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Taking recycled concrete as the research object, fly ash was selected to replace cement. By adjusting the proportion of fly ash, high performance fly ash recycled concrete with different replacement rates (0, 10%, 30%, 50% and 70%) was prepared. The effects of different replacement rates of fly ash on the micro morphology, mechanical properties, flexural toughness and frost resistance of recycled concrete were studied. The results showed that there wasn't new hydration product after adding fly ash, but the hydration reaction rate was accelerated, the diffraction peak strength of Ca(OH)2 was increased, and the fly ash particles were more closely combined with the hydration product gel, which enhanced the compactness of recycled concrete. When the re-placement rate of fly ash was 50%, the structure of recycled concrete was the most dense. With the increase of replacement rate of fly ash. the compressive strength and flexural strength of recycled concrete increased first and then decreased. When the replacement rate of fly ash was 50%, the compressive strength and flexural strength at 28 d reached the maximum value, 44.2 and 5.96 MPa, respectively, and the deflection reached the maximum value of 7.7 mm, with the strongest deformation resistance. With the increase of freeze-thaw cycles, the surface peeling phenomenon of recycled concrete intensified. With the increase of replacement rate of fly ash, the mass loss of recycled concrete decreased first and then increased, and the relative dynamic elastic modulus increased first and then decreased. When the freeze-thaw cycle was TOO times and the replacement rate of fly ash was 50%, the minimum mass loss rate of recycled concrete was -0.09%, the maximum relative dynamic modulus of elasticity was 94.52%, and the frost resistance was the best. [ABSTRACT FROM AUTHOR]

The design and synthesis of photocatalytic materials and their application in environmental pollution control and resource recycling have been reported in many literatures. However, most photocatalytic materials contain transition metal ions, and the environmental risks of leaching 1imit the application of catalytic materials. Silicon carbide (SiC), as the representative of the third generation of semiconductor materials, has a good potential application prospect in environmental pollution prevention because of Is characteristics such as no transition metal ions, high temperature and acid-alkali resistance, strong stability and so on. In recent years, some literatures have reported the synthesis, modification and application of SiC as photocatalyst n environment and resource recycling -fields. However, few temperatures have reviewed the application progress of SiC photocatalyst. In view of the above situation, the progress in the -field of SiC photocatalysis application in recent years was reviewed in tins paper, including synthesis method, doping medication and application, and the prospects of the photocatalyst system were also prospected. [ABSTRACT FROM AUTHOR]