Structure Of Transition Zone Research Articles

Performance Research and Engineering Application of Fiber-Reinforced Lightweight Aggregate Concrete.

Low strength and low impact toughness are two of the main issues affecting the use of lightweight aggregate concrete in harsh cold environments. In this study, the strength of concrete was improved by adding high-strength fibers to bear tensile stress and organize crack propagation. Four sets of comparative experiments were designed with freeze-thaw cycles of 0, 50, 100, and 150 to study the mechanical properties of fiber-reinforced lightweight aggregate concrete under freeze-thaw conditions. A detailed study was conducted on the effects of freeze-thaw on the compressive strength, flexural strength, impact toughness, and microstructure of concrete with different fiber contents (3, 6, and 9 kg/m3). The results show that for ordinary lightweight aggregate concrete, under the freeze-thaw cycle, the internal pore water of the concrete froze and generated expansion stress, resulting in tensile cracks inside the concrete. The cracks gradually accumulated and expanded, ultimately leading to cracking and damage of concrete structures. After 150 cycles, the strength loss rate exceeded 25%. When adding a reasonable amount of fiber (6 kg/m3), the fiber took on the tensile stress and hindered the development of internal cracks, significantly enhancing the splitting tensile strength, flexural strength, and impact toughness of lightweight aggregate concrete. And the failure pattern of concrete was significantly improved. At the beginning of the freeze-thaw cycle, the internal tensile stress was less than the fiber tensile strength and the fiber-matrix bonding strength, and the strength reduction rate of the concrete was slow. Relying on the friction absorption capacity between the fiber and the matrix, the fiber used its own deformation to resist the tensile stress. In the late stage of the freeze-thaw cycle, due to the destruction of the fiber-matrix transition zone structure, the bond strength decreased, the crack resistance and toughening effect decreased, and the strength of the concrete decreased rapidly. Moreover, the reduction in impact toughness was greater than the compressive strength and flexural strength under static load.

The potential of solid waste as a viable replacement for quartz sand in the ultra-high performance concrete: a comprehensive review

ABSTRACT Ultra-high performance concrete (UHPC) is renowned for its dense structure and exceptional mechanical properties, including durability. However, its widespread adoption is hindered by the high costs of essential fine aggregates like quartz sand and the associated environmental impact. Additionally, using industrial solid waste raises pollution concerns, contradicting global sustainability goals. Numerous studies have shown that it is feasible to produce eco-friendly UHPC with excellent performance by solid waste. This comprehensive review thoroughly investigates the workability, mechanical properties (including compressive strength, flexural strength and tensile strength), microstructure (encompassing pore structure and interfacial transition zone) and durability of UHPC incorporating solid waste in its production. The paper emphasizes the critical influence of factors, such as the solid waste substitution rate and the physical and chemical properties of solid waste. The paper also outlines the current application of UHPC with solid waste in pavement engineering and highlights the urgent need to address challenges such as high production costs, the lack of design standards and construction technique deficiencies, thereby emphasising the urgency surrounding the design and advancement of solid waste-incorporated UHPC in pavement engineering as it can reduce the environmental impact of traditional UHPC and improve the efficient use of solid waste.

Physical properties of cement composite with monoethanolamine

This study analyzed the fluidity, air content, flexural strength, compressive strength and carbon dioxide adsorption performance of cement, furnace slag and fly ash-based cement composite using appropriate substitution values of MEA derived from preliminary experiments. Fluidity and air content were found to increase as the fly ash substitution rate increases. It is believed that the increases are due to the fly ash ball bearing effect in combination with the creation of micropores by MEA. The compressive strength was found to decrease with lower furnace slag substitution ratios. This is believed to have resulted because the Pozzolanic reaction of the fly ash plays a more dominant role in determining the compressive strength than does the latent hydraulic activity of furnace slag as the furnace slag substitution rate is decreased. It is determined that the compressive strength was reduced because the Pozzolanic reaction reduces the density of the texture and pore structure of the interfacial transition zone. Carbon dioxide values increase as the furnace slag substitution rate was increased.

RETRACTION: Structural Characteristics and Development Model of Fluid Diapirs Within the Structural Transition Zone, Northern South China Sea

RETRACTION: Y. Qin, C. Liu, G. Peng, L. Huang, C. Liang, H. Li, Z. Wu and L. Yang, “,” Geological Journal 59, no. (2024): 1906–1923, https://doi.org/10.1002/gj.4968. The above article, published online on 28 April 2024 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the authors; the journal Editor‐in‐Chief, Ian D. Somerville and Yunpeng Dong; and John Wiley & Sons Ltd. The retraction has been agreed as some of the data included within the article was not authorized for publication. Furthermore, the authors are not confident that the fluid diapir labels shown in figure 7 are correct and admit they may be problematic. As a result the editors have decided to retract this article.

Effect of hybrid lead-PVA fibers on microstructure and radiation shielding properties of high-performance concrete

With the widespread application of nuclear technology in the medical and energy fields, the demand for efficient radiation shielding materials is increasing. Employing only lead or polyvinyl alcohol (PVA) fiber reinforcement cannot achieve improvements in the brittleness of high-performance concrete (HPC) while also enhancing radiation shielding efficiency and mechanical properties. This study develops a novel HPC for radiation attenuation, incorporating magnetite as the aggregate and reinforced with hybrid lead-PVA fibers (RSHPC). The synergistic effects of various proportions of hybrid lead-PVA fibers on the mechanical properties, three-dimensional microstructure, pore structure, and interfacial transition zone (ITZ) were investigated. In addition, the radiation attenuation capacities of RSHPC with different hybrid lead-PVA fiber proportions were evaluated through experimental and simulation analysis. The results show that hybrid lead-PVA fibers notably improve the air-void structure of RSHPC. The incorporation of PVA fibers, by improving the ITZ of matrix, effectively mitigates the negative impact of lead fibers on mechanical performance. The refinement of pore structure and the introduction of light and heavy nuclides lead to a significant enhancement in the gamma-ray and neutron radiation attenuation capabilities of RSHPC. Utilizing X-ray computed tomography (X-CT) for three-dimensional reconstruction further indicates the optimization impact of hybrid lead-PVA fibers on the microstructure, notably in the improvement of pore distribution and fiber dispersion, thus enhancing the overall properties and radiation attenuation performance of RSHPC.

Is the mantle transition zone uniform beneath Precambrian shields?

In the present study, we examine the mantle transition zone (MTZ) structure below the prominent Precambrian shields on the Earth to understand its thermal and compositional properties and depth distribution of MTZ discontinuities. For this study, we used data from Canadian, Brazilian, Baltic, African and Australian Shields. We migrate the receiver functions to the depth domain using 3D tomographic models to examine the topography of MTZ discontinuities that define the upper and lower boundaries of the MTZ. The depth migration results were obtained using two different 3D tomographic velocity models, LLNL_G3D_JPS and GyPSuM. The analysis shows that both models yield similar results. The findings indicate a thinner than usual MTZ beneath all the Precambrian shields with an average thickness of ∼238 ± 8 km. Notably, the present study reveals the upper boundary of the MTZ (410 km discontinuity) displays distinctive topography; in contrast, the lower boundary of the MTZ (660 km discontinuity) is situated at shallower depths. Therefore, the main factor causing the variation in MTZ thickness is the shallowing of the 660 km discontinuity, indicating that the post-spinel transition occurred at higher temperatures with a negative Clapeyron slope, supporting the theory of whole-mantle convection. This suggests that mantle plumes have some appreciable impact on the MTZ beneath Precambrian shields, which are limited to the base of the MTZ. Alternatively, the global mantle warming explanation could be invoked, as it best explains the similar characteristics of the 660 km discontinuity beneath the Precambrian shields. However, this phenomenon needs to be tested through numerical modelling.

Transition Zone Structure in the Fast-Cutting Surfaced Layer – Substrate System

Transition Zone Structure in the Fast-Cutting Surfaced Layer – Substrate System

Global variability of the composition and temperature at the 410-km discontinuity from receiver function analysis of dense arrays

Seismic boundaries caused by phase transitions between olivine polymorphs in Earth's mantle provide thermal and compositional markers that inform mantle dynamics. Seismic studies of the mantle transition zone often use either global averaging with sparse arrays or regional sampling from a single dense array. The intermediate approach of this study utilizes many densely spaced seismic arrays distributed around the globe. We systematically compute teleseismic P-to-S receiver functions for each seismic array and invert for the 1-D seismic velocity structure of the mantle transition zone beneath each array to facilitate a comparison between densely sampled regions. We stack 3,600 receiver functions on average at 67 arrays in total. The stack is used in a probabilistic inversion to estimate the mantle transition zone interface depths and velocities beneath each array. We focus on the 410-km discontinuity (410) because it is a prominent seismic interface that is clearly linked to a single mineral phase transition between olivine and wadsleyite. The depths and velocity contrasts of the 410 are mapped to temperatures and compositions using mineral physics constraints. The depth of the 410 ranges from ∼405–440 km, which is consistent with a ∼360 K temperature range in a dry mantle and a ∼260 K temperature range in a wet mantle (2 wt. % water). The Vs contrast across the 410 ranges from ∼2.5–8 %, which is consistent with ∼20–70 vol. % olivine composition in a dry mantle and ∼25–80 vol. % in a wet mantle. The bulk composition of the upper mantle near the 410-km discontinuity is typically considered to be well-mixed because there is no thermodynamic impediment to convection at the olivine to wadsleyite phase transition. However, the wide range of inferred olivine content from our study suggests that there are large lateral variations in the bulk composition of the upper mantle near the 410-km discontinuity.

Utilization of recycled fine aggregate in ultra-high performance concrete: Mechanical strength, microstructure and environment impacts

Recycled aggregate derived from construction and demolition (C&D) waste offers new opportunities for the construction industry due to the shortage of natural aggregate. This study presents the feasibility of utilizing recycled fine aggregate (RFA) in ultra-high performance concrete (UHPC) to alleviate autogenous shrinkage, mitigate environmental effects, and further improve mechanical strengths. Three types of RFA with different particle sizes (0–0.6 mm, 0.6–1.18 mm, and 1.18–2.36 mm) are pre-saturated and then used as substitutes for quartz sand in UHPC. The influences of pre-saturated RFA on the workability, internal relative humidity, autogenous shrinkage, compressive strength, resistance to chloride ion penetration, and microstructure of UHPC are investigated. Experimental results showed that, compared to the plain UHPC, incorporation of 20 % RFA with particle size of 1.18–2.36 mm provides efficient internal curing, maintaining a higher internal relative humidity, and thus reducing autogenous shrinkage by 78.5 % at the age of 7 days. The compressive strengths of the UHPC containing 20 % RFA with particle size of 1.18–2.36 mm shows 7.1 % increase at the ages of 28 days. While it has a negligible effect on the fluidity and resistance to chloride penetration. The underlying mechanisms for the enhancement of properties involve the improved hydration degree of UHPC due to internal curing, which optimizes the structure of the interface transition zone and reduces the number of large pores. Furthermore, the sustainability analysis indicated that the use of RFA in UHPC exhibits 7.0 % lower carbon emissions and 7.8 % lower energy consumption, respectively. This study successfully proposes an effective approach for mitigating the autogenous shrinkage of UHPC without sacrificing strengths.

The Mantle Transition Zone Structure Beneath the Pamir Plateau and Western Tian Shan and Adjacent Regions

The Mantle Transition Zone Structure Beneath the Pamir Plateau and Western Tian Shan and Adjacent Regions

Recycled glass concrete with cementitious materials: Study of mechanical prediction model and dry shrinkage mechanism

Recycled Glass Concrete (RGC) exhibits low mechanical strength due to the loose structure of its interfacial transition zone. Adding supplementary cementitious materials is an effective approach to address the issues of low mechanical performance and durability in RGC. In order to improve the performance of recycled glass concrete, three series of tests were prepared for mechanical testing, drying shrinkage testing and microstructure analysis: single-doped limestone powder (RGC-L), single-doped metakaolin (RGC-M), and limestone-metakaolin mix (RGC-LM). The mechanical results demonstrate that RGC, with the addition of 5 % limestone powder and 5 % metakaolin, exhibits optimal strength improvement. Specifically, compressive strength increased by 23.3 %, splitting tensile strength by 38.1 %, and flexural strength by 7.3 %. Additionally, a mechanical prediction model for RGC was proposed, yielding relational equations for splitting tensile strength (ft), flexural strength (fr), and compressive strength (fc): ft=0.14fc0.93,fr=0.72fc0.56. The drying shrinkage results indicate that RGC containing 10 % limestone powder and 20 % metakaolin exhibits the best performance, with a 32.5 % reduction in shrinkage rate. Microstructural analysis revealed that the reaction between Al₂O₃ in metakaolin and limestone powder produces CO₃-AFm, which results in a denser structure in the interfacial transition zone of the recycled glass concrete. Ultimately, this study elucidates the micro-mechanisms and drying shrinkage mechanisms of limestone powder and metakaolin in RGC, offering a promising approach for the effective utilization of construction waste.

The Influence of Slag Content on the Structure and Properties of the Interfacial Transition Zone of Ceramisite Lightweight Aggregate Concrete.

Ceramisite lightweight concrete has excellent performance and relatively light self-weight characteristics. At the same time, the recent development of green high-performance concrete and prefabricated components has also brought the abundant utilization of these mineral mixture. An interfacial transition zone exists between the hardened cement paste and the aggregate, which is the weakest part of the concrete, characterized by high porosity and low strength. In order to study the effect of slag content on the interfacial transition zone in lightweight high-strength concrete, experiments were designed to replace cement with slag at different contents (0%, 5%, 10%, 15%). A series of studies was conducted on its macro-strength, microstructure, and composition. The results indicated that the addition of slag improved the porosity and width of the interfacial transition zone. Adding slag did not reduce the thickness of the concrete interfacial transition zone significantly at 3 d, but it led to significant improvement in the thickness of the interfacial transition zone at 28 d, and the thickness of the interfacial zone at 28 d was reduced from 19 μm to 8.5 μm, a reduction of 55%. The minimum value of microhardness in the slurry region of the interfacial specimens also increased from 19 MPa to 26 MPa, an increase of 36%. In addition, the structural density of the interfacial region was further increased, resulting in varying degrees of improvement in the macroscopic anti-splitting strength. One of the important reasons for this phenomenon is that the addition of slag optimizes the chemical composition of the interface and promotes the continuation of the pozzolanic reactivity, which further enhances the hydration at the interface edge.

A bibliometric review on research progress, interest evolution and future trend in the field of recycled concrete by using CiteSpace (2004–2023)

The popularization of recycled concrete (RC) is an important way to achieve efficient resource utilization of construction solid waste (CSW), which can coordinate the sustainable economic development with environmental protection. In this paper, CiteSpace software is used to quantitatively analyze the literatures on RC field, identifying its research hotspots and recent developments. Based on the Web of Science database, we screened published literatures in the field of RC from 2004 to 2023, and obtained 2011 articles. CiteSpace software and knowledge graph technology are adopted to visually analyze the literature information, including the collaborators, keywords and citation status. The results show that, Xiao JZ from Tongji University, Poon CS from Hong Kong Polytechnic University and Tam VWY from University of Western Sydney publish a large number of articles and are frequently cited. It indicates that their researches are widely recognized in academic circles. There is a research team with a large size formed in the Chinese mainland, and the core members include Xiao JZ, Li WG, Chen ZP. At present, the research interest gradually shifts from recycled coarse aggregate to recycled fine aggregate, mainly focusing on microscale research of pore structure and interfacial transition zone. In addition, 8 co-citation clusters of selected references and the potential development trends are detailly analyzed. This study is helpful for researchers to fully understand the current hotspots and future research trends in the field of RC.

RETRACTED: Structural characteristics and development model of fluid diapirs within the structural transition zone, northern South China Sea

Fluid diapirs are widespread in the northern South China Sea (SCS), are significant indicators of the existence and distribution of hydrocarbons and natural gas hydrates and are of great petroleum geological significance. Based on high‐precision 3D seismic and drilling data, this paper analyses the tectonic features and genetic mechanism of a fluid diapir zone in the northern SCS and a development model of fluid diapirs is proposed herein. Studies have revealed that the northern SCS large‐scale fluid diapir zone is located within a concealed structural transition zone, which is consistent with the spatial distribution location and direction of a concealed structural transition zone and that the formation of a fluid diapir zone is strongly influenced by the structural transition zone. Fluid diapirs are large continuously spreading bright reflection zones in shallow surface layers and are downwards converging high‐variance ribbons in middle and shallow layers, all of which are spreading in a NW–NNW orientation on the plane. The profile shows a conical or mushroom‐shaped shape that converges from shallow to deep, with a height of approximately 7 km and is characterized by a compound gas chimney fuzzy zone. The main body of the concealed structural transition zone is a slope structure and is flanked by large‐scale NW–NNW‐oriented fault systems. Minor en echelon spreading NW–NNW‐oriented faults and fractures are developed within the structural transition zone and are soft linkages that match well with the distribution direction and location of the fluid diapirs. On the profile, the overall display is a composite flower‐like structure dispersed from deep to shallow, which belongs to a large strike‐slip fault zone with a tectonic transformation effect. A comprehensive analysis suggests that the formation and development of the structural transition zone are mainly controlled by pre‐existing structures in the basement and that minor faults, fractures and slope zones within the structural transition zone serve as dominant pathways for the migration of deep overpressure fluids and gas hydrates. Consequently, the concealed structural transition zone provides favourable conditions for fluid diapirs to develop. Moreover, the stratigraphic overpressure systems mainly caused by gas generation provided the main driving force for the formation of fluid diapirs. Obviously, the development location, distribution direction, formation and evolution of the northern SCS fluid diapirs are jointly controlled by internal minor faults and fractures of the Eocene‐Miocene structural transition zone and the overpressure of the rifting period after the Pliocene. The main development period of the northern SCS large‐scale fluid diapirs was the second phase of the Dongsha Movement. During the exploration of gas hydrates and hydrocarbons in the Pearl River Mouth Basin, it is essential to consider the mutually restricting relationships between fluid diapir structures and gas hydrates and hydrocarbons.

A Tilted Broad Plume Underneath the Greenland Cratonic Keels

AbstractTo advance our comprehension of the complex geological history and mantle dynamics in the North Atlantic region, we employ all available broadband seismic data recorded in Greenland to reveal an abnormal mantle transition zone (MTZ) structure. Central and eastern Greenland exhibits depressed 410 and 660 km discontinuities (d410 and d660, respectively) bordering the MTZ, indicative of a substantial thermal anomaly associated with an underlying plume, surpassing the 1,800°C threshold for post‐garnet phase transitions at the d660. Variations in MTZ thickness across Greenland stem from differing temperature anomalies at the d410 and d660, possibly linked to a tilted plume within the MTZ. These findings corroborate geodynamic models, elucidating the interaction between post‐garnet phase transitions and upwelling plumes. The results shed light on the origin of the enigmatic Icelandic hotspot track and its influence on the thermal and lithospheric structures beneath Greenland.

Mechanical properties and discrete element simulation of KH-560 modified polystyrene concrete

Polystyrene foam (EPS) concrete is a composite concrete material commonly used in construction, which has excellent thermal insulation and thermal insulation properties, but also has defects of weak bonding interface.KH-560 can significantly improve the characteristics of EPS particles and concrete matrix, which have different physical and chemical properties and are difficult to combine. In this study, the effects of different levels of KH-560 on the enhanced mechanical properties of EPS concrete were studied from the aspects of macroscopic mechanical properties, microstructure characteristics, chemical composition and discrete element simulation, and the mechanism of action was discussed. The results of mechanical experiments show that the compressive strength and flexural strength of EPS concrete mixed with KH-560 are higher than those of ordinary EPS concrete, and its mechanical properties gradually increase with the increase of KH-560 content. XRD, FT-IR and SEM observations showed that more C-S-H gels would be produced under the action of KH-560, which made the structure of the weak interface transition zone of EPS concrete more compact. The results of discrete element simulation show that the peak strength of EPS concrete increases with the increase of friction coefficient, but has little effect on its elastic modulus.

Effect of negative bias voltage on microstructure and thermal stability of Cu/Nb nano-multilayers deposited by FCVA technique

he deposition energy is a crucial factor in the preparation of nano-metallic multilayers using the physical vapor deposition method. To study the effect of deposition energy on the microstructure and performance of coatings, Cu/Nb nano-multilayers were prepared by the FCVA technique with different negative bias voltages. The surface morphology, composition, and interface structure were investigated by SEM, XRD, and TEM. The results indicated that the increased negative bias voltage leads to compressive stress and the temperature rise effect, which promotes the formation of psedo-diffuse transition zones and the transformation of columnar to equiaxed crystals. In addition, the difference in hardness is used to characterize the structural integrity of the laminate structure of the material after heat treatment. Even after one hour of annealing at 600 °C, the sample retains a highly stable laminate structure when the negative bias voltage is set to -100 V, and its hardness reduces by just 22.3%. The mechanisms of the pseudo-diffuse transition zone and crystal structure on thermal stability were discussed.

Analysis on frost resistance and pore structure of phase change concrete modified by Nano-SiO2 under freeze-thaw cycles

To study the effect of nano-SiO2 on the frost resistance of phase change concrete, and to further explore the deterioration of its internal pore structure under the effect of freeze–thaw cycles, X-ray tomography was applied to the rapid freeze–thaw test for the study of frost resistance, and the pore structure of the modified concrete was reconstructed during the freeze–thaw cycles. By image processing and registration techniques, the change pattern of mesoscopic pore inside the phase change concrete modified by nano-SiO2 and the development and ductility characteristics of the pore structure in the interface transition zone were analyzed. The results showed that the admixture of nano-SiO2 and phase change materials could effectively improve the frost resistance of concrete. Frost resistance life was improved by at least 43 % and up to 71 %. Additionally, nanomaterials could constrain the change of pore structure inside the composite modified concrete and densify the interface transition zone. The ITZ porosity of ordinary concrete increased by 10.58 times after 150 freeze–thaw cycles, while the secondary modified phase change concrete with 10mPCMs/1.5NS only increased by 1.2 times.

Microstructure and chloride transport of aeolian sand concrete under long-term natural immersion

Abstract River sand was consumed in large quantities, and alternatives to river sand were urgently needed. There are a large number of natural resources of aeolian sand in western China. Aeolian sand was prepared into aeolian sand concrete (ASC). It can greatly reduce the consumption of river sand and inhibit the process of desertification to protect the environment. ASC is a new type of concrete material prepared by using aeolian sand as fine aggregate. To clarify the chloride ion transport behaviour in the ASC under long-term natural immersion, the aeolian sand was 100% substituted for the river sand to prepare the full ASC with three water–binder ratios. The ASC was naturally immersed in 3 and 6% NaCl solutions for a long time, and nuclear magnetic resonance and microscopic scanning electron microscopy techniques were used. The change rule of chloride ion content at different depths of the ASC was studied, and its microstructure characteristics under different erosion times were analysed. The results showed that the free chloride ion concentration at different depths of the ASC increased with increasing water–binder ratio, immersion time, and chloride concentration. After soaking in the salt solution, the hydration products in the ASC reacted with chloride ions to form Friedel salt, which filled the internal pores and microcracks of the ASC, improved its interface transition zone structure, and increased the compactness of the test piece. The porosity of the three groups of ASC with different water–binder ratios decreased by 0.95, 1.03, and 1.15% after soaking in 6% salt solution for 12 m. To study the diffusion law of chloride ions in ASC, combined with influencing factors such as temperature, humidity, D value, deterioration effect and chloride ion combination, Fick’s second law was modified, and a chloride ion diffusion model of ASC with high accuracy was established, with a fitting correlation number above 0.93, which provided a reference for the research and application of ASC in saline areas.

Effects of the metal-ceramic continuous transition region on the tensile strength and crack propagation behavior of 8YSZ/CoNiCrAlY coating

In this study, micro-8YSZ/CoNiCrAlY continuous transition coatings and double-layer coatings were prepared by atmospheric plasma spraying (APS) technology. The microhardness of the continuous transition coating changed in a manner consistent with the microstructure, and the average bond strength of the continuous transition coating was 1.40 times higher than that of the double-layer coating, and conducted an in-depth study of the role of the continuous transition zone in the coating stretching process. During the stretching process, not only the ceramic coating breaks, but also the continuous transition zone breaks. In the continuous transition zone, cracks undergo deflection and bridging during initiation and propagation. In addition, the existence of approximately saddle-shaped CoNiCrAlY metal splat was also found. The approximately saddle-shaped metal splat absorbs and dissipates energy by deforming during the stretching process. In summary, the interlocking structure, crack deflection and bridging mechanisms in the continuous transition zone, and the deformation of the approximately saddle-shaped metal splat synergistically improve the bonding strength of the coating.