Browsing by Author "Markov P."

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    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.
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    SYNTHESIS AND CHARACTERIZATION OF NANOPARTICLES FROM COAL FLY ASH
    (2024-01-01) Markov P.; Chernev G.; Nintianova D.; Kazakova N.; Karakostov H.
    In this study, amorphous nanoparticles were extracted from fly ash using a sol-gel method. The obtained nanoparticles were characterized using XRF spectroscopy, XRD, FT-IR and TEM. The XRD curves show the presence of both crystalline and amorphous phases. FT-IR analysis indicated the presence of silanol and siloxane groups. Upon analysis, the primary nanoparticles were found to exhibit a roughly spherical shape with an average size of approximately 65 nm. The findings of this study demonstrate the feasibility of applying the sol-gel method to synthesize nanoparticles derived from coal fly ash (CFA), thereby avoiding other expensive and energy-intensive methods of nanoparticle synthesis.