Abstract:The research on the dynamic response of slopes under seismic action currently focuses on a single mainshock without considering the effect of aftershocks, and the spatial variability of material parameters is generally ignored. In this paper, the spatial variability of parameters is fully considered, and a reliability analysis framework based on the Newmark method and probaility density evolution method (PDEM) is proposed to quantify the effects of aftershocks and spatial variability on the dynamic reliability. First, the physical random function model, Copula function and the narrowband harmonic group superposition method are combined to generate the mainshock-aftershock sequence (MAS). In addition, the random field is generated based on the spectral representation and parameters are assigned to the finite element model based on the corresponding coordinates. Then, the permanent displacement of the slope considering the spatial variability of parameters subjected to the MAS was batch calculated based on the Newmark method, and the effects of the coefficient of variation of cohesion and friction angle (COV_C and COV_F), aftershock, and peak ground acceleration (PGA) on the permanent displacement of the slope were analyzed by the mean of the displacement. Finally, based on PDEM, the effects of COV and aftershocks on the dynamic reliability of the slope are explained from a probabilistic point of view. The results of the study show that the mean of displacements shows a gradual increase with an increase of coefficient of variation (COV). In contrast, the COV_F has a more pronounced effect on the slope displacement . In addition, the mean of displacement of the slope subjected to the MAS is greater compared to that of the single mainshock. If the spatial variability of parameters and the influence of aftershocks are ignored, the seismic performance of the slope would be overestimated.

Abstract:Aiming to address the limitation of current non-probabilistic reliability methods for slopes, which can only construct an uncertain domain with regular boundaries and a large envelope when using the convex set model to describe parameter uncertainty, this study proposes a novel non-probabilistic reliability analysis method for slopes based on the multi-convex set model. The approximate performance function of the slope is formulated by the quadratic response surface method in conjunction with Latin hypercube sampling. Furthermore, both the traditional interval model and the PCA (principal component analysis)-based interval model are established. By integrating these two models, a multi-convex set model is constructed. The HL-RF (Hasofer-Lind and Rackwitz-Fiessler) iterative algorithm is employed to identify the most probable failure point of the limit state function, while the simplex optimization algorithm is utilized to locate the extreme point. Based on the definition of the non-probabilistic reliability index as a distance ratio, the non-probabilistic reliability of the slope is calculated, and its stability status is assessed accordingly. The feasibility of the proposed method is validated through case studies. Compared with non-probabilistic reliability methods for slopes based on the interval and ellipsoid model, the results obtained by the presented method exhibit greater consistency with those derived from the Monte Carlo method. As the variability and correlation of shear strength parameters increase, the non-probabilistic reliability index of the slope decreases. When applied to slope stability analysis, the judgment outcomes align well with those obtained via various reliability approaches.

Abstract:Accurate probabilistic stability analysis of slope under rainfall effects requires a comprehensive consideration of both the randomness of rainfall and the spatial variability of soil parameters. However, existing studies typically focus on only one of these factors. To address this, a method for probabilistic stability analysis of slope that simultaneously considers both factors has been proposed. The Karhunen-Loève expansion method is employed to simulate the spatial variability of soil parameters, while a bounded random cascade model is used to simulate the randomness of rainfall. The generated rainfall time series is then applied as the upper boundary condition for the seepage and stability analysis of the slope, followed by the calculation of slope failure probability using the Latin Hypercube Sampling (LHS) method. Analysis is conducted using the landslide in Juanxuan Village, Suichuan County, Ji’an City, Jiangxi Province, as a case study. The results indicate that the probability analysis results of slope stability obtained by considering both random rainfall and spatial variability of soil parameters are consistent with engineering practice. The continuous infiltration of water stored in the terraced fields at the top of the slope gradually expands the influential range of the slope’s pore water pressure of the slope, while the increase in pore water pressure gradually diminishes, ultimately approaching zero. In comparison to rainfall infiltration, the influ of rainfall redistribution on slope stability is marginal.

Abstract:In order to study the influence of gravel shape on the stability and deformation damage characteristics of gravel-bearing granite residual soil slopes under rainfall conditions, the macroscopic vertical displacement and deformation damage of slopes as well as the change of wetting front were comparatively analyzed by carrying out rainfall slope modeling test and combining with the numerical simulation of CFD-DEM to analyze the developmental pattern of displacement field and sliding surface, the fine-scale contact force chain, coordination number, and group structure anisotropy. The results show that: the safety coefficient of slopes containing rounded gravel is the smallest and that of slopes containing angular gravel is the largest. With the increase of precipitation time from 0 to 3 hours, the safety coefficients of slopes containing rounded gravel, pebble gravel and angular gravel decrease by 40%, 33% and 32%, respectively, and the degree of influence by rainfall is in descending order of rounded gravel, pebble gravel and angular gravel slopes. With the increase of the aspect ratio and prism angle, the embedded occlusion effect of gravel is gradually enhanced, and the three damage modes of circular arc damage, toothed arc damage, and offset damage appear in the corresponding slopes in descending order; after the slope’s destabilization and failure, the strong contact force chains of the rounded gravel-containing, pebble gravel-containing, and angular gravel-containing slopes are characterized by intertwined, weak continuity, and unevenness distribution; with the increase of the aspect ratio and prism angle of the gravels, the extent of the contact anisotropy of rounded gravel-containing, pebble gravel-containing and angular gravel-containing slopes is gradually increased.

Abstract:Current slope stability analysis under the combined effects of reservoir water level and rainfall is estimated commonly via the deterministic analysis methods. However, these methods cannot accurately evaluate the slope stability due to the inherent spatial variability of geotechnical parameters. Therefore, in this study, the slope stability influenced by reservoir water level and rainfall is analyzed based on the monitored data during an annual cycle of rainfall and reservoir water level, taking the bank slope of Heishui River in Baihetan reservoir area as an example. Firstly, the three most unfavorable cases are determined through deterministic analysis. Accordingly, the influences of stationary and non-stationary random fields on the results of slope reliability analysis are compared using the stochastic finite difference method (RFDM), considering the spatial variability of effective cohesion c′, effective friction angle φ′ and saturated permeability coefficient k_s, respectively. Results show that, compared with the rainfall infiltration, the reservoir water level fluctuation plays a crucial role in slope stability, and the minimum safety factor occurs during the rapid drawdown. Meanwhile, the combined effects of rainfall and reservoir water level would significantly increase the slope failure probability and sliding volume. In addition, the depth-dependent characteristics of geotechnical parameters require to be considered when conducting stochastic analyses of slope stability, otherwise the slope stability would be underestimated.

Abstract:Reservoir water level fluctuations and rainfall are the primary factors to the destabilization and damage of landslides in the Three Gorges Reservoir Area (TGRA). This Liangshuijing landslide is influenced by experimental water storage in the reservoir area, which triggers an early warning. Although the landslide activity has stabilized, the underlying deformation mechanism remains indistinct. Consequently, the investigation of the landslide deformation mechanism in the TGRA has gained significant attention since the impoundment of the Three Gorges Reservoir. By utilizing recent monitoring data and focusing on the stepwise evolution of displacement, this study establishes a hydraulic calculation model for the Liangshuijing landslide. The research incorporates long-term data on reservoir water level fluctuations and rainfall to investigate the seepage field, stability, and displacement patterns under the combined influence of reservoir water level fluctuations and rainfall. Additionally, the study explores the intrinsic deformation mechanism of the Liangshuijing landslide. The results indicate that the seepage field in the front and back of the landslide is primarily influenced by the reservoir water level and rainfall, respectively, while the middle part is affected by the combination of both. The stability coefficient exhibits periodic changes corresponding to the rise and fall of the reservoir water level, and rainfall further diminishes the overall landslide stability. The surface displacement demonstrates an incremental trend, with a decrease in reservoir water level causing the displacement to increase incrementally, while an increase in reservoir water level tends to stabilize the displacement. Overall, the deformation of the Liangshuijing landslide is primarily caused by reservoir water level fluctuations and rainfall, which subsequently impact the underground seepage field and hydraulic conditions, resulting in deformation. Generally, the current deformation is primarily concentrated at the foot of the slope, gradually extending towards the rear. Stabilization of deformation is observed in the middle and rear regions. Changes in the reservoir water level have a more pronounced impact on landslide deformation, and during years with greater fluctuations in the reservoir water level, it is crucial to enhance early warning monitoring of the deformation.

Abstract:The Rongxar Qu, located on the southern flank of the Himalayas, is characterized by active tectonics and features abundant glacial lakes and moraines. Its stability was further compromised by the 2015 Nepal Gorkha Ms 8.1 earthquake. Following the clustered debris flows in the region on June 15, 2021, in-depth analysis has been limited, with little focus specifically on the activity patterns of the source materials. This study utilized pre- and post-disaster remote sensing data from GF-1B, BJ-2, and Planet satellites to interpret the debris sources of the debris flows. Additionally, the boundaries of typical glacial lakes were extracted using Landsat 5, Landsat 8, and Sentinel-2 remote sensing data through the calculation of the Normalized Difference Water Index (INDW). Furthermore, the Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) technique was applied to process 184 ascending Sentinel-1A data, enabling the acquistion of surface deformation in the region from 2014 to 2021 data. The results indicate that the study area experienced an overall trend of gradual subsidence from 2014 to 2021. In the landslide bodies, the most significant settlement occurred in the mid-upper sections, followed by the front edges, while the rear edges exhibited relatively minor deformation. This spatial differentiation pattern is attributed to the combined effects of frontal traction and middle-rear pushing forces, which caused the deformation to propagate toward the rear edges and resulted in overall slippage. Moraine-type rock glaciers demonstrated pronounced seasonal deformation, with the most intense deformation concentrated in their central zones, gradually decreasing toward the marginal zones and termini. This deformation pattern is primarily controlled by the freeze-thaw cycle of the active permafrost layer and the accumulation and release of meltwater in the central zones. Notably, Yalong Co Glacial Lake expanded by nearly 43% between 2000 and 2021, accompanied by significant deformation on both sides of the terminal moraine. Therefore, regional disaster prevention and mitigation efforts should focus on enhancing the monitoring of cryospheric hazards, including glacial lakes and rock glaciers, as well as the changes in debris sources connected to gully systems, particularly during the monsoon season.

Abstract:To investigate the mechanical response characteristics of debris flow deposits under impact load, a combination of geotechnical tests on deposits, similar model tests under impact load, and numerical simulation was adopted to analyze the time-history curves of acceleration, velocity, displacement, and stress of cylindrical projectiles penetrating debris flow deposits, as well as the evolution characteristics of motion attitude, resistance, and cavity during the projectile penetration process. The experimental results show that when the projectile penetrates the debris flow deposit, the displacement increases rapidly. With the instability of the projectile’s motion attitude in the debris flow deposit, the deceleration gradually increases. When the axial direction of the projectile is perpendicular to its motion direction, the contact surface is the largest, the resistance reaches the maximum, and the negative acceleration also reaches the maximum. During penetration, the projectile displaces the debris flow deposit to the surrounding area to form a large cavity, and the velocity of the projectile decreases while the displacement tends to slow down. With the increase of time, the projectile flips over, and finally the tail faces forward. Additionally, the contact surface between the projectile and the debris flow deposit decreases, the resistance reduces, the acceleration decreases, the speed slows down relatively, and the curvature of the displacement curve decreases as the speed decreases.

Abstract:To enhance the solidification effect of enzyme-induced calcium carbonate precipitation (EICP) technique, this study employed EICP combined with kaolin to treat standard sand for solidification. Two experimental variables were set: the amount of kaolin added and the curing time. Macroscopic and microscopic experiments were conducted on solidified sands under different variable combinations. The experimental results revealed that the unconfined compressive strength of the EICP-combined kaolin solidified sand continued to increase with the increase in kaolin content and curing time. The compressive strength after curing with 4% kaolin content for 14 days was 722.19 kPa, which was 13.15 times that of pure EICP solidified sand. The calcium carbonate precipitation rate did not continue to increase with curing time or kaolin content. The efficiency of calcium carbonate precipitation was highest when cured with 3% kaolin content for 7 days. As the kaolin content increased, the porosity first decreased and then increased, with the minimum porosity observed at a kaolin content of 2%. The pore structure of the solidified sand before and after adding kaolin changed from being dominated by medium pores (accounting for over 90%) to being dominated by small pores (around 80%), indicating a significant improvement in the pore structure. The calcium carbonate crystals deposited between the particles of the EICP-combined kaolin solidified sand were mainly aragonite spheres, which were stacked and filled in the interstices between sand particles and covered the surface of sand particles, significantly enhancing the bonding effect between sand particles.

Abstract:Desiccation cracking is a typical deterioration in archeological sites in wet environments. To explore the correlation between the development degree of desiccation cracking and soil properties in the Sanxingdui sacrifice archeology site, we conduct soil property analysis and quantitative characterization of deterioration, adopt the Grey Relation Analysis (GRA) to calculate the correlation degree between the six relevant indicators of soil properties and the development degree and damage degree of desiccation cracking. This research aims to study the magnitude and mechanism of each indicator’s influence on the deterioration degree, and explore the feasibility of preventing and controlling deterioration by intervening in soil properties. The result shows that the correlation degree between soil properties and the desiccation cracking degree in descending order is as follows: clay particle content > clay mineral content > plasticity index > initial dry density > initial moisture content and organic matter content. The clay particle content, clay mineral content, and plasticity index are control indexes affecting the development of desiccation cracking, showing a positive correlation with it. The initial dry density, initial moisture content, and organic matter content are relevant indices, the smaller the initial dry density the more considerable the damage degree of desiccation cracking. Intervening in soil properties can only control the development of desiccation cracking to a certain extent; for example, increasing the initial dry density can change the morphology of desiccation cracking.

Abstract:Currently, there is a lack of in-situ or model test results for cone penetration tests (CPTs) conducted in deep, dense sand layers under high overburden stresses, restricting the development of empirical relationships between CPT results and the characteristics of such deep, dense sand layers. This study addresses this gap by proposing an empirical relationship to predict the relative density of dense silica sand based on stress level and cone tip resistance. The relationship was developed through CPTs performed in a calibration chamber using dense sand specimens (with relative densities of 74%-91%) subjected to high stresses (under overburden stresses of 0.5-2.0 MPa) and numerical simulations employing the large deformation finite element method. The Arbitrary Lagrangian Eulerian method was used to regularly regenerate the mesh to prevent soil element distortion around the cone tip. Additionally, the modified Mohr-Coulomb model was integrated to capture the stress-strain behavior of dense silica sand under high stresses. A reasonable agreement was achieved between the numerical and experimental penetration profiles, which verifies the reliability of the numerical model. A sufficient number of parametric analyses were carried out, and then an empirical equation was proposed to establish the relationship between the relative density of dense sand, stress level and cone resistance. The empirical equation provides predictions with acceptable accuracy, as the discrepancies between the predicted and measured relative density values fall within ±30%.

Abstract:The construction of urban subways involves undercrossing existing municipal pipelines, which may threaten pipeline safety. Most of the existing prediction theories for pipeline deformation use elastic foundation models such as the Winkler model and the Pasternak model，which cannot account for the nonlinear deformation characteristics of soil. Therefore, an existing municipal pipeline with rigid joints was regarded as a continuous beam on a nonlinear foundation and a nonlinear deformation prediction method for pipelines was established. Firstly, the ground displacement along the axis of the pipeline caused by single-line and double-line tunneling was calculated respectively, using the Peck empirical formula and the modified Peck empirical formula that considers the tunnel construction sequence. Then, the differential governing equation for pipeline deformation caused by tunneling was established, and the deformation solution of the pipeline was obtained using the finite difference method and the Newton iteration method. Finally, the rationality and applicability of the proposed method were verified by comparing its results with monitoring data from a centrifuge experiment and two engineering cases. The results show that the proposed method is in better agreement with the measured data compared with other foundation models such as the Winkler model, Pasternak model, and Kerr model. It can also predict the pipeline deformation caused by twin-tunnel undercrossing while considering the effect of tunnel construction sequence.

Abstract:To investigate the bond performance between glass fiber reinforced polymer (GFRP) ribbed bars and concrete and improve the practicality of existing constitutive models, 14 sets of specimens were prepared for beam-end tests, which aimed to explore the influences of concrete strength, thickness of cover, stirrup configuration and the interaction between GFRP ribbed bars on the bond performance. The tests were conducted using displacement-controlled loading; loading force, free end slip value, and loading end slip value were recorded, the failure mode of the bond interface was observed, and a method for proposing a simplified bond-slip constitutive model was proposed based on the test results. The results showed that the beam-end tests mainly resulted in pull-out and splitting failures; the slip value of the bond-slip curve was related to the rib spacing, and the peak spacing was essentially consistent with the rib spacing; concrete strength and configuration of stirrups would affect the failure mode and damage degree of the bond interface, thereby affecting bond-slip performance; the increase in cover thickness had a beneficial effect on the bond-slip performance within a certain range; the results of the second pull-out test showed that there was a mutual influence on the bond performance of the GFRP ribbed bars in the specimens. The simplified bond-slip constitutive model can accurately fit the test data and further enhance the practicality of the constitutive model.

Abstract:The uniaxial compression performance of rusted hoop-restrained concrete serves as the foundation for the elastoplastic analysis and seismic performance research of multi-age reinforced concrete (RC) structures. The precise study of its deterioration rule is of great importance for durability evaluation, residual seismic capability prediction and numerical simulation of multi-age RC structures. In this paper, the research status of uniaxial compression behavior of concrete restrained by rusted stirrup is reviewed from the aspects of test method, compressive strength and stress-strain constitutive relation. Different test methods are introduced in detail, and their advantages, disadvantages, and applicabilities are analyzed systematically. The factors affecting the uniaxial compressive performance of rusted stirrup confined concrete, the uniaxial compressive performance degradation model and the uniaxial stress-strain constitutive relationship model are summarized. The shortcomings and trends of current research on the uniaxial compression performance of concrete restrained by rusted stirrups are analyzed. A summary of existing research results shows that the current research on the uniaxial stress-strain constitutive relationship of rusted stirrup confined concrete under repeated loads is very limited. Finally, the shortcomings and research trends of existing studies are discussed.

Abstract:To exploit wind energy resources in areas with low wind speeds and high shear, the hub height of a wind turbine must be increased. There are three main engineering solutions for high towers, namely all-steel towers, all-concrete towers, and concrete-steel hybrid towers (hybrid towers). Firstly, this paper compares the technical characteristics of the three types of towers. The results show that the hybrid towers combine the advantages of both all-steel and all-concrete towers, overcome their disadvantages, and are the preferred solution to address the challenges of high towers. Secondly, this paper reviews the development history and research status of hybrid tower technology focusing on tower types (chamfered square, cone, chamfered triangle, kidney shape, regular polygon, and “self-elevating”), and summarizes the domestic technological development of hybrid towers into three development stages and three technical schools. Thirdly, this paper introduces the domestic and international industry standards for hybrid towers, and outlines the existing key technology research on improving their performance, optimizing costs, shortening the construction cycle, and conducting health monitoring of hybrid towers. Finally, this paper summarizes the problems and challenges in the research of hybrid tower technology, including structural unification, application of sub-model analysis techniques, reliability research, upgrading of old hybrid towers, and research on ultra-high hybrid towers, which provides references for new product development. With high stability, a long service life and low construction costs, hybrid towers can meet the development needs of large wind turbines.

Abstract:In order to explore a new type of composite box girder with light hosting weight, convenient construction and high durability, a new prestressed RC-UHPC composite box girder with ultra-high performance concrete (UHPC) as web and bottom plate and reinforced concrete (RC) as top plate was designed and fabricated. A flexural test was carried out to investigate the failure mechanism and failure mode of the specimens; the finite element software was utilized to simulate the test, and the calculation accuracy of the finite element method was verified by comparing the finite element calculation results with the test data, on the basis of which 16 finite element analysis models were established to analyse the influence of various parameters on the flexural strength. The results show that the failure mode of the specimen is adequate reinforcement failure, which shows that the RC top slab in the pure bending section is crushed after the yielding of the longitudinal tensile reinforcement and the fracture of some prestressing reinforcement; the tensile strength of UHPC and the reinforcement ratio of prestressing tendons exert a greater influence on the flexural strength; the longitudinal strain of the specimen’s is basically consistent with the plane section assumption in the height direction. Combined with the theoretical analysis, the formulas for calculating the flexural strength were proposed. The ratios of the calculated value to the test value and the finite element calculated value are 1.014 and 0.960, respectively, which indicates a high calculation accuracy.

Abstract:In order to investigate the feasibility of the virtual static load test method for evaluating the stiffness of the main girder of a large-span cable-stayed bridge, a cable-stayed bridge was subjected to a static load test and a modal test under environmental excitation. The static deflection of the measuring points at the mid-span section of the main girder was measured in the static load test. Modal expansion of the measured mode shapes of the cable-stayed bridge was carried out, and the Kriging interpolation method was applied to predict the modal deflection of the mid-span section of the cable-stayed bridge under the static load test. A virtual static load test scheme meeting the loading efficiency requirement was designed, and the deflection calibration coefficient under virtual static load was calculated to evaluate the stiffness of the main girder of the cable-stayed bridge. The results show that the modal test under ambient excitation can accurately obtain the bridge vibration information; the relative error between the modal deflection predicted by the Kriging interpolation method using only the first four orders of vertical modal parameters and the measured static load deflection is less than 10%, which meets the engineering accuracy requirement; the deflection calibration coefficient obtained by the virtual static load test method is close to that from the static load test, and the evaluation results are less than 1.0, which indicates that the main girder of the cable-stayed bridge is in good bearing condition and verifies the feasibility of the virtual static load test method for evaluating the stiffness of the main girder of a large-span cable-stayed bridge under normal traffic conditions.

Abstract:To reveal the corrosion and failure mechanisms of bolts in complex environments at the micro level, molecular dynamics methods were introduced into the corrosion research of bolts. To this end, a molecular dynamics model was established using Materials Studio, and the molecular dynamics simulations were conducted using Lammps. The corrosion characteristics of pre-stressed bolts in chloride ion environments were simulated and studied, and the micro interaction laws between chloride ion solution and the surface of bolts was explored. The results show that under the coupling effect of pre-stress and chloride ions, the iron matrix will absorb more oxygen atoms, promote the binding between oxygen atoms and iron, and accelerate the oxidation corrosion passivation of the bolts; The application of pre-stress weakens the binding of atoms inside the bolts, increasing the movement trend of iron atoms and making it easier to combine with other atoms; Chloride ions increase the strength of the interaction between iron and oxygen atoms, promoting the binding of iron and oxygen, and chloride ions will gradually become active with the increase of prestress; With the increase of pre-stress, the movement characteristics of oxygen atoms in the solution gradually weaken because they are more likely to react with iron to form stable chemical bonds. After the oxidation reaction is completed, an oxide film will form on the surface of the iron substrate. In the chloride solution environment, the thickness of the oxide layer increases significantly, and the greater the pre-stress, the thicker the oxide layer.

Abstract:Concrete has exceptional mechanical properties and durability. Nevertheless, conventional curing methods are ineffective in addressing the issues of autogenous shrinkage and cracking during its early stages. Internal curing technology can effectively enhance the internal moisture distribution of concrete, mitigate shrinkage cracking, and improve its durability. This paper investigates the internal curing mechanism of concrete and analyzes its influence on the durability of concrete. Incorporating pre-wetted lightweight aggregates or super-absorbent polymers into concrete releases water, as the moisture surrounding the aggregates decreases. This process fills the unsaturated pores in the concrete and increases the meniscus radius of the pore solution, thereby achieving internal curing. Internal curing promotes cement hydration around the aggregates, improves the compactness of the interfacial transition zone, alleviates concrete cracking caused by self-desiccation, and enhances cracking resistance. Moreover, it obstructs the transmission path of corrosive media, improves concrete permeability, and enhances corrosion resistance against ions, gases, and other corrosive agents. After water release, the internal curing materials create a substantial number of pores within the concrete. These pores aid in releasing the expansion pressure resulting from the freezing of the concrete pore solution, thereby improving frost resistance. Additionally, the pores of lightweight aggregates provide space for the deposition of expansive gel, thereby reducing the occurrence of alkali-aggregate reaction.

Abstract:To address the issues of low activity and difficult treatment of burnt coal cinder, the preparation technology and calcination effect of geopolymers based on burnt coal cinder were investigated, with the concept of low carbon and environmental protection as the core. The influence of calcination temperature, activator dosage and liquid-solid ratio on the compressive strength of geopolymers based on burnt coal cinder was investigated by single factor tests, and the optimal mix ratio was subsequently determined. Using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), the hydration products and micromorphology of geopolymers were studied. Revealing mineral phase changes during calcination and the geopolymerization process, and clarifying the mechanism of strength enhancement. The results indicate that the combined activation method with calcium oxide as the main and trisodium phosphate dodecahydrate (TSPH) as the auxiliary was successfully employed to prepare the geopolymers with a compressive strength of 34.5 MPa at 28 days. The alkaline environment and nucleation sites provided by calcium oxide, along with the phosphate radicals supplied by TSPH, all contribute to the dissolution of active components in the burnt coal cinder and the formation of complex gel phases, which is an important source of compressive strength for geopolymers. Furthermore, at calcination temperatures of 1 000 ℃, burnt coal cinder lacks the thermal activation property of solid wastes such as coal gangue and fly ash, and high-tempera ture calcination diminishes its chemical reactivity.

Abstract:Concrete bridges, as critical components of highway construction, generate substantial carbon emissions during their construction phase, necessitating the development of a relatively precise carbon emission estimation model to promote low-carbon construction practices. The present study categorizes the sources of carbon emissions during the construction of highway concrete bridges into material production, transportation, off-site processing, and on-site construction. The carbon emission factor method is employed to calculate the carbon emissions during the construction period of 31 concrete bridges on a newly built expressway. An analysis of carbon emission characteristics and their correlations reveal that factors such as bridge length, total material weight, and machinery working hours significantly influence emissions during bridge construction. The Spearman correlation coefficients for these factors are 0.96, 0.88 and 0.82, respectively, with collinearity observed among them. Employing these variables, ridge regression, Lasso regression, and elastic net regression models were developed to mitigate collinearity. The Lasso regression model demonstrates the highest accuracy in estimating carbon emissions, with an R² of 0.976 2, thus making it the preferred model for estimating emissions during bridge construction. This model can calculate the carbon emissions for a variety of design and construction plans of concrete bridges based on bridge length and total material weight, serving as a methodological reference for the development of low-carbon designs and the optimization of carbon reduction strategies during the construction process.

Abstract:Filtration is a prevalent treatment modality in the domain of wastewater management. Depending on the materials and properties of the filtration media, filtration can be classified into four main categories: microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. The present study focuses on the preparation of a novel porous CaCO? microfiltration membrane, which is based on the microbial-induced calcium carbonate precipitation (MICP) biomineralization process. Initially, CaCO₃ crystal particles with urease activity are prepared by controlling the MICP mineralization process. Secondary microbial mineralization is used to cement the loose calcium carbonate particles, forming a continuous porous solid CaCO? membrane with certain mechanical strength. Filtration tests on bacterial cells, extracellular proteins, and polysaccharides show that the MICP-driven porous CaCO₃ membrane effectively removes Escherichia coli, Brachybacterium sp.， and activated sludge, with removal rates of 99.998%, 99.983%, and 99.996%, respectively. Compared to conventional filter paper, this porous CaCO₃ membrane demonstrates superior capability in removing extracellular polymers (EPS). Furthermore, the CaCO₃ microfiltration membrane prepared using the MICP process also exhibits ideal pore space, non-blocking characteristics, and high permeability.

Abstract:Sewage sludge is a semi-solid byproduct of wastewater treatment, with a water content of over 80%. The available methods for disposal and recycling usually require the water content to be within 50%-70%, and sludge dewatering is an important prerequisite for its disposal and resource utilization. In this paper, the structure and composition of water in sludge and the reasons for the difficulty in dewatering residual sludge are analyzed, and the key bottleneck is the effective removal of bound water and intracellular water. The roles and core mechanisms of physical, chemical, and biological pretreatment methods are described; especially, the mechanism, dewatering effects, and combination processes of enhanced residual sludge dewatering by chemical conditioners such as flocculants and filter aids are focused on. The selection principles and application scope of mechanical dewatering equipment for residual sludge are discussed. This paper analyzes the resource utilization approaches of dewatered residual sludge, including the preparation of fertilizer, building materials, biochar, and high-value products. Finally, the key problems that need to be solved in the future are proposed, so as to provide references for the theoretical research and technological application of residual sludge deep dewatering and resource utilization.