Series Of Tests Research Articles

Shear modulus of sand-rubber mixtures: element testing and constitutive modeling

In this study, a series of resonant column tests was conducted to measure the shear modulus of sand-rubber mixtures at small strain amplitudes (i.e. between 10−4% and 10−2%), considering different rubber percentages and confining stress levels. The results were then combined with data obtained by dynamic hollow cylinder tests to investigate shear modulus degradation of the mixtures over a wider shear strain range. Based on the test results, a new expression was proposed to improve the prediction of maximum shear modulus of sand-rubber mixtures using the modified equivalent void ratio concept. A new constitutive model was also developed for estimation of strain-dependent shear modulus of the mixtures based on the modified hyperbolic framework. The shear modulus of the mixtures was found to be a function of rubber percentage, confining stress, the modified equivalent void ratio and the relative shear stiffness of rubber and sand. The experimental data and the developed models showed that the shear modulus decreased with rubber percentage and increased with confining stress. Moreover, the reference shear strain of the modified hyperbolic model increased with both rubber percentage and confining stress while its curvature coefficient increased more considerably with rubber percentage compared to the confining stress.

Measuring online political activity: introducing the digital society project dataset

ABSTRACT Political engagement is deeply enmeshed with online activity. However, there has been a lack of publicly available cross-country datasets enabling researchers and policymakers to understand how politics and digital space intersect. This paper introduces the Digital Society Project (DSP), which aims to provide systematic, cross-country measurement of political institutions and behavior that manifest online or are affected by online activity. Using the Varieties of Democracy Project infrastructure, DSP provides annual global data from 2000 to 2021. The dataset features 35 indicators measuring online censorship, politicization of social media, coordinated information operations, foreign influence, monitoring of domestic politics, and regime cyber capacity. This article introduces the DSP data collection effort, overviews the resulting dataset, and validates key indicators by conducting a series of diagnostic tests. We demonstrate that the DSP dataset aligns with extant datasets measuring internet freedom and offers expanded coverage across countries and over time. We analyze two case studies, walking through how the DSP data can be used to extend existing work on China to generalize this case to other contexts, and examining in depth the case of Ethiopia, which differs the most between DSP and Freedom House’s Freedom on the Net.

Long-term aging simulation of asphalt mixture: A comparative experimental study

In this study, the efficacy of the extended oven aging procedure outlined in NCHRP 973 for generating laboratory-produced reclaimed asphalt pavement (RAP) was explored. The study also sought to establish a correlation between the results obtained from the aged bitumen extracted from oven-aged asphalt mixture and PAV-aged bitumen. Both aging techniques, with varying durations, were applied, and a series of tests, encompassing penetration, softening point, rotational viscosity, bending beam rheometer, temperature sweep using dynamic shear rheometer, and FTIR, were conducted for comprehensive comparison. The outcomes revealed that the oven aging procedure has limited applicability for simulating the long-term aging of asphalt mixtures. At the temperature of 95°C, an increase in the oven aging duration had minimal impact on the degree of aging, especially beyond five days, as evidenced by various parameters such as penetration, softening point, viscosity, master curves of viscoelastic properties, aging index, and low-, intermediate-, and high-temperature characteristics of the different aged bitumens. Furthermore, a comparative analysis between PAV and bitumen extracted from oven-aged asphalt mixture indicated that bitumen aged for five days in the oven exhibited analogous properties to bitumen subjected to 1 cycle of PAV aging, encompassing chemical, rheological, and physical test results. In conclusion, while some researchers have suggested that performing 2 or 3 cycles of PAV aging may be necessary to simulate long-term aging, the findings indicate that oven aging of asphalt mixture cannot effectively simulate aging characteristics beyond 1 cycle of PAV aging.

Probing the effect of displacement on electrical contact tribological behavior at the risk frequency of nuclear safety DCS equipment

Purpose This paper aims to study the tribological characteristics of the electrical contact system under different displacement amplitudes. Design/methodology/approach First, the risk frequency of real nuclear safety distributed control system (DCS) equipment is evaluated. Subsequently, a reciprocating friction test device which is characterized by a ball-on-flat configuration is established, and a series of current-carrying tribological tests are carried out at this risk frequency. Findings At risk frequency and larger displacement amplitude, the friction coefficient visibly rises. The reliability of the electrical contact system declines as amplitude increases. The wear morphology analysis shows that the wear rate increases significantly and the degree of interface wear intensifies at a larger amplitude. The wear area occupied by the third body layer increases sharply, and the appearance of plateaus on the surface leads to the increase of friction coefficient and contact resistance. EDS analysis suggests that oxygen elements progressively arise in the third layer as a result of increased air exposure brought on by larger displacement amplitude. Originality/value Results are significant for recognizing the tribological properties of electrical connectors in nuclear power control systems. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0098/

On the influence of the shearing rate on the monotonic and cyclic response of Malaysian kaolin

This article experimentally evaluates the influence of shearing rate on the monotonic and cyclic response of isotropically-consolidated samples of Malaysian kaolin. On the one hand, a series of undrained monotonic triaxial tests were performed with varying shearing displacement rate. On the other hand, undrained cyclic triaxial tests were conducted considering different deviatoric stress amplitudes and loading frequencies. The well-known soil rate-dependency under monotonic loading was confirmed up to a displacement rate threshold. The experimental results under cyclic loading suggest that for the given loading frequency, the variation of the deviatoric stress amplitude remarkably influences the strains and pore water pressure accumulation rates. In addition, the results suggest that depending on the loading frequency different shapes of mobilized effective stress loops are obtained. Larger loading frequencies lead to banana-shaped effective stress loops, while smaller frequencies reproduce eight-shaped effective stress loops. Furthermore, higher loading frequencies result in a larger number of cycles required to reach failure conditions. The reasons for the observed differences in the behavior are thoroughly analyzed and discussed.

Exploring Combat Tourniquet Application Errors and Duration Among Skilled and Novice Medical Trainees.

The use of tourniquets in combat medicine continues to be a key focus as they have consistently been shown to combat one of the leading causes of preventable death on the battlefield, massive hemorrhage to extremities. The present study analyzed tourniquet application among combat medics (68W) and combat lifesavers (CLSs) in a training environment to determine whether trainees' performance is consistent among one another and whether performance can be associated with participant demographics such as experience or role. Study participants treated male and female patient simulators within a tactical field care phase, both of which experienced an amputated leg and required the application of a Combat Application Tourniquet (CAT). To assess tourniquet application variability and performance, a series of application subtasks and potential errors were measured via video coding of the scenarios by a team of 5 coders. Time to tourniquet application and tourniquet application duration were also coded to assess correlations between application duration and variability or performance. Results from analyzing tourniquet application subtasks and errors through a series of one-way ANOVA tests showed that application of the CAT first, hasty CAT application, and high tourniquet application were not predictive of participant role, time within the role, and self-reported tourniquet skill, confidence, or experience. Such demographic variables were also not predictive of successful tourniquet application as defined by the number of windlass rod rotations. Results from binomial logistic regressions showed that participant role and self-reported tourniquet skill and experience were predictors of tourniquet application duration. The findings suggest that high variability in CAT application methodology and performance exists among CLS and combat medics, which is largely not predictable by various demographics such as role, experience within the designated role, and self-reported confidence, skill, or experience. The observed disconnect between training or experience and CAT application performance suggests substantial variability in the consistency of training for both CLS and 68W soldiers. These inconsistencies may stem from variability in instructor knowledge, teaching styles, or training materials or may be developed through informal methods such as experiences in the field or recommendations from colleagues and experts. These findings highlight a potential need to reassess CAT application training, particularly in regard to consistency and validation. Finally, it should be noted that the study's findings may be limited or fail to capture some study effects because of the sample size and wide range of reported experience among participants.

Effects of passive confinement on out-of-plane robustness of unreinforced masonry infill walls

Unreinforced masonry (URM) walls are vulnerable to out-of-plane (OOP) collapse under lateral loads; however, URM structures are still popular in developing countries. Even in many countries classified as developed by the United Nations, URM walls are still commonly applied as exterior and interior infills in engineered buildings, resulting in severe OOP failure during strong earthquakes. The objectives of this study were: 1) to experimentally examine the OOP behavior and performance of URM infills with construction deficiencies commonly found in Asian countries, 2) to investigate the impact of construction quality on resistance to OOP collapse and 3) to propose a promising approach using passive confinement to improve the lateral resistance of URM infills and a method to evaluate their seismic performance. To attain these objectives, the study used two full-scale, single wythe, brick masonry specimens with specific boundary conditions at the top, a control specimen representing URM infills with construction flaws frequently found in Asian countries and a well-constructed specimen subjected to passive confinement under lateral excitation. A series of incremental dynamic shaking table tests was performed on both specimens under OOP unidirectional one-way bending. The test results revealed the positive effects of construction with passive confinement on OOP performance. The results indicated that the OOP robustness of infills can be improved without specific retrofit materials, leading to advantages such as simplicity, cost-effectiveness, and swift execution. Moreover, a theoretical method to evaluate the lateral resistance of infills was presented and verified for practical applications. This method can contribute to reducing the potential for earthquake damage in engineered buildings.

Effects of periodic sequential arrangement of subscale miura-foldcore under quasi-static compression

This study presents experimental and numerical investigations on the quasi-static compressive responses of various subscale Miura-foldcore composites. A series of quasi-static compression tests were conducted on standard Miura foldcore specimens fabricated using carbon/epoxy woven fabric prepregs. Representative volume element (RVE) models, incorporating periodic boundary conditions (PBCs), were developed to predict the size-dependent compressive response of subscale Miura foldcores. The effective properties of the carbon/epoxy woven fabric composite used in this study were calculated using the NASA multiscale analysis tool (NASMAT) via two-step homogenization process. The FE model exhibited comparable agreement with experimental results, showcasing variations of less than 7% and 12% in maximum compressive load and compressive stiffness, respectively. The implementation of PBC in the foldcore RVE models improved modeling accuracy by <4%, but drastically increased total computational time (>50%). The periodic pattern of foldcore unit-cells, where two single foldcore unit-cells were placed in parallel or perpendicular, imposed geometric constraints, resulting in small variations in predicted stress and strain distribution contours. The key findings highlighted in this study suggest that a 1 × 1 foldcore unit-cell model without PBC is sufficient to predict accurate quasi-static compressive responses of foldcore composites. This study advances the understanding of subscale Miura-foldcore composites and provides valuable insights into the limitations associated with the use of PBC in foldcore RVE models. The findings also offer a practical guide for fabricating and analyzing traditional Miura folding patterns, promoting a more efficient and accurate approach for optimizing foldcore composite designs considering both structural performance and manufacturability.

The impact of IT use on supply chain coordination: the moderating role of environmental uncertainty

Purpose This study aims to empirically test the direct effects of three types of information technology (IT) use on three dimensions of supply chain coordination (SCC). It further explores the spillover effects of IT use on coordination beyond its domain across the SC. Besides, this study probes into the moderating effects of environmental uncertainty (EU). Design/methodology/approach Structural equation modelling (SEM) is used to examine data collected from 202 firms in Hong Kong. Furthermore, multi-group SEM analysis with a series of invariance tests was used to test the moderating effects of EU. Findings Internal, supplier and customer IT use have direct effects on internal, supplier and customer coordination, respectively. Besides, IT use generates forward spillover effects beyond its domain along the forward physical flow in an SC. EU positively moderates the relationships between external IT use and SCC but does not shape the effectiveness of internal IT use in enhancing SCC. Moreover, under a high EU, the spillover effects of IT use on coordination can be intensified. Besides, the spillover effects further expand to benefit coordination on a larger scale of the SC under a high EU. Originality/value This study contributes by revealing that in addition to direct effects, IT use in a specific domain could generate spillover effects on coordination beyond its domain throughout an SC. More importantly, it contributes by explaining the difference in the effectiveness of IT use under different levels of EU using multi-group SEM analysis.

Centrifuge modelling on seismic failure of MSW landfills with high water level

Landfill failure threatens the safety of surrounding cities and causes soil and water pollution. High water levels can usually spur landfill failure. With the presence of earthquake, landfill instability is triggered in a greater possibility. However, the dynamic response and failure mechanism of landfills with high water level subjected to earthquakes are not yet clearly understood, and relevant experimental studies are quite scarce. This study includes a series of seismic centrifuge tests to investigate the seismic response of the landfill at different water levels. An improved method is proposed to prepare synthetic municipal solid wastes (MSWs) with similar static-dynamic properties to the actual MSWs. The failure and evolution mechanism of landfills with high water levels induced by the earthquake is revealed. Significant transitions are observed in the dynamic response of deformation, acceleration, and pore-water pressure as the water level changes. With the rise of water level, the settlement at the top of the landfill decreases first and then increases, while the horizontal displacement at the toe increases slowly, followed by a sudden drop; the acceleration amplification coefficient in the middle of the landfill increases first and then decreases; the dynamic pore-water pressure gradually decreases from positive to negative, but oscillates at the moderate water level. Three failure criteria and a hydro-earthquake coupled failure limit are proposed to demonstrate the combined effect of water level and earthquake on landfill stability. The test results provide a basis to establish seismic failure standards for landfills with different water levels and guide the seismic instability design of landfills with high water level.

Prospect of trade and innovation in renewable energy deployment: A comparative analysis between BRICS and MINT Countries

The current study explores the impact of technological innovation and trade openness on clean energy while accounting for economic growth, access to electricity, pollution, industrial restructuring, and urbanization using data from 1990 to 2020 for both the MINT and BRICS economies. A series of tests were performed for a robust analysis using second generation econometrics approaches before proceeding to investigate the long-run linkages between renewable energy and the duo of innovation and trade using the Prais-Winsten regression model with panel-corrected standard errors (PCSE). The Driscoll-Kraay standard errors test was applied for robustness checks. The results, firstly confirm the presence of heterogeneity, cross-sectional dependence, and cointegration among the selected variables. Secondly, technological innovation as a renewable energy determinant demonstrated negative elasticities in both BRICS countries and the full sample, but a positive elasticity in the MINT countries. Thirdly, concerning trade liberalisation, negative elasticities were obtained for the full sample and MINT countries, while the elasticities were positive for the BRICS bloc. Fourthly, the roles of economic growth and environmental pollution reveal a negative impact on renewable energy consumption for all samples while urbanisation and industrial restructuring promote renewable energy developments only in the BRICS bloc. Policy implications are discussed.

Akkermansia muciniphila isolated from forest musk deer ameliorates diarrhea in mice via modification of gut microbiota.

The forest musk deer, a rare fauna species found in China, is famous for its musk secretion which is used in selected Traditional Chinese medicines. However, over-hunting has led to musk deer becoming an endangered species, and their survival is also greatly challenged by various high incidence and high mortality respiratory and intestinal diseases such as septic pneumonia and enteritis. Accumulating evidence has demonstrated that Akkermannia muciniphila (AKK) is a promising probiotic, and we wondered whether AKK could be used as a food additive in animal breeding programmes to help prevent intestinal diseases. We isolated one AKK strain from musk deer feces (AKK-D) using an improved enrichment medium combined with real-time PCR. After confirmation by 16S rRNA gene sequencing, a series of invitro tests was conducted to evaluate the probiotic effects of AKK-D by assessing its reproductive capability, simulated gastrointestinal fluid tolerance, acid and bile salt resistance, self-aggregation ability, hydrophobicity, antibiotic sensitivity, hemolysis, harmful metabolite production, biofilm formation ability, and bacterial adhesion to gastrointestinal mucosa. The AKK-D strain has a probiotic function similar to that of the standard strain in humans (AKK-H). An invivo study found that AKK-D significantly ameliorated symptoms in the enterotoxigenic Escherichia coli (ETEC)-induced murine diarrhea model. AKK-D improved organ damage, inhibited inflammatory responses, and improved intestinal barrier permeability. Additionally, AKK-D promoted the reconstitution and maintenance of the homeostasis of gut microflora, as indicated by the fact that AKK-D-treated mice showed a decrease in Bacteroidetes and an increase in the proportion of other beneficial bacteria like Muribaculaceae, Muribaculum, and unclassified f_Lachnospiaceae compared with the diarrhea model mice. Taken together, our data show that this novel AKK-D strain might be a potential probiotic for use in musk deer breeding, although further extensive systematic research is still needed.

Exploring high-temperature deformation and damage behaviour in high-performance ferritic (HiperFerSCR) steel with Laves phase particles

The mechanical behaviour at high temperatures and the corresponding microstructural characteristics of a newly developed high-performance ferritic, salt-corrosion-resistant (HiperFerSCR) steel containing Laves phase particles were studied to investigate the active deformation mechanisms and the evolution of damage. A series of tensile tests were conducted at both room temperature and elevated temperatures (550, 600, and 650 °C), along with detailed microstructural analyses using scanning electron microscopy and electron backscatter diffraction. The tensile flow characteristics of HiperFerSCR at room temperature exhibit significant strain hardening, which is due to the Laves phase particles that encourage planar slip, demonstrated by the formation of numerous slip bands and low-angle grain boundaries. The intersections of these slip bands with grain boundaries appear to be the initiation sites for cracks, which then propagate intergranularly as well as within grain interiors along the slip bands. At high temperatures, the flow characteristics show strain softening, which is attributed to a dynamic recovery (DRV) mechanism, evident in the formation of subgrain boundaries decorated with Laves phase particles. During high-temperature deformation, damage initiates in the particle-free zone (PFZ), which expands at higher temperatures, leading to strain localisation, void formation along the grains, and eventually, grain boundary decohesion.

Experimental Study on the Horizontal Bearing Characteristic of a Strip-Walled Underground Diaphragm Wall

Researching and developing a new type of diaphragm wall foundation can solve the probl em that the traditional diaphragm wall structure may not meet the high standards of safety and stability of underground structures in some specific engineering environments. This paper focuses on the horizontal bearing characteristic of a new form of foundation, a strip-walled underground diaphragm wall, through a series of model tests. In the tests, nine plexiglass models with different section sizes, wall spacings and wall heights, as well as loading strategies (horizontal loads along and against the wall in the model), were conducted. The influence of the above factors on the horizontal bearing performance of the foundation and the soil resistance distribution around the wall was studied. The results show that when the horizontal load applied along the wall is greater than 50 N, the growth rate of total displacement at the top of the wall gradually decreases; when a horizontal load is applied against the wall, with a uniform change in wall height, the optimal wall spacing is 11 cm. When the same displacement occurs, the bearing performance of the model under the former loading strategy is generally 10% higher than that under the later loading strategy. In addition, the depth where the maximum bending moment along the wall occurred gradually moves downward with the increase in horizontal load, and the increase in wall spacing and wall height has a positive effect on the horizontal bearing characteristic. With the application of load, the maximum bending moment of the wall will gradually decrease along the depth. The increase in wall spacing and wall height can improve the overall flexural stiffness and horizontal bearing performance of the foundation. Lastly, the group wall effect coefficient, β, is put forward, and a simplified formula for calculating the horizontal bearing capacity of a strip wall foundation is proposed. In the formula, β is negatively correlated with the buried depth of the wall and positively correlated with the distance between the walls, and its coefficient is greater than 1.

The response mechanism and testing method of the rock elastic modulus while drilling

The elastic modulus is a basic parameter reflecting the deformation resistance and energy concentration characteristics of rock. The traditional testing method of the rock elastic modulus needs to core the surrounding rock and testing it in the laboratory, which has difficulty reflecting the rock mechanical properties under the engineering site environment, and uncontrolled broken surrounding rock is difficult to core for testing. Digital drilling technology provides a new idea for in situ testing of the rock’s elastic modulus. The key is to establish a quantitative relationship between the elastic modulus and drilling data. In this paper, the relationship between rock cutting energy density and drilling data is established, and a series of rock digital drilling tests are carried out. The response law of the drilling data and cutting energy density to the rock elastic modulus is clarified. The inversion model of the rock elastic modulus while drilling (DP-E model) is established. The verification test results indicate that the average difference rate of the test results based on the DP-E model is 7.06% compared with the compression test method, which verifies the effectiveness of the model. This study provides a theoretical basis for in situ testing of the rock elastic modulus.

Mechanical Properties of Raw Filaments and Printed Specimens: Effects of Fiber Reinforcements and Process Parameters.

Fused Deposition Modeling (FDM) is a well-established manufacturing method for producing both prototype and functional components. This study investigates the mechanical properties of FDM components by material and process-related influencing variables. Tensile tests were conducted on seven different materials in their raw filament form, two of which were fiber-reinforced, to analyze their material-related influence. To cover a wide range from standard to advanced materials relevant for load-carrying components as well as their respective variations, polylactic acid (PLA), 30% wood-fiber-reinforced PLA, acrylonitrile butadiene styrene (ABS), polycarbonate (PC), a blend of ABS and PC, Nylon, and 30% glass-fiber-reinforced Nylon were selected. The process-related influencing variables were studied using the following process parameters: layer thickness, nozzle diameter, build orientation, nozzle temperature, infill density and pattern, and raster angle. The first test series revealed that the addition of wood fibers significantly worsened the mechanical behavior of PLA due to the lack of fiber bonding to the matrix and significant pore formation. The polymer blend of ABS and PC only showed improvements in stiffness. Significant strength and stiffness improvements were found by embedding glass fibers in Nylon, despite partially poor fiber-matrix bonding. The materials with the best properties were selected for the process parameter analysis. When examining the impact of layer thickness on part strength, a clear correlation was evident. Smaller layer thicknesses resulted in higher strength, while stiffness did not appear to be affected. Conversely, larger nozzle diameters and lower nozzle temperatures only positively impacted stiffness, with little effect on strength. The part orientation did alter the fracture behavior of the test specimens. Although an on-edge orientation resulted in higher stiffness, it failed at lower stresses. Higher infill densities and infill patterns aligned with the load direction led to the best mechanical results. The raster angle had a significant impact on the behavior of the printed bodies. An alternating raster angle resulted in lower strengths and stiffness compared to a unidirectional raster angle. However, it also caused significant stretching due to the rotation of the beads.

Effects of Sprint Interval Training Surface on Physical Fitness Attributes of Collegiate Female Soccer Players: Identifying Individual Responses to Training on Grass, Sand, and Land Surfaces.

This study aimed to identify the optimal surface for sprint interval training to maximize transfer effects on physical performance measures on the grass pitch. Using a randomized controlled trial design, 40 collegiate female soccer players were equally assigned to three experimental groups performing short sprint interval training (SSIT: 4 sets of 10 repetitions with 5 seconds all-out running, with a 50-second recovery period between each effort and a 3-minute rest interval between sets) on SAND, GRASS, LAND, and a control group. Before and after a 7-week training period, participants underwent a series of field-based tests to evaluate countermovement jump (CMJ), 20-m linear sprint, Illinois change of direction (CoD) speed, Yo-Yo IR1, 2.4 km time trial, and maximal kicking distance (MKD) performance. A two-way analysis of variance with repeated measures was conducted on the data, along with Bonferroni post hoc testing. After the intervention, the control group did not show any changes, while the SAND, GRASS and LAND training groups demonstrated improvements (p = 0.001) in their performance as follows: CMJ (effect size [ES] = 1.21, 0.97, 0.64), 20-m linear sprint (ES = -0.81, -0.55, -0.41), Illinois CoD (ES = -0.72, -0.79, -0.41), Yo-Yo IR1 (ES = 1.86, 1.19, 1.12), 2.4 km time trail (ES = -0.82, -0.62, -0.49), and MKD (ES = 0.60, 0.90, 0.72), respectively. Comparative analysis of SAND, GRASS, and LAND revealed that performing SSIT on SAND results in a significantly greater gain in CMJ than LAND (p = 0.041). Analyzing individual responses to training interventions indicated that the training surface had a favorable influence on CMJ (SAND vs. LAND, p = 0.009), but on other variables no statistically significant (p > 0.05) differences were observed. Considering these findings, it is advised that strength and conditioning coaches use the SAND surface as the initial choice for SSIT sessions regarding greater gains (i.e., ES) in performance. This recommendation aims to facilitate more favorable transfer in physical fitness adaptation on a soccer grass pitch. In case of unavailability of SAND surface, GRASS surface would be a suitable alternative to enhance the physical fitness of collegiate female soccer players.

Simultaneous photocatalytic hydrogen peroxide production and pollutant degradation via bipyridine-based polyimide covalent organic framework

Covalent organic framework (COF) photocatalysts for hydrogen peroxide (H2O2) production are receiving significant attention because of the ever-increasing demand for H2O2. Despite the redox-active property and notable photophysical characteristics of polyimide (PI), the potential of PI-based COFs (PICs) for photocatalytic H2O2 production remains unexplored. Herein, we present a dual redox-active bipyridine-containing PIC (PIC-BPY) as an efficient photocatalyst for H2O2 production. PIC-BPY demonstrated exceptional performance by achieving an H2O2 production rate of 2772 μmol gcat.−1, which is three times higher than its biphenyl-based counterpart. We elucidated the reaction pathway through a series of scavenger tests and electron spin resonance analysis, thereby confirming the additional active role of BPY along with that of PIC framework. Furthermore, we harnessed hydroxyl radicals generated during photocatalysis to explore the potential of PIC-BPY for concurrent pollutant degradation and H2O2 production.

True triaxial unloading test on the mechanical behaviors of sandstone: Effects of the intermediate principal stress and structural plane

A series of true triaxial unloading tests are conducted on sandstone specimens with a single structural plane to investigate their mechanical behaviors and failure characteristics under different in situ stress states. The experimental results indicate that the dip angle of structural plane (θ) and the intermediate principal stress (σ2) have an important influence on the peak strength, cracking mode, and rockburst severity. The peak strength exhibits a first increase and then decrease as a function of σ2 for a constant θ. However, when σ2 is constant, the maximum peak strength is obtained at θ of 90°, and the minimum peak strength is obtained at θ of 30° or 45°. For the case of an inclined structural plane, the crack type at the tips of structural plane transforms from a mix of wing and anti-wing cracks to wing cracks with an increase in σ2, while the crack type around the tips of structural plane is always anti-wing cracks for the vertical structural plane, accompanied by a series of tensile cracks besides. The specimens with structural plane do not undergo slabbing failure regardless of θ, and always exhibit composite tensile-shear failure whatever the σ2 value is. With an increase in σ2 and θ, the intensity of the rockburst is consistent with the tendency of the peak strength. By analyzing the relationship between the cohesion (c), internal friction angle (φ), and θ in sandstone specimens, we incorporate θ into the true triaxial unloading strength criterion, and propose a modified linear Mogi-Coulomb criterion. Moreover, the crack propagation mechanism at the tips of structural plane, and closure degree of the structural plane under true triaxial unloading conditions are also discussed and summarized. This study provides theoretical guidance for stability assessment of surrounding rocks containing geological structures in deep complex stress environments.

Freeze-Thaw Cycle Durability and Mechanism Analysis of Zeolite Powder-Modified Recycled Concrete.

The inferior mechanical performance and freeze-thaw (FT) resistance of recycled concrete are mostly due to the significant water absorption and porosity of recycled coarse particles. In this study, different dosages of zeolite powder were used in recycled concrete. A series of macroscopic tests were used to evaluate the workability and FT durability of zeolite powder-modified recycled concrete (ZPRC). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to reveal the micro-mechanisms of FT resistance in ZPRC. The results show that the increase in zeolite powder content leads to a decrease in the slump and water absorption of ZPRC. Additionally, ZPRC with 10% zeolite powder has superior mechanical characteristics and tolerance to FT conditions. The higher strength and FT resistance of the ZPRC can be attributed to the particle-filling effect, water storage function, and pozzolanic reaction of zeolite powder, which results in a denser microstructure. The particle-filling effect of zeolite powder promotes the reduction of surface pores in recycled coarse aggregates (RCAs). The water storage function of zeolite powder can provide water for the secondary hydration of cement particles while reducing the free water content in ZPRC. The pozzolanic reaction of zeolite powder can also promote the generation of hydrated calcium silicate and anorthite, thereby making the microstructure of ZPRC more compact. These results provide theoretical guidance for the engineering application of recycled concrete in cold regions.