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Povzetek: This study presents the in-situ synthesis of hydroxyapatite (HAp) within the structure of beech and pine wood. The modification process utilized a two-step vacuum-pressure impregnation coupled with chemical precipitation using calcium nitrate tetrahydrate and diammonium hydrogen phosphate solutions, followed by exposure to ammonium hydroxide vapors. While the initial focus was on the overall physicochemical changes, microstructural characteristics and fire behavior of the mineralized wood, the main aim is to specifically investigate the effects of leaching. Because HAp synthesis produces water-soluble ammonium nitrate (NH4NO3) as a by-product, this research systematically addresses how the removal of this component affects the final properties of wood. HAp formation was confirmed by FTIR and X-ray diffraction, while scanning electron microscopy and microcomputed tomography revealed HAp deposits primarily in the cell lumen of both wood species. Fire behavior was evaluated using thermal analysis and the cone calorimeter. The incorporation of non-flammable HAp synthesized within the wood structure may act as a barrier and mass transfer during pyrolysis. This results to comparable or slightly enhanced key fire performance parameters when comparing leached HAp synthesized samples with leached reference samples. In contrast, the unleached HAp synthesized samples, which still contained residual NH4NO3, showed deterioration in fire growth rate (FIGRA) and heat release rate (HRR) parameters, confirming that NH4NO3 acts as an oxidant. However, this oxidative property also leads to improvements in total heat release (THR) and total smoke production (TSP) parameters compared to unleached references, representing a complex interaction when studying the fire properties of mineralized wood.
Ključne besede: chemical precipitation method, fire retardancy, hydroxyapatite, HAp, leaching process, wood
Objavljeno v DiRROS: 17.04.2026; Ogledov: 23; Prenosov: 14
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Povzetek: 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 haz- ard 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.
Ključne besede: wood ash, metakaolin, alkali-activated materials, radionuclides
Objavljeno v DiRROS: 24.03.2026; Ogledov: 132; Prenosov: 125
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Povzetek: The hydration kinetics, phase assemblage, microstructure and mechanical properties of belite–ye’elimite–ferrite (BYF) cement containing different secondary raw materials (red mud and waste concrete) and cured at 5, 20 or 608C were examined. Different secondary raw materials were found to lead to changes in cement hydration. The influence of these materials on the hydration processes of belite and ferrite became more noticeable at a curing temperature of 58C, but diminished with an increase in curing temperature. The BYF cement made with red mud exhibited accelerated hydration, particularly at 58C, due to higher contents of mayenite and alkali sulfate compared with cement with natural materials and waste concrete. Red mud inhibited early ettringite formation due to the presence of aphthitalite but promoted monosulfate through accelerated ye’elimite hydration. Ferrite hydration was delayed by red mud, as alkali sulfates promote belite reactivity and calcium silicate hydrate (C-S-H) formation over stra¨tlingite. Periclase increased siliceous hydrogarnet formation at higher temperatures, supporting delayed yet stable strength development. The curing temperature impacted the morphology of the C-S-H (transitioning from a fine fibrillar-like structure to a foil-like structure) and affected the chemical composition of hydrates, resulting in a lower incorporation of iron in hydrogarnet and C-S-H at higher temperatures. Increased curing temperatures promoted aluminium uptake in calcium aluminium silicate hydrate.
Ključne besede: belite–ye'elimite–ferrite (BYF) cement, cement, cement paste, cementitious materials, hydrated cement, secondary raw materials, temperature
Objavljeno v DiRROS: 28.01.2026; Ogledov: 280; Prenosov: 269
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Povzetek: Calcium sulfoaluminate (CSA)-based cements represent a promising alternative to traditional Portland cement, offering benefits such as rapid strength development, low shrinkage, and reduced carbon footprint. Despite their commercial availability and proven performance, the adoption of CSA cements remains hindered by gaps in standardization and understanding. This RILEM Technical Committee (TC) CSA aims to review current knowledge, identify research needs, and address challenges related to clinkering, hydration mechanisms, durability, applications, nomenclature, standardization, and testing of CSA-based cements. The outcomes will further the understanding of manufacturing, technical performance, use, and specification of CSA-based cements, ultimately leading to broader acceptance in concrete construction.
Ključne besede: calcium sulfoaluminate cement, ye'elimite, belite, ettringite, low-CO2 cement
Objavljeno v DiRROS: 14.01.2026; Ogledov: 286; Prenosov: 214
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Povzetek: The phase assemblage evolution of binders with novel supplementary cementitious materials (SCMS) during exposure to adverse environments needs to be quantified to accelerate their adoption, and further optimize binder formulation. As such, the interaction between chloride and cementitious matrices with novel SCMs needs to be quantified. The goal of workgroup 2 of RILEM TC EBD-298 is to assess the methods used to quantify chloride binding. This state-of-the-art report reviews the standardized and novel methods to measure chloride binding through an average content (acid/water soluble) or a specific bound content per phase (XRD, TGA, SEM–EDS, …). Each method is presented with respect to our current understanding of chloride binding and speciation in cementitious materials. The discussion around the purpose, use and reporting of each method highlights the gaps limiting the comparison between studies, in particular the lack of standard protocol, and complementary characterization. This review is the groundwork for a “cookbook” of experimental workflows to investigate chloride binding in modern cementitious binders.
Ključne besede: cement, chloride, supplementary cementitious materials, CSMs
Objavljeno v DiRROS: 12.01.2026; Ogledov: 294; Prenosov: 161
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