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Reinforced concrete structures play a pivotal role in island and reef engineering projects. Given the resource constraints typical of island regions, substituting traditional manufactured sand aggregate with reef limestone not only reduces reliance on river sand but also addresses the issue of disposing of waste reef limestone slag generated during excavation. However, the performance characteristics of reef limestone concrete, particularly its bond strength with reinforcing steel, warrant further investigation. This is particularly true for the bond–slip behavior of the reinforcement. This study aims to elucidate the effects of various parameters on the bond performance between steel and reef limestone concrete through central pullout tests. These parameters include the type and diameter of the reinforcement, bond length, and loading rate. The investigation encompasses the analysis of load–slip curves, bond failure modes, and variations in bond stress. Additionally, using the Abaqus software, a numerical simulation was conducted to analyze the mesoscopic stress characteristics, thereby revealing the mechanisms of bond formation and failure modes between steel reinforcement and reef limestone concrete. The results indicate that the bond–slip curve for reef limestone concrete reinforced with ribbed rebars and Glass Fiber-Reinforced Polymer (GFRP) rebars can be broadly categorized into four phases: minor slip, slip, decline, and residual, with the residual phase exhibiting a wave-like pattern. The predominant failure modes in reef limestone concrete are either pulling out or splitting. The bond stress in reef limestone concrete decreases with an increase in rebar diameter and bond length; conversely, it increases with the loading rate, although the ultimate slip decreases. The mesoscopic failure characteristics of reinforced reef limestone concrete, as simulated in Abaqus, are consistent with the experimental outcomes. [ABSTRACT FROM AUTHOR]

Nuclear power is a high-quality clean energy source, but nuclear waste is generated during operation. The waste continuously releases heat during disposal, increasing the adjoining rock temperature and affecting the safety of the disposal site. Basalt is widely considered a commonly used rock type in the repository. This study of basalt's mechanical characteristics and damage evolution after thermal damage, with its far-reaching engineering value, was conducted by combining experimental work and theory. Uniaxial compression tests were conducted on basalt exposed to 25 °C, 500 °C, 700 °C, 900 °C, and 1100 °C conditions, and acoustic emission (AE) equipment was utilized to observe the acoustic emission phenomenon during deformation. This study was carried out to examine the mechanical characteristics, the sound emission features, the progression of damage laws, and the stress–strain framework of basalt after exposure to different types of thermal harm. As the temperature rises, the rock's maximum strength declines steadily, the peak strain rises in tandem, the rock sample's ductility is augmented, the failure mode changes from shear to tensile failure, and cracks in the failure area are observed. At room temperature, the acoustic emission signal is more vigorous than in the initial stage of rock sample loading due to thermal damage; however, after the linear elastic stage is entered, its activity is lessened. In cases where the rock approaches collapse, there is a significant surge in acoustic emission activity, leading to the peak frequency of acoustic emission ringing. The cumulative ring count of acoustic emission serves as the basis for the definition of the damage variable. At room temperature, the damage evolution of rock samples can be broken down into four distinct stages. This defined damage variable is more reflective of the entire failure process. After exposure to high temperatures, the initial damage of the rock sample becomes more extensive, and the damage variable tends to be stable with strain evolution. The stress–strain constitutive model of basalt deformation is derived based on the crack axial strain law and acoustic emission parameters. A powerful relationship between theoretical and experimental curves is evident. [ABSTRACT FROM AUTHOR]

Strainburst often occurs in the loading process of tangential stress concentration from surrounding rocks after excavation and unloading of deep rock mass. The concentrated tangential stress is relatively larger on the tunnel walls, which decreases towards the interior of surrounding rocks with a certain gradient. To explore the fracture evolution characteristics of surrounding rocks under different tangential gradient stresses and understand various phenomena in the strainburst process, a large‐scale true‐triaxial gradient and hydraulic‐pneumatic composite loading rockburst test device was adopted to carry out the strainburst tests under four different gradient stresses. Based on the macroscopic failure phenomena, distribution of rockburst debris, macro‐micro morphology of failure cross section, and monitored data of acoustic emission (AE), the fracture evolution of rockburst specimens was analyzed under different stress gradient loadings. The results indicate that the stress gradient has an obvious influence on the fracture characteristics, resulting in different rockburst phenomena. With the increase of stress gradient, the failure stress of rockburst decreases, while the dynamic failure characteristics of rockburst trends to be significant. The increase of stress gradient contributes to higher fragmentation degree of debris, more uniform distribution and better continuity. The total number of cracks in the model decreases with the rise of the stress gradient, and the proportion of shear failure increases, which is the main reason for the enhancement of the rockburst intensity. [ABSTRACT FROM AUTHOR]

Sulfide minerals (mainly FeS2) contained in lead-zinc tailings are easy to be acidified in the air. The acidification mechanism is that the tailing sand generates sulfuric acid and sulfate under the catalysis of oxidant, water and oxygen. The acidic liquid generated by the reaction will continue to react with metal oxides to form an insoluble precipitate.In order to reveal the corresponding changes of chemical properties and physical properties of lead-zinc tailing sand during acidification, a series of reaction processes of tailings under natural conditions were simulated by immersion test in laboratory.It is found through the test that with the deepening of acidification, the coarse particles of tailing sand dissolve, resulting in the decrease of iron concentration in the compound, the increase of fine particles, the increase of specific surface area, the decrease of surface friction and occlusion friction between particles, resulting in the decrease of internal friction angle, and the decrease of the safety of tailings dam. words.

Understanding the effects of thermal fatigue damage on the failure mechanisms of rocks is a key concern in underground engineering. The effects of high temperature on the physical–mechanical behaviors and the failure mechanism of basalt under uniaxial compression are investigated with a combination of acoustic emission (AE), computed tomography (CT), and scanning electron microscope (SEM). The high temperature heavily affects the physical–mechanical properties of basalt but has no effect on the mineral compositions. The evolution characteristics of inter‐event time function F(τ) and cumulative AE energy can be employed to characterize the fracture process of thermally damaged basalt. The damage mechanisms of thermal fatigue are attributed to the occurrence of intergranular cracks, intragranular cracks, and transgranular cracks and irregular holes within basalt. The failure mechanisms of basalt change from shear fracture to mixed tensile–shear fracture and finally to tensile fracture based on the statistical characteristics of low and high dominant frequencies. Highlights: The thermal fatigue effects on the physical–mechanical behaviors of basalt are studied.The relationship between failure process and AE characteristics is constructed.The damage mechanisms of thermal fatigue for basalt are revealed.The failure mechanisms of basalt under uniaxial compression are revealed. [ABSTRACT FROM AUTHOR]

Particle flow numerical simulation was used to reproduce the transient unloading process of a deep-buried single fracture tunnel. The influence of fracture characteristics on the transient unloading effect was analyzed from the aspects of stress state, deformation characteristics, fracture propagation, and energy conversion. The results shows that the surrounding rock stress field of the deep-buried tunnel is divided into four areas: weak stress area I, strong stress area II, stress adjustment area III, and initial stress area IV. The fracture has an important impact on the stress adjustment process of transient unloading of the deep-buried tunnel, and the stress concentration area will be transferred from the bottom corner of the chamber and the vault to the fracture tip. With the increase in the fracture length, the distance from the stress concentration area at the fracture tip to the free surface gradually increases, and the damage area of the surrounding rock gradually migrates to the deep area of the rock mass. At this time, the release amount of strain energy gradually decreases and tends to be stable, while the dissipation energy shows a near 'U' shape change trend of decreasing first and then increasing. Under different fracture angles, the number of mesocracks is significantly different. Among them, the number of mesocracks in the 60° and 30° fractured surrounding rocks is greater followed by the 0° fractured surrounding rock, and the number of mesocracks in the 45° and 90° fractured surrounding rocks is relatively less. In addition, the proportion of compression-shear cracks shows a change trend of increasing first and then decreasing with the increase in the fracture angle, and it reaches the maximum value in the 45° fractured surrounding rock. [ABSTRACT FROM AUTHOR]

Among the factors affecting rock mass failure, the stress state has the greatest influence on the mechanical behavior of rock. The mechanical behavior of rock depends on the change of stress path, and the stress of rock mass is closely related to deformation and failure. In order to study the influence of surrounding rock stress state on the failure mode of surrounding rock, based on the theory of elastic mechanics and fracture mechanics, this paper analyzed the stress state of surrounding rock element and crack propagation of surrounding rock, and estimated the potential failure mode of surrounding rock in different areas of a phosphate mine in Yichang. The results showed that: the surrounding rock element is affected by the gradient stress, and a larger stress gradient corresponds to a larger principal stress ratio and variation direction of the surrounding rock. The failure mode of surrounding rock is affected by the coupling effect of principal stress ratio and principal stress direction. Under the action of certain crack angle and appropriate confining pressure, different fracture mechanisms may occur in the surrounding rock compression. But the partition of surrounding rock failure mode region can predict the surrounding rock failure mode to a certain extent. [ABSTRACT FROM AUTHOR]

To investigate the mechanical properties and damage characteristics of granite under frequent disturbance loads in the process of underground engineering construction, laboratory uniaxial compression tests were conducted on granite under combined dynamic and static loading conditions. The following conclusions were reached: (1) under a dynamic disturbance, the failure stress of granite grows gradually as the initial stress and disturbance load rise due to the coupling of damage and strain-rate effect; (2) the characteristic stresses of granite specimens grow with the increasing amplitude of disturbance Δσ under the disturbing loads; with the same Δσ, the characteristic stresses show an increase trend with the increasing initial stress σm; (3) the particle size distribution of rock fragments broken under the disturbance load follows the fractal law, and the fractal dimension F gradually enlarges with the growth of Δσ, indicative of an increased degree of fragmentation; and (4) the damage variable grows rapidly at first, then steadily, and, finally, shows a rapid growth trend again under the disturbance loads. The Δσ significantly influences the number of cycles and rate of change of the damage variable during the steady increase. This research has certain theoretical significance and engineering guidance value for dynamic disaster recognition and control. [ABSTRACT FROM AUTHOR]

Dynamic characteristics of rock masses are an important part of the safety and stability analysis in rock mass engineering. The split Hopkinson pressure bar (SHPB) tests on the phosphate rock in Yichang are conducted, combined with the Split-desktop digital image method and mesoscopic discrete element method (DEM). Both macroscopic and mesoscopic characteristics of the phosphate rock have been studied from such perspectives as stress and strain, fractal characteristics of fragment size, and the spatial and temporal evolution of cracks. The research results show that the dynamic strength of the phosphate rock presents obvious strain rate effect, but the dynamic elasticity modulus is not so sensitive to the strain rate. There is a great correlation between the failure degree of rock specimens and the strain rate. The fractal characteristics of specimen fragments can be used to quantitatively evaluate the rock failure degree under impact loading. According to the characteristics of crack propagation, the rock failure process under the impact can be divided into four stages, namely the elastic crack-free stage, the crack initiation stage, the rapid crack growth stage, and the slow crack development stage. Moreover, with the increase of impact loading, micro-cracks are activated in large quantities. The specimens gradually change from the local damage mode to the axial splitting failure mode and to the crushing failure mode, and in this process, the number of tensile cracks takes an absolute advantage compared with the number of shear cracks. [ABSTRACT FROM AUTHOR]

In order to explore the specimen failure characteristics during rock-burst under different gradient stress conditions, in this paper, a novel experimental technique was proposed; a common series of tests under two gradient stress paths were conducted on rock similar material specimens using the true-triaxial gradient and hydraulic-pneumatic combined test apparatus. And plaster was used as the rock similar material. In the experimental process, several rock-burst debris with area sizes of 100 mm2 were collected, and the fractal dimensions of typical detrital section crystal contours were analyzed and calculated using a scanning electron microscopy (SEM) method. The results showed that the specimens' failure characteristics which had been induced by the two gradient stress processes were various. Also, the mesoscopic morphology of the rock-burst detrital section had effectively reflected its macroscopic failure characteristics. It was found that the fractal dimensions of the crystal contours of the specimen's detrital section had fractal characteristics, and the box-counting dimension based on the SEM image could quantitatively describe the rock-burst failure characteristics. Furthermore, under the same magnification, the fractal dimensions of the crystal contours of the splitting failures were found to be relatively smaller than those of the shearing failures. [ABSTRACT FROM AUTHOR]

Background. Parkinson’s disease is a neurodegenerative disease in elder people, pathophysiologic basis of which is the severe deficiency of dopamine in the striatum. The purpose of the present study was to evaluate the neuroprotective effect of low-frequency rTMS on Parkinson’s disease in model mice. Methods. The effects of low-frequency rTMS on the motor function, cortex excitability, neurochemistry, and neurohistopathology of MPTP-induced Parkinson’s disease mice were investigated through behavioral detection, electrophysiologic technique, high performance liquid chromatography-electrochemical detection, immunohistochemical staining, and western blot. Results. Low-frequency rTMS could improve the motor coordination impairment of Parkinson’s disease mice: the resting motor threshold significantly decreased in the Parkinson’s disease mice; the degeneration of nigral dopaminergic neuron and the expression of tyrosine hydroxylase were significantly improved by low-frequency rTMS; moreover, the expressions of brain derived neurotrophic factor and glial cell line derived neurotrophic factor were also improved by low-frequency rTMS. Conclusions. Low-frequency rTMS had a neuroprotective effect on the nigral dopaminergic neuron which might be due to the improved expressions of brain derived neurotrophic factor and glial cell line-derived neurotrophic factor. The present study provided a theoretical basis for the application of low-frequency rTMS in the clinical treatment and recovery of Parkinson’s disease. [ABSTRACT FROM AUTHOR]

Due to huge carbon emissions associated with the production of Portland cement (PC), the pursuit of sustainable and efficient cementitious materials is a major challenge to manage solid wastes including urban river sludge. As an eco-friendly alternative to PC, granulated blast furnace slag (GBFS)-modified magnesium oxychloride cement (MOC) is innovatively introduced in sludge solidification. The slag modification to MOC and their synergistic efficiency on sludge treatment is systematically evaluated by unconfined compressive strength (UCS), durability and microstructural tests, considering slag dosage, molar ratio of MgO/MgCl 2 and curing age. The obtained results suggest that MOC-slag mixture is efficient in sludge solidification and the inclusion of slag overcomes the strength retraction of MOC solidified sludge. The mechanical behaviour is closely concerned with the formation of phase 5, brucite and C–S–H gels, which imposes a dominant impact on the morphology and microstructure of solidified sludge. Especially, the physic-chemical effect of slag is able to improve the durability of MOC solidified sludge, and induces an enhancement of its long-term stability. The C–S–H gels formed by alkaline activation of slag are the crucial cause of improvement in long-term strength and durability of MOC-slag solidified sludge. In brief, the combined agent of slag-modified MOC shall be deemed as an effective and eco-friendly approach for urban sludge disposal. • Magnesium oxychloride cement is innovatively introduced to dispose of waste sludge. • Slag overcomes strength retraction and improves durability of MOC solidified sludge. • Strength is highly dependent on MgO/MgCl 2 molar ratio, slag dosage and curing time. • MOC-slag system governs strength, durability and microstructure of solidified sludge. • Phase 5, C–S–H and brucite are detected as mechanisms of MOC-slag solidified sludge. [ABSTRACT FROM AUTHOR]

• The evolution of the temperature fields under different stress gradients is studied. • The spatial distribution of high-temperature points is quantitatively analyzed. • The evolution of the average temperature of high-temperature points is analyzed. • Gradient stress affects theevolution characteristics of temperature fields. • The temperature anomalies that occurred on the samples indicate rockburst zones. To study the influence of gradient stress on the evolution characteristics of the temperature field during rockburst, the gradient and hydraulic-pneumatic composite loading true-triaxial apparatus was used to perform the rockburst tests under true-triaxial gradient loading. The temperature data of the unloading face of each sample under gradient loading were continuously recorded using the infrared thermal imager until the rockburst occurred. For the high-temperature points in temperature field, the variance-mean ratio (VMR) was introduced and the relative average temperature of high-temperature points (RAHPT) was proposed for joint analysis to quantify the evolution characteristics of temperature field. It was found that: (1) the VMR and RAHPT adopted in this paper successfully reflect the evolution characteristics of the temperature fields of all the samples under different stress gradients. The VMR and RAHPT increase initially with the increasing loads but subsequently show upward or downward trends in the late stage of loading under different stress gradients; (2) the VMR and RAHPT curves of each sample exhibit similar trends and obvious changes in phase with the increasing load; (3) the samples show obvious differences in rockburst precursors under different stress gradients, and the temperature differentiation of unloading faces appears shortly before the rockbursts, accompanied by the sudden increases in the VMR and RAHPT curves under high stress gradients; (4) the temperature anomalies that occurred on the samples under loading indicate the damage zones of the impending rockbursts. The research results provide a theoretical basis for infrared early-warning technology of rockbursts in underground openings. [ABSTRACT FROM AUTHOR]