Segregation Potential Research Articles

Learning grain boundary segregation behavior through fingerprinting complex atomic environments

Although continuum-scale segregation is a well-documented behavior in multi-species materials, detailed site-specific behavior remains largely unexplored. This is partially due to the complexity of analyzing materials at the requisite time and length scales for describing segregation with full atomic accuracy. Here, we better evaluate the segregation behavior of disordered grain boundary (GB) atomic environments through leveraging a set of Strain Functional Descriptors (SFDs) to generate an atomic descriptor (i.e., fingerprint). Using this atomic fingerprint, we resolve key relationships between atomic structure and segregation energy. Machine learning (ML) techniques are utilized in concert with this SFD fingerprint to elucidate complex relationships relating segregation potential to changes in specific features of the local Gaussian density captured by the SFDs. Finally, we identify relationships that indicate both individual and joint structure-property correlations. Linking atomic segregation energy to key structural features demonstrates the value of higher-order descriptors for uncovering complex structure-property relationships at an atomic scale.

Synthetic Clay Application to Reduce the Segregation of Barite-Based Oil-Well Cement.

In the oil and gas industry, cement segregation is a significant concern that can have disastrous consequences, such as the failure of cement. The change of hardened cement's properties is observed, resulting in a decrease in its strength and an increase in its permeability. Therefore, providing some solutions to prevent this is crucial. The objective of this study is to assess the efficacy of synthetic clay in mitigating the problem of segregation in cement having barite. Six concentrations of synthetic clay were used to prepare six heavy-weighted cement samples with a high density of 18 lb/gal using the barite weighting material. The approaches of density distribution and nuclear magnetic resonance (NMR) were employed to characterize the heterogeneity in the hardened cement samples with the aim of identifying the potential of cement segregation. Then, the optimum concentration of the synthetic clay was selected and its effects on the rheological, strength, petrophysical, and elastic properties were evaluated and compared with the properties of the base cement (without synthetic clay). The results showed that 0.4% by weight of cement (BWOC) synthetic clay was the optimum concentration, which yielded the minimum cement segregation as represented by a 61% reduction in the density variation compared to the control specimen. The results obtained from the NMR technique validated the findings of the density distribution method, indicating that the porosity distribution of the synthetic clay cement with a concentration of 0.4% BWOC exhibited uniformity across its top, middle, and bottom sections, with a slight deviation window, while the porosity distribution of the control cement specimen displayed noticeable variation. Moreover, the synthetic clay had better properties than the control cement specimen. For example, the rheological properties were improved as represented by a 22% reduction in plastic viscosity and 42 and 11% increase in the yield point and gel strength, respectively. Compared to the base cement, the compressive and tensile strength were increased by 39 and 43%. The synthetic clay decreased the permeability and porosity by 73 and 24%, respectively. The synthetic clay enhanced the elastic properties as represented by a 1.5% reduction in Young's modulus and a 1.3% increase in Poisson's ratio compared to the base cement sample.

A frost heave pressure model for fractured rocks subjected to repeated freeze-thaw deterioration

Rock engineering in the Tibetan Plateau is usually suffered severe freeze-thaw (F-T) deterioration, triggering numerous geotechnical engineering disasters. As the essential triggering factor of F-T damage, the frost heave pressure (FHP) in rocks should be quantitatively described and predicted. In this study, a novel theoretical model is established and validated to estimate the critical entire evolution process of FHP in fractured rocks subjected to repeated F-T deterioration, in which the influence of fracture geometric configuration, rock mechanical properties and F-T conditions are comprehensively considered. Besides, given the obvious five-stage manner of FHP evolution, the combination effect of different dominant mechanisms in different stages is theoretically addressed. During freezing, after a silence stage induced by temperature above freezing point of water, volumetric expansion and frost-heave cracking separately controls the generation and reduction stages of FHP, and the solutions are obtained based on elastic mechanics and Griffith energy balance theory, respectively. During thawing, ice segregation dominates the second-arising stage of FHP that is quantitatively described via segregation potential and water migration velocity, and then the FHP enters the dissipation stage owing to complete melting of fracture ice. In addition, a decay coefficient is introduced to estimate the influence of F-T cycle number on FHP, and a piecewise FHP model is finally constructed for fractured rocks subjected to repeated F-T deterioration. To validate our new model, a total of 12 F-T cycle tests with real-time FHP monitoring are conducted on granite and sandstone specimens considering three typical influencing factors, i.e., fracture width, rock types and freezing temperatures. A rational consistency is identified between the theoretical and testing results in terms of the FHP evolution curves and the peak FHPs in rock fracture, demonstrating the generalizability and robustness of our proposed model.

Investigation of JGS frost susceptibility testing method

Frost heave is a type of frost action that occurs when the soil temperature is below freezing temperature. Construction in cold regions is challenging and can cause severe damage to structures due to frost heave. The segregation potential (SP) is widely accepted in engineering design and for frost heave predictions as an indicator for frost susceptibility classification. The purpose of this study is to investigate the frost heave experiments in the JGS method and to evaluate the JGS frost susceptibility testing results for different soil mixtures with different SP through numerical simulation with a Thermal-Hydraulic coupled model. The results show good agreement between numerical simulation and test results for different degrees of frostsusceptible soils. This model is expected to provide accurate predictions of the frost heave behavior of different soils.

The Space Between Us: Questioning Multi-Spatial Justice in the Upcoming Indonesia’s Capital

Land is not only defined as an object of ownership by certain community groups, especially indigenous communities. Land has intrinsic value inherent in the way of life and culture, thus affecting the quality of life. This article examines the potential implications of the land acquisiton process in the prospected Nusantara Capital in regards to the fulfillment of the right to an adequate standard of living. It is reviewed by engaging multi-spatial justice within the context of city development and urban transformation with learning lessons from Brasilia and Jakarta. Utilizing a qualitative socio-legal approach, the research employs systematic and structural interpretation of various legal instruments. It incorporates the concept of multi-spatial justice as part of a critical legal geography and urban sociology theory to understand the potential of segregation and gentrification in the Nusantara Capital. The results highlight three key aspects. Firstly, the concept of multi-spatial justice underscores the need to consider diverse spatial entities and their equitable treatment. Secondly, analyzing the State Capital Law reveals both promising and concerning aspects of spatial justice. While it aims to balance development and inclusivity, inconsistencies within the law's provisions raise concerns about potential injustices. Lastly, the study anticipates future inequities between local and urban spatials due to unequal land compensation. These findings emphasize the importance of addressing procedural and substantive fairness in land acquisition, fostering inclusive urban development, and aligning legal instruments with principles of multi-spatial justice.

Towards compartmentalized micelles: Mixed perfluorinated and hydrogenated ionic surfactants in aqueous solution

HypothesisAqueous solutions of mixtures of hydrogenated and perfluorinated ionic surfactants are known to display anomalous aggregation behavior due to the mutual phobicity between hydrogenated and perfluorinated chains. Despite all efforts, different experimental limitations prevented so far a definite interpretation of the existing experimental results: both intermicellar and intramicellar segregation remain acceptable possibilities. MethodThe potential for segregation of mixtures of fluorinated and hydrogenated ionic surfactants in water was assessed using atomistic molecular dynamics simulations. Aqueous mixtures of hydrogenated and perfluorinated ionic surfactants were studied: mixtures of anionic surfactants (sodium dodecylsulfate (SDS) + sodium perfluoro-octanoate (SPFO)) and catanionic surfactants (decyltrimethylammonium bromide (DeTAB) + SPFO) were simulated. FindingsThe mixture of anionic surfactants, SDS + SPFO, exhibits clear intramicellar segregation between fluorinated and hydrogenated chains, displaying hydrogenous-rich and fluorous-rich regions. Compartmentalized micelles are thus clearly formed. The simulation results also suggest the possibility of intermicellar segregation. Conversely, catanionic mixtures of DeTAB and SPFO in water solution assemble into a large oblate structure, containing all available molecules in the simulation box, resembling a double layer membrane or a vesicle wall. In this case mixing between fluorinated and hydrogenated surfactants is dictated by charge alternation.

Stabilization of DNA-encapsulating Droplets through Negative Charge at the Droplet Interface

Abstract It was found that stable cell-sized droplets entrapping DNA molecules are spontaneously generated through micro segregation. To clarify the mechanism, we performed measurements of the electrification by adapting a polymer solution with polyethylene glycol/dextran. We determined the Donnan potential for macroscopic phase segregation in both the presence and absence of DNA, together with the measurements of Zeta potentials of the microphase solution with number of small droplets. We confirmed that the droplets entrapping DNA are negatively charged.

Deep characterization of heavy-weighted oil well cement segregation by a novel nuclear magnetic resonance (NMR) technique

Oil well cement segregation is one of the catastrophic issues in drilling operations. It changes the properties of hardened cement, such as reducing its strength and increasing its permeability. This can lead to severe consequences, such as cement failure. Therefore, the early identification of cement segregation is crucial to provide some solutions to minimize it. However, conventional techniques that evaluated cement segregation need enhancing. In this work, four heavy-weight cement samples were prepared with a high density of 18 ppg using the four common weighting materials: barite, ilmenite, hematite and Micromax. To identify the potential of cement segregation, a new proposed approach by nuclear magnetic resonance (NMR) was utilized to characterize the cement segregation by measuring the porosity differences and heterogeneity in the hardened cement samples. Moreover, the NMR results were compared with the existing techniques, such as the direct weight and volume method and computer tomography (CT) scan. The results of the conventional direct weight and volume method and CT scan technique showed critical cement segregation of barite, ilmenite and hematite-based cement samples, which can result in several problems related to zone isolation. By applying the evaluation method involving NMR, the NMR approach confirmed the results of the conventional direct weight and volume method and CT scan technique in which severe cement segregation was found in the barite, ilmenite and hematite-based cement samples. To validate the ability of NMR to identify the cement segregation issue, the Micromax cement samples were also examined. The NMR method confirmed the results of the direct weight and volume method and CT scan technique, showing that Micromax had no segregation issue. NMR results showed that the porosity distribution of Micromax weighted cement was mainly the same in which there was no deviation window between its top, middle and bottom sections, while there was obvious variation in the porosity distribution of the barite, ilmenite, and hematite-based cement samples with large deviation window along the cement column. The NMR method allowed a rigorous investigation of the cement segregation in the hardened cement samples. The NMR successfully identified segregation by looking for the pore size distribution and its relation with porosity variation. The novelty of this work is applying a new approach to determine the heavy-weight cement segregation by NMR. Findings from this work have led to an effective method of determining cement segregation for basic laboratory tests of oil well cement.

Designed Y3+ Surface Segregation Increases Stability of Nanocrystalline Zinc Aluminate.

The thermal stability of zinc aluminate nanoparticles is critical for their use as catalyst supports. In this study, we experimentally show that doping with 0.5 mol % Y2O3 improves the stability of zinc aluminate nanoparticles. The dopant spontaneously segregates to the nanoparticle surfaces in a phenomenon correlated with excess energy reduction and the hindering of coarsening. Y3+ was selected based on atomistic simulations on a 4 nm zinc aluminate nanoparticle singularly doped with elements of different ionic radii: Sc3+, In3+, Y3+, and Nd3+. The segregation energies were generally proportional to ionic radii, with Y3+ showing the highest potential for surface segregation. Direct measurements of surface thermodynamics confirmed the decreasing trend in surface energy from 0.99 for undoped to 0.85 J/m2 for Y-doped nanoparticles. Diffusion coefficients calculated from coarsening curves for undoped and doped compositions at 850 °C were 4.8 × 10-12 cm2/s and 2.5 × 10-12 cm2/s, respectively, indicating the coarsening inhibition induced by Y3+ results from a combination of a reduced driving force (surface energy) and decreased atomic mobility.

Two-dimensional finite element modeling of long-term frost heave beneath chilled gas pipelines

Proper estimation of frost heave over the lifetime of a buried chilled gas pipeline is a key design concern. Previously conducted full-scale and centrifuge tests were continued for a limited period of time. Similarly, the numerical analyses with modeling of the coupled thermo-hydro-mechanical process of frost heave were limited to less than half of the design life of typical pipelines. Few studies estimated the long-term frost heave based on decoupled analyses where the heat transfer and frost heave were calculated separately, although both are interrelated processes. This study presents a two-dimensional coupled finite element (FE) modeling of frost heave under chilled gas pipelines buried in frost susceptible soil. The Konrad–Morgenstern segregation potential (SP) model is implemented in commercially available software using user subroutines. Simplified elastic-plastic models that recognize the key influencing factors, including temperature and volumetric ice fraction of frozen soil, are used for modeling the mechanical behaviour of soil. The present numerical approach can properly calculate the temperature gradient in the frozen fringe, which is essential in the SP model to define the volumetric expansion due to water migration to the frozen fringe. The FE calculated heave and frost front penetration are compared with the Calgary full-scale test results. The moisture content profiles obtained from FE simulation show a similar pattern as reported from a full-scale test. The challenges in modeling long-term heave resulting from continued ice accumulation in front of the final ice lens and potential warming of the leading part of the frozen bulb when the pipe moves further up are discussed.

Residential waste segregation: The interconnection with SDG 2 zero hunger

In the scientific literature, academics and practitioners have advocated the interconnection between Sustainable Development Goal 2 (SDG 2) and composting. However, despite the importance of separating organic waste at home and this activity's contribution to producing quality compost, relatively few scholars have explored its interconnection with SDG 2. To fill this gap, this article explores the potential of waste segregation in residential areas to meet SDG 2. This quantitative, non-experimental case study is based on an exploratory survey conducted with residents of two middle-class neighborhoods in the capital city of a state in northwestern Mexico, adjacent to the United States of America. The survey aims to measure the practices and knowledge of the participants related to home separation and composting and their understanding of SDG 2. Findings show that the interconnection between residential waste segregation and SDG 2 is harder to prove, even though waste segregation is essential to composting. Results also suggest that SDG 2 is usually pursued on national agendas; thus, it is unlikely that the home segregation of organic waste for small-scale home composting may influence national progress toward SDG 2. Still, this study would provide valuable insights for policymakers to develop comprehensive waste segregation policies that align with SDG 2.

Assessing the effect of different compaction mechanisms on the internal structure of roller compacted concrete

Compaction plays a pivotal role in the formation of the aggregate skeleton of concrete mixtures, especially for stiff mixes such as Roller Compacted Concrete (RCC). RCC is compacted in the field with combinations of different energies (kneading/shear, impact, static & vibratory pressure), whereas various compactors are used, viz. modified Proctor (MP), vibratory hammer (VH), vibratory table (VT), and gyratory compactor (GY) in the laboratory to mimic the field compaction. Since the compaction mechanism is different in these compactors compared to field rollers, the behaviour of RCC is also distinct and warrants a fundamental study. In this study, the dominating parameters affecting the mesostructural arrangement of aggregates within the concrete skeleton when compacted with different mechanisms are comprehensively studied and compared with the field compacted specimens using several image processing techniques. The mesostructural parameters considered are interparticle spacing & distribution, aggregates segregation, orientation, morphology & breakage post-compaction, and crack length. The results indicate a higher possibility of getting better aggregate distribution and strength while a lower segregation potential when compacted with VH, followed by MP. However, the use of MP could alter the aggregates’ morphological characteristics due to the breakage of particles during the compaction process. On the other hand, VT and GY could exhibit similar interparticle distances to the field specimens but could not demonstrate similar performance in terms of strength and durability. The dominating parameters affecting aggregates’ spatial distribution are found to be aggregate-to-mortar ratio, interparticle distance, and the mechanism associated with each compaction technique.

Rheological studies and numerical investigation of barite sag potential of drilling fluids with thermochemical fluid additive using computational fluid dynamics (CFD)

The growing advancement in drilling technology had necessitated the development of self-destructive mud cake, which is composed of encapsulated thermochemical fluids (TCF) to facilitate dissolution of filter cake. However, segregation of weighting component, commonly the Barite particles, can lead to various operational problems that should be avoided. In this investigation, the segregation potential of Barite particles (“Barite Sag”) in drilling fluids has been investigated. The experimental data from rheological studies have been employed to guide CFD modeling and simulation of multiphase flow of a dense suspension mimicking the conventional oil-based mud (OBM), water-based mud (WBM), and those comprises thermochemical additives viz. OBM_TCF and WBM_TCF. The results revealed that the drillings fluids conform to the shear thinning pseudoplastic behavior within the conditions operated in this study. Notably, the apparent viscosity of the WBM was observed to decrease with increasing temperature between 25 and 50 °C but increased afterwards. Evaluation of gravitational settling characteristics revealed that the conventional OBM might have lower sagging potential, at lower temperature, compared with the conventional WBM, due to higher settling velocity of Barite particles in the later. In comparison, at higher temperature, which corresponds to the conditions of the newly formulated muds (i.e., the OBM_TCF and WBM_TCF), it was found that the WBM_TCF exhibit lower potential for Barite sag due to lower settling velocity of the particles compared with that of OBM_TCF. The reason essentially has to do with higher viscosity of the WBM_TCF. The CFD studies have considered both the hydrodynamic forces and shear induced migration of the particles. Analyses of various simulation results including particle flux, particle mass fraction, mixture viscosity, and the pressure drop, consistently revealed that the WBM_TCF might have lower Barite segregation potentials compared with other types of drilling fluids considered in this study.

A 3D cellular automata ore stockpile model – Part 1: Simulation of size segregation

This paper describes a 3D cellular automaton (CA) for modelling ore pile formation that incorporates size segregation due to surface stratification. Ore stockpiles and bins are essential in mining operations as a buffer between the mine and the mineral processing plant, and their operation plays an important role in the overall performance of the downstream equipment. Size segregation can occur if the feed size to the pile varies over time or due to a variety of segregation mechanisms occurring in the pile itself. In particular,it can occur as a result of percolation stratification within surface flows. The structure of the newly developed CA model is described, and the simulated surface profile and size segregation response is validated through a series of laboratory-scale piles for characterizing the segregation potential of the feed particles. It is found that the model adequately describes the segregation behaviour at a range of model scales where coarse particles roll to the outside of the pile and fine particles are concentrated around the centre of the pile. Moreover, it is found that the model is sufficiently fast to use in real-time applications such as dynamic process control and digital twins.

Atomistic Simulation Informs Interface Engineering of Nanoscale LiCoO2.

Lithium-ion batteries continue to be a critical part of the search for enhanced energy storage solutions. Understanding the stability of interfaces (surfaces and grain boundaries) is one of the most crucial aspects of cathode design to improve the capacity and cyclability of batteries. Interfacial engineering through chemical modification offers the opportunity to create metastable states in the cathodes to inhibit common degradation mechanisms. Here, we demonstrate how atomistic simulations can effectively evaluate dopant interfacial segregation trends and be an effective predictive tool for cathode design despite the intrinsic approximations. We computationally studied two surfaces, {001} and {104}, and grain boundaries, Σ3 and Σ5, of LiCoO2 to investigate the segregation potential and stabilization effect of dopants. Isovalent and aliovalent dopants (Mg2+, Ca2+, Sr2+, Sc3+, Y3+, Gd3+, La3+, Al3+, Ti4+, Sn4+, Zr4+, V5+) were studied by replacing the Co3+ sites in all four of the constructed interfaces. The segregation energies of the dopants increased with the ionic radius of the dopant. They exhibited a linear dependence on the ionic size for divalent, trivalent, and quadrivalent dopants for surfaces and grain boundaries. The magnitude of the segregation potential also depended on the surface chemistry and grain boundary structure, showing higher segregation energies for the Σ5 grain boundary compared with the lower energy Σ3 boundary and higher for the {104} surface compared to the {001}. Lanthanum-doped nanoparticles were synthesized and imaged with scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) to validate the computational results, revealing the predicted lanthanum enrichment at grain boundaries and both the {001} and the {104} surfaces.

Reduced Fine API Agglomeration After Dry Coating for Enhanced Blend Uniformity and Processability of Low Drug Loaded Blends.

The impact of dry coating on reduced API agglomeration remains underexplored. Therefore, this work quantified fine cohesive API agglomeration reduction through dry coating and its impact on enhanced blend uniformity and processability, i.e., flowability and bulk density of multi-component blends API loading as low as 1 wt%. The impact of dry coating with two different types and amounts of silica was assessed on cohesion, agglomeration, flowability, bulk density, wettability, and surface energy of fine milled ibuprofen (~ 10µm). API agglomeration, measured using Gradis/QicPic employing gentler gravity-based dispersion, resulted in excellent size resolution. Multi-component blends with fine-sized excipients, selected for reduced segregation potential, were tested for bulk density, cohesion, flowability, and blend content uniformity. Tablets formed using these blends were tested for tensile strength and dissolution. All dry coated ibuprofen powders exhibited dramatic agglomeration reduction, corroborated by corresponding decreased cohesion, unconfined yield strength, and improved flowability, regardless of the type and amount of silica coating. Their blends exhibited profound enhancement in flowability and bulk density even at low API loadings, as well as the content uniformity for the lowest drug loading. Moreover, hydrophobic silica coating improved drug dissolution rate without appreciably reducing tablet tensile strength. The dry coating based reduced agglomeration of fine APIs for all three low drug loadings improved overall blend properties (uniformity, flowability, API release rate) due to the synergistic impact of a minute amount of silica (0.007 wt %), potentially enabling direct compression tableting and aiding manufacturing of other forms of solid dosing.

Aggregate Subgrade Improvements Using Quarry By-Product Fines: A Case Study

This paper presents a case study for constructing aggregate subgrade improvement (ASI) layers using quarry by-product aggregates (QBA)—a quarry mix of large primary crushed rocks (PCR) and sand-sized quarry fines. The construction took place at Larry Power Road in Bourbonnais Township in Kankakee County, Illinois, where the Illinois Department of Transportation (IDOT) placed two QBA mixes for performance evaluation. The first mix (QBA_M1) consisted of 45% quarry by-products (QB) and 55% railroad ballast-sized PCR. The second mix (QBA_M2) consisted of 31% QB and 69% PCR. Two conventional ASI sections with only PCR were also constructed. All sections consisted of a 229 mm (9 in.) QBA/PCR layer topped with a 76 mm (3 in.) thick dense-graded capping layer. Laboratory studies preceded the construction to recommend optimum QB percentages for the QBA materials and construction practice. The quality and uniformity of the construction was ensured through field testing using dynamic cone penetrometer (DCP), lightweight deflectometer (LWD), and falling weight deflectometer (FWD). The segregation potential of the QBA mixes was monitored by visual inspection, aggregate stockpile sampling, and image analysis techniques. Short-term field evaluation of the constructed QBA layers, particularly QBA_M2 with 31% QB, showed no evidence of major segregation. The QBA ASI layers had slightly lower but comparable strength and stiffness profiles to the conventional ASI sections. The use of QBA materials in ASI was therefore field validated in this case study as a sustainable construction practice to provide stable pavement foundation layers.

Assessing soil index parameters to determine the frost susceptibility of crushed rock aggregates

In Norway, crushed rock aggregates are widely used in all layers of pavement infrastructures. Frost heave severely affected the Norwegian road network during cold winters of 2009/10 and 2010/11, including newly built roads. In 2016, the Frost Protection for Roads and Railways project (FROST) was set up in part to investigate frost susceptibility and frost heave of crushed rock aggregates. Twenty-three frost heave tests were performed on the 0–4 mm fraction with nine types of different rock, in which 2 series were measured at different crushing stages in a production line. The tests succeeded to expand knowledge on the frost susceptibility of crushed rock aggregates, using the segregation potential as frost susceptibility criterion. However, the cost and time necessary for laboratory work were important. Since budget for road construction and rehabilitation are variable, a methodology to estimate the segregation potential using soil index properties was tested. A laboratory investigation was carried out to compare segregation potentials determined in laboratory (SP0 lab) to those calculated using the normalized segregation potential equations (SP0.n), which requires only four soil index parameters: the specific surface area of the fine fraction, the mean grain-size diameter of the fine fraction, the water content, and the liquid limit of the fine fraction, the fine fraction being <75 μm. Results showed a good correlation between the SP0 lab and the SP0.n. Results also showed a strong correlation between the SP0 lab and the crushed rock aggregates with a specific surface area of the fine fraction of <8 m2/g, which was the case for 19/23 samples. High specific surface area estimations (≈12.5 m2/g) found in early stage crushing aggregates are believed to be cause by weak mineral content enrichment and/or grain-surface irregularities in the fine fraction. In conclusion, this study confirms that the estimation of the segregation potential of a crushed rock aggregate from the normalized segregation potential equations is possible and reliable. The relationship developed using the specific surface area to determine the segregation potential is promising and should be validated furthermore to reinforce the relationship.

The Temperature Field Evolution and Water Migration Law of Coal under Low-Temperature Freezing Conditions.

This study examines the evolution law of the coal temperature field under low-temperature freezing conditions. The temperature inside coal samples with different water contents was measured in real-time at several measurement points in different locations inside the sample under the condition of low-temperature medium (liquid nitrogen) freezing. The temperature change curve was then used to analyse the laws of temperature propagation and the movement of the freezing front of the coal, which revealed the mechanism of internal water migration in the coal under low-temperature freezing conditions. The results indicate that the greater the water content of the coal sample, the greater the temperature propagation rate. The reasons for this are the phase change of ice and water inside the coal during the freezing process; the increase in the contact area of the ice and coal matrix caused by the volume expansion; and the joint action of the two. The process of the movement of the freezing front is due to the greater adsorption force of the ice lens than that of the coal matrix. Thus, the water molecules adsorbed in the unfrozen area of the coal matrix migrate towards the freezing front and form a new ice lens. Considering the temperature gradient and water content of the coal samples, Darcy’s permeation equation and water migration equation for the inside of the coal under freezing conditions were derived, and the segregation potential and matrix potential were analysed. The obtained theoretical and experimental results were found to be consistent. The higher the water content of the coal samples, the smaller the matrix potential for the hindrance of water migration. Furthermore, the larger the temperature gradient, the larger the segregation potential, and the faster the water migration rate.

Frost susceptibility of Nordic metal mine tailings

The mining industry produces significant amounts of waste materials, with the greatest volumes generated during enrichment. These waste materials or by-products, tailings, may be used as alternative civil engineering materials, reducing the need for natural resources. In cold climates, the frost behaviour of materials is one critical functional requirement in civil engineering applications. The frost behaviour of tailings classified as sand, silty sand, or sandy clayey silt (EN ISO), from four metal mines located in northern Finland and Sweden, was evaluated in this study using basic laboratory characterisation and one-dimensional freezing tests. The laboratory results were compared with existing guidelines on estimating the frost susceptibility of natural soils. Based on grain size distribution, the tailings samples were characterised as non-susceptible or frost-susceptible. Capillary rise values indicated that the frost susceptibility of the samples ranged from negligible to strong. In the one-dimensional frost heave test, measured frost heave after 96 h was 0.1–23.1 mm and calculated segregation potential (SP) was 0–9.7 mm2/Kh. Based on the frost heave test, the frost susceptibility of the samples ranged from low to strong. The results indicated that the finest samples classified as sandy clayey silt (L1−L3) generated the majority measured amount of frost heave and were classified as frost-susceptible material. The coarser tailings samples (K1-K3 and AK1) classified as sand or silty sand were classified non-susceptible, and measured frost heave amounts were low <1.0 mm (after 96 h). Thus, the tailings samples behaved like natural soils, indicating that classification methods developed for natural soils are valid for evaluation of the frost susceptibility of mine tailings. However, the influence of added reagents should be considered, and standardised frost behaviour methods should be developed.