The aim of this study was to investigate the interaction between macrocell and microcell corrosion processes in a concrete column exposed to tidal conditions simulated by sinusoidal water-level changes. Macrocell corrosion currents were continuously measured for 19 weeks along the column height using coupled multi-electrodes (CMEs). Cumulative corrosion damage and the morphology of corrosion products were analysed using X-ray microCT, SEM, and Raman spectroscopy. The results showed complex patterns of anodic and cathodic activity, including sinusoidal and switch-like current behaviour, which depended on the water level position and exposure time. Corrosion typically initiated in the upper tidal zone, but the most corroded individual electrode was located near mid-tide. Damage distribution was influenced by both microcell and macrocell corrosion, where microcell corrosion was most prevalent in the high-tide area, whereas macrocell activity contributed to corrosion damage in several exposure zones. SEM and Raman analyses confirmed a correlation between corrosion type and corrosion product morphology. An attempt was made to explain the recognised corrosion patterns along the vertical position and the ratios between microcell and macrocell corrosion on individual electrodes were estimated. Additionally, new questions were raised that highlight the complexity of corrosion processes under tidal cycling and emphasise the need for further research into these phenomena.
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.
Steel slag is an abundant by-product of steelmaking and a promising candidate for CO2 sequestration due to its favorable chemical composition and mineralogy. In this study, the CO2 sequestration capacity of the processed steel slag Ekominit was analyzed. Ekominit is a mineral product obtained by processing a mixture of electric arc furnace (EAF) stainless steel slag and ladle slag, currently used only for simple engineering constructions. The study demonstrated a promising sequestration capacity of 127.4 g CO2 per kg of Ekominit, measured using direct semi-dry carbonation under ambient pressure at 40 ± 0.5 °C, 80 ± 3.2
We estimate the cosmic dust flux to Earth through the study of rare micrometeorites that preserve part of their precursor features during atmospheric entry heating, namely unmelted and scoriaceous subtypes. Combining high-precision mass balance measurements, X-ray computed microtomography and scanning electron microscopy, we studied mass, size and petrography of 207 micrometeorites recovered from sediment traps in the Transantarctic Mountains (TAM), ranging from similar to 170 to similar to 1650 & micro;m. Chondrules were identified in similar to 14% of the micrometeorites, particularly among coarse-grained and composite particles. The analysed population shows a bimodal size-frequency distribution, with peaks at similar to 305 & micro;m and similar to 470 & micro;m. A similar bimodal distribution was previously reported from the TAM cosmic spherule population, yet shifted towards lower sizes. This size-shift is consistent with an average mass loss of similar to 87% during atmospheric entry heating. The mass-size relationship follows a power-law, where the spherical equivalent diameter (d & micro;m) and mass (m & micro;g) of the micrometeorite are related by: . The size-frequency distribution of the fine- and coarse-grained micrometeorites reveals two well-separated clusters, with peaks at similar to 315 & micro;m and similar to 550 & micro;m, respectively. These observations suggest that the bimodal distribution in the micrometeorite flux reflects contrasting lithological end-member components with different physical properties and fragmentation behaviours during dust production in space. Based on earlier mass flux estimates from TAM melted micrometeorites and accounting for the mass loss due to atmospheric entry derived here, we calculate a time-averaged pre-atmospheric mass flux of similar to 12,000 (+/- 6,000) t/yr over the Quaternary, suggesting that the influx has remained stable over the last few million years.
Carbon-based nanomaterials have been widely used as bitumen modifiers because of their excellent mechanical and functional properties. Among carbon-based nanomaterials, carbon nanotubes (CNTs) have attracted particular attention because of their high aspect ratios and strong reinforcing potential. However, the interfacial failure mechanism of CNT-reinforced bitumen at the micro- and nanoscale remains unclear. This study employs molecular dynamics simulations to investigate the interfacial failure behavior of CNT-reinforced bitumen at the micro- and nanoscale. Utilizing the LAMMPS platform, a representative volume element model of CNT-reinforced bitumen was developed to evaluate both tensile and shear loading across two distinct CNT alignments: parallel and orthogonal. Through these models, the interfacial mechanical responses, crack evolution, and atomic-scale interaction morphologies were examined to elucidate the fundamental load-transfer behavior. The findings indicate that CNTs aligned parallel to the interface offer superior performance in tensile load bearing and transfer, whereas CNTs aligned orthogonal to the interface exhibit greater resilience under shear stress. During tensile deformation, failure is primarily driven by a loss of interfacial adhesion, as demonstrated by the observed crack propagation patterns and shifts in the atomic interaction morphology. In contrast, shear-induced damage is largely localized within the bitumen matrix, indicating that the cohesive failure remains the dominant degradation mode. These simulation results are further compared with direct tensile tests and SEM observations, which provide experimental evidence for interfacial sliding, CNT pull-out, and local matrix fracture in CNT-reinforced bitumen. Additional rheological characterization further demonstrates that CNT-modified bitumen has enhanced overall viscoelastic performance and deformation resistance compared with base bitumen. By detailing at the atomic scale the toughening mechanisms of CNT-reinforced bitumen, this work provides a theoretical framework for understanding and optimizing CNT-reinforced bitumen for pavement engineering applications.
