Reinforced concrete is susceptible to corrosion caused by high pressure CO2, which leads to structural damage within a short term. Exposure to a CO2 pressure of 1000 kPa results in a carbonation corrosion effect on reinforced concrete that is approximately 7500 to 10000 times greater than that observed under typical atmospheric carbonation conditions. This study examined the steel corrosion mechanisms and the impact of high pressure CO2 on reinforced concrete in various environments, utilizing electrochemical methods such as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) to characterize steel corrosion in concrete. The EIS of the steel subjected to carbonation corrosion revealed both high and low frequency capacitive arcs. As the reaction time increased, the capacitive arcs shifted towards higher frequencies, indicating an escalation in steel corrosion. Within the 28 days of the reaction, no distinct capacitive arc was observed, suggesting that complete corrosion of the steel did not occur. As CO2 pressure raised, the accumulation of corrosion products and the development of a corrosion product film contributed to a reduction in the corrosion rate of steel. Under the dry gas and 70% relative humidity (RH) environments, the EIS of the reinforced concrete after reaction displayed high, medium, and low frequency capacitive arcs. Over time, the capacitive arcs progressively shifted towards lower frequencies, representing a decrease in the corrosion of steel, which was caused by concrete carbonation. In the pure water environment, the absence of a medium frequency capacitive arc was attributed to the dissolution of hydration and corrosion products. The corrosion rate of steel was reduced when protected by concrete. However, under conditions of 70% RH and 1000 kPa CO2, the impedance of the concrete decreased and the corrosion of the steel intensified after 14 days of reaction.

The reinforced concrete structure is exposed to long-term chloride ion erosion in the hydraulic environment, which can lead to steel corrosion and crack expansion, significantly affecting its durability and service life. Traditional repair methods often fail to simultaneously achieve crack healing and chloride ion removal, resulting in limited repair effectiveness. This study proposes a remediation technology that combines electric field-induced hydration of calcium silicate (C-S-H) gel with electrochemical chlorine removal. It systematically explores the synergistic effects of current density (0.5-2.5 A/m2) and sodium silicate concentration (0.05-0.30 mol/L) on the remediation outcome. By measuring the macroscopic properties of the specimens (chloride ion removal rate, crack healing rate, flexural strength recovery rate, chloride ion diffusion coefficient, half-cell potential) and the microstructural characterization (SEM, XRD, TG), researchers investigate the mechanism of the electrochemical parameters on the formation of the repair products and the recovery of structural properties. The results show that at a current density of 2.0 A/m2 and a sodium silicate concentration of 0.15 mol/L, the repair system achieved optimal synergy: the chloride removal rate reached 58.293%, the crack healing rate reached 100%, the filling depth reached 17.203 mm, the flexural strength recovery rate reached 19.070%, and the chloride diffusion coefficient decreased by 18.465%. The corrosion risk of the reinforcing steel decreased from the high-risk zone to the moderate-risk zone after the repair process. Microstructural analysis revealed that under these conditions, a composite structure of "crystalline skeleton-C-S-H gel-AFt crystals" formed, with a Ca/Si ratio close to 1.17, resulting in the densest product. This research can provide a theoretical basis and technical references for repairing cracks in reinforced concrete structures and enhancing their durability.

To ensure the application of microbial self-healing concrete (MSHC) in practical engineering, it is imperative to investigate its constitutive model and the effect of microbial self-healing agent (MSHA) dosage on concrete properties. In this study, a constitutive model for MSHC is established using a Weibull-lognormal statistical distribution, and the effect of MSHA dosage on concrete performance is investigated. Results show that MSHA dosages of 0.30 m(3) and 0.45 m(3) serve as critical thresholds for compressive strength and splitting tensile/flexural strength, respectively, beyond which mechanical properties decline sharply. The optimal MSHA content was determined to be 0.33 m(3) per unit volume of concrete. Based on the constitutive model and ordinary concrete parameters, the mechanical behaviour of MSHC at any MSHA dosage can be effectively predicted. With the optimal dosage, MSHC healed cracks narrower than 1.02 mm after 28 days, achieving area and permeability repair rates of 96.02% and 77.65%, respectively.

This study explores the effect of early-age low-pressure curing on freeze-thaw damage evolution of concrete in plateau environments with low pressure and large temperature differentials. Freeze-thaw tests were performed at curing pressures of 63, 74, and 101 kPa and minimum temperatures of -10, -20, and -30 degrees C, using macroscopic evaluation, nuclear magnetic resonance, and a Thermal-Hydraulic-Mechanics mesoscopic model. Results show that low-pressure curing significantly coarsens the initial pore structure. Decreasing temperature narrows the freezing front transition zone, leading to severe deformation gradients and stress concentrations at specimen boundaries and in the Interfacial Transition Zone. Damage-mechanism transitions: at similar to-10 degrees C, frost-heave stress from pore-water phase change dominates; below -20 degrees C, freezable-water depletion shifts dominance to thermal-incompatibility stress from differential aggregate-mortar thermal expansion. This reveals the intrinsic correlation between low-pressure curing and extreme low-temperature service, providing theoretical support for frost-resistance optimization and reliability evaluation of plateau hydraulic structures.

The application of microbe-induced carbonate precipitation (MICP) to self-healing concrete cracks has broad prospects, where the mix design of a microbial self-healing agent (MSHA) is the key to smooth concrete crack repair. In this study, expanded perlite was used as a microbial carrier to investigate the immobilization capacity of microorganisms under different pressure conditions. The optimum mix proportion of sugar coating layer material and protective layer material used to wrap microbial carriers to prepare MSHA were determined. Moreover, the repair effects of different wrapping layers on concrete cracks were investigated. Results showed that the immobilization capacity of small-pore expanded perlite (EP) was the greatest when the adsorption pressure was 0.05 MPa and the immobilization time was 20 min. The optimum ratio of water to cement (W/C) of sulphoaluminate cement for the sugar coating material was 0.52, and the optimum spraying ratio was 4.0. The best W/C of ordinary portland cement for the protective layer was 0.46, the best waterproofing material content was 7.5%, and the best spraying ratio was 3.5. The wrapping of a sugar coating layer and a protective layer around the carrier surface significantly improved MSHA performance and had excellent compatibility with concrete materials. When the crack width was 0.9 mm, the MSHA with this proportion completely repaired cracks after 14 days.

In this study, the effects of the particle size gradient and dosage of polyacrylic acid superabsorbent resin (SAP) on the mechanical properties of recycled aggregate concrete (RAC) were analyzed through macroscopic experiments. Using response surface methodology optimization, the optimal SAP parameters were determined to be a particle size of 67.17 mesh and a dosage of 0.248%. Salt-frost cycle tests revealed that compared with ordinary RAC, SAP-RAC reduced the mass loss rate by 17.4%, the compressive strength loss rate by 7%, and the chloride ion permeability coefficient by 6%. The established salt-frost damage model closely matched the experimental data. Nuclear magnetic resonance testing and scanning electron microscopy analysis indicated that SAP promotes secondary hydration reactions by absorbing and releasing water, thereby refining the pore structure of SAP-RAC. However, the salt-freezing coupling effect weakens the thickness and density of the interfacial transition zone (ITZ).

This paper systematically reviews the research progress on the mechanism of concrete performance degradation and durability improvement techniques under the multi-factor coupling environment of low pressure, freeze-thaw cycles, salt erosion, and ultraviolet radiation. The results show that the multi-factor coupling effect presents significant nonlinear synergy and temporal accumulation characteristics, and its damage evolution follows the phased law from micro-deterioration to macro-failure. In terms of the deterioration mechanism, low air pressure, freeze-thaw cycles, salt erosion, and ultraviolet radiation interact through physical, chemical, and mechanical pathways, collectively accelerating the deterioration process of the concrete's microstructure. In terms of enhancing technology, the application potential and limitations of multiple types of technologies, such as material modification, microstructure regulation, and surface protection, were pointed out, and it was made clear that building a multi-level protection system through technological collaboration is an effective strategy to deal with complex coupled damage.

Chloride ion erosion can lead to cracking in reinforced concrete and cause corrosion of steel bars. This study explores the feasibility of a remediation method that combines electric-field-induced C-S-H deposition with electrochemical Cl− extraction. Accelerated repair tests with varying current densities and Ca/Si ratios were conducted to systematically analyze the effects of repair parameters on chloride-ion removal efficiency, crack-geometric repair indices, and the durability of reinforced concrete. A three-dimensional, transient, multi-field-coupled ion migration model was developed, revealing the electrochemical-mechanical coupling mechanism. The results show that an appropriate current density (2.0 A/m2) and a moderate Ca/Si ratio (1/1–4/3) can achieve the optimal crack-filling effect and chloride removal efficiency. This combination generates a dense C-S-H gel network with high stability. The contour distribution of the comprehensive repair indices further indicates that the current density of 1.5–2.0 A/m2 and the calcium-silicon ratio of 1/1–4/3 constitute the optimal parameter window. Through the multi-field coupling model, the electro-chemical-mechanical coupling law of the combined repair was clarified: the electric field acts as the core driving force for ion migration, regulating the directional aggregation of reactive ions and the intensity of interface reactions, while the Ca/Si ratio can affect the reaction balance of ions in the system; the precipitation and filling of hydration products dynamically reduce the porosity of concrete, which in turn acts on ion migration, forming a self-inhibition mechanism. This study can provide an experimental and theoretical basis for crack filling and chloride removal in hydraulic reinforced concrete structures.

The crack width and the healing age significantly influence the self-healing efficacy of microbial self-healing concrete (MSHC). This study investigated the effects of crack width and healing age on the crack repair performance of MSHC incorporating Bacillus cohnii under standard laboratory water immersion curing conditions. A kinetic model based on the first-order reaction equation is established to describe the autogenous healing process of MSHC, enabling analysis of the microbial self-healing agent (MSHA) effective duration under varying crack widths. The results indicate that cracks with widths of 0.5 mm, 1.0 mm, and 1.2 mm were substantially healed after healing ages of 7 d, 14 d, and 28 d, respectively. Cracks of 1.5 mm in width failed to achieve complete healing after 28 d. The healing efficacy of MSHC manifested two distinct stages with increasing healing age: (I) rapid enhancement, (II) stabilization. The developed self-healing kinetic model, combined with crack width data, the effectiveness of MSHC crack repair can be efficiently predicted for any specified healing age, allowing for thorough investigation of the healing progression. The functional duration of the MSHA spanned approximately 9 d, 21 d, 45 d, and 76 d for cracks of 0.5 mm, 1.0 mm, 1.2 mm, and 1.5 mm width, respectively. This provides a theoretical foundation for assessing the impact of crack width and healing age on the self-healing efficacy of MSHC.

Early-age concrete cracking, driven by the complex interplay of thermal, hydration, moisture, and stress (THMS) fields, significantly compromises the durability of concrete structures. Conventional models often oversimplify concrete as a homogeneous material and fail to capture this complexity. To address this limitation, this study develops a mesoscopic-scale THMS coupling model that explicitly accounts for the heterogeneity of aggregates, mortar, and the interfacial transition zone (ITZ), each possessing distinct constitutive properties. The governing equations are discretized and solved using the finite element method (FEM), enabling high-precision simulation of multiphysics interactions. The model is rigorously validated against macroscopic experiments, with simulations demonstrating close agreement with measured data-accurately replicating the internal temperature increase (peaking at 27.2-27.6 degrees C between 72 and 96 h) and the humidity decrease (from 0.98 to 0.71-0.80 after 672 h). Combined with microhardness testing and scanning electron microscopy (SEM) analysis of the microstructural evolution of the ITZ, a mechanistic explanation for the simulation results is provided: within 3-6 days, the internal stress exceeds the tensile strength, with the cracking risk index surpassing 0.7. Microhardness tests indicate that the mechanical properties of the ITZ are significantly weaker than those of the mortar matrix at this stage. Further analysis demonstrates that a higher aggregate content intensifies restraint stress, thereby accelerating the cracking process. The proposed model offers a powerful tool for predicting cracking risk and optimizing curing strategies, contributing to the enhancement of structural durability.

The application of nanomaterials provides new approaches to improve the chloride ion corrosion resistance of concrete. This study aims to explore the mechanism by which nanomaterials enhance the durability of concrete in chloride-rich environments and establish a time-dependent lifespan prediction model that comprehensively considers nanomaterial parameters and concrete degradation effects. The research measured the apparent chloride ion diffusion coefficients of ordinary Portland cement (OPC) and nanomodified concretes (nano-SiO2 (NS), nano-Fe3O4 (NF), and nano-TiO2 (NT)) at 28 days through non-steady-state chloride ion diffusion tests (RCM). Combined with artificial seawater immersion simulations, it tracks chloride ion transport patterns over the full aging period (91-365 days). Based on experimental data, an improved Fick's second law lifespan prediction model was ultimately constructed. And, XRD, thermogravimetric analysis (TG), and SEM-EDS were employed to reveal microscopic mechanisms. The results indicate: 1) The ranking of the chloride ion penetration resistance of the three nanomaterials is NT > NS > NF. Under the best condition, the apparent diffusion coefficients of NS, NF, and NT are 3.59 x 10(-12), 4.20 x 10(-12), and 2.87 x 10(-12) m(2) s(-1), respectively, which are 49.95 %, 41.50 %, and 60.02 % lower than OPC. The apparent diffusion coefficient shows a trend of "first decreasing and then increasing" with the dosage and particle size. The optimal parameters are a dosage of 5 % and a particle size of 10 nm. 2) The full-ageing period diffusion coefficients exhibit a trend of "sharp decline from 28d to 90d (average reduction of 60 %)-> stabilization after 270d", with the NT group having the highest aging decay factor m (0.418-0.561). 3) Lifespan predictions show: when the protection layer thickness of NT-modified concrete increases from 40 mm to 65 mm, the lifespan rises from 2.96 years to 27.03 years (an 813.18 % increase). Mechanistic analysis reveals: NS, NF, and NT can promote cement hydration through the "nucleation effect," consuming C2S and C3S to form C-S-H gel. NT exhibits a significantly higher mass loss rate than the NS and NF groups due to its abundant surface hydroxyl groups. SEM reveals that the interface transition zone (ITZ) of the NT group has only a small number of closed pores, with dense C-S-H gel. EDS spectra show a uniform distribution of Ti with Ca and Si, resulting in a more compact structure. While the ITZ of the NS group is less dense, the NF group is relatively loose. This study provides a quantitative reference for the durability design of concrete structures in chloride-rich environments.

Particle breakage is prevalent in rockfill materials and significantly influences the deformation and stability of rockfill dams. In this study, the discrete element method (DEM) was used to examine particle breakage in rockfill materials under flexible boundary triaxial compression and to further analyse the corresponding macro- and micromechanical responses. The microscopic parameters were calibrated using the results from laboratory triaxial tests. Realistic particle shapes were reconstructed using the bonded-particle method, and a coupled FDM-DEM approach was adopted to achieve a freely deformable flexible membrane boundary. On this basis, a DEM triaxial model incorporating realistic particle geometry was established to analyse the macroscopic mechanical behaviour of rockfill, including the shear strength, dilatancy, critical state behaviour, and internal friction angle, under different confining pressures (63). The influence of 63 on the evolution of particle breakage was clarified, and the reliability of the results was verified through comparisons with previous studies. The mechanisms underlying the macroscopic responses were subsequently interpreted from a microscopic perspective by analysing the evolution of the mean coordination number, contact fabric, force chains, and contact anisotropy associated with particle breakage. Finally, the correlation between the fabric anisotropy of rockfill and its shear strength was quantified within the branch-vector framework, highlighting its contribution to shear resistance. The results indicate that increasing 63 intensifies particle breakage, leading to a rightward and upward shift of the gradation curve. However, the changes in the volumetric fraction of coarse particles is minimal, and shear deformation mainly increases the fraction of fine particles. Enhanced particle breakage under higher 63 reduces the volumetric and stress dilatancy, friction angle, and anisotropy of the mean normal contact force. The anisotropy of the normal force is generally greater than that of the contact normal and tangential forces. During the initial shear stage, the anisotropy of the normal force dominated, whereas the anisotropy of the contact normal became dominant in the post-peak stage. In other words, the peak shear strength primarily originates from the anisotropy of the normal force, whereas the residual strength is governed mainly by that of the contact normal. The anisotropy of the tangential force varies little throughout the shearing process.

This article addresses the impact and mechanism of a low-pressure environment on concrete performance. Samples were prepared under different conditions by simulating low-pressure conditions, and the air content was measured. The workability, mechanical properties, durability, and air content of the concrete were measured, and the response surface method (RSM) was used to optimize the water-cement ratio (WCR) of the concrete in low-pressure environments. Freeze-thaw damage modeling of low-pressure cured concrete at various WCRs was developed. The internal microstructure and pore distribution of low-pressure cured concrete under different WCRs were studied by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) techniques. The results show that the compressive strength, flexural strength, and air content of concrete decrease in low-pressure environments with increasing WCR. The flexural strength of the concrete reached its peak at a WCR of 0.3. The response surface method optimization revealed that the overall performance of the concrete is better when the WCR of the concrete is between 0.3 and 0.35. The established freezethaw damage model is highly consistent with the experimental data. In addition, SEM analysis and NMR testing revealed that a decrease in air pressure and an increase in WCR could lead to an increase in the thickness and porosity of the interfacial transition zone (ITZ), a decrease in compactness, and a predominance of tiny pores in the concrete pore distribution.

The joint structure between the asphalt concrete core and the concrete plinth is a critical and vulnerable part of the asphalt concrete core dam (ACCD). Shape parameters of the core-plinth joint structure are directly related to joint structure behavior and thus affect the core safety, but there is currently a lack of relevant quantitative research. In this paper, the shape parameters of the joint structure were optimized to obtain an economical joint form under the condition of ensuring the stress safety of the joint structure. Abutment slope ratio i, core enlarged angle theta, and depth of the core embedding into the plinth h were taken as optimization parameters. The maximum shear stress, maximum tensile stress, and minimum arch effect of the core were taken as constraint conditions, and the joint structure volume was taken as the objective function to establish a mathematical optimization model for the joint structure. The regression relationship between the constraint conditions and the joint structure parameters was fitted based on the central composite design and response surface method. A three-dimensional zone of joint structure parameters that can satisfy the constraints was further constructed. Combined with the linear programming method, an optimization calculation method for joint structure parameters was proposed. Taking the dam with the highest core among the ACCDs that have been built as an engineering example, an optimization analysis of the joint structure between the core and plinth was conducted. The results indicated that the stress and the arch effect of the joint structure improve as the abutment slope becomes gentler. As h increases, the arch effect and shear stress at the joint weaken. The increase in theta will increase the possibility of core shear failure and make the core suffer a stronger arch effect. Compared with the original engineering (theta and h are 75.96 degrees and 0.3 m, respectively), when the theta and h are set as 80 degrees and 0.39 m, the joint structure volume reduces by 6.67% under the condition of i of 1:0.33, which can achieve better economic efficiency under the premise of satisfying the core safety.

This study utilized microbial-induced carbonate precipitation (MICP) technology and modified recycled aggregates with Bacillus cohnii. To enhance the performance of recycled aggregate concrete(RAC) by improving the inherent defects of the aggregates. This study explored the optimal bacterial concentration for modification effects, investigated the mechanical and frost resistance of modified recycled aggregate concrete (MRAC) at various substitution rates, and established a uniaxial compressive constitutive model for MRAC. The internal microstructure and chemical composition of MRAC were studied using SEM electron microscopy and thermogravimetric analysis techniques. The results showed that the optimal bacterial concentration for modification was 1.262 x 108 cells/mL. Based on this concentration, the water absorption rate of the modified recycled aggregate decreased from 4 % before modification to 2.4 %, and the apparent density reached 2920 kg/m3. The maximum substitution rate for modified recycled aggregate is 40 %. At this time, the overall performance of MRAC is equal to that of natural aggregate concrete(NAC). Compressive, flexural, and tensile strengths are 38.59 MPa, 3.9 MPa, and 2.22 MPa. The results of SEM electron microscopy and thermogravimetric analysis indicate that the main component of the mineralized sedimentary products of Bacillus subtilis is calcium carbonate. The mineralization effect of Bacillus subtilis can effectively repair the pores and microcracks of recycled aggregates, improve the bonding effect within ITZ, and enhance the performance of concrete.

To explore the effects of temperature and strain rate on the damaging mechanism of asphalt concrete under uniaxial compression, experimental and numerical investigations were conducted. Firstly, uniaxial compressive test of asphalt concrete at various temperatures (− 10 °C 20 °C) and strain rates (10–5/s 10–2/s) were conducted. Then, based on the viscoelastic-plastic damage constitutive model and discrete element method (DEM), the complete stress–strain curves of asphalt concrete at various temperatures and strain rates were well simulated. Finally, the damaging mechanisms of asphalt concrete under uniaxial compression were analyzed based simulated results. The results indicate that the interface between asphalt mortar and coarse aggregate is prone to damage, and there are more shear cracks compared to tensile cracks. In addition, the fragments number relates to crack evolution rate. Temperature effect on mechanical behaviors is mainly due to the gradual transformation between elasto-plasticity and viscoelasticity of asphalt concrete. The strain rate effect mainly affects crack evolution rate, meanwhile affects temperature effect to some extent.

Chloride ion corrosion significantly impacts concrete structures and will lead to the loss of structural load-bearing capacity and service life. This article starts with the corrosion mechanism of chloride on reinforced concrete and reviews and researches the repair measures of reinforced concrete affected by chloride ion corrosion. Based on the mechanism of action and operating characteristics, this article divides repair measures into direct repair and electrochemical repair; according to the different degrees of structural damage, the corresponding direct repair measures are divided into crack repair and structural repair. Repair methods using anti-corrosion materials have additional advantages, such as flexible sealing, epoxy resin filling, etc. It should be noted that all the direct repair methods mentioned above have considerable applicability in general construction projects. The structural repair focuses on the additional reinforcement method and summarizes the additional reinforcement process for reinforced concrete damaged by corrosion. Ignoring chlorine removal and sacrificial anode protection measures, this process is also considered a general procedure for construction engineering. For repair materials, polymer cement concrete exhibits excellent resistance to chloride salt erosion, but is easily affected by temperature changes. Fiber-reinforced concrete has strong mechanical and corrosion resistance. Among which textile-reinforced concrete (TRC) is best, and the strength benefits are also quite prominent. Ultra-high-performance concrete (UHPC) is extremely resistant to corrosion and has other high-strength benefits, making it an ideal repair material for key parts of structures such as bridges and tunnels. For electrochemical extraction (ECE), titanium platinum is the optimal anode material and lithium-based electrolyte is considered the optimal electrolyte, with a recommended current density of 0.5-1.0A/m2. Bidirectional electromigration (BIEM) can introduce corrosion inhibitors on the surfaces of concrete and steel bars while extracting chloride salts. Triethylenetetramine has the best comprehensive repair effect, but the 28-day repair efficiency is relatively low. Electrochemical deposition treatment (EDT) can repair small cracks, and the repair effect of MgSO4 in conventional electrolytes is the best, with the highest economic benefits after 28 days. Pulse current can greatly improve repair efficiency, and the optimal pulse power is Ton/Toff=0.8ms/0.8ms. However, for wide cracks, a combination of direct repair and electrochemical repair can achieve the best results. This article can serve as a guide for repairing reinforced concrete in an environment corroded by chloride ions.

Corrosion of steel wires has a considerable effect on pipes and may even result in failure. To investigate the failure mode of a PCCP with corroded prestressed steel wires and the effect of corrosion on the bearing capacity of the pipe, a finite element model of a buried PCCP with the effect of corrosion on steel wires was established. By applying loads to pipes with different degrees of steel wire corrosion (5%, 10%, 15%, 20%, 25%, 30%, and 32%) and proportions of corroded steel wires (10%, 15%, and 20%), researchers have analyzed the strain response law of pipes, investigated the failure mechanism, and established a function model of the carrying capacity. The results show that both the development of the degree of steel wire corrosion and the proportion of corroded steel wires cause an increase in the circumferential strain of the pipe, but the maximum affected area of corrosion is affected mainly by the proportion of corroded steel wires. The failure process of the pipe is dynamic. The main reason for failure is that the prestress loss caused by corrosion forms a fragile zone inside the structure. Steel wire corrosion and cracks promote each other, the steel wires break, and the pipe ultimately fails. The degree of steel wire corrosion has a greater effect on the pipe load-bearing capacity than does the proportion of corroded steel wires. The ultimate bearing capacity model established by researchers has extremely high accuracy. This study can provide a reference for PCCP corrosion failure analysis.

Pumped storage power stations usually arrange galleries in the backfill area at the bottom of the reservoir basin. Under the influence of uneven deformation, the galleries may be difficult to adapt to deformation and generate cracking, which can affect dam safety. In this study, the upper reservoir of Hohhot pumped storage power station was taken as a case study. Through a combination of monitoring data and numerical simulation, the deformation characteristics of the galleries on the backfill foundation were analyzed, and the causes and mechanisms of galleries cracking and structural joints damage were revealed. The in situ monitoring records cover the internal settlement of the dam, the deformation and seepage flow of the galleries, and the ambient temperature. Based on actual engineering data, a numerical model considering the structure and filling method of dam, backfill area, and gallery was established, and the calculation parameters of rockfill material constitutive model were inverted by the direct back analysis method. The monitoring data analysis and numerical calculations showed that the long length of the gallery and the sudden drop of the ambient temperature were the main reasons for the longitudinal microcracks in the top arch of the galleries in the backfill area; the strong constraint of bedrock and the uneven settlement of backfill foundation were the root causes for the penetrating cracks in the galleries at the junction of backfill area and bedrock. In addition, the depth of the gallery embedded in the bedrock determines the deformation form (torsional deformation or bending deformation) of the galleries at the junction of the backfill area and bedrock. Based on the monitoring and numerical simulation, the long-term deformation of the galleries and the development of structural joints were also predicted.

With the advances in infrastructure construction in various countries around the world, extensive requirements have been promoted for the mechanical properties and durability of concrete. In this article, the effects of single and compound additions of nano-SiO2 (NS) and nano-Fe2O3 (NF) on the mechanical properties and durability of concrete were evaluated through different experiments. Moreover, the optimal contents of these additions corresponding to their different properties were explored. The macroscopic test results indicated that the addition of nanomaterials had a perceptible effect on the mechanical properties and durability of concrete. The concrete mixed with 1.0