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Abstract:
Strain-induced changes of ZnTe energy gap in ZnTe/ZnMgTe core/shell nanowires arising from lattice mismatch between the core and the shell semiconductor are studied by means of optical methods. It is shown that the increase of the Mg content in the shell, as well as the increase of the shell thickness result in an effective redshift of the near band edge photoluminescence from ZnTe nanowire cores, which reflects directly the decrease of energy gap under tensile strain conditions. The conclusions are supported by theoretical calculations in terms of the valence force field model. The observed change of ZnTe energy gap can be as large as 120 meV with respect to the unstrained conditions and can be tuned in a continuous manner by adjusting shell parameters, which open a path towards an effective band gap engineering in these structures.

Keywords:
Nanowires, II-VI semiconductors, Magnesium, Band gap, Quantum effects

Abstract:
The experimental investigation on the frost-salt scaling resistance of air-entrained concrete containing CEM II/B-S 42.5N and CEM III/A 42.5N-HSR/NA slag-blended cements was performed. The air void system in concrete was evaluated in fresh concrete using AVA and in hardened concrete using an automated image analysis procedure. The mass of scaled material was increased for an increased slag content, in spite of increased compressive strength and flexural strength, decreased water absorption and decreased depth of water penetration of concrete. Increasing slag content resulted in a decrease of the total volume of air in hardened concrete and in a corruption of the air void system exhibited by a decrease of micropores content. The increase of mass of scaled material was proportional to the increase of the spacing factor of air voids, except for CEM III/A cement concrete exhibiting accelerated scaling.

Keywords:
Air-entrained concrete, Air voids, Frost-salt scaling, Image analysis, Slag-blended cement

Abstract:
The possibility for using coal combustion by-products in concrete exposed to frost-salt aggression was investigated. The research was aimed to assess an influence addition of circulating fluidized bed combustion (CFBC) fly ash on frost-salt scaling of air-entrained concrete. For evaluation of the resistance of concrete to frost salt scaling the test called ‘‘depth sensing indentation’’ (DSI) was applied. The DSI test method was implemented on a universal testing frame using a standard Vickers indenter. Experimental tests were performed on cement paste specimens and concrete specimens designed with partial replacement of cement with coal combustion by-products. The mass of scaled material in standard frost salt scaling resistance tests on concrete was inversely proportional to the Vickers hardness of the paste containing CFBC fly ash; the best-fit arithmetic relationship is provided.

Keywords:
Air entrained concrete, CFBC fly ash, Frost scaling resistance, Hardened cement paste, Microhardness

Abstract:
The increased use of advanced coalburning technologies for power generation, such as circulating fluidized bed combustion (CFBC), results in new waste products. The potential for using CFBC fly ash in air-entrained concrete was investigated in order to assess the influence of CFBC fly ash on the microstructure of air voids in hardened concrete. A special specimen surface preparation technique for contrasting the image and enabling measurements of air voids size and distribution using an automated image analysis procedure was used. The microstructure of air voids was evaluated on the basis of the total air content, the spacing factor, and the specific surface of air voids. It was found that a satisfactory air void system in concrete could be produced when using CFBC fly ash for partial replacement of cement. The air-void system was characterized by a decreased specific surface of voids and an increased spacing factor

Keywords:
CFBC fly ash, Image analysis, Microstructure, Air-entrained concrete

Abstract:
The phase composition of the cement paste phase of concrete containing fly ash from circulating fluidized bed combustion (CFBC) was studied. The motivation was to broaden the knowledge concerning the microstructure and the durability of concrete containing new by-products from the power industry. Several air-entrained concrete mixes were designed with constant water to binder ratio and with substitution of a part of the cement by CFBC fly ash (20%, 30% or 40% by weight). X-ray diffraction tests and thermal analysis (DTG, DTA and TG) were performed on cement paste specimens taken from concrete either stored in water at 18◦C or subjected to aggressive freeze-thaw cyclic action. The evaluation of the phase composition as a function of CFBC fly ash content revealed significant changes inportlandite content and only slight changes in the content of ettringite. The cyclic freeze-thaw exposure did not have any significant influence on the phase composition of concrete with and without the CFBC fly ash.

Keywords:
air-entrained concrete, fluidized bed fly ash, freeze-thaw durability, waste management

Abstract:
Przeprowadzono badania rozmieszczenia porów powietrznych w betonie napowietrzonym, zawierającym popioły lotne ze spalania węgla kamiennego w kotłach fluidalnych. Dodatek popiołów lotnych z kotłów fluidalnych stosowano jako zamiennik części cementu CEM I w mieszance betonowej. Na podstawie badania zawartości powietrza w mieszance metodą ciśnieniową stwierdzono, że zastosowanie popiołów lotnych z kotłów fluidalnych do betonu wymaga zwiększenia ilości domieszki napowietrzającej: stwierdzony wzrost był proporcjonalny do wzrostu zawartości dodatku. Przy wykorzystaniu automatycznej analizy obrazu na próbkach stwardniałego betonu określono rozmieszczenie i rozkład wielkości porów. Przy wzrastającej zawartości dodatku popiołów lotnych z kotłów fluidalnych stwierdzono zmiany mikrostruktury porów, odzwierciedlone wzrostem wskaźnika rozmieszczenia porów powietrznych oraz spadkiem powierzchni właściwej porów.

Keywords:
automatyczna analizy obrazu, domieszka napowietrzająca, charakterystyka porów, mikrostruktura, popiół lotny fluidalny, powierzchnia właściwa porów, wskaźnika rozmieszczenia porów