Browsing by Author "Todorova E."
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Item Influence of metakaolinite and stone flour on the properties of self-compacting concrete(2013-05-21) Todorova E.; Chernev G.; Markov P.Self-compacting concrete is the new generation composites, characterized with high filling and passing ability, as well as high resistance to segregation. The flexibility and spreading without external vibrations make these materials prefered for producing tense elements. Powder additives and chemical admixtures play an important role for structural behavior and potential abilities of this type of concrete. The aim of the present study was the manifacture and characterization of mixture for self-compacting concrete with participation of powder additives (metakaolinite and stone flour) and super plasticizers (Viscocrete 5370 and Viscocrete 5800). The influence of chemical admixtures and powder additives on concrete properties were made by the different methods: sorption ability; S; FTIR and ζ- potential. Physical and mechanical properties as compressive strength; spreading and fluidity were measured. Using SEM and FTIR analyses were observed structure behavior of prepared samples. FTIR spectra showed characteristic peaks of the used components, without chemical interactions between them. SEM images showed evenly distribution of the fine fraction in concrete mixture. Tendency of decreasing sorption ability with increasing pH of the media is observed. Higher sorption ability showed mixtures with addition of chemical admixture Viscocrete 5370. With increasing amount of chemical admixture decreases ζ- potential of cement paste. Mixtures, containing metakaolinite showed higher values of strength pressure, spreading ability and fluidity.Item Sol - gel silica hybrid materials applicable for external treatment of concrete defects(2015-01-01) Todorova E.; Chernev G.; Djambazov S.; Tsvetkova Y.The sol-gel silica hybrids are materials with application in different fields - pharmacy, medicine, sensors, etc. Concrete self - healing is a new area of applications of this kind of materials. It is connected with filling the cracks and preventing their further destruction as well as providing materials able to form CaCO3 as filler. A combination of hybrid materials containing calcium ions and bacterial cells is the optimal choice for that purpose. The material should exhibit stability, durability and ability to penetrate in the cracks. Furthermore, it should be reactive and biocompatible in order to interact with bacterial cells and promote further formation of CaCO3. Hybrid materials based on silica network and in situ incorporated organic components (chitosan and polyethylene glycol) is synthesized by the sol - gel method. The silica matrix obtained from tetraethylorthosilicate provides the structure with stability and durability, while the organic components account for its flexibility, biocompatibility and reactivity. The results from the structural analysis (XRD, FTIR, SEM and AFM) show that hybrids thus obtained have an amorphous, homogeneous structure. Formation of the silica network and backbone organic units is observed by FTIR spectroscopy. The AFM surface micrographs show the presence of particles of a size from 50 nm to 1 μm. They serve as reactive centers for potential interactions with the bacterial cells. The results from the structural characterization show that the synthesized materials can be used as carriers for bacterial cells' immobilization and applied further as fillers for external treatment of concrete defects.Item Structure and properties of innovative silica hybrid materials synthesized for environmental applications(2015-07-21) Todorova E.; Chernev G.; Okolie N.; Salvado I.M.Today, environmental protection is one of the main goals in the strive to preserve the human existence. Development in this area requires invention of new materials, which can reduce the levels of pollution. Hybrid materials are suitable for this purpose, because they combine different desirable properties existing in separate sources into one unique and accessible structure. Most of the commonly used materials for the degradation of different kind of pollutants are based on titanium dioxide, because of its photocatalytic activity under UV irradiation. Innovative silica hybrid materials, containing an organic component (chitosan) and titanium nanoparticles, were successfully synthesized via the sol gel method and tetraethyl orthosilicate was used as a silica source and network former. Interaction between the chitosan and titanium units, and their influence on the structure of final material, were observed and discussed. A homogeneous structure with an even distribution of titanium and chitosan particles was visible from scanning electron microscopy (SEM) micrographs and the particle size varied between 50 and 150 nm. The formed silica network, characteristic peaks of chitosan and titanium groups and possible interactions between them are observed from Fourier transform infrared (FTIR) spectroscopy spectra and nuclear magnetic resonance (NMR) spectroscopy results. The behaviour of the synthesized silica hybrids after thermal treatment was investigated via differential thermal/thermo-gravimetric analysis (DTA/TG) analysis and the sorption and degradation activities of the obtained hybrid materials were investigated using a solution of methyl orange as model pollutant. The structure and properties of the synthesized silica hybrid materials assert their potential application in environmental remediation due to their photocatalytic degradation and sorption activities against pollutants.