This study investigates the microhardness and geometric degradation mechanisms of interfacial transition zones (ITZs) in recycled aggregate concrete (RAC) exposed to saline soil attack, focusing on the influence of supplementary cementitious materials (SCMs). Ten RAC mixtures incorporating fly ash (FA), granulated blast furnace slag (GBFS), silica fume (SF), and metakaolin (MK) at 10 %, 15 %, and 20 % replacement ratios were subjected to 180 dry-wet cycles in a 7.5 %MgSO4-7.5 %Na2SO4-5 %NaCl solution. Key results reveal that ITZ's microhardness and geometric degradation decreases with exposure depth but intensifies with prolonged dry-wet cycles. The FAGBFS synergistically enhances ITZ microhardness while minimizing geometric deterioration, with ITZ's width and porosity reduced to 67.6-69.0 mu m and 25.83 %, respectively. In contrast, FA-SF and FA-MK exacerbate microhardness degradation, increasing porosity and amplifying microcrack coalescence. FA-GBFS mitigates the diffusion-leaching of aggressive/original ions and suppresses the formation of corrosion products, thereby inhibiting the initiation and propagation of microcracks. In contrast, FA-SF and FA-MK promote the formation of ettringite/gypsum and crystallization bloedite/glauberite, which facilitates the formation of trunk-limb-twig cracks.

Uneven frost heave is frequently encountered in the subgrade-bridge transition zones (SBTZ) in seasonally frozen soil regions, which could lead to the deformation of track and even jeopardize running safety of vehicles. To this end, this paper conducts dynamic analysis of a vehicle-track coupled system accounting for the effect of frost heave deformation. Initially, the finite element method is used to obtain the relationship between rail irregularity and frost heave deformation. Then, a vehicle-track vertically coupled dynamics model is established, and its accuracy is validated by the measured data, published results and existing model. The time-domain dynamic responses of a vehicle-track coupled system under typical frost heave are analyzed. Afterwards, parametric analysis of frost heave deformation is conducted. Finally, the control threshold of frost heave is proposed from aspects of vehicle running safety, comfort, and track deformation. Numerical results indicate that the allowable amplitude of frost heave should be respectively restricted to 5, 20, and 25 mm for frost heave wavelengths less than 10 m, between 10 and 15 m, and greater than 15 m. The research findings offer theoretical support for the maintenance and operation of track in the SBTZ in seasonally frozen soil regions.

The mining of deep underground coal seams induces the movement, failure, and collapse of the overlying rock-soil body, and the development of this damaging effect on the surface causes ground fissures and ground subsidence on the surface. To ensure safety throughout the life cycle of the mine, fully distributed, real-time, and continuous sensing and early warning is essential. However, due to mining being a dynamic process with time and space, the overburden movement and collapse induced by mining activities often have a time lag effect. Therefore, how to find a new way to resolve the issue of the existing discontinuous monitoring technology of overburden deformation, obtain the spatiotemporal continuous information of the overlying strata above the coal seam in real time and accurately, and clarify the whole process of deformation in the compression-tensile strain transition zone of overburden has become a key breakthrough in the investigation of overburden deformation mechanism and mining subsidence. On this basis, firstly, the advantages and disadvantages of in situ observation technology of mine rock-soil body were compared and analyzed from the five levels of survey, remote sensing, testing, exploration, and monitoring, and a deformation and failure perception technology based on spatiotemporal continuity was proposed. Secondly, the evolution characteristics and deformation failure mechanism of the compression-tensile strain transition zone of overburden were summarized from three aspects: the typical mode of deformation and collapse of overlying rock-soil body, the key controlling factors of deformation and failure in the overburden compression-tensile strain transition zone, and the stability evaluation of overburden based on reliability theory. Finally, the spatiotemporal continuous perception technology of overburden deformation based on DFOS is introduced in detail, and an integrated coal seam mining overburden safety guarantee system is proposed. The results of the research can provide an important evaluation basis for the design of mining intensity, emergency decisions, and disposal of risks, and they can also give important guidance for the assessment of ground geological and ecological restoration and management caused by underground coal mining.

The production of ferrous as well as non-ferrous metals generates slag as a byproduct material. Ferrous slags are extensively used in the construction sector as supplementary cementitious material (SCM) and aggregates. In this regard, the investigation of potential applications in similar areas for slags derived from the production of non-ferrous metals can help to address issues associated with their disposal, dumping, environmental concerns, etc. The primary aim of this research is to assess the pozzolanic activity of copper slag (CS), a type of non-ferrous slag. This investigation is conducted to replace a portion of ordinary Portland cement (OPC) incorporating CS as an SCM for sustainable construction. To assess the reactivity of the CS, comparisons were drawn with a known pozzolanic material fly ash (FA), and an inert material quartz powder (QP). The processing of raw CS (granular material) was carried out using a laboratory scale ball mill to achieve varying fineness to evaluate the effect of specific surface area (SSA) on reactivity. Initially, the investigations were conducted on paste samples of OPC-CS and suspensions of CScalcium hydroxide (CH) and were later extended to mortar studies. Mechanical characteristics such as compressive strength and open porosity of mortar specimens were determined to correlate with the paste studies results. The findings suggest that CS does exhibit pozzolanic characteristics although its reactivity is comparatively lower than that of FA. An increase in the fineness of the CS resulted in enhanced pozzolanic activity. Analysis of the hydrated suspension samples showed the formation of Fe-siliceous hydrogarnet phase indicating Fe from CS was involved in the reaction with CH. Although OPC-CS mortar samples exhibited similar open porosity compared to OPC-QP mortar samples, the interfacial transition zone (ITZ) porosity in mortar samples of OPC-CS was observed to be reduced indicating the densification of the region due to the pozzolanic reaction of CS. The permissible replacement of OPC with CS as a substitute for FA can be adjusted according to the material's fineness and the desired compressive strength.

Concrete is subject to the combined erosive effects of physical and chemical activities in cold, salty soil regions. In this work, durability tests of recycled concrete (RC) subjected to sulfate freeze-thaw cycles were conducted. The macroscopic performance deterioration law of RC under the influence of the replacement rate (0%, 50%, 100%) and the moisture content of coarse recycled concrete aggregate (CRCA) (0%, 50%, 100%) was investigated by analyzing the change characteristics of apparent damage, mass loss rate, and Relative dynamic modulus of elasticity (RDME) of RC during the erosion process. At the same time, nuclear magnetic resonance (NMR) and microhardness testing equipment were used to examine the multi-parameter evolution features such as porosity, pore distribution, interfacial transition zone (ITZ) width, and strength. The findings indicate that the main cause of the variation in the degree of damage to the RC surface layer is the variance in the effective water-cement (w/ c) ratio of the mortar due to replacement rate and moisture content. The strength and area of erosion damage increase when the CRCA replacement rate rises due to the easier inward penetration of the sulfate solution. CRCA with a 50% moisture content could increase the strength of the mortar by decreasing the mortar's effective w/c ratio. The rate and effectiveness of salt solution replenishment inward were simultaneously slowed down by the improved ITZ performance. In erosive situations, the fractal dimension of RC reduces to varying degrees. This is due to the expansion of the pore structure. The porosity/fractal dimension is employed as the comprehensive pore parameter eta in this research so as to take into account the integrity of the pore structure and the specificity of the pore distribution. The improved microstructure damage variables can reflect the erosive microstructure deterioration process of RC.

The increasing demand for high-speed railways has risen, to solve the age-old problem of bridge abutments, the step between the backfill and the bridge deck. Examples prove that inadequate technical solutions can generate damage that may require long-term speed restrictions or lead to short maintenance cycles, significantly increasing the total cost of ownership. The problems associated with the transition zones require complex analysis. The complex interaction of structural elements with different stiffnesses and different dynamic behavior varies over time due to the time-dependent behavior of the soil, and in addition, a bridge deck and its connecting elements can be constructed in several sequences. This study investigated a typical single-span railway bridge and its soil environment using PLAXIS 3D geotechnical finite element software. Different constitutive soil models were used to approximate the behavior of the bridge and the connecting elements. To model the soil behavior, the HS-small constitutive model was implemented. Loads of the structure are transferred onto the subsoil by 60 cm diameter piles modeled as embedded piles. Six different construction schedules were analyzed using time-domain analyses. The importance of high-speed railways was highlighted, and a 250 km/h train speed was applied, using dynamic analysis. The study focuses on the effect of different construction schedules on settlement, consolidation time, the behavior of the transition, and the substructure movements. The results of this study show that geotechnical approaches by themselves are not enough to solve the problem of the transition zone, highlighting the collaboration of geotechnical, structural and railway engineers.

The leaf is an important site for energy acquisition and material transformation in plants. Leaf functional traits and their trade-off mechanisms reflect the resource utilisation efficiency and habitat adaptation strategies of plants, and contribute to our understanding of the mechanism by which the distribution pattern of plant populations in arid and semi-arid areas influences the evolution of vegetation structure and function. We selected two natural environments, the tree-shrub community canopy area and the shrub-grass community open area in the transition zone between the Qinghai-Tibet Plateau and the Loess Plateau. We studied the trade-off relationships of leaf area with leaf midvein diameter and leaf vein density in Cotoneaster multiflorus using the standardised major axis (SMA) method. The results show that the growth pattern of C. multiflorus, which has small leaves of high density and extremely small vein diameters, in the open area. The water use efficiency and net photosynthetic rate of plants in the open area were significantly greater than those of plants growing in the canopy area. The adaptability of C. multiflorus to environments with high light and low soil water content reflects its spatial colonisation potential in arid and semiarid mountains. The leaf is an important site for energy acquisition and material transformation in plants. Leaf functional traits and their trade-off mechanisms reflect the resource utilisation efficiency and habitat adaptation strategies. We studied the trade-off relationships of leaf area with leaf midvein diameter and leaf vein density in Cotoneaster multiflorus. The results show the adaptability of C. multiflorus to environments with high light and low soil water content, which explains the expansion in the shrub's geographic distribution.

Mongolia is one of the most sensitive regions to climate change, located in the transition of several natural and permafrost zones. Long-term trends in air freezing and thawing indices can therefore enhance our understanding of climate change. This study focuses on changes of the spatiotemporal patterns in air freezing and thawing indices over Mongolia from 1960 to 2020, using observations at 30 meteorological stations. Our results shows that the freezing index ranges from -945.5 to -4,793.6 degrees C day, while the thawing index ranges from 1,164.4 to 4,021.3 degrees C day over Mongolia, and their spatial patterns clearly link to the latitude and altitude. During the study period, the trend in the thawing index (14.4 degrees C-day per year) was larger than the trend in the freezing index (up to -10.1 degrees C-day per year), which results in the net increase of air temperature by 2.4 degrees C across Mongolia. Overall, the increase in the thawing index was larger in the low latitudes and altitudes (e.g., the Gobi-desert, steppes, the Great lake depression and major river valleys) than in high latitudes and altitudes (mountain regions), while it was the opposite for the freezing index. The highest values for both thawing index and freezing index (i.e. the least negative values) have occurred during the last 2 decades. As the trends in the freezing and thawing indices and mean annual air temperature confirm intensive climate warming, increased permafrost degradation and shallower seasonally frozen ground are expected throughout Mongolia.

The acceleration of permafrost thaw due to warming, wetting, and disturbance is altering circumpolar landscapes. The effect of thaw is largely determined by ground ice content in near-surface permafrost, making the characterization and prediction of ground ice content critical. Here we evaluate the spatial and stratigraphic variation of near-surface ground ice characteristics in the dominant forest types in the North Slave region near Yellowknife, Northwest Territories, Canada. Physical variation in the permafrost was assessed through cryostructure, soil properties, and volumetric ice content, and relationships between these parameters were determined. Near-surface ground ice characteristics were contrasted between forest types. In black spruce forests the top of the permafrost was ice-rich and characterized by lenticular and ataxitic cryostructures, indicating the presence of an intermediate layer. Most white spruce/birch forests showed similar patterns; however, an increase in the active layer thickness and permafrost thaw at some sites have eradicated the transition zone, and the large ice lenses encountered at depth reflect segregated ground ice developed during initial downward aggradation of permafrost. Our findings indicate that white spruce/birch terrain will be less sensitive than black spruce forests to near-surface permafrost thaw. However, if permafrost thaws completely, white spruce/birch terrain will probably be transformed into wetland-thaw lake complexes due to high ground ice content at depth.

Research treating permafrost-climate interactions is traditionally based on a two-layer conceptual model involving a seasonally frozen active layer and underlying perennially frozen materials. This conceptualization is inadequate to explain the behaviour of the active-layer/permafrost system over long periods, particularly in ice-rich terrain. Recent research in North America supports earlier Russian conclusions about the existence of a transition Zone that alternates in status between seasonally frozen ground and permafrost over sub-decadal to centennial time scales. The transition zone is ice-enriched, and functions as a buffer between the active layer and long-term permafrost by increasing the latent heat required for thaw. The existence of the transition zone has an impact on the formation of a cryogenic soil structure, and imparts stability to permafrost under low-amplitude or random climatic fluctuations. Despite its importance, the transition zone has been the focus of relatively little research. The impacts of possible global warming in permafrost regions cannot be understood fully without consideration of a more realistic three-layer model. The extensive data set under development within the Circumpolar Active Layer Monitoring (CALM) program will provide a significant source of information about the development, characteristics, behaviour, and extent of the transition zone. This paper is focused on the uppermost part of the transition zone, which joins the active layer at sub-decadal to multi-centennial time scales. This upper part of the transition zone is known as the transient layer. Copyright (c) 2005 John Wiley & Sons, Ltd.