This study is focused on the experimental investigation of compressive strength and durability properties of lightweight concrete mixtures with fine expanded glass and expanded clay aggregates using different microfillers. The paper proposes the relationships between the compressive strength and density of concrete mixtures with different proportions of the lightweight aggregates mentioned above. The performed experimental studies have revealed the tendencies of possible usage of different amounts of fine lightweight aggregates and their combinations in the production of concrete mixtures depending on the demands of practical application. Following the requirements for structural concrete subjected to environmental effects, durability properties (alkaline corrosion and freeze–thaw resistance) of the selected concrete mixtures with expanded glass aggregate were studied. The results of the experimental investigations have shown that durability of tested concrete specimens was sufficient. The study has concluded that the mixtures under consideration can be applied for the production of structural elements to which durability requirements are significant.
This investigation was made to examine how the conditions of hydrothermal synthesis influence the crystal structure of xonotlite and its morphology. For synthesis we used amorphous silica fume and SiO2/CaO molar ratio equal to 1.0, water-solids ratio W/S = 10 and W/S = 15. The samples were cured hydrothermally in the rotation autoclave with mixing rod for 2 and 4 hours at 200°C. The products were characterized by X-ray diffraction, differential thermal analysis, thermogravimetry, SEM, atomic force microscopy and mercury intrusion porosimetry. The low W/S ratio and mixing intensity had a decisive effect on processes of formation of xonotlite. During the 4-hour synthesis at W/S = 15, well formed xonotlite fiber of 0.2 mm diameter was obtained. Under the same conditions, but at W/S = 10, the obtained xonotlite was poorly formed, with fiber of 0.07 mm diameter. The mercury intrusion porosimetry method was used to examine and compare the surface of synthesized xonotlite. In the case of well formed xonotlite, the surface equals to 8.027 m2/g and that of poorly formed xonotlite 22.328 m2/g. The investigation of pressed xonotlite powder by XRD shows the rise in diffraction peak intensity (0.700; 0.324) nm and the drop in diffraction peak intensity (0.308; 0.184) nm. With tobermorite, there is a rise in diffraction peak intensity (1.13; 0.542) nm.
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