Strength Of Skeleton Research Articles

Rapid ambient pressure drying preparation of bulk ZrO2-SiO2 aerogels with high thermal stability

In this study, the sol-gel stage co-precursor method was used to hydrophobically modify the gel and increase the content of alkali catalyst in the gel, thereby reducing the capillary force generated during ambient pressure drying and enhancing the strength of the gel skeleton. This improvement makes the gel skeleton structure not easy to destroy during the rapid drying process, thus greatly reducing the preparation time of atmospheric pressure drying, which could be as short as 10 h. It is worth mentioning that this method does not require extensive use of modifiers and organic solvents, so it has low cost, high efficiency, and broad industrial production application prospects. The experimental results show that the DDS/ZSA aerogel exhibits the lowest thermal conductivity (0.035 W m−1 K−1) when the dilute ammonia content is 5 ml. However, it should be noted that too low or too high an amount of dilute ammonia will lead to a decrease in aerogel performance, so it needs to be controlled within the appropriate range. In addition, the prepared aerogel has excellent hydrophobic properties with a contact angle greater than 140° and excellent thermal stability at 1000 °C, which can be used in harsh, humid, and high-temperature environments.

Remediation effectiveness of aging diesel-contaminated soil using thermochemical treatment: Soil microstructure transformation and reusability

This study investigated the microstructure transformation observed in an aging diesel-contaminated soil after thermochemical treatment (DT150°C + PS) to explore its impact on engineering reusability. Three thermal remediation procedures (i.e., DT150°C, DT350°C, and DT550°C) were selected as the control group. The results show that: (a) Pyrolytic carbon was produced in the DT350°C and DT550°C, while none was produced in DT150°C and DT150°C + PS; (b) Iron-based minerals and organic matter in DT150°C + PS, DT350°C, and DT550°C were combusted and decomposed to release the Fe(II) substances; under stronger oxidation environments, Fe(II) substances would further transform into more stable Fe(Ⅲ) substances; and (c) Halloysites and illites were formed in DT350°C, palygorskites and cordierites were formed in DT550°C, and oxidation in DT150°C + PS produced the sulfate minerals. The formed sulfate minerals in the DT150°C + PS sample filled pores and provided the skeleton strength, resulting in high unconfined compressive strength and poor permeability. Using a self-developed assessment model, only the DT150°C + PS sample showed an improvement (calculated as 2.96 × 10−5) in engineering performance and other methods led to the deterioration of soil mechanical properties. Thermochemical treatment is more suitable for engineering reuse, and this study can provide a theoretical basis for evaluating the greener reusability of contaminated soil after thermal or thermochemical remediation.

Hot Tearing Susceptibility and Solidification Behavior of Mg-xGd-(4-x)Y-2Ni-0.5Zr Alloys

The hot tearing susceptibility (HTS) of Mg-xGd-(4-x)Y-2Ni-0.5Zr (x = 0, 1, 2, 3, 4, wt%) alloys was evaluated using a T-shape mold method. When the Gd element increased and the Y element decreased, the HTS of the alloys decreases gradually. The Mg-4Y-2Ni-0.5Zr has the highest while Mg-4Gd-2Ni-0.5Zr has the lowest HTS value. Microstructure observation reveals that the grains of the magnesium alloy were refined to a certain extent when the Gd element increased and the Y element decreased. The ‘pinning’ effect of the LPSO phase precipitated along the grain boundary effectively increases the solid skeleton strength of the alloy and reduces the HTS of the magnesium alloy to a certain extent. The thin and uniform liquid film at the fracture can disperse the solidification shrinkage stress. In addition, the binary phase precipitated in the alloy forms a fast channel of residual liquid phase feeding on the liquid film, which is beneficial to feeding hot cracks. Solidification behavior of the alloys by thermal analysis showed that with the increase of the Gd element and the decrease of the Y element, the dendrite coherency temperature of the dendrites of the alloy decreases, and the residual liquid phase feeding is easier. The solid fraction of dendrite coherency increases, the skeleton strength of the alloy increases, and the HTS of the alloy decrease. In Mg-xGd-(4-x)Y-2Ni-0.5Zr (x = 0, 1, 2, 3, 4, wt%) alloys, when x is 1, 2, 3, 4, the HTS of the alloy is reduced by 25%, 49%, 63%, 81%, respectively compared with that when x is 0.

Influence of coarse aggregate morphology on the mechanical characteristics of skeleton in porous asphalt concrete

ABSTRACT The properties of coarse aggregates have a great influence on the mechanical characteristics of porous asphalt concrete (PAC). The objective of this study is to reveal the influence of coarse aggregate morphology on the skeleton mechanical characteristics of PAC-13. To achieve this goal, a microstructure analysis method based on X-ray CT was developed to acquire three-dimensional morphological characteristics of coarse aggregates, and the morphology parameters were proposed. Based on the morphology of the actual aggregate, the coarse aggregate skeleton structure and skeleton penetration test were simulated by the discrete element method (DEM) and the values of skeleton strength under different morphologies were determined. The sensitive influences of coarse aggregate morphology parameters on the skeleton strength were quantified by the GA-BP neural network and the recommended value ranges of morphology parameters were proposed. The results show that the morphology of coarse aggregates within the size range of 4.75∼9.5mm and 9.5∼13.2mm has the greatest influence on the skeleton strength of PAC-13. The composite flat-elongated index and composite texture index of aggregates in 9.5∼13.2mm and 4.75∼9.5mm, and the composite angularity index of aggregates in 4.75∼9.5mm, which are referred to as Icom(9.5∼13.2), Icom(4.75∼9.5), Tcom(9.5∼13.2), Tcom(4.75∼9.5), AIcom(4.75∼9.5), are the high-sensitive influencing factors to the skeleton strength of PAC-13.

Study on the influence mechanism of recycled concrete aggregate on strength of asphalt mixtures

Recycled concrete aggregate (RCA) has great potential use in pavement. However, unclear characteristics of RCA and its relationship with the properties of asphalt mixture hinder severely its promotion. The objective of this study is to characterize the microscopic morphology and structure of RCA, further investigate its impact on the strength of asphalt mixture and associated mechanisms, by means of various test method. Results showed that cement mortar was the vital factor to affect the properties of RCA. Hence, the asphalt mixtures with RCA had characteristics of higher air voids (VV) and voids in the mineral aggregate (VMA), lower asphalt saturation (VFA), compared with conventional asphalt mixtures (CAM). In addition, according to the results of Micro-Scratch (MS) test, the compression depths of aggregate, interfacial transition zone (ITZ) and asphalt mortar in RAM are larger than that in CAM. Therefore, the influence of RCA on the performance of asphalt mixture is mainly in the following two aspects: reducing the strength of asphalt mortar; decreasing the skeleton strength of asphalt mixtures.

Digital twin exploration of a blended-wing-body underwater glider skeleton in the laboratory environment

ABSTRACT Due to the inherent unpredictability of marine trial conditions, safety issues in the launching and recovery process are commonplace. For these issues, digital twin (DT) maintenance offers a novel idea. In this paper, a blended-wing-body underwater glider skeleton is selected as a research object. And a simple demo is created to investigate the major technologies that may be involved in DT maintenance. According to this specimen, the necessary development environments are developed to obtain physical information and produce a DT model in cyberspace respectively. An attitude sensor is used as the physical data collector, while real-time structural field prediction and virtual reality visualisation are employed. By using the attitude angles and structural data, it is possible to achieve real-time monitoring of the skeleton strength. Through the means of this straightforward case study, the key technologies are supported and can be applied to far more complex inquiries.

Cyclic stress–strain characteristics of red clay treated with permeable water-soluble polyurethane

Red clay, a globally distributed type of chemical weathering soil, is commonly utilized as a road base in road infrastructure. However, due to its susceptibility to water and vibrations, it is prone to settlement and formation of potholes during operation, consequently leading to damage in the pavement structure. This paper employs a dynamic triaxial apparatus to simulate realistic traffic loads and investigates the dynamic properties of red clays treated with permeable water-soluble polyurethane (PSP). Additionally, a series of microscopic tests are conducted to elucidate the microstructural mechanisms of using PSP for improving red clay, as well as the microscopic deformation mechanisms of the PSP-treated red clay (PSP clay) under cyclic loading. The results provide detailed insights into the influence of soil moisture content and PSP content on key parameters, including the resilient modulus, damping ratio, permanent deformation, and strength of PSP clay after repeated loading. Moreover, the overall performance of PSP clay is evaluated under varying loading amplitudes and confining pressures. These results are complemented and interpreted in conjunction with the findings from the microscopic tests. The findings reveal that the inclusion of PSP improves the strength of the soil skeleton by enveloping and interlocking with the clay particles. Furthermore, it is observed that the engineering properties of high-moisture-content red clay soils can be significantly improved with low levels of PSP. Under specific conditions, repeated loading further compact the PSP clays, thereby enhancing their mechanical properties. The experimental findings presented in this study are of utmost importance for the improvement and application of red clays through the utilization of rapid solutions, such as PSP.

The Self‐Adaptive Nanosystem for Implant‐Related Infections Theranostics via Phase‐Change Driven Anti‐Biofilm and the Enhancement of Immune Memory

AbstractImplant‐related infections (IRIs), characterized by the formation of bacterial biofilms and immunosuppressive microenvironment, are a common but tricky clinical issue. In this study, a self‐adaptive theranostics nanosystem is designed based on phase change material (PCM) for IRIs therapy, which can monitor the severity of infection in real time and automatically provide the most appropriate treatment on demand. The nanosystem called CaAlg/LOD/POD@MNO/FAs (CLPM) is made of the fatty acids (FAs) core with dissolved minocycline (MNO) and the calcium alginate (CaAlg) shell with an immobilized lactate oxidase/pyruvate oxidase (LOD/POD) enzyme‐linked system. When the level of infection is mild (wound temperature < 39 °C), the CLPMs perform a bacteriostatic function by slowly releasing MNO from the solid‐phase FAs core. When the infection deteriorates (wound temperature > 39 °C), the solid‐to‐liquid phase change of FAs not only enables a rapid release of MNO but also disrupts the mechanical strength of the biofilm skeleton doped with CLPM, performing a bactericidal function. In addition, CLPM can reduce the accumulation of bacteria‐derived lactate to address lactate‐induced immunosuppression and enhance immune memory response, thereby inhibiting infection recurrence.

Synthesis and Performance Evaluation of a Novel Nanoparticle Coupling Expanded Granule Plugging Agent.

This study focuses on the characteristics of fractured and vuggy high-temperature and high-salt reservoirs in the Tahe Oilfield. The Acrylamide/2-acrylamide-2-methylpropanesulfonic copolymer salt was selected as a polymer; the hydroquinone and hexamethylene tetramine was selected as the crosslinking agent with a ratio of 1:1; the nanoparticle SiO2 was selected, and its dosage was optimized to 0.3%; Additionally, a novel nanoparticle coupling polymer gel was independently synthesized. The surface of the gel was a three-dimensional network structure, with grids arranged in pieces and interlaced with each other, and the structure was very stable. The SiO2 nanoparticles were attached to the gel skeleton, forming effective coupling and enhancing the strength of the gel skeleton. To solve the problem of complex gel preparation and transportation, the novel gel is compressed, pelletized, and dried into expanded particles through industrial granulation, and the disadvantage of the rapid expansion of expanded particles is optimized through physical film coating treatment. Finally, a novel nanoparticle coupling expanded granule plugging agent was developed. Evaluation of the performance of the novel nanoparticle coupling expanded granule plugging agent. With an increase in temperature and mineralization, the expansion multiplier of granules decreases; aged under high-temperature and high-salt conditions for 30 days, the expansion multiplier of granules can still reach 3.5 times, the toughness index is 1.61, and the long-term stability of the granules can be good; the water plugging rate of granules is 97.84%, which is superior to other widely used particle-based plugging agents.

Effect of addition of minor amounts of Sb and Gd on hot tearing susceptibility of Mg-5Al-3Ca alloy

The effects of addition of minor amount of (0.5 wt.%) antimony (Sb) or gadolinium (Gd) and combined addition of Sb and Gd (0.5 wt.%, respectively) on the hot tearing susceptibility (HTS) of Mg-5Al-3Ca alloy were investigated experimentally using a “T-shaped” hot tearing measuring system. Various solidification parameters of the alloys were measured and calculated through thermal analysis experiments. The microstructure, grain size, and morphology of the crack zone were characterized by scanning electron microscopy and electron backscatter diffraction, and the crystal phases of the alloys were analyzed by X-ray diffraction and energy-dispersive X-ray spectroscopy. The results showed that the addition of 0.5 wt.% Gd resulted in the increase in the vulnerable temperature range (Tv) and reduced the eutectic structure content that could participate in feeding, thereby improving the HTS of the alloy. However, addition of 0.5 wt.% Sb or combined addition of Gd and Sb (0.5 wt.%, respectively) to the Mg-5Al-3Ca alloy shortened the Tv and improved the skeleton strength of the alloy, thereby reducing HTS. Moreover, significantly refined structure of Mg-5Al-3Ca-0.5Gd-0.5Sb alloy improved the feeding ability of the eutectic structure, thus the alloy exhibited the lowest HTS.

Behavior of steel reinforced UHPC-filled stainless steel tubular columns under eccentric loads

This study was conducted to examine the behavior of steel-reinforced ultra-high performance concrete-filled stainless steel tubular (SRUHPCFSST) intermediate columns under eccentric loads. There were nine columns tested in the test program, all of which were subjected to static eccentric loading with consideration given to the effects of the eccentricity, diameter-to-thickness ratio, steel ratio, and eccentric direction. The columns were evaluated to determine their performance characteristics such as ductility, load-displacement relationships, load-strain relationships, and failure modes. The intermediate SRUHPCFSST columns demonstrated good load-carrying and deformation capacity as well as a clear instability failure under eccentric compression after reaching their maximum load. The ultimate bearing strength of the columns decreased significantly with the increase of the diameter-to-thickness ratio and eccentricity, and the increase of the steel ratio or loading in the major axis of the steel skeletons effectively improved the ultimate bearing strength and ductility of the columns. The numerical simulation of the eccentric compression on the SRUHPCFSST was carried out with the finite element software ABAQUS, and the effects of the L/D ratio, concrete strength, steel skeleton strength, and large eccentricities on its eccentric bearing strength were expanded and analyzed. The eccentric bearing strength of the SRUHPCFSST intermediate columns was calculated using a formula derived from the test data and the numerical analyses. The results of the equation correlated well with the experimental data and can serve as a reference for future research in this area.

Study on Pore Structure Evolution Characteristics of Weakly Cemented Sandstone under Freeze–Thaw Based on NMR

Taking saturated, weakly cemented sandstone as the research object, nuclear magnetic resonance (NMR) tests were performed before and after six freeze–thaw cycles without water replenishment in order to study and reveal the evolution characteristics of the pore structure of weakly cemented sandstone under a freeze–thaw cycle. The evolution of pore structure under repeated freeze–thaw cycles was studied using T2 fractal theory and spectral peak analysis. The results show that the evolution of the pore structure of weakly cemented sandstone can be divided into three stages during the freeze–thaw cycle. In stage 1, the rock skeleton can still significantly restrict frost heave, and the effect of rock pore expansion occurs only on the primary pore scale, primarily in the transformation between adjacent scales. In stage 2, as the restraint effect of the skeleton on frost heave decreases, small-scale secondary pores are gradually produced, pore expansion occurs step by step, and its connectivity is gradually enhanced. In stage 3, as rock pore connectivity improves, the effect of pore internal pressure growth in the freezing process caused by water migration is weakened, making it impossible to break through the skeleton constraint. Thus, it becomes difficult for freezing and thawing to have an obvious expansion effect on the rock pore structure. The strength of the freeze–thaw cycle degradation effect is determined by the effect of the rock skeleton strength under the freeze–thaw cycles and the connectivity of small-scale pores in the rock. The lower the strength of the rock skeleton, the worse the connectivity of pores, and the more obvious the freeze–thaw degradation effect, and vice versa.

Modeling the Behavior of an Aggregate Skeleton during Static Creep of an Asphalt Mixture Based on a Three-Dimensional Mesoscale Random Model

The aggregate skeleton and its evolution under external loads are crucial to evaluate the mechanical properties of the asphalt mixture. This study developed a method to identify the three-dimensionally (3D) aggregate skeleton based on geometry information. The proposed method can identify the evolution process of the aggregate skeleton during loading in the finite element method (FEM). Random models based on the Gilbert–Johnson–Keerthi (GJK) algorithm are used to study the influence of the concave–convex degree of the gradation curve and the magnitude of the creep load on the aggregate skeleton during the creep process. The results indicate that the aggregate skeleton undergoes three stages during creep: aggregate redistribution, skeleton formation, and skeleton failure after reaching the ultimate load, while the increase of load causes the aggregate skeleton to lose its bearing capacity faster. More coarse aggregate raises the strength of the aggregate skeleton, but it is more likely to break down quickly once it reaches the strength. More fine aggregate enhances the stability of the aggregate skeleton. The proposed identification method can serve as a general tool to investigate the evolution process of the internal aggregate structure of the asphalt mixture.

Study of triethanolamine on regulating early strength of fly ash-based chemically foamed geopolymer

This study investigates the role of triethanolamine (TEA) in regulating the early strength of ultra-lightweight (∼460 kg/cm3) fly ash-based chemically foamed geopolymer. The reaction kinetics, pore distribution and skeleton strength were examined using isothermal calorimetry, X-ray microtomography, and solid-state nuclear magnetic resonance spectroscopy, respectively. The three-dimensional pore spatial distribution patterns were statistically assessed by applying the Nearest-neighbor distance-based techniques. The results showed that TEA can regulate the early strength of geopolymer foam by rendering homogeneous pore sizes and spatial distributions even when the geopolymerization of the skeleton is retarded. Furthermore, 0.3 % TEA reduced the compressive strength of the skeleton by 13.4 %, from 105.8 MPa to 91.6 MPa, but doubled the specific strength of the geopolymer foam from 2271 N·m/kg to 4662 N·m/kg. The proposed mechanism suggests that foaming kinetics can be regulated for a homogeneous pore distribution by manipulating the complexing effect.

Facile Synthesis of Dual Modal Pore Structure Aerogel with Enhanced Thermal Stability

Regarding the preparation of aerogels by the co-precursor method, the skeleton collapse caused by its low strength is one of the key problems that needs to be solved urgently. In this study, vinyl-functionalized silica aerogel was prepared under atmospheric drying conditions (APD) with vinyltriethoxysilane (V) and water glass (W) as co-precursors. The performance of aerogels varied with the components of co-precursors. When the V:W ratio was 0.8, the aerogel had excellent properties of low thermal conductivity (0.0254 W/(m·K)), super hydrophobicity (hydrophobic angle of 160°), high specific surface area (890.76 m2/g), high porosity (96.82%), and low density (0.087 g/cm3). Test results of SEM and BET showed that the V:W ratio affected the pore structure. When the V:W ratio was around 0.8, the aerogel had a dual modal pore structure composed of both small (6–8 nm) and large (20–30 nm) mesopores, which could contribute to enhance the skeleton strength of the aerogel. On the other hand, the addition of vinyltriethoxysilane promoted the skeleton stability by reducing the capillary force. The vinyltriethoxysilane and water glass as novel co-precursor combinations can provide guidance for the preparation of aerogels under APD conditions.

Compaction performance of cold recycled asphalt mixture using SmartRock sensor

Due to the lack of essential understanding of the interaction mechanism between the aggregates under compaction, engineering problems such as uneven compaction and over-compaction are prone to occur. This paper presents three indicators to quantitatively evaluate the characteristics of cold recycled asphalt mixture at different compaction stages, and develops a novel method to determine the locking point of the mixture. The stress, rotation and acceleration changes of aggregates under gyratory compaction can be continuously monitored by SmartRock sensor. By analyzing these dynamic responses, the compaction workability, skeleton strength and stability of the mixture are analyzed. Results showed that by a combined use of SmartRock and the new evaluation indexes, the compaction state of the mixtures can be accurately captured and monitored by looking closer into the microstructural changes of asphalt mixture. It is recommended to further advance the application of embedded sensors in field conditions and in that, to achieve a global monitoring of compaction response the array layout design of sensors inside pavement structure could be an important focus of next stage.

Effect of Coarse Recycled Aggregate on Failure Strength for Asphalt Mixture Using Experimental and DEM Method

Coarse aggregate is the major part of asphalt mixture, and plays an essential role in mechanical performance of pavement structure. However, the use of poor-quality coarse recycled aggregate (CRA) reduces the strength and stability of the aggregate skeleton. It is a challenge to predict accurately the influence of CRA on the performance of asphalt mixture. In this study, both a uniaxial compression test and a direct tensile test were carried out to evaluate the failure strength of asphalt concrete with four CRA content. The discrete element method (DEM) was applied to simulate the specimen of asphalt concrete considering the distribution and properties of CRA. The results showed that temperature and loading rate have a significant influence on failure strength, especially when the CRA content was more than 20%. With the increase of CRA content, both cohesion force and internal friction angle were gradually weakened. The proposed model can be used to predict the failure strength of asphalt mixture, since both experimental and simulated results had a high consistency and repeatability. With the decrease of CRA strength, the nominal cohesion force of the specimen decreased, while the internal friction angle increased.

Coupled thermo-hydro-mechanical mechanism in view of the soil particle rearrangement of granular thermodynamics

This paper established a coupled thermo-hydro-mechanical mechanism in view of the soil particle rearrangement for saturated/unsaturated soils under the framework of granular thermodynamics. This model avoids concepts such as the flow rule, yield function, dissipation potential function, and hardening criterion. The effects of the loading path and the soil structure are reflected by constructing a density function of elastic potential energy considering the structural strength of a solid skeleton with a degradation factor. That is, the changes in the stress states are closely related to soil particle rearrangement and the transitions between different matter phases. A generalized effective stress principle is derived and is suitable for the coupled thermo-hydro- mechanical process. The deduced generalized phase stresses differ from the classical effective principle based on linear elastic porous media and can automatically consider the impact of the stress path, temperature path and soil structure. The established model spans the complete process from unsaturated to saturated soils and is verified by the typical test results.

Mechanical Effects of Solid Water on the Particle Skeleton of Soil: Mechanism Analysis

It is generally accepted that the adsorbed water layer on the surface of the mineral particle has significant effects on the mechanical properties of soils. By defining the concepts of “solid water” and “particle skeleton” after a brief review on adsorbed water, therefore, the mechanical mechanism about how solid water affects the deformation and strength of particle skeleton is theoretically clarified, which could be the physical basis of the reasonability of two assumptive conditions for effective stress equation. Considering solid water as a two-dimensional liquid with appreciable normal strength and lubricity, if soil particles are always wrapped by solid-water layer, the only mechanical effect due to water pressure is to compress particles; while if the interparticle solid water could be extruded undergoing enough force with suitable confinement, the mechanical effects due to increasing water pressure are not only to compress particles more but also to enhance interparticle friction because the indirect interparticle contact could be changed into direct contact to consequently alter the interparticle friction. Because solid water is not likely to be extruded by pressure alone, if the particle compression is negligible relative to the soil-mass compression, two assumptive conditions for effective stress equation are reasonable. Moreover, a simple monitoring test on water content is conducted to certify that the solid-water layer should always exist in soils under ambient conditions, so the ordinarily oven-dried soil samples used in conventional geotechnical tests carried out under ambient conditions could be just “nominally dry” samples with the effects due to solid water.

Research on application feasibility of limestone in sublayer of Double-Layer permeable asphalt pavement

In double-layer permeable pavement, upper layer provides better road performance, and sublayer ensures better lateral drainage capacity. The mechanical properties of limestone are weak, so its application in upper layer is limited, while the sublayer does not directly contact with vehicle load, and the application feasibility of limestone aggregate in sublayer of double-layer permeable asphalt pavement is confirmed in this paper. Optimum asphalt contents and reasonable number of Marshall blows of limestone and basalt PAC-16 (Permeable Asphalt Concrete mixture whose nominal maximum aggregate size is 16 mm) were determined, temperature stability, water stability and water permeability were obtained. Gyratory compaction tests were designed and the compaction characteristics, mechanical properties and aggregate crushing characteristics of limestone and basalt PAC-16 were investigated. Considering the disadvantages of the existing testing methods, the concept of “actual crushing proportion (ACP)” was proposed to calculate the crushing degree of aggregate in mixture under load. It was found that the optimum asphalt content of limestone PAC-16 was higher than that of basalt mixture, and the laboratory properties related to field performance of limestone PAC-16 met the requirements of specifications in general. The equivalent compacting times of limestone mixture are slightly less than that of basalt in order to achieve the same void ratio, and the void ratio decay rate of limestone mixture is much faster than that of basalt mixture after opening to traffic. The ACP results showed that limestone aggregate > 13.2 mm can be replaced by basalt aggregate to ensure the strength of aggregate skeleton.