As coal mining progresses to greater depths, the mechanical behavior and fracture mechanisms of composited roadway under complex hydrogeological conditions become critical for ensuring deep mining safety. This paper investigates the mechanical degradation and acoustic emission (AE) characteristics of coal–rock combined body under hydrochemical scouring-dissolution. Uniaxial compression tests combined with digital image correlation (DIC), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) characterize the distinct fracture mechanics and microstructural responses of coal–sandstone combined body to varying pH levels and flow rates. Key findings include: (1) Under more acidic solutions and higher flow rates, coal exhibits a transition from brittle to ductile failure, characterized by microcrack propagation and localized deformation, while sandstone undergoes significant fracture network development due to mineral dissolution and cementation degradation. (2) AE analysis demonstrates coal exhibits uniform microcrack propagation through dense low-energy emissions and stable b-values driven by flow forces, whereas sandstone displays localized high-energy AE bursts with unstable b-values during acid-induced macrofracture development. (3) Microstructural analysis highlights that sandstone is more sensitive to pH-induced dissolution, with rapid pore-fracture expansion, while coal exhibits greater susceptibility to flow rate-driven scouring, causing interlayer delamination and surface erosion. These findings underscore the critical role of groundwater chemistry in shaping the mechanical behavior of coal–rock systems, providing a foundation for safer and more efficient deep mining practices.

To investigate the influence of weak interlayers on the mechanical properties and energy evolution mechanism of gently inclined slate under deep high-strain conditions, this study takes a deep phosphor mine in Guizhou Province as the engineering background. Through on-site sampling, rock samples including interlayers and those without interlayers were prepared. The Zts-844 type triaxial unequal-direction stress unloading test system was used to conduct triaxial loading and acoustic emission tests. The results show: (1) The peak strength, peak axial strain, and elastic modulus of both types of rock samples increase with the increase of confining pressure, while the Poisson’s ratio decreases. (2) In terms of energy evolution, the rock sample without interlayers shows typical brittle failure energy response under low confining pressure; the dissipated energy ratio increases from 21.08

Excavating water-saturated rock strata inevitably induces slippage and alters effective stress, significantly affecting the rock's strength and deformation capacity. Understanding the hydro-mechanical coupling characteristics of these strata is essential for the safe excavation of vertical shafts. This study employs triaxial compression tests on water-saturated sandstone using the MTS-815 rock mechanics test system to investigate these characteristics. Tests were conducted at confining pressures (σ3) of 10, 20, and 30 MPa, with pore water pressures set at 0%, 20%, 40%, 60%, and 80% of the respective confining pressures. The effective stress coefficient (α) was analyzed concerning the rock's deformation and strength. A novel method for calculating the effective stress coefficient, based on the effective stress principle and the Mohr-Coulomb criterion, is proposed, leading to several key conclusions. The results indicate: (1) A positive linear correlation exists between the peak strength attenuation coefficient of sandstone specimens and the effective stress coefficient, with a correlation coefficient of 0.82. (2) The effective stress coefficient α is a bilinear function of pore water pressure p and volumetric stress Θ, with a fitting analysis correlation coefficient of 0.986. Furthermore, α is positively linearly correlated with p and negatively linearly correlated with Θ. (3) Under hydro-mechanical coupling, rock porosity is positively exponentially correlated with the effective stress coefficient. At constant confining pressure, the effective stress coefficient is positively linearly correlated with Poisson's ratio and negatively linearly correlated with the elastic modulus. This criterion addresses the limitations of pore elasticity theory in determining the effective stress coefficient for the peak strength of rocks and significantly enhances the prediction of the mechanical properties of aquifer rocks.

Urban renewal and improving the structural resilience of infrastructure are the hotspots of attention in all walks of life. The structural resilience of existing infrastructure and engineering structures is deteriorating with the increase in service life. In order to quickly improve the structural resilience and service life of existing engineering structures, a new method of rapid reinforcement for in-service concrete beams is proposed in this paper, which is the external prestressed reinforcement method of the side façade. The specific procedure involves creating a penetration hole at each end of the side surface of the concrete beam, inserting a prestressed support rod into the hole and subsequently installing a prestressed long bolt within the support rod. External prestress is applied to the side façade of the concrete beam through prestressed bolts. A total of 21 reinforced concrete beams were designed and manufactured, including 3 contrast beams of ordinary concrete, 9 concrete beams reinforced with traditional external prestressing steel and 9 concrete beams reinforced with externally prestressed steel on side façades. Different initial prestressing forces were applied to the reinforced beams, and flexural shear tests and numerical analyses were carried out on the concrete beams. The failure modes and shear resistances were analyzed. This research demonstrates that, in comparison with the control beam, the ultimate bearing capacity of the traditionally externally prestressed concrete beams increased by 137.8% to 140.8%, depending on the initial prestress difference. For the externally prestressed concrete beams applied to the side façade, these increases range from 42.6% to 52.0%. Furthermore, the cracking load and yield load of the reinforced concrete beams are significantly enhanced, thereby improving their operational performance. Additionally, the numerical results confirm that the theoretical calculations align well with the experimental findings.

The steep slopes of carbonaceous mudstone experience complex time-dependent deformation due to long-term dry-wet cycles and stress induced damage, which often causes slope engineering disasters and is difficult to predict. Establishing a creep model that can accurately characterize the creep characteristics of carbonaceous mudstone under dry-wet cycles is the key to the theoretical calculation and numerical analysis of the stability of carbonaceous mudstone slopes. This study investigates the creep and damage characteristics of carbonaceous mudstone under dry-wet cycles. An improved creep damage model was developed based on damage and component model theories to characterize the nonlinear creep behavior under dry-wet cycles. This model consists of viscoelastic and viscoplastic elements, which account for the damage effects of dry-wet cycles, time, and stress across different creep stages. These damage effects are described by initial, time-dependent, and crack propagation damage variables; their corresponding functions were derived from porosity, time-dependent elastic modulus, and crack propagation parameters. In the stable creep stage, only the viscoelastic element is work, adjusted by initial and time-dependent damage variables. In the unstable creep stage, both viscoelastic and viscoplastic elements are collaborative work, with the crack propagation damage variable introduced to calibrate the viscoplastic elements. The findings demonstrate that the proposed model effectively captures the nonlinear creep characteristics of carbonaceous mudstone. In addition, the model's parameters have clear physical interpretations and accurately represent the coupled effects of dry-wet cycles, time, and stress on creep damage.

China has a vast number of infrastructure projects, with concrete structures accounting for the majority. To achieve the rapid and effective reinforcement and renovation of existing engineering structures, this paper proposes a novel approach for the rapid strengthening of concrete beams: an external prestressed reinforcement method applied to the side facade. To investigate the effectiveness of this new reinforcement method, we used three ordinary concrete beams serving as control specimens without prestress application, nine beams reinforced using traditional external prestressing, and nine beams reinforced with external prestressing applied to the side facade. The results indicated that, in comparison to the control beam and depending on the initial prestress level, the ultimate bearing capacity of the concrete beams reinforced with traditional external prestressing increased by 152% to 155%. Additionally, for the concrete beams reinforced with external prestressing on the side face, the ultimate bearing capacity improved by 53% to 61%. Both the cracking load and yield load of the reinforced concrete significantly increased, thereby enhancing the overall working performance. Based on the finite element simulation results, it can be observed that the simulation calculation outcomes aligned closely with the experimental test results.

This paper presents a theoretical analysis of the damage evolution law of carbonaceous mudstone during compressive failure process under dry–wet cycling. In this study, microscopic testing and uniaxial compression synchronous acoustic emission testing systems are employed to examine the microstructure, mechanical properties, and failure acoustic signal of carbonaceous mudstone. The results demonstrated that dry–wet cycling aggravated the mesostructure damage of carbonaceous mudstone. As the dry–wet cycling increased, the pores of carbonaceous mudstone increased, and the disorganization of the mesostructure became more serious, leading to reductions in peak stress, elastic modulus, and cumulative acoustic emission signals. The analysis of PFC (Partical Flow Code) revealed that the number of crack propagation in carbonaceous mudstone increased, and the crack morphology became more complex under dry–wet cycling. A comprehensive framework was developed to incorporate crack propagation into the damage process, where in the growth of cracks exhibits an "S-shaped" pattern with axial strain. As the number of dry–wet cycling increased, the threshold strain for the accelerated damage increased, and the crack growth rate decreased, along with a decrease in the initiation damage stress. This damage pattern was further evidenced by the identification of the crack propagation morphology and rock failure localization during dry–wet cycling. The proposed method showed good consistency with the experimental test results and numerical simulations, enabling quantitative calculation of compression-induced damage in carbonaceous mudstone.

Energy storage technology can effectively reconcile the imbalance between energy supply and demand, offering significant potential for applications in areas such as waste heat recovery and utilization, as well as building energy efficiency. For this purpose, three types of hollow glass microspheres with varying particle sizes were employed as the base materials in this study. Paraffin was incorporated into the porous aggregates using three methods: porous aggregate adsorption, vacuum adsorption, and negative pressure circulation adsorption, to fabricate paraffin-based composite phase change aggregates. A novel phase change energy storage concrete was developed by incorporating composite phase change aggregate and copper powder into ordinary concrete, based on the experimental evaluation of thermal conductivity and compressive strength of the composite phase change aggregate. The thermal and mechanical properties of the resulting concrete were systematically investigated. Finally, by taking the weather conditions in Hunan Province, China as the reference operating scenario, a numerical simulation model of the phase change energy storage concrete test chamber was developed using Fluent software. Research indicates that among the three adsorption methods evaluated, the negative pressure circulation adsorption method demonstrates the most effective adsorption performance. When the particle size ranges from 0.85 to 1.56 mm, the paraffin adsorption rate in the phase change aggregate is 20 to 35% higher compared to that of the other two particle sizes. When the composite phase change aggregate has a volume replacement rate of 20%, the compressive strength of C30 concrete reaches 31.4 MPa, which complies with the specified requirements. Increasing the dosage of composite phase change materials can significantly improve the energy storage efficiency and thermal conductivity of concrete, however, it may lead to reductions in apparent density, compressive strength, and thermal performance. With increasing copper powder incorporation rate, the thermal conductivity and compressive strength of phase change energy storage concrete exhibit a linear increase. Compared with conventional concrete test chambers, phase change energy storage concrete test chambers demonstrate a more pronounced capability in mitigating indoor temperature fluctuations through effective peak load reduction and valley filling, as well as significantly delaying the occurrence of peak temperatures.

The application environment for concrete is becoming increasingly complex, accompanied by an intensification of its functional requirements. This paper presents a method for developing self-compacting concrete with conductive properties using limonite and graphite as the concrete conductive phases. In the process of concrete preparation, the limonite is initially treated by a pre-wetting method to prevent the surface depression caused by the addition of limonite during the concrete curing process. The second stage of the process involved optimising different proportions of limonite and graphite and different dosages of water-reducing agent, defoamer and dispersant to prepare concrete. The influence of different dosages of limonite and graphite and different dosages of water-reducing agent on the mechanics and electrical conductivity of concrete was studied in order to obtain self-compacting conductive concrete with performance indicators meeting the requirements of self-compacting and electrical conductivity. The results demonstrate that the mechanical and electrical properties of self-compacting conductive concrete prepared with polycarboxylic acid superplasticizer and retarding superplasticizer combined with superplasticizer are satisfactory, and the composite superplasticizer can function in conjunction with dispersant. The self-compaction index, slump expansion, expansion time T50 and J-ring expansion of fluid concrete meet the requisite standards. Once the concrete has reached the designated curing age, its compressive strength and flexural strength align with the anticipated design expectations, while its resistivity meets the stipulated conductivity index requirements.

In order to obtain conductive concrete with good electrical conductivity and good mechanical properties, nanographite and magnetite sand excited by different activators and their combinations are added to ordinary concrete to obtain high quality and efficient conductive concrete. The optimal mixture ratio of alkali-excited conductive concrete and the effects of different activators and their combinations on the mechanics and electrical conductivity of concrete were studied. The microstructure of alkali-excited conductive concrete was analyzed by scanning electron microscope (SEM) to study its conductive mechanism. Results show that the conductive concrete obtained by compounding sodium hydroxide, sodium sulfate and calcium hydroxide has optimal mechanical and electrical properties when the graphite is 6% cement, and magnetite sand is 40% fine aggregate. The conductive concrete sample prepared by this method has a flexural strength of 6.84 MPa, a compressive strength of 47.79 MPa and a resistivity of 4805 Ω·cm (28 days). Compared with ordinary concrete (no nanographite and no magnetite sand), the compressive strength of conductive concrete is increased by 122.3%, the bending strength is increased by 116.5%, and the resistivity is reduced by 99.1%. SEM shows that the distribution of conductive materials in concrete is more uniform due to alkali excitation and calcium silicate hydrate (CSH) gel can be formed, which leads to better performance. The research in this paper is only a preliminary exploration of the characteristics of green conductive concrete, and the conductive heating characteristics and electromagnetic wave absorption properties of concrete, along with strength characteristics after adding conductive fillers, need to be further studied. It is suggested that further research should be carried out on the deicing characteristics of conductive concrete and the electromagnetic wave absorption properties used in stealth military engineering.

Stainless steel has the characteristics of oxidation resistance, high temperature resistance, corrosion resistance, high strength, and high yield ratio. The use of stainless steel bars can extend the life of a structure, reduce later maintenance costs, and reduce the whole life cycle cost of the structure. In this paper, nine concrete columns reinforced with duplex stainless steel (S2205) (DSSRC) and nine ordinary reinforced concrete columns (ORC) were poured with the diameter of steel bars as the parameter, and axial compression tests were carried out on these eighteen concrete columns. The failure mode of the concrete columns is analyzed, and the compressive performance indexes of the two kinds of concrete columns are compared. The results show that, compared with the ORC, the cracking load of DSSRC is increased by 33%, the ultimate load is increased by 30.7%, and the deformation performance of the DSSRC is also improved significantly. On the basis of the test, the finite element model of DSSRC was established with the help of ABAQUS software, and the obtained failure law was consistent with the test; the experimental value, the calculated value, and the numerical simulation value of the axial compression capacity were in good agreement, which verified the feasibility of the test and provided a theoretical basis for practical engineering applications.

In order to explore the corrosion resistance of duplex stainless steel under seawater corrosion and the compressive stiffness of its reinforced concrete columns, this study first performed seawater corrosion resistance tests on HRB400 ordinary steel rebar and S32205 duplex stainless steel rebar. The effect of the corrosion product film on the corrosion behavior was investigated through polarization curve tests and electrochemical impedance spectroscopy tests. The results showed that the corrosion rate of S32205 duplex stainless steel in a seawater environment was approximately 1/15 that of the HRB400 ordinary steel rebar. The anodic polarization curve of duplex stainless steel rebars exhibited a greater slope than that of carbon steel rebars. In the simulated seawater environment, the corrosion rate of these two kinds of steel bars showed different trends. The corrosion rate of ordinary steel bar HRB400 first decreased and then increased, while that of duplex stainless steel S2205 increased steadily. Furthermore, 18 short concrete columns reinforced with ordinary and duplex stainless steel rebars were subjected to the axial compression test and stiffness analysis; the stiffness of the short columns was calculated from the test data. The theoretical values agreed with the test values, with a stiffness calculation error of less than 5%.

Conductive concrete with nanographite–cupric nickel sulfate ore was prepared in this paper. As a new type of multifunctional multiphase conductive building material with conductive, electrothermal, electromagnetic shielding, piezoresistive properties, etc., nanographite–cupric nickel sulfate ore conductive concrete will have a wide range of applications in snow melting, electromagnetic shielding, cathodic protection and structural health monitoring, and other fields. In this paper, different dosage of nanographite and cupric nickel sulfate ore admixture that the mixture was excited by alkali excitation, ultrasonic vibration and combined alkali excitation and ultrasonic vibration, respectively were used to study the electrical conductivity and mechanical properties of conductive concrete, 36 groups of nanographite–cupric nickel sulfate ore conductive concrete specimens and seven groups of comparative specimens were cured for 28 days, and the unconfined compression test, three-point bending test, and electrical conductivity test were carried out. The results show that the electrical conductivity and mechanical properties of the specimens with 6% nanographite and 60% cupric nickel sulfate ore were the best, with the compressive strength, flexural strength and resistance reaching 40.83 MPa, 6.81 MPa, and 5,850  Ω ·cm, respectively. Compared with the comparative specimens, the compressive strength and the flexural strength of the specimens are increased by 38.5% and 20.4%, respectively, and the resistivity is decreased by 55.7%. This shows that the alkali excitation-ultrasonic vibration activation method can not only improve the electrical conductivity of nanographite–cupric nickel sulfate ore conductive concrete pavement but also ensure the stability of its mechanical properties.

Electrically conductive cementitious composite (ECCC) features structural material functions, electrical conductivity, and piezoresistivity properties broadly applied in snow melting, electromagnetic shielding, cathodic protection system, and structural health monitoring (SHM). Nano-graphite is an ideal ECCC functional filler since its ability to fill molecular pores, reduce concrete shrinkage and significantly improve their electrical conductivity. However, nano-graphite is high-cost and its excessive amounts can lead to particle agglomeration. Therefore, copper slag (CS) can partially replace NG to beneficially reuse the waste by-products and save energy for protecting the environment. Nevertheless, a single blend of fillers hardly exploits the potential mechanical and conductive properties. Consequently, different activation methods were adopted to obtain desirable dispersion and performances. This paper explored the influences of chemical alkali excitation, ultrasonic vibration, and combined activation on copper slag and nano-graphite wrapped ECCC. Experimental results from a total of 387 ECCC specimens with 16 design ratios demonstrated that the combined treatment of alkali excitation and ultrasonic vibration was superior to any single treatment. The optimal samples based on 3 wt% ratio of NG and 60 wt% of copper slag activated with combined treatment exhibited 44.55 MPa compressive strength, 6.65 MPa flexural strength, and 8180 omega.cm electrical resistance. Lastly, an SEM was conducted to analyze the microstructure of the mixture and ECCC and a schematic diagram was proposed.

The bedrock used for underground construction has obvious traces of hydrodynamic scouring damage, and the mechanical properties of bedrock especially are severely damaged under a groundwater environment. On this basis, considering the excavated bedrock under various saturations, the uniaxial compression test of diorite is carried out. Meanwhile, scanning electron microscopy (SEM), electron energy spectroscopy (EDS) and X-ray diffraction (XRD) are used in the experiment. The variation law of the elastic p-wave velocity and microstructure and the response characteristics of the strength, deformation and mechanical parameters of rock under different flow rates and pH values are analyzed in detail. The results indicate that: (1) Saturations with a faster flow rate and lower pH value cause greater relative changes in the elastic longitudinal wave velocity of the samples. (2) The uniaxial compressive strength of the samples under various treatment conditions showed a decreasing trend. Compared with the dried samples, the uniaxial compressive strength of the samples under saturation with field flow rate v = 300 mm·s−1 and pH = 1 decreased by 46.08%, and the strength decreased by 35.67% under saturation with a field pH value = 6.56 and flow rate v = 900 mm·s−1. (3) The saturation with a stronger acidity, greater flow rate and longer action time causes the apparent dense structure of the diorite sample to be loose and accompanied by microcracks, which weakens its macromechanical properties. (4) Acid and hydrodynamic saturation produce water–rock chemical and physical effects on diorite, which weaken the connection force between mineral particles and the friction between fracture surfaces, reduce the elastic modulus, increase Poisson’s ratio and accelerate the failure of diorite.

Electrically conductive cementitious composite (ECCC) is a multifunctional material utilized in structural health monitoring (SHM), electromagnetic shielding, and pavement deicing. The addition of nano-graphite (NG) in ECCC can prominently enhance the electrical behavior and improve the mechanical strength due to its filling of molecular pores. Besides, magnetite can replace part of graphite owing to its excellent mechanical performance. To enhance molecular dispersion and bring out the potential of the composite, three various modifying treatments were carried out. This paper explored the modifying effects of alkali excitation, ultrasonic vibration coating, and combined activation on magnetite-nano-graphite incorporated ECCC. In total, 360 ECCC specimens were proposed for electrical resistance, compression strength, and flexural strength. The results indicate that chemical activation facilitated the pozzolanic reactivity of fly ash-cement system. Meanwhile, the ultrasonic vibration prompted the uniform distribution of magnetite-nano-graphite. The combined surface treatment is superior to any single treatment, endowing ECCC balanced in great mechanical properties and electrical conductivity. A 6 wt% ratio of NG, 60 wt% of magnetite with combined activation is illustrated as the optimum design with 6.92 MPa of flexural strength, 46.75 MPa of compressive strength, and 3430 omega cm of resistance. Finally, a microstructure analysis of ECCC was performed by SEM to investigate the conductive mechanism and a schematic diagram was proposed.

A new external reinforcement method is proposed in this research by using the prestressed angle steel plate to fully wrap a reinforced concrete column with a rectangular cross section. To study the axial compression characteristics of the new proposed structure, twenty pieces of the concrete columns were built using the normal reinforcement: five control columns and fifteen reinforced concrete columns, with three groups of different prestressed angle steel plates. These columns were tested under axial compression after the completion of the reinforcement. The experimental results showed that the ultimate load-bearing capacities of the three groups of the reinforced concrete columns with different prestress levels were increased by 35.6%, 52.7%, and 61.7% compared with the control columns. Both the ultimate strain and the deformation were improved significantly. The load-bearing capacity equation of the reinforced column was deduced based on the unified strength theory, and the accuracy of the equation was validated. Moreover, a finite element simulation was performed for the new structure, and the simulation results were in good agreement with the test results. Simulation results are in good agreement with the experimental results.

The electrically conductive cementitious composite (ECCC) offers plenty of advantages such as high conductivity and strain sensitivity. The ECCC can also act as a conductive sensor in a cathodic protection system for structural health monitoring. Before the ECCC application, it is essential to understand and predict the uniaxial compressive stress (UCS) and electrical resistivity. In this study, we produced ECCC with three conductive fillers: graphite powder (GP), waste steel slag (SS) as well as ground granulated blast-furnace slag (GGBS). By changing the content levels of the three conductive fillers, cement and curing ages, we prepared 81 mixture proportions for UCS test and 108 mixture proportions for resistivity test. The results show that although GP improves the conductivity more significantly than the other conductive fillers but it simultaneously has a higher negative influence on UCS. Meanwhile, slag solids (GGBS and SS) enhance the conductive performance but reduce UCS after their replacement ratio is larger than 20%. Compared with GGBS, ECCC containing SS has higher UCS and conductivity. Besides, we proposed a random forest (RF) based machine learning model to predict the UCS and resistivity. The hyperparameters of the RF model were tuned by the beetle antennae search (BAS) algorithm. This hybrid BAS-RF model has high prediction accuracy, as indicated by high correlation coefficients on test sets (0.986 for UCS and 0.98 for resistivity, respectively). We simulated the influence of different conductive fillers on UCS and conductivity using the developed BAS-RF model. The simulation results agree well with the results obtained by laboratory experiments. This study offers a new idea to use waste slags to produce ECCC and paves the way to intelligent construction.