 91 days. The degree of deterioration of concrete samples has been studied on the base of the pH changes of leachate, the concentrations of selected ions such as S, Ca and Si and the mass changes. It has been clearly confirmed, that in the presence of bacteria, the pronounced degradation of the samples occurred with exception of HC sample, which behaviour proved differences to the other samples. The HC concrete possessed more alkali leachate in comparison with the others. The concentration of sulphur S in leachate was increased by metabolic activity of bacteria due to biogenic H2SO4 formation. The increase of S concentration acidified leachate and so promoted leaching next substances from the samples. The concentration of silicon Si in leachate was promoted by metabolic activity of bacteria, as well. The development of Ca leaching concentration has been similar at all composite samples as in the case of reference CEM I 42,5 N concrete, however the smallest portion of leached Ca has been determined at HC concrete. The Ca leaching concentration has been increasing with the amount of GGBS being added to the composite CEM III concretes. The different tendency has been also observed at the HC samples in regards to the mass changes. The increase in mass has been measured at all concrete samples with exception of HC concrete, at which the mass decrease has been found out. The results confirmed the resistance of the concrete composite samples containing GGBS and HC to the sulphate attack and the HC sample showed the highest resistance to the sulphate biocorrosion.

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.

Investigation of the Precipitates on the Concrete Surface due to Sulphate Exposure

Abstract The aim of this study is to investigate the durability of cement-based materials subjected to the effects of sulphuric acid in terms of surface deterioration. Damaged concrete surfaces and the samples’ mass changes were studied during 270-day simulation of both chemical and biological attacks. Chemical corrosion was simulated by sulphuric acid with pH of 3.0 and 4.0, respectively, while biological corrosion was simulated by activity of bacteria Acidithiobacillus thiooxidans. XRD and SEM analyses confirmed a massive sulphate precipitate formation on the concrete surface due to chemical and biological sulphate corrosion.

Deterioration of Cement Composites with Silica Fume Addition due to Chemical and Biogenic Corrosion Processes

The paper is aimed at comparative study of resistance of Portland cement composites with addition of silica fume as durability increasing factor in various aggressive environments (sulphuric acid with pH 4, the medium of activated bacteria and the cultivating medium without bacteria) during 150 days under model laboratory conditions. Experimental studies confirmed: the leaching of silicon ions calculated to 1 g of concrete sample affected with bacteria Acidithiobacillusthiooxidans was 2.5 times lower (31.78 mg/g of sample) for concrete sample with silica fume addition comparing to concrete sample of ordinary CEM I Portland cement without any additives (82.98 mg/g of sample). The highest concentration of calcium ions released (60.808 mg/g of sample) was observed for reference sample without silica fume addition placed in the cultivating medium. Silica fume based concrete samples were found to have better performance in terms of calcium ions leaching for all environments and silicon ions leaching.