Transition Zone Research Articles

Designing biphasic nanocellulose hydrogels to mimic the complex cartilage-bone interface

Osteochondral lesions, which affect both the cartilage and the bone, present significant challenges in treatment due to the complex mechanical and biochemical properties of these tissues. A crucial consideration in developing tissue replacements for these lesions is the simultaneous regeneration of cartilage and calcified cartilage, which forms the transition zone to bone. Our current study aims to fabricate a bilayer polymeric hydrogel designed not only to support cartilage regeneration but also to serve as an interface between cartilage and bone. The bilayer hydrogel was created by combining oxidized bacterial nanocellulose, gelatin, and alginate in one layer, while the other layer consisted of the same three biopolymers and hydroxyapatite. The bacterial nanocellulose was effectively oxidized (20%) with sodium periodate and then mineralized with calcium and phosphorus (Ca/P ratio = 0.97), as confirmed by EDX analysis. Remarkably, both layers of the biphasic hydrogel demonstrated cytocompatibility with chondrocytes. Moreover, the addition of hydroxyapatite significantly improved the mechanical strength from 72 kPa (OBC/Gel/Alg) to 90 kPa (MOBC/Gel/Alg). This bilayer hydrogel holds promise for promoting bone-cartilage integration and has the potential to contribute to the healing of osteochondral defects, offering new possibilities in the field of orthopedic tissue engineering and regenerative medicine.

A Scene–Object–Economy Framework for Identifying and Validating Urban–Rural Fringe Using Multisource Geospatial Big Data

Rapid urbanization has led to the emergence of urban–rural fringes, complex transitional zones that challenge traditional urban–rural dichotomies. While these areas play a crucial role in urban development, their precise identification remains a significant challenge. Existing methods often rely on single-dimensional metrics or administrative boundaries, failing to capture the multi-faceted nature of these zones. This study introduces a novel “Scene–Object–Economy” (SOE) framework to address these limitations and enhance the precision of urban–rural fringe identification. Our approach integrates multisource geospatial big data, including remote sensing imagery, nightlight data, buildings, and Points of Interest (POI), leveraging machine learning techniques. The SOE framework constructs feature from three dimensions: scene (image features), object (buildings), and economy (POIs). This multidimensional methodology allows for a more comprehensive and nuanced mapping of urban–rural fringes, overcoming the constraints of traditional methods. The study demonstrates the effectiveness of the SOE framework in accurately delineating urban–rural fringes through multidimensional validation. Our results reveal distinct spatial patterns and characteristics of these transitional zones, providing valuable insights for urban planners and policymakers. Furthermore, the integration of dynamic population data as a separate layer of analysis offers a unique perspective on population distribution patterns within the identified fringes. This research contributes to the field by offering a more robust and objective approach to urban–rural fringe identification, laying the groundwork for improved urban management and sustainable development strategies. The SOE framework presents a promising tool for future studies in urban spatial analysis and planning.

Substantial Global Radial Variations of Basalt Content Near the 660‐km Discontinuity

AbstractMid‐ocean ridges generate basalt and harzburgite, which are introduced into the mantle through subduction as a mechanical mixture, contributing to both lateral and radial compositional heterogeneity. The possible accumulation of basalt in the mantle transition zone has been examined, but details of the mantle composition below the 660‐km discontinuity (hereafter d660) remain poorly constrained. In this study, we utilize the subtle waveform details of S660S, the underside shear‐wave reflection off the d660, to interpret the seismic velocity, density, and compositional structure near, and particularly below, the d660. We identify a significant difference in S660S waveform shape in subduction zones compared to other regions. The inversion results reveal globally enriched basalt at the d660, with a notably higher content in subduction zones, consistent with the smaller impedance jump and S660S peak amplitude. The basalt fraction decreases significantly to less than 10% near 800‐km depth, forming a global harzburgite‐enriched layer and resulting in a steep seismic velocity gradient just below the d660, in agreement with 1D global reference models. The striking compositional radial variations near the d660 verify geodynamic predictions and challenge the applicability of homogeneous radial compositional models in the mantle. These variations may also affect the viscosity profile and, consequently, the dynamics at the boundary between the upper and lower mantle.

Evidence of repeated zoonotic pathogen spillover events at ecological boundaries

Anthropogenic modifications to the landscape have altered several ecological processes worldwide, creating new ecological boundaries at the human/wildlife interface. Outbreaks of zoonotic pathogens often occur at these ecological boundaries, but the mechanisms behind new emergences remain drastically understudied. Here, we test for the influence of two types of ecosystem boundaries on spillover risk: (1) biotic transition zones such as species range edges and transitions between ecoregions and (2) land use transition zones where wild landscapes occur in close proximity to heavily impacted areas of high human population density. Using ebolavirus as a model system and an ensemble machine learning modeling framework, we investigated the role of likely reservoir (bats) and accidental host (primates) range edges and patterns of land use (defined using SEDAC categories) on past spillover events. Our results show that overlapping species range edges and heightened habitat diversity increase ebolavirus outbreaks risk. Moreover, we show that gradual transition zones, represent by high proportion of rangelands, acts as a buffer to reduces outbreak risks. With increasing landscape changes worldwide, we provide novel ecological and evolutionary insights into our understanding of zoonotic pathogen emergence and highlight the risk of aggressively developing ecological boundaries.

Heterogeneous interfaces of aluminum bronze/Inconel 718 dissimilar alloys under different wire arc directed energy deposition sequences

Abstract The layer-by-layer deposition strategy of additive manufacturing makes it ideal to fabricate dissimilar alloy components with varying functionality, which has promising application potential in a large number of industrial areas. In this study, two components composed of ERCuAl-A2 aluminum bronze (CuAl9) and Inconel 718 nickel-based superalloy were fabricated with different deposition orders by wire-arc directed energy deposition. Subject to changes in heat input and thermophysical properties of the substrate, the transition region of the deposited Cu–Ni component with the bottom half of CuAl9 and the top half of Inconel 718 is narrow and serrated. This region features a laminated intermetallic compound layer due to the convection and rapid cooling in the molten pool. In contrast, the Ni–Cu component deposited in the opposite order exhibits a 2 mm gradient transition zone. Within this region, a large number of diverse precipitates were found as well as regional variations in grain size due to the multi-layer partial remelting. Both two components show strong bonds and their tensile specimens tested along the vertical direction always fracture at the softer CuAl9 side. Excellent tensile properties along the horizontal direction were obtained for Cu–Ni (Ultimate tensile strength: 573 MPa, yield stress: 302 MPa, elongation: 22%), while those of Ni–Cu are much lower due to the existence of the solidification cracks in the transition zone. The results from this study provide a reference for the additive manufacturing of Cu/Ni dissimilar alloy components, as well as their microstructure and mechanical properties control.

Research trends of biomechanics in scoliosis from 1999 to 2023: a bibliometric analysis.

Despite the abundance of research on the biomechanics of scoliosis, there is a lack of a comprehensive bibliometric analysis. This study utilizes bibliometric methods to elucidate the research trends and hotspots within this domain. The data for this study were obtained from the Web of Science Core Collection and then analyzed using the open-source Bibliometrix R package and Citespace. The analysis encompassed 410 publications published from 1999 to 2023. There is a sustained increase in the number of publications within the field. Utilizing citation analysis and keyword analysis, the study identified key research focuses. Burst keyword analysis identified 19 keywords. The period from 1999 to 2023 has witnessed significant research attention on the biomechanics of scoliosis. The demographic shift towards an aging population has recently increased interest in ASD. Proximal biomechanical changes and transitional zones in PJK and PJF are hotspots in research, offering emerging scholars in this discipline valuable opportunities for exploration.

Deep mantle plumes feeding periodic alignments of asthenospheric fingers beneath the central and southern Atlantic Ocean

High-resolution full waveform seismic tomography of the Earth's mantle beneath the south and central Atlantic Ocean brings into focus a series of asthenospheric low shear velocity channels, or "fingers" on both sides of the southern and central mid-Atlantic ridge (MAR), elongated in the direction of absolute plate motion with a spacing of [Formula: see text]1,800 to 2,000 km, and associated with bands of shallower residual seafloor depth anomalies that suggest channeled flow over thousands of kilometers. Each of the three most clearly resolved fingers on the African side of the MAR corresponds to a separate group of whole mantle plumes rooted in distinct patches at the core-mantle boundary, feeding hotspots, and volcanic lines with distinct isotopic signatures. Plumes of a given group appear to merge at the top of the lower mantle before separating again, suggesting interaction of deep mantle flow with a more vigorous mesoscale circulation in the upper mantle. The corresponding hotspots are generally offset from the location of the deep mantle plume roots. The distinct isotopic signatures of these hotspot groups are also detected in the mid-ocean ridge basalts at the location where the fingers meet the ridge. Meanwhile, at least some of the variability within each plume group could originate in the upper mantle and extended transition zone where plumes in a given group appear to merge and pond. This study also adds to mounting evidence that the African large low shear velocity province is not a uniform, unbroken pile of dense material rising high above the core-mantle boundary, but rather a collection of mantle plumes rooted in patches of distinct composition.

MINERALOGICAL, PETROGRAPHIC, AND LITHOCHEMICAL FEATURES OF THE UPPER JURASSIC–LOWER CRETACEOUS SECTION OF THE NORDVIK PENINSULA (NORTH OF EASTERN SIBERIA)

Some intervals of the Jurassic–Cretaceous strata of the Anabar-Lena sedimentary basin have a certain oil and gas production potential, which can be realized in the synchronous offshore horizons of the adjacent territories of the Arctic shelf. Among the most representative objects in this regard are the outcrops of Upper Jurassic and Lower Cretaceous formations of the Nordvik Peninsula. The main data on the composition and structure of this section were obtained mainly at the beginning of the second half of last century. The results of complex mineralogical, petrographic, and lithochemical studies of the Urdyuk-Khaya and Paksa formations of Cape Urdyuk-Khaya of the Nordvik Peninsula presented in here enabled us to identify 10 boundaries for changing of sedimentation regimes of the paleobasin. It was found that the Urdyuk-Khaya Formation was formed mainly in the conditions of the shelf transition zone (moderate deep water) with low rates of terrigenous material intake, some depletion of oxygen in bottom waters, and a trend towards an increase in the depths of the basin. The basal stratum of the Paksa Formation was formed in offshore conditions with periodically occurring dioxic conditions in bottom waters and extremely low rates of terrigenous material intake. The overlying part of the formation was formed in various parts of offshore transition conditions with a gradual decrease in the depths of the basin, an increase in the oxygen content in the bottom layer of water, and the rate of terrigenous material intake. The main provenance area was igneous rocks of mafic, possibly intermediate composition. There was some influence of felsic igneous rocks, or ancient sedimentary rocks rich in quartz. The parent strata were subjected to moderate and severe chemical weathering, in a warm humid climate. The revealed features of the studied strata are similar to the characteristics of the same-age sediments of the lower reaches of the Anabar River, which determines their high correlation potential and allows us to judge the evolution of the western part of the Anabar-Lena basin.

Latitudinal patterns in ocean C:N:P reflect phytoplankton acclimation and macromolecular composition

The proportions of carbon (C), nitrogen (N), and phosphorus (P) in surface ocean particulate matter deviate greatly from the canonical Redfield Ratio (C:N:P = 106:16:1) in space and time with significant implications for global carbon storage as this matter reaches the deep ocean. Recent work has revealed clear latitudinal patterns in C:N:P, yet the relative importance of ecological, physiological, or biochemical processes in creating these patterns is unclear. We present high-resolution, concurrent measurements of particulate C:N:P, macromolecular composition, environmental conditions, and plankton community composition from a transect spanning a subtropical-subpolar boundary, the North Pacific Transition Zone. We find that the summed contribution of macromolecules to particulate C, N, and P is consistent with, and provides interpretation for, particulate C:N:P patterns. A decline in particulate C:N from the subtropical to subpolar North Pacific largely reflects an increase in the relative contribution of protein compared to carbohydrate and lipid, whereas variation in C:P and N:P correspond to shifts in protein relative to polyphosphate, DNA, and RNA. Possible causes for the corresponding trends in C:N and macromolecular composition include physiological responses and changes in community structure of phytoplankton, which represented approximately 1/3rd of particulate C across the transect. Comparison with culture experiments and an allocation-based model of phytoplankton macromolecular composition suggest that physiological acclimation to changing nutrient supply is the most likely explanation for the latitudinal trend in C:N, offering both a mechanistic interpretation and biochemical basis for large-scale patterns in C:N:P.

The emerging middle ground: A case study of vernacular Hakka settlements in the peri-urban areas of southern China through an architectural heritage analysis

Rapid urban expansion is transforming rural areas globally, prompting scholars to challenge the traditional urban-rural dichotomy and focus on transitional zones such as the rural-urban fringe and peri-urban areas. This article documents the evolution of architectural morphology in traditional Hakka settlements in peri-urban areas of southern China and coins the hybrid architectural landscape combined with urban and rural characteristics in these ambiguous territories as the “Middle Ground.” Fieldwork was conducted in four Hakka villages in Heyuan, northeast Guangdong, China, between 2021 and 2023. An explorative case study was employed to analyze the architectural morphology of the Middle Ground by mapping village fabric, dwellings, and street markets through aerial photography. A participatory perspective was also incorporated, involving observation, interviews, and documentation of the daily life of local villagers. This research examines how authority and mobility have shaped the Middle Ground, potentially leading to a state of “placelessness,” and explores the role of rural heritage in this context. This research contributes to the broader discourse on peri-urban areas by offering an architectural heritage atlas as an addition to existing research.

Past and future impacts of marine heatwaves on small-scale fisheries in Baja California, Mexico

Marine heatwaves are globally occurring events that can negatively impact fisheries, but their impacts on small-scale operations remain understudied. We investigate the historical and future impacts of marine heatwaves on small-scale fisheries operating along a biogeographic transition zone in the Baja California Peninsula, Mexico. We estimate the impacts of the most intense marine heatwave regime on record on fisheries production of 43 economic units operating in a system of 55 Territorial Use-Rights for Fisheries. During this regime, aggregate landings in the lobster, sea urchin, and sea cucumber fisheries decreased between 15 and 58%. Most operations (56%) presented large reductions in landings, whose losses more than outweigh the small increase detected for the other 44%. Notably, impacts were larger for fisheries operating near an equatorward biogeographic break, and for operations in areas of high historical environmental variation and low historical variation in fisheries production. Climate models predict an increase in the frequency and intensity of exposure to marine heatwaves for all fisheries, but the change in frequency and intensity will be greater for those in the north. In the face of extreme environmental shocks such as marine heatwaves, small-scale fisheries operating near biogeographic transition zones are among the most vulnerable.

Detecting Clinically Significant Prostate Cancer in PI-RADS 3 Lesions Using T2w-Derived Radiomics Feature Maps in 3T Prostate MRI

Prostate Imaging Reporting and Data System version 2.1 (PI-RADS) category 3 lesions are a challenge in the clinical workflow. A better detection of the infrequently occurring clinically significant prostate cancer (csPCa) in PI-RADS 3 lesions is an important objective. The purpose of this study was to evaluate if feature maps calculated from T2-weighted (T2w) 3 Tesla (3T) MRI can help detect csPCa in PI-RADS category 3 lesions. In-house biparametric 3T prostate MRI examinations acquired between January 2019 and June 2023 because of elevated prostate-specific antigen (PSA) levels were retrospectively screened. Inclusion criteria were a PI-RADS 3 lesion and available results of an ultrasound-guided targeted and systematic biopsy. Exclusion criteria were a simultaneous PI-RADS category 4 or 5 lesion and hip replacement. Target lesions with the International Society of Urological Pathology (ISUP) grade group 1 were rated clinically insignificant PCa (ciPCa) and ≥2 csPCa. This resulted in 52 patients being included in the final analysis, of whom 11 (21.1%), 8 (15.4%), and 33 (63.5%) patients had csPCa, ciPCa, and no PCa, respectively, with the latter two groups being combined as non-csPCa. Eight of the csPCas were located in the peripheral zone (PZ) and three in the transition zone (TZ). In the non-csPCa group, 29 were located in the PZ and 12 in the TZ. Target lesions were marked with volumes of interest (VOIs) on axial T2w images. Axial T2w images were then converted to 93 feature maps. VOIs were copied into the maps, and feature quantity was retrieved directly. Features were tested for significant differences with the Mann–Whitney U-test. Univariate models for single feature performance and bivariate models implementing PSA density (PSAD) were calculated. Ten map-derived features differed significantly between the csPCa and non-csPCa groups (AUCs: 0.70–0.84). The diagnostic performance for TZ lesions (AUC: 0.83–1.00) was superior to PZ lesions (AUC: 0.74–0.85). In the bivariate models, performance in the PZ improved with AUCs >0.90 throughout. Parametric feature maps alone and as bivariate models with PSAD can (?) noninvasively identify csPCa in PI-RADS 3 lesions and could serve as a quantitative tool reducing ambiguity in PI-RADS 3 lesions.

Slow-fast dynamics in non-linear enzyme cascades gives rise to spatial multiscaling.

Slow-fast dynamics in a well-mixed biological system is known to be associated with functional modularity with temporal hierarchy of processes. Yet, the significance of slow-fast dynamics in spatially distributed reaction-diffusion systems remains to be clarified.We assessed such systems with slow-fast dynamics, such as blood coagulation and predator-prey models to identify spatial patterns with independent parametric regulation, and performed their reaction-rate based sensitivity analysis with the help of computational one-dimensional reaction-diffusion models.In blood coagulation, spatial distribution of fibrin had two scales: a larger region with a high and almost constant fibrin concentration (corresponding to solid blood clot) and a narrow transition zone, where fibrin concentration decayed to zero (semi-liquid clot). Slow variables (e.g., the concentration of the coagulation factor IXa) regulated the clot size (large scale), while fast variables (e.g., concentrations of thrombin and factor Xa) regulated the thickness of the gel-to-liquid transition zone (small scale). Analysis of the simplified model of blood coagulation, composed only of factor X and IX activation, and of the predator-prey model confirmed this finding to be sufficiently general, and revealed that the limitation of fast enzyme production (due to precursor depletion or to kinetics with saturation) was crucial for this multi-scaling. Independent regulation of spatial scales also required species with slow kinetics to be upstream from species with fast kinetics.The shared slow-fast dynamics of the examined systems endow them with the ability to form spatial patterns, representing a new mechanism complementing the Turing-type and the Positional Information type pattern formation.

Development of a horizontal seepage test system of constructed wetland and research on the seepage characteristics based on micro-pollution water

Horizontal subsurface flow constructed wetlands (HSFCW) were widely used as an effective biotechnology for wastewater treatment. However, clogging of the substrate bed was a key factor restricting its application. In this study, a horizontal seepage test system was independently developed, which was used to reveal the development trends of hydraulic resistance in HSFCW, as well as changes in permeability coefficients with time. The relationship between the average permeability coefficient and purification effect was further analyzed. The results showed that the new test system has proved the law of resistance development in HSFCW. The distribution characteristics of the isobaric surface indicate that the blockage of the HSFCW gradually spreads from the lower part to the lower part. The seepage resistance of homogeneous subbed in HSFCW was mainly concentrated in the front end. The growth rate of hydraulic loss in the core zone ranged from 0.685 to 19.515 cm·month−1, the growth rate in the transition zone ranged from 0.223 to 0.695 cm·month−1, and little change occurred in the safety zone. At the end of the HSFCW operation, the widths of the core, transition, and safety zones account for approximately 20–30 %, 50–70 %, and 10–20 % of the entire wetland length, respectively. Meanwhile, the SS removal rate stabilized at over 92 %, when the average permeability coefficient reached 41.45 m·d−1. The removal rate of COD and TN was higher when the average permeability coefficient is between 59.45 and 41.45 m·d−1 and 27.08–59.45 m·d−1, respectively. This study provided a horizontal testing method to accurately understand the changes in the seepage field in HSFCW.

Rice husk ash and recycled sand as synergistic substitutes in ultra-high performance concrete: Microstructural, mechanical performance, and eco-economic analysis

Quartz sand and silica fume (SF), commonly used in UHPC production, are costly and contribute to dust pollution and significant carbon emissions. In this work, we explored the preparation of an environmentally friendly ultra-high performance concrete (e-UHPC) by substituting SF and quartz sand with rice husk ash (RHA) in ratios of 10 %, 20 %, and 30 %, and recycled building sand (RS) in ratios of 25 %, 50 %, and 75 %. We assessed the impact of these substitutions on workability, mechanical strength, hydration products, and the micromechanical characteristics of the interfacial transition zone. In addition, an environmental and economic assessment index for e-UHPC was introduced. Results showed that while RHA and RS reduced the flowability of e-UHPC, RHA helped mitigate the compressive strength loss due to RS (3.9 %-9.7 %). RHA accelerated early hydration, and improved densification in the transition zone, enhancing late hydration and refining the pore structure of e-UHPC. Notably, a 10 % RHA replacement rate optimally improved early hydration efficiency and minimized CH content. The combination of 10 % RHA and 25 % RS proved most effective in optimizing the interfacial transition zone and improving the pore structure of e-UHPC. Importantly, e-UHPC reduces the carbon footprint at a lower cost and offers significant environmental and economic advantages over traditional UHPC. The results of this study will promote the incorporation of construction and agricultural wastes into concrete.

Comparison of methods measuring electrical conductivity in coastal aquifers

Coastal aquifers, the transition zone between freshwater and saltwater, show large salinity contrasts in the subsurface. Salinity is a key parameter to understand coastal groundwater flow dynamics and consequently also geochemical and microbial processes. For mapping porewater salinity, a variety of methods exists, mainly using electrical conductivity as a proxy. We investigate methods including hydrological/geochemical (well sampling, fluid logger) as well as geophysical method (direct push, geoelectrics) utilising measurements near the high-water line of a high-energy beach at the North Sea island of Spiekeroog. We compare the methods, discuss their benefits and limitations and assess their spatial and temporal resolution. One key to enable a comparison is the estimation of formation factors transforming bulk conductivity measured by geophysical tools in to fluid conductivities obtained from direct measurements. We derive depth-dependent formation factors derived from time-series measurements of fluid loggers and a vertical electrode installation. Using these formation factors, the vertical electrode chain proves to provide reliable salinities at high spatial and temporal dimension. Direct-push profiling data provide the highest vertical resolution. However, a careful calibration is needed to allow for salinity quantification. On the other hand, electrical resistivity tomography (ERT) exhibits the lowest spatial resolution, but can image two-dimensional salinity distributions. We found ERT to fit very well to all other methods, but the data analysis should be aimed at salinities instead of bulk conductivities, i.e. including formation factors and temperature models into the inversion process.

Assessing spatiotemporal variations of soil organic carbon and its vulnerability to climate change: a bottom-up machine learning approach

Soil organic carbon (SOC) is a crucial component of the terrestrial carbon cycle and essential for agricultural productivity. Quantifying its sensitivity to future climate change is vital for sustaining agricultural practices and mitigating greenhouse gas emissions. However, this remains a challenge as long-term SOC data are scarce and substantial uncertainties regarding future climate scenarios. This study presents a bottom-up machine learning framework to assess the spatiotemporal variations of SOC and its vulnerability to climate change in the Jinghe River Basin, a typical loess hilly and gully watershed. Firstly, the long-term (2000-2023) dynamics of SOC was estimated by integrating in-situ measurements with machine learning techniques. Results show that the high SOC values are primarily distributed in the farmland of the mountain-loess transition zone, while the low-value areas are mainly found in the loess region. During the study period, the SOC content exhibited a slight increasing trend with a rate of 0.02 g kg⁻1 yr⁻1 (p = 0.449). The vulnerability of farmland surface SOC to future climate change was then evaluated by combining a robust machine learning model with the bottom-up framework. To this end, the study explored a wide range of possible future climates to identify critical climate thresholds and their spatial variation across the basin’s farmlands. Based on this analysis, this research found that the farmland in the northern basin is generally more susceptible to changing climate with even marginal rises in temperature could lead to severe loss in SOC. These results highlight the need for proactive climate adaptation strategies to safeguard SOC in vulnerable agricultural landscapes, ensuring soil health and resilience in the face of climate change.

Numerical analysis of failure mechanics of concrete under true dynamic triaxial loading using a four-phase meso-model

In the present paper, the failure mechanics of concrete under true triaxial dynamic loading is investigated. A four-phase concrete meso-model is developed. The meso-model consists of aggregate, mortar, interfacial transition zone (ITZ) and macropores. A finite element (FE) model of a split Hopkinson pressure bar is also created to apply true triaxial dynamic loading. The development of cracks in concrete is presented for the uniaxial, biaxial and triaxial loading cases. The presence of local discontinuity is modelled, and its effect on the failure of concrete is extensively investigated and discussed. In the last, the effect of aggregate distribution is also analysed. It is found that the internal structure of concrete changes the stress distribution from true triaxial to compression or extension triaxial, which is the prime cause of internal cracking.

Long term properties of Nano-engineered temperature self-controlled concrete served for mass concrete structure

Due to the advantages of low-cost and superior electrical conductivity, Nano-carbon black (NCB) can endow hydraulic concrete with long-term and stable self-heating capacities at affordable costs, thus allowing active and intelligent temperature control for high-altitude and high-latitude dams. This study, for the first time, investigated the long-term mechanical behaviors, freeze-thaw resistance and impermeability of temperature self-controlled concrete (TSC). Moreover, the modification mechanisms of TSC were revealed with the help of mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Finally, the long-term performance and cost assessment of TSC are comprehensively evaluated by the entropy weight method. The results indicate that the incorporation of 4.5wt% NCB improves the compressive and splitting tensile strengths of TSC at 180 days by 17.4% and 7.9%, respectively, and shows an excellent response against impermeability and a slightly lower response against frost resistance. Besides, NCB accelerates the hydration degree and repairs the interfacial transition zone of TSC. The presence of NCB densifies the microstructures of the matrix and reduces the content of harmful pores by nearly 50%. Finally, TSC with 4.5wt% NCB is the optimal mixture that shows excellent comprehensive performances.

Shear tests and meso-scale simulation of cold joint structures in rock-filled concrete: Considering the mutual contact effects between component materials

To realistically reflect the shear performance of the rock-filled concrete (RFC) between layers, this study relies on an RFC dam project in Guizhou Province. Test blocks, measuring 5 m × 4 m × 2 m with cold joints, were cast on site and subjected to shear tests. Additionally, a three-dimensional four-phase meso-model was developed, considering the mutual contact effects between component materials. The mechanical response and damage mechanism of the interlayer were analyzed using the cohesive zone model. The results confirm that the cohesive zone model effectively simulates interlayer cold joint structures. The damage modes of the RFC interlayer include cold joint debonding damage (Mode I) and plastic extrusion damage of self-compacting concrete (Mode II). As the exposed height of the rocks increases, the damage mode shifts from Mode I to Mode II, and higher normal stresses intensify Mode II damage. Meanwhile, the paths of crack extension depend on the distribution of shear-resistant rocks, with weak interfacial transition zones serving as “bridges’’ for crack propagation. The interlayer shear strength is positively correlated with the average exposed height of rocks and normal stresses, with the former having a more significant impact. Finally, the accuracy of the proposed shear strength prediction model for the RFC interlayer was validated by comparing it with results from other studies, providing useful references for meso-numerical modeling of RFC.