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Fly ash and phosphogypsum were used as Naturally Occurring Radioactive Materials (NORM) by-products for the synthesis of belite-sulfoaluminate clinkers. The influence of raw mixture composition and firing temperature was investigated. Clinkers and cements were examined by X-ray powder diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The compressive strength of the cements was determined after 28 days. Clinker phases identified included ye’elimite, ß-phase of belite, ternesite and gehlenite, while the main hydration product of the cement pastes was ettringite. The results showed that belite-sulfoaluminate cements can be fabricated with a compressive strength of 45.9 N/mm2 by firing the raw mixture (70 wt.% marl, 10 wt.% bauxite and 20 wt.% phosphogypsum) at a temperature of 1320°C/1h.

Dense ceramics are produced from fly ash from REK Bitola, Republic of Macedonia. Four types of fly ash from electro filters and one from the collected zone with particles < 0.063 mm were the subject of this research. Consolidation was achieved by pressing (P= 133 MPa) and sintering (950, 1000, 1050 and 11000C and heating rates of 3 and 100/min). Densification was realized by liquid phase sintering and solid state reaction where diopside [Ca(Mg,Al)(Si,Al)2O6] was formed. Ceramics with optimal properties (porosity 2.96±0.5%, bending strength - 47.01±2 MPa, compressive strength - 170 ±5 MPa) was produced at 1100ºC using the heating rate of 10ºC/min

Huge quantities of fly ash and bottom ash are generated from thermal power plants and it presents great concern for country, mainly due to the environmental effects. In this study, fly ashes and bottom ash were characterized from technical and radiological aspects. Health effect due to the activity of radionuclides 226Ra, 232Th and 40K was estimated via radium equivalent activity (Raeq), external hazards index (Hex), the external absorbed dose rate (D) and annual effective dose rate (EDR). The specific surface area (40.25 m2 g−1), particle density (1.88 g cm−3) and LOI (23.49%) were typical for bottom ash. Siliceous fly ash contained 32% reactive silica. The annual effective dose rate for all ashes is ≤ 0.2 mSv y−1. Both, fly ash and bottom ash present potential secondary raw materials to be used for building purposes as result of their technological and radiological assessment.

Waste glass and reclaimed brick are types of construction and demolition waste (C&DW) that could potentially be used as secondary raw materials in the production of ceramics. Ceramics based on clay, waste demolished brick (5-15 wt.%) and waste glass (5-20 wt.%) were produced by pressing (P = 68 MPa) and subsequently sintered at 900, 950, 1000, and 1050 oC for one hour. The physical and mechanical properties of the ceramics obtained were evaluated. The addition of demolished brick decreased the density and mechanical properties of the clay specimens and increased the water absorption. The incorporation of waste glass improved the sintering behavior and its mechanical properties. The addition of 20 wt.% waste glass and 10 wt.% waste demolished brick into the clay matrix improved the flexural strength by up to 20.6 % and decreased the water absorption by up to 22 %. The approach presented promotes an opportunity to recycle construction and demolition waste into alternative resource materials, and represents a positive contribution to the environment.

Abstract:The fl y ash, produced by power plant in Republic of Macedonia have been milled and sintered with addition of waste glass to obtain glass-ceramics. The physical, chemical and mechanical properties of fl y ash and waste glass were determined. Through adequate sintering time and temperature, the glass-ceramic materials were manufactured. Chemical, physical and mechanical properties of the obtained composites were defi ned. The optimal composition of the composite was fl y ash with the addition of 40% waste glass. Optimal sintering condition was 1000 o C with 1h isothermal time at fi nal temperature and heating rate of 10 o /min. The addition of 40%wt of waste glass in the fl y ashes increased the E-modulus from 4.24±1 to 30.55±2 GPa and increased the bending strength from 9.93±1 to 63.18±4 MPa Porosity of the compacts decreased from 44.34±3 to 14.32±2%. Investigation of durability of the produced systems did not show presence of any harmful elements in the obtained solution.Owning to combination of the macroscopic appearance, microstructure, mechanical and thermal properties developed, dense materials could be used in the civil engineering.

Fly ash, a waste by-product obtained in a thermal power plant has been a generated problem of the disposal all over the world. Morphological characteristics, physicochemical properties and pozzolanic activity make this waste potential material for production of ceramics. In this study high density ceramics compacts were produced by using fl y ash from the power plant REK Bitola, Republic of Macedonia. In order to increase geometrical factor of activity, the mechanical activation of the fl y ash was applied. The process of optimization of the main process parameters is conducted, such as time of mechanical activation, sintering temperature and heating rate and their interactions on the properties of obtained dense ceramic porosity and bending strength as a response function. The optimization was performed through application of 3D surface method and the obtained results are presented in the graphical and analytical form using "Statgraphics Centurion" software package.

In this study the 3D surface model was successfully applied in investigating the influence of the process parameters on the physical and mechanical properties of the glass-ceramics. Glassceramics was produced from coal fly ash and waste glass through the sintering method. The raw material was taken from "REK Bitola", a thermal power plant in the Republic of Macedonia. Glass-ceramics was obtained through the process of consolidation. Compacts with different ratio of