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The potential use of steel slag from treated steel slag in belite-sulfoaluminate cements was investigated in this study. Cement clinkers with two phase compositions were synthesized, allowing the incorporation of different amounts of steel slag. The phase composition and microstructure of cement clinkers at three different sintering temperatures were studied by X-ray powder diffraction and the Rietveld method, as well as scanning electron microscopy with energy dispersive spectrometry. The results showed that the targeted phase composition of clinkers was achieved at a sintering temperature of 1250 °C. However, a higher amount of perovskite instead of ferrite was detected in the clinker with a higher content of Ti-bearing bauxite. Apart from the main phases, such as belite, calcium sulfoaluminate, and ferrite, several minor phases were identified, including mayenite, perovskite, periclase, and alkali sulfates. In both clinker mixtures, a higher content of MgO in the steel slags resulted in the formation of periclase. Furthermore, the hydration kinetics and compressive strength at 7 and 28 days were studied in two cements prepared from clinkers sintered at 1250 °C. As evidenced by the results of isothermal calorimetry, the hydration kinetics were also influenced by the minor clinker phases. Cement with a higher content of calcium sulfoaluminate phase developed a higher compressive strength.

The objective of this study was to demonstrate the potential utilization of fly ash (FA), wood ash (WA), and metakaolin (MK) in developing new alkali-activated materials (AAMs) for the removal of cadmium ions from waste water. The synthesis of AAMs involved the dissolution of solid precursors, FA, WA, and MK, by a liquid activator (Na2SiO3 and NaOH). In concentrated solutions of the activator, the formation of an aluminosilicate gel structure occurred. DRIFT spectroscopy of the AAMs indicated main vibration bands between 1036 cm−1 and 996 cm−1, corresponding to Si-O-Si/Si-O-Al bands. Shifting vibration bands were seen at 1028 cm−1 to 1021 cm−1, indicating that the Si-O-Si/Si-O-Al bond is elongating, and the bond angle is decreasing. Based on the X-ray diffraction results, alkali-activated samples consist of an amorphous phase and residual mineral phases. The characteristic “hump” of an amorphous phase in the range from 20 to 40° 2θ was observed in FA and in all AWAFA samples. By the XRD patterns of the AAMs obtained by the activation of a solid three-component system, a new crystalline phase, gehlenite, was identified. The efficiency of AAMs in removing cadmium ions from aqueous solutions was tested under various conditions. The highest values of adsorption capacity, 64.76 mg/g (AWAFA6), 67.02 mg/g (AWAFAMK6), and 72.84 mg/g mg/g (AWAMK6), were obtained for materials activated with a 6 M NaOH solution in the alkali activator. The Langmuir adsorption isotherm and pseudo-second kinetic order provided the best fit for all investigated AAMs.

Since recycled technologies usage is mandatory for environmental safety, and in this regard, it is important to examine new materials that can be used in construction and are primarily produced from fly ash. In addition to characteristics such as hardness and compressive strength, the given materials must also be radiologically and environmentally safe. The main concept of engineered geopolymer gel composites based on fly ash residues is focused on developing binder materials via gel formation processes that can replace ordinary cement materials. This study is unique in researching the potential use of fly ash from the Nikola Tesla thermal power plant in Serbia, where the hybrid geopolymeric materials synthesized from fly ash are experimentally examined with the addition 1 wt% and 2 wt% of polyvinyl alcohol (PVA). This paper aims to investigate the structural, morphological, mechanical, and radiological properties of hybrid materials with the addition of PVA and without additive in the period of ageing for 28 days at room temperature. The phase composition was investigated using X-ray powder diffraction (XRPD) analysis, while morphological characteristics of these materials were examined using scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDS). Vibrational spectra of obtained samples are investigated using diffuse reflectance infrared Fourier transform (DRIFT) and Fourier transform infrared (FTIR) techniques. The hardness and compressive strength are also examined, indicating that the 1 wt% addition in geopolymeric matrix results in the best mechanical properties. Radiological measurements of investigated all geopolymer samples show decreasing activity concentrations of radionuclides for 50% compared to fly ash.

Garnets (19 pieces) of Late Antique S-fibulae from the archaeological site at Lajh-Kranj (Slovenia) were analysed with Raman microspectroscopy to obtain their mineral characteristic, including inclusion assemblage. Most garnets were determined as almandines Type I of pyralspite solid solution series; however, three garnets showed a higher Mg, Mn and Ca contents and were determined as almandines Type II. Most significant Raman bands were determined in the range of 169–173 cm−1 (T(X2+)), 346–352 cm−1 (R(SiO4)), 557–559 cm−1 (ν2), 633–637 cm−1 (ν4), 917–919 cm−1 (ν1), and 1042–1045 cm−1 (ν3). Shifting of certain Raman bands toward higher frequencies was the result of an increase of the Mg content in the garnet composition, which also indicates the presence of pyrope end member in solid garnet solutions. Inclusions of apatite, quartz, mica, magnetite, ilmenite, as well as inclusions with pleochroic or radiation halo and tension fissures (zircon), were found in most of the garnets. Rutile and sillimanite were found only in garnets with the highest pyrope content. Spherical inclusions were also observed in two garnets, which may indicate the presence of melt or gas residues. The determined inclusion assemblage indicates the formation of garnets during medium- to high-grade metamorphism of amphibolite or granulite facies. According to earlier investigations of the garnets from Late Antique jewellery, the investigated garnets are believed to originate from India.

The influence of temperature on the early hydration of belite-calcium sulfoaluminate cements with two different calcium sulfate to calcium sulfoaluminate molar ratios was investigated. The phase composition and phase assemblage development of cements prepared using molar ratios of 1 and 2.5 were studied at 25, 40 and 60 °C by in situ X-ray powder diffraction. The Rietveld refinement method was used for quantification. The degree of hydration after 24 h was highest at ambient temperatures, but early hydration was significantly accelerated at elevated temperatures. These differences were more noticeable when we increased the temperature from 25 °C to 40 °C, than it was increased from 40 °C to 60 °C. The amount of calcium sulfate added controls the amount of the precipitated ettringite, namely, the amount of ettringite increased in the cement with a higher molar ratio. The results showed that temperature also affects full width at half maximum of ettringite peaks, which indicates a decrease in crystallite size of ettringite at elevated temperatures due to faster precipitation of ettringite. When using a calcium sulfate to calcium sulfoaluminate molar ratio of 1, higher d-values of ettringite peaks were observed at elevated temperatures, suggesting that more ions were released from the cement clinker at elevated temperatures, allowing a higher ion uptake in the ettringite structure. At a molar ratio of 2.5, less clinker is available in the cement, therefore these differences were not observed.

This paper deals with the characterisation of cementitious materials from selected cultural heritage structures in Slovenia. The mineralogical–petrographic compositions of an aggregate, a type of binder and secondary minerals were studied via electron microscopy and X-ray powder diffraction. The porosity and pore network were determined using a mercury porosimeter. The results show that the aggregate of the samples was highly diverse, ranging from limestone, dolomite, quartz, feldspar and mica. The binder of the investigated samples was cementitious; either ordinary Portland cement was used, or ordinary Portland cement blended with ground granulated blast furnace slag was used. Some samples consisted of cement–lime binders. The investigated examples entailing cement materials for their construction contribute to a better understanding of the technology used to prepare historical cementitious and cement–lime mixtures.

The bottleneck in the process for increasing production of low CO[sub.2] mineral binders, based on BCSA (belite sulfoaluminate) clinkers, is the availability of Al-rich raw materials. For that purpose, a new registry of Al-containing secondary mineral residues (industrial and mine waste) has been developed and is presented in this paper. The methodology of creating the registry consists of three main steps: Gathering ideas, consolidation of ideas, and implementation. In order to achieve this, the following methodology was adopted: Analysis of similar registries by potential end-users and seeking potential solutions and tools to be used, and conducting 3 rounds of stakeholder consultations via workshops in order to determine crucial parameters and features the registry needs to contain. The key discussion points were about which data the registry needs to contain, who shall be the potential users, and what are the stakeholder’s expectations from the registry’s portal. Potential individual registry variables were identified as being relevant/irrelevant or available/unavailable, and potential solutions for the registry’s sustainability were explored. Each Al-rich waste/residue data entry is divided into 10 slots, describing legal status, location, quantities, chemical (REE included), mineralogical, physical and radiological properties, life-cycle assessment, additional data, and data relevancy. The registry will act as a matchmaking tool between producers/holders of Al-rich secondary raw materials and potential producers of cement clinkers.

The present study characterizes mortars from Thanjavur Palace (Thanjavur, India) to illustrate ancient production methods and the raw materials used. The mineralogical-petrographic composition of mortars was determined using optical microscopy, supported by scanning electron microscopy with energy-dispersive spectroscopy and X-ray powder diffraction. The chemical composition and organic content of the binder were also determined. The aggregate-binder ratio and particle size distribution of the mortars were investigated. Results showed that the composition of both the aggregate and binder varied between mortars. The aggregate consisted mainly of quartz, with small quantities of feldspar and individual grains of limestone and other lithic grains present. The majority of the mortars contained a lime binder, but kaolinite was also identified, indicating a clay binder. Kaolinite primarily occurred in bedding mortars rather than plaster mortars. All samples were in a deteriorated state due to the presence of gypsum and halite. Analysis of particle size distribution confirmed the size of the aggregates to range between 1.18 and 0.3 mm, showing that the aggregates must have been ground in order to allow for the dispersion of binders. Furthermore, biomolecules in the form of carbohydrates, proteins and fats, which could serve as natural admixtures to improve properties in both the fresh and hardened state, were identified in all mortar samples.

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.

This study investigates the gel characteristics of alkali-activated materials (AAMs) synthesized using wood ash (WA), and metakaolin (MK) as solid precursors. The research explores the influence of precursor type and sodium hydroxide (NaOH) concentrations in the alkali activator solution on the resulting physicochemical, microstructural, mechanical, and radiological properties of gels. The alkaline activators were prepared by mixing sodium hydroxide solutions (6 M and 12 M) with a sodium silicate (water glass) solution at a volume ratio of 1.5. The physicochemical characteristics of raw materials and AAMs were thoroughly analyzed using X-ray fluorescence (XRF), Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) with EDS elemental mapping. FTIR analysis confirmed the formation of an amorphous gels geopolymer network. XRD revealed the presence of characteristic crystalline phases (quartz, calcite) within an amorphous matrix. Mechanical properties, such as compressive strength, depended on precursor type and alkali molarity: metakaolin (12 M) reached ~14 MPa, while wood ash showed ~4 MPa (6 M) and ~0.5 MPa (12 M) due to high CaO, low Si and Al, and unfavorable SiO2/Al2O3 (5.71) and Na2O/Al2O3 (3.19) ratios. Furthermore, this research estimates radiological doses by quantifying radionuclide content via gamma-spectrometry. Alkali activation significantly reduced radiological hazard parameters, with radium equivalent activity (Raeq) decreasing to 238.0 Bq/kg and the external hazard index (Hex) to 0.643 for A12MK, while the annual effective dose rate for A12WA was only 0.265 nSv/y-all values remaining well below the recommended safety limit of 370 Bq/kg (≤1 mSv/y). The decrease in activity concentration index (Iγ), Raeq, and Hex with increasing NaOH concentration indicates effective radionuclide immobilization within the geopolymer matrix, confirming the suitability of these alkali-activated materials for safe use in construction from a radiation protection perspective.