Emilija Fidanchevski

Self-cleaning coatings have the potential to protect building material surfaces against the effects of climate change and air pollution. In this study, composite powders containing 3 and 10 wt-% nano-TiO ₂ impregnated on mineral illite clay were synthesised by mechanical activation. The particle size distribution, mineralogical composition, and photocatalytic activity of the composite powders were characterised. A coating prepared from the 10 wt-% nano-TiO ₂ /illite composite was applied to three different substrates (highly porous, porous and non-porous), and their surface properties, functional properties and durability were evaluated. The self-cleaning and photocatalytic activities of the coating were evaluated by measuring the initial contact angle and degradation efficiency, respectively. Rhodamine B was chosen as the model pollutant. The varying functional behaviours of the coating were analysed in relation to its structural, textural and morphological properties. The 10 wt-% nano-TiO ₂ /illite coating exhibited pronounced hydrophilicity and demonstrated potential applicability for both porous and non-porous substrates.

Reducing the carbon dioxide (CO2) footprint in the construction industry is a key global objective in the pursuit of sustainability, especially considering that Ordinary Portland Cement (OPC) production is a significant contributor to global CO₂ emissions. Numerous advanced technological solutions have been explored to mitigate this impact, with one promising approach being the partial replacement of cement with supplementary cementitious materials (SCMs), aligning with the principles of a circular economy. This study aimed to develop green mortars by replacing 16 wt.% of cement with mechanically activated fly ash. In addition, the effects of the addition of 1 wt.% crystalline admixture and 0.25 wt.% transitional nano-alumina on the fresh properties, the hardened mechanical properties, and self-healing efficiency were examined. The inclusion of mechanically activated fly ash caused a slight delay in the setting time compared with the reference mortar. However, incorporating 1 wt.% crystalline admixture into the fly ash–modified mortar resulted in a significant delay in the setting time. The mechanical properties of the modified mortars remained consistent with the expected values for conventional mortars. The highest self-healing efficiency was observed in mortars containing 16 wt.% mechanically activated fly ash and 1 wt.% crystalline admixture, achieving 36% self-healing efficiency after 28 days, which increased to 89% after 56 days, and 96% after 90 days of curing. Similarly, mortars incorporating 0.25 wt.% transitional nano-alumina also achieved 96% self-healing efficiency after 90 days. However, the addition of 0.25 wt.% transitional nano-alumina exhibited a delayed self-healing effect, with only 10% self-healing efficiency after 28 days and 63% after 56 days of curing. Keywords: mechanically activated fly ash, mortars, self-healing, circular economy, crystalline admixture, transitional nano-alumina

The increase in industrial waste generation presents a global problem that is a consequence of the needs of modern society. To achieve the goals of the EU Green Deal and to promote the concept of circular economy (CE), the valorization of industrial residues as secondary raw materials offers a pathway to economic, environmental, energetic, and social sustainability. In this respect, Al-containing industrial residues from alumina processing (red mud), thermal power plants (fly ash and bottom ash), and metallurgy (slag), as well as other industries, present a valuable mineral resource which can be considered as secondary raw materials (SRMs) with the potential to be used in construction, supporting the concept of circular economy. This paper focuses on the characterization of 19 secondary raw materials from the East South-East Europe (ESEE) region regarding their physical, chemical, mineralogical, and radiological characteristics. The goal is to provide a foundation for future innovations based on secondary raw materials, in alignment with the EU Green Deal and the principles of circular economy. The results showed that fly ash has the potential to be the best material among those analyzed to be used in the cement industry, mainly due to its favorable radiological and mineralogical properties. However, it is important to control the amount of free lime in the mixture, ensuring it remains below 10%. After evaluating secondary mineral raw materials for metal recovery, the results indicate that these materials are not viable sources for base metals or other technology-critical metals, such as REEs.

The cement industry could potentially consume large amounts of solid industrial waste in order to improve its sustainability. The suitability of selected quarry and mine waste as secondary raw materials (SRM) was examined for the sustainable production of cement following the concept of a circular economy. The chemical, mineralogical, and radiological characterization of SRM was conducted in this study. Its potential use in low-carbon and low-energy belite-sulfoaluminate cement was investigated by incorporating the examined SRM into cement clinker. Various characterization methods were used to characterize the cement, including X-ray powder diffraction (XRD), thermal analysis (DTA/TG), and isothermal calorimetry. Depending on the chemical composition of the waste, lower or higher amounts were allowed to be incorporated into the raw clinker mixture for a targeted clinker phase composition. Among the samples, differences were observed in the phase composition of synthesized clinkers, which slightly influenced the reactivity of the cement but did not significantly change the compressive strength of the final product.

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 (H_ex), the external absorbed dose rate (D) and annual effective dose rate (EDR). The specific surface area (40.25 m^2 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.

The application of self-cleaning coatings presents one of the most effective ways to protect the surfaces of the building materials. The effect of TiO₂/kaolin based coatings applied to three types of substrates: non-porous, porous and highly porous, was investigated. Mechanical activation was applied for the impregnation of the active TiO₂ component (in content of 3 and 10 wt. %) into the kaolin support. Surface properties (roughness, hydrophilicity and micro-hardness) and functional properties (photocatalytic activity and self-cleaning efficiency) were studied in order to define the optimal formulation of the applied coatings. The effect of the photocatalytic behavior of the coated substrates in terms of self-cleaning ability was assessed by the photodegradation of Rhodamine B, performed before and after durability tests. The results obtained in this paper showed that photocatalytic activity of the TiO₂/kaolin composite coating generally depends on the procedure of TiO₂ impregnation into the kaolin clay and the loaded TiO₂ content.

The aim of this investigation was the synthesis of nanocomposite coatings based on Zn-Al layered double hydroxides (Zn-Al LDH) and TiO2. The Zn-Al LDH material, which acted as the catalyst support of the active TiO2 component (in the content of 3 and 10 wt. %), was synthesized by a low super saturation co-precipitation method. The interaction between the Zn-Al LDH and the active TiO2 component was accomplished by using vacuum evaporation prior to the mechanical activation and only by mechanical activation. The final suspension based on Zn-Al LDH and 10wt. % TiO2, impregnated only by mechanical activation, showed the optimal characteristics from the aspect of particle size distribution and XRD analysis. These properties had a positive effect on the functional properties of the coatings (photocatalytic activity and self-cleaning efficiency) after the water rinsing procedure.

This work is concerned with development of sol–gel method for preparation of nanoscaled TiO₂ using organometallic precursor—titanium tetraisopropoxide (TTIP) and determination of the present crystalline phases depending on the temperature of further thermal treatment. The characteristic processes and transformations during the thermal treatment were determined by means of thermal gravimetric analysis and/or differential thermal analysis (TGA/DTA) method. The crystalline structure and size of the TiO₂ crystallites were analyzed by means of Raman spectroscopy and X-ray powder diffraction (XRPD) method. At 250 °C, cryptocrystalline structure was detected, where amorphous TiO₂ is accompanied with crystalline anatase. The anatase crystallite phase is stable up to 650 °C, whereas at higher temperature rutile transformation begins. It was observed that at 800 °C, almost the whole TiO₂ is transformed to rutile phase. According to XRPD analysis, the increase of the temperature influences on the increase of the size of the crystalline particles ranging from 6 nm at 250 °C to less than 100 nm at 800 °C. The size and shape of the TiO₂ crystalline particles were observed by transmission electron microscopy (TEM). The shape of the studied samples changes from nanospheres (250, 380, and 550 °C) to nanorods (650 and 800 °C). Morphology of the formed TiO₂ aggregates was observed by scanning electron microscopy (SEM).