Microbial corrosion of hydraulic concrete structures(HCSs)has received increasing research concerns.However,knowledge on the morphology of attached biofilms,as well as the community structures and functions cultivated...Microbial corrosion of hydraulic concrete structures(HCSs)has received increasing research concerns.However,knowledge on the morphology of attached biofilms,as well as the community structures and functions cultivated under variable nutrient levels is lacking.Here,biofilm colonization patterns and community structures responding to variable levels of ammonia and sulfate were explored.From field sampling,NH_(4)^(+)-N was proven key factor governing community structure in attached biofilms,verifying the reliability of selecting target nutrient species in batch experiments.Biofilms exhibited significant compositional differences in field sampling and incubation experiments.As the nutrient increased in batch experiments,the growth of biofilms gradually slowed down and uneven distribution was detected.The proportions of proteins and β-d-glucose polysaccharides in biofilms experienced a decrease in response to elevated levels of nutrients.With the increased of nutrients,themass losses of concretes exhibited an increase,reaching a highest value of 2.37%in the presence of 20 mg/L of ammonia.Microbial communities underwent a significant transition in structure and metabolic functions to ammonia gradient.The highest activity of nitrification was observed in biofilms colonized in the presence of 20 mg/L of ammonia.While the communities and their functions remained relativelymore stable responding to sulfate gradient.Our research provides novel insights into the structures of biofilms attached on HCSs and the metabolic functions in the presence of high level of nutrients,which is of significance for the operation and maintenance of hydraulic engineering structures.展开更多
With the development of modern society,people put forward higher requirements for building safety,which makes the construction project face new challenges.Reinforced concrete frame structure as a common engineering ty...With the development of modern society,people put forward higher requirements for building safety,which makes the construction project face new challenges.Reinforced concrete frame structure as a common engineering type,although the construction technology has been relatively mature,but its earthquake collapse ability still needs to be strengthened.This paper analyzes the specific factors that affect the seismic collapse ability of reinforced concrete frame structure,summarizes the previous research results,and puts forward innovative application of fiber-reinforced polymer(FRP)composite materials,play the role of smart materials,improve the isolation and energy dissipation devices,etc.,to promote the continuous optimization of reinforced concrete frame structure design,and show better seismic performance.展开更多
By adding zeolite aggregate with good adsorption properties,different mix ratios of added zeolite pervious concrete(ZPC)were designed to compare the water purification effect of ordinary pervious concrete and water pu...By adding zeolite aggregate with good adsorption properties,different mix ratios of added zeolite pervious concrete(ZPC)were designed to compare the water purification effect of ordinary pervious concrete and water purification tests that were conducted.The pore characteristics of the pervious concrete were identified using three-dimensional reconstruction software and the relationship between pore structure and water purification performance was quantified by gray entropy correlation analysis.The results showed that the purification efficiency of zeolite-doped pervious concrete was 17.6%-22.3%higher than that of ordinary pervious concrete.The characteristic parameters of the pore structure of permeable concrete,i.e.planar porosity and tortuosity,were determined using three-dimensional reconstruction software.The correlation between the degree of tortuosity and the removal rate reached more than 0.90,indicating that the internal pore structure of pervious concrete has a good correlation with the water purification performance.展开更多
We conducted a series tests on surface layers of plateau concrete at the ages of 180 and 540 days,including the most superficial cement paste,the 5 mm thick surface mortar,and the 50 mm thick surface concrete.Thermogr...We conducted a series tests on surface layers of plateau concrete at the ages of 180 and 540 days,including the most superficial cement paste,the 5 mm thick surface mortar,and the 50 mm thick surface concrete.Thermogravimetry and nitrogen absorption porosimetry on cement past,mercury intrusion porosimetry on mortar,and microhardness test on interface transition zone between mortar and coarse aggregate were conducted to evaluate the hydration degree and characterize the micro-structure.Whilst,tests for the rebound strength,abrasion resistance,and chloride ion impenetrability of concrete were conducted to assess the macro-performance.The experimental results show that,affected by the harsh plateau climate,outward surfaces have lower hydration degrees and worse pore structure than inward surfaces.As the hydration of concrete surface is ongoing after the age of 180 days,both the micro-structure and the macro-performance are continuously improved.In the long-term,either the orientation or the depth towards surface does not significantly affect concrete performance.Surface carbonation brings positive effects on mechanical properties but negative effects on the durability.Additionally,standard test result of chloride ion impenetrability is found significantly affected by the atmospheric pressure.For a same batch of concrete,charge passed in plateau regions is obviously lower than that in common regions.展开更多
The cultivation of engineering capabilities aims to equip engineering professionals with high-level expertise to meet the demands of society and industry development,thereby enhancing their competitiveness and career ...The cultivation of engineering capabilities aims to equip engineering professionals with high-level expertise to meet the demands of society and industry development,thereby enhancing their competitiveness and career potential.This article focuses on engineering capability development,exploring teaching strategies for the Reinforced Concrete Structure course.It aims to provide insights for educators in engineering programs at universities and vocational colleges in China.By doing so,teaching plans that meet the needs of engineering capability development,laying a solid educational foundation for the healthy growth of engineering professionals in the new era,and enhancing their application of knowledge and skills can be developed.展开更多
Nowadays,education and teaching have become a hot topic,and teaching in colleges and universities is facing a brand-new development direction.Principles of Concrete Structure Design,as one of the main courses,transmit...Nowadays,education and teaching have become a hot topic,and teaching in colleges and universities is facing a brand-new development direction.Principles of Concrete Structure Design,as one of the main courses,transmits professional knowledge for students,enhances the students’professional ability,and further carries out in-depth research on the course to bring a better teaching effect for students.The article mainly focuses on the research of the principles of concrete structure design course,conducts an analysis of the teaching characteristics of the principles of concrete structure design course,and reasonably sets the teaching content from the optimization of the course teaching objectives;innovative course teaching methods can deepen the effect of knowledge understanding;reform of experimental practice teaching can lay down the effect of the internalization of knowledge,etc.The in-depth description and discussion of the relevant aspects of the research aim to provide guidelines for related research.展开更多
Based on the durability characteristics of prestressed concrete structures,the durability limit states of carbonation and chloride ion attack are defined, respectively.Durability predicting models on the basis of reli...Based on the durability characteristics of prestressed concrete structures,the durability limit states of carbonation and chloride ion attack are defined, respectively.Durability predicting models on the basis of reliability mathematics and stochastic processes areconstructed, and the pure theoretical formulae of failure probability of prestressed concretestructures are analyzed. In addition, a simple durability design method for carbonation ofstructures is put forward. According to the analysis, the durability of prestressed concretestructures is superior to that of traditional structures. The research also indicates that theconcrete cover prescribed in the current code (GB 50010-2002) is not adequate. The rational coverthickness should notbe less than 35 or 45 mm according to carbonation or chloride ion attack,respectively.展开更多
Durability zonation standard （DZS） is proposed to provide useful parameters for durable concrete structure design. It deals not only with the influence of environment on structures, but also with types, functions an...Durability zonation standard （DZS） is proposed to provide useful parameters for durable concrete structure design. It deals not only with the influence of environment on structures, but also with types, functions and importance of structures based on the theory of life cycle cost（LCC）. First, the basic concept of DZS for concrete structure design is defined. Then the basic principles for DZS are established. The factors for zonation according to natural environmental conditions and structural importance are identified. The usefulness of DZS by citing a real application for concrete highway bridges in Zhejiang Province is demonstrated. Finally, durability regulations are provided accordingly to zonation.展开更多
When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on ...When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on the design of the tensioning plans and selection of control measures for the BSS.In order to accurately obtain the bending stiffness of CFST beam and clarify its impact on the mechanical properties of composite BSS during con-struction,the influence of some factors such as height-width ratio,wall thickness of steel tube,elasticity modulus of concrete,and friction coefficient on the bending stiffness are analyzed parametrically by the numerical simula-tion technology based on an actual project.The calculation formula of the equivalent bending stiffness of CFST is also established through mathematical statistical simulation.Then,the equivalent bending stiffness is introduced into the construction and use stages of the composite BSS,respectively,and the mechanical properties such as prestress-tensioning control value,structural deformation,and internal force of key members are comparatively analyzed when adopting two different construction plans.Moreover,the optimal construction plan of concrete placementfirst and then prestress-tensioning is proposed.展开更多
The construction industry faces significant challenges due to the inherent brittleness and cracking tendency of traditional concrete,which compromises structural durability and necessitates frequent,costly repairs.Thi...The construction industry faces significant challenges due to the inherent brittleness and cracking tendency of traditional concrete,which compromises structural durability and necessitates frequent,costly repairs.This paper explores the groundbreaking development of self-healing concrete as a transformative material technology for sustainable architecture.We examine three primary autogenous healing mechanisms:encapsulated polymer/microbial healing agents,vascular networks,and shape memory alloys.Through a review of recent laboratory experiments and pilot projects,this study analyzes the crack-sealing efficiency,recovery of mechanical properties,and long-term durability of these materials.A comparative case study of a demonstration building facade incorporating microbial self-healing concrete is presented,showing a potential 30%reduction in maintenance costs over a 20-year lifecycle.The findings indicate that self-healing concrete not only enhances structural resilience but also significantly reduces the carbon footprint associated with building maintenance,aligning with the core principles of sustainable development.The paper concludes by discussing current limitations in mass production and cost-effectiveness and proposes directions for future research to facilitate widespread adoption in architectural engineering.展开更多
The plateau environment not only affects the development of concrete's early strength but also damages its durability during its service life.This paper summarized and analyzed the impact of plateau environments o...The plateau environment not only affects the development of concrete's early strength but also damages its durability during its service life.This paper summarized and analyzed the impact of plateau environments on concrete’properties and proposed methods to improve the performance of concrete in plateau environment.The results indicated that low humidity and high evaporation rates in plateau regions inhibit the hydration of cement in concrete,leading to an increased content of micro-pores ranging from 500 to 1000 nm and raising the risk of early-stage cracking,thus reducing the impermeability of concrete.The low atmospheric pressure(AP)condition of 60 kPa decreases the entrained air content in concrete by over 20%,diminishes the pores under 200μm,and increases the average air-voids diameter and spacing factor,resulting in a decrease of more than 5%in the 28 d compressive strength of concrete.Consequently,the durability of concrete is compromised.Saponin and rosinbased air-entraining agents are recommended to improve the performance of concrete in plateau environments.Nanoparticles also aid in stabilizing bubbles in such conditions.Selecting low-heat specialty cements,increasing the amount of cement used,and extending the curing period are also vital measures to enhance the performance of plateau concrete.展开更多
Computed tomography(CT)can inspect the internal structure of concrete with high resolution,but improving the accuracy of measurements remains a key challenge due to the reliance on complex image processing and signifi...Computed tomography(CT)can inspect the internal structure of concrete with high resolution,but improving the accuracy of measurements remains a key challenge due to the reliance on complex image processing and significant manual intervention.This study aims to optimize CT scanning parameters to enhance the accuracy of measuring crack widths and rebar volumes in reinforced concrete.Nine sets of specimens,each with varying rebar diameters and concrete cover thicknesses,were scanned before and after corrosion using an Optima CT scanner,followed by three-dimensional reconstructions using Avizo software.The effects of threshold values and“Erosion”coefficients on measurement accuracy were evaluated.The results demonstrated that an optimal lower threshold of 2950,combined with an‘Erosion’coefficient of 6,effectively limits the measurement error of rebar volumes to within 1%.The optimal threshold for measuring crack widths was influenced by the crack width,rebar diameter,and concrete cover thickness.Additionally,an optimized formula for determining crack measurement thresholds was proposed.This study significantly improves the accuracy of CT-based non-destructive testing(NDT)techniques,providing valuable insights for structural health monitoring(SHM).展开更多
This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi...This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.展开更多
Squat reinforced concrete(RC)shear walls are essential structural elements in low-rise buildings,valued for their high strength and stiffness.However,research on their seismic behavior remains limited,as most studies ...Squat reinforced concrete(RC)shear walls are essential structural elements in low-rise buildings,valued for their high strength and stiffness.However,research on their seismic behavior remains limited,as most studies focus on tall,slender walls,which exhibit distinct failure mechanisms and deformation characteristics.This study addresses this gap by conducting an extensive review of existing research on the seismic performance of squat RC shear walls.Experimental studies,analytical models,and numerical simulations are examined to provide insights into key factors affecting wall behavior during seismic events,including material properties,wall geometry,reinforcement detailing,and loading conditions.The review aims to support safer design practices by identifying current knowledge gaps and offering guidance on areas needing further investigation.The findings are expected to aid researchers and practitioners in refining seismic design codes,ultimately contributing to the development of more resilient squat RC shear walls for earthquake-prone regions.This research underscores the importance of improving structural resilience to enhance the safety and durability of buildings.展开更多
Semantic segmentation of concrete bridge defect images frequently encounters challenges due to insufficient precision and the limited computational capabilities ofmobile devices,thereby considerably affecting the reli...Semantic segmentation of concrete bridge defect images frequently encounters challenges due to insufficient precision and the limited computational capabilities ofmobile devices,thereby considerably affecting the reliability of bridge defect monitoring and health assessment.To tackle these issues,a concrete defects dataset(including spalling,crack,and exposed steel rebar)was curated and multiple semantic segmentation models were developed.In these models,a deep convolutional network or a lightweight convolutional network were employed as the backbone feature extraction networks,with different loss functions configured and various attention mechanism modules introduced for conducting multi-angle comparative research.The comparison of results indicates that utilizing VGG16 as the backbone network of U-Net for semantic segmentation of multi-class concrete defects images resulted in the highest recognition accuracy,achieving a Mean Intersection over Union(MIoU)of 80.37%and a Mean Pixel Accuracy(MPA)of 90.03%.The optimal combination of loss functions was found to be Focal loss and Dice loss.The lightweight convolutional network Mobile NetV2-DeeplabV3 slightly reduced recognition accuracy but significantly decreased the number of parameters,resulting in a faster detection speed of 71.87 frames/s,making it suitable for real-time defect detection.After integrating the SE(Squeeze-and-Excitation),CBAM(Convolutional Block Attention Module),and Coordinate Attention(CA)modules,both VGG16-U-Net and MobileNetV2-DeeplabV3 achieved improved recognition accuracy.Among them,the CAmodule(Coordinate Attention)effectively guides the model to accurately identify subtle concrete defects.The improved VGG16-U-Net can identify previously the new untrained concrete defect images in the concrete structural health monitoring(SHM)system,and the recognition accuracy can meet the demand for intelligent defect image recognition for structural health monitoring of concrete structures.展开更多
To examine the influences of waste polypropylene fiber(PPF)on the strength and internal pore structure of recycled aggregate concrete incorporating iron ore tailings,both the cubic compressive strength and axial compr...To examine the influences of waste polypropylene fiber(PPF)on the strength and internal pore structure of recycled aggregate concrete incorporating iron ore tailings,both the cubic compressive strength and axial compressive strength of the concrete were measured.Additionally,the microstructure was analyzed using scanning electron microscopy.The evolution of pore structure parameters,including pore size distribution,pore type distribution,and nuclear magnetic resonance spectral area in the concrete,was investigated through nuclear magnetic resonance(NMR)analysis.A model correlating the concrete's pore structure with its macroscopic performance was subsequently developed based on fractal theory.The results demonstrate that an appropriate amount of PPF created a bridging effect that decelerated the progression of macro cracks,enhanced the ductility of the concrete's failure mode,and increased both cubic compressive strength and axial compressive strength,with the most effective dosage being approximately 0.6%.An appropriate amount of PPF(ranging from 0.3%to 0.6%)facilitated the formation of harmless pores and shifted the pore size distribution towards medium and small sizes.Specifically,a fiber content of 0.6%resulted in the most significant reduction in the T2 spectral area.Furthermore,the pore structure of concrete exhibits distinct fractal characteristics.As the PPF content increased,the fractal dimension initially rose and then declined,demonstrating a strong correlation with the mechanical properties.展开更多
The main purpose of this paper is to investigate the effect of core eccentricity on the structural behavior of concrete tall buildings.Concrete buildings of 55 floors with plan dimensions 48.0×48.0 m2 were invest...The main purpose of this paper is to investigate the effect of core eccentricity on the structural behavior of concrete tall buildings.Concrete buildings of 55 floors with plan dimensions 48.0×48.0 m2 were investigated.Three cases of main core locations are studied:centric(A),eccentric by one sixth(B)and one third(C)of building width.The three-dimensional finite element method has been used in conducting structural analysis through ETABS software.Gravity and lateral(wind and seismic)loadings are applied to all building cases.It has been concluded that the core location is the prime parameter governing the structural behavior of tall buildings.Although the first two cases(A,B)have acceptable and similar structural behaviors conforming to code limits,in the third case(C),the building behavior came beyond code limits.The author introduced remedial action by adding two secondary cores in the opposite direction of the main core(C-R)to restore the building behavior to the code limits.The results of this action were satisfactory.展开更多
The influence of binder composition and pore structure of concrete on chloride diffusion coefficient in concrete were investigated by the natural immersion test, MIP test, SEM and EDS test, respectively. The experimen...The influence of binder composition and pore structure of concrete on chloride diffusion coefficient in concrete were investigated by the natural immersion test, MIP test, SEM and EDS test, respectively. The experimental results showed that the effect of binder composition on chloride diffusion coefficient was the comprehensive result of concrete pore structure and binder hydration products, and the porosity and pore size distribution were the main factors that influence the changes of diffusion coefficient. The chloride diffusion coefficient decreased with increasing the curing temperature and the relative humidity. The hydration degree were promoted by improving curing temperatures, and then the porosity of concrete decreased and the proportion of gel pore and transitional pore increased, respectively. But the water evaporation decreased with increasing the relative humidity and then decreased porosity and increased the proportion of gel pore and transitional pore. Additionally, The chloride diffusion coefficient of concrete got the lower value when the appropriate replacement of fly ash in the ranges of 10%-20%, when the double-adding fly ash and slag content was 50%. The porosity increased and the ratio of C/S in C-S-H decreased with further increasing the fly ash content, which led to increase the chloride diffusion coefficient in concrete.展开更多
To study the effect of atmospheric pressure on the properties of fresh and hardened airentrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus(Lhasa, 61 ...To study the effect of atmospheric pressure on the properties of fresh and hardened airentrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus(Lhasa, 61 kPa) and the plains(Beijing, 101 kPa). Air content, slump, compressive strength and pore structure of the three air-entrained concretes were tested in these two places. It is found that the air content of concrete under low atmospheric pressure(LAP) is 4%-36% lower than that of concrete under normal atmospheric pressure(NAP), which explaines the decrease of slump for air-entrained concrete under LAP. Pore number of hardened concrete under LAP is reduced by 48%-69%. While, the proportion of big pores(pore diameter >1 200 μm) and air void spacing factor are increased by 1.5%-7.3% and 51%-92%, respectively. The deterioration of pore structure results in a 3%-9% reduction in the compressive strength of concrete. From the results we have obtained, it can be concluded that the increase of critical nucleation energy of air bubbles and the decrease of volumetric compressibility coefficient of air in the concrete are responsible for the variation of air content and pore structure of concrete under LAP.展开更多
Structure characteristics of three kinds of ceramsite with different water absorption and the influence on microstructure of interfacial zone as well as performance of chloride permeabil-ity and frost resistance of co...Structure characteristics of three kinds of ceramsite with different water absorption and the influence on microstructure of interfacial zone as well as performance of chloride permeabil-ity and frost resistance of combined aggregate concrete were investigated. The results show that, dense shell and closed internal pore have sharp effects on lowering water absorption of ceramsite. However, the ceramsite with high water absorption has obvious effect on the densification of interfa-cial paste which would develop a structure with lower porosity, finer aperture and higher microhard-ness. Furthermore, the impermeability and frost-resistance of concrete can be improved due to the ef-fect of water absorption and releasing by ceramsite with higher water absorption.展开更多
基金supported by the National Key Research and Development Project of China(No.2021YFB2600200)the National Natural Science Foundation of China(Nos.52470185 and 52170159)the Open Research Fund of National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety,the Fund of National Key Laboratory of Water Disaster Prevention and Key Research and Development Program of Jiangsu Province(No.BE2022601).
文摘Microbial corrosion of hydraulic concrete structures(HCSs)has received increasing research concerns.However,knowledge on the morphology of attached biofilms,as well as the community structures and functions cultivated under variable nutrient levels is lacking.Here,biofilm colonization patterns and community structures responding to variable levels of ammonia and sulfate were explored.From field sampling,NH_(4)^(+)-N was proven key factor governing community structure in attached biofilms,verifying the reliability of selecting target nutrient species in batch experiments.Biofilms exhibited significant compositional differences in field sampling and incubation experiments.As the nutrient increased in batch experiments,the growth of biofilms gradually slowed down and uneven distribution was detected.The proportions of proteins and β-d-glucose polysaccharides in biofilms experienced a decrease in response to elevated levels of nutrients.With the increased of nutrients,themass losses of concretes exhibited an increase,reaching a highest value of 2.37%in the presence of 20 mg/L of ammonia.Microbial communities underwent a significant transition in structure and metabolic functions to ammonia gradient.The highest activity of nitrification was observed in biofilms colonized in the presence of 20 mg/L of ammonia.While the communities and their functions remained relativelymore stable responding to sulfate gradient.Our research provides novel insights into the structures of biofilms attached on HCSs and the metabolic functions in the presence of high level of nutrients,which is of significance for the operation and maintenance of hydraulic engineering structures.
文摘With the development of modern society,people put forward higher requirements for building safety,which makes the construction project face new challenges.Reinforced concrete frame structure as a common engineering type,although the construction technology has been relatively mature,but its earthquake collapse ability still needs to be strengthened.This paper analyzes the specific factors that affect the seismic collapse ability of reinforced concrete frame structure,summarizes the previous research results,and puts forward innovative application of fiber-reinforced polymer(FRP)composite materials,play the role of smart materials,improve the isolation and energy dissipation devices,etc.,to promote the continuous optimization of reinforced concrete frame structure design,and show better seismic performance.
基金Hunan Provincial Department of Water Resources:Research on Formula Optimization and Performance Evaluation System of Ecological Concrete for River Water Quality Purification Based on the Dual Carbon Goal(Project No.:XSKJ2024064-44)。
文摘By adding zeolite aggregate with good adsorption properties,different mix ratios of added zeolite pervious concrete(ZPC)were designed to compare the water purification effect of ordinary pervious concrete and water purification tests that were conducted.The pore characteristics of the pervious concrete were identified using three-dimensional reconstruction software and the relationship between pore structure and water purification performance was quantified by gray entropy correlation analysis.The results showed that the purification efficiency of zeolite-doped pervious concrete was 17.6%-22.3%higher than that of ordinary pervious concrete.The characteristic parameters of the pore structure of permeable concrete,i.e.planar porosity and tortuosity,were determined using three-dimensional reconstruction software.The correlation between the degree of tortuosity and the removal rate reached more than 0.90,indicating that the internal pore structure of pervious concrete has a good correlation with the water purification performance.
基金Funded by the Science&Technology Project of the Department of Transport of Tibet Autonomous Region(No.XZJTKJ2020[04])。
文摘We conducted a series tests on surface layers of plateau concrete at the ages of 180 and 540 days,including the most superficial cement paste,the 5 mm thick surface mortar,and the 50 mm thick surface concrete.Thermogravimetry and nitrogen absorption porosimetry on cement past,mercury intrusion porosimetry on mortar,and microhardness test on interface transition zone between mortar and coarse aggregate were conducted to evaluate the hydration degree and characterize the micro-structure.Whilst,tests for the rebound strength,abrasion resistance,and chloride ion impenetrability of concrete were conducted to assess the macro-performance.The experimental results show that,affected by the harsh plateau climate,outward surfaces have lower hydration degrees and worse pore structure than inward surfaces.As the hydration of concrete surface is ongoing after the age of 180 days,both the micro-structure and the macro-performance are continuously improved.In the long-term,either the orientation or the depth towards surface does not significantly affect concrete performance.Surface carbonation brings positive effects on mechanical properties but negative effects on the durability.Additionally,standard test result of chloride ion impenetrability is found significantly affected by the atmospheric pressure.For a same batch of concrete,charge passed in plateau regions is obviously lower than that in common regions.
文摘The cultivation of engineering capabilities aims to equip engineering professionals with high-level expertise to meet the demands of society and industry development,thereby enhancing their competitiveness and career potential.This article focuses on engineering capability development,exploring teaching strategies for the Reinforced Concrete Structure course.It aims to provide insights for educators in engineering programs at universities and vocational colleges in China.By doing so,teaching plans that meet the needs of engineering capability development,laying a solid educational foundation for the healthy growth of engineering professionals in the new era,and enhancing their application of knowledge and skills can be developed.
文摘Nowadays,education and teaching have become a hot topic,and teaching in colleges and universities is facing a brand-new development direction.Principles of Concrete Structure Design,as one of the main courses,transmits professional knowledge for students,enhances the students’professional ability,and further carries out in-depth research on the course to bring a better teaching effect for students.The article mainly focuses on the research of the principles of concrete structure design course,conducts an analysis of the teaching characteristics of the principles of concrete structure design course,and reasonably sets the teaching content from the optimization of the course teaching objectives;innovative course teaching methods can deepen the effect of knowledge understanding;reform of experimental practice teaching can lay down the effect of the internalization of knowledge,etc.The in-depth description and discussion of the relevant aspects of the research aim to provide guidelines for related research.
文摘Based on the durability characteristics of prestressed concrete structures,the durability limit states of carbonation and chloride ion attack are defined, respectively.Durability predicting models on the basis of reliability mathematics and stochastic processes areconstructed, and the pure theoretical formulae of failure probability of prestressed concretestructures are analyzed. In addition, a simple durability design method for carbonation ofstructures is put forward. According to the analysis, the durability of prestressed concretestructures is superior to that of traditional structures. The research also indicates that theconcrete cover prescribed in the current code (GB 50010-2002) is not adequate. The rational coverthickness should notbe less than 35 or 45 mm according to carbonation or chloride ion attack,respectively.
基金The Key Project of National Natural Science Foun-dation of China (No50538070)
文摘Durability zonation standard （DZS） is proposed to provide useful parameters for durable concrete structure design. It deals not only with the influence of environment on structures, but also with types, functions and importance of structures based on the theory of life cycle cost（LCC）. First, the basic concept of DZS for concrete structure design is defined. Then the basic principles for DZS are established. The factors for zonation according to natural environmental conditions and structural importance are identified. The usefulness of DZS by citing a real application for concrete highway bridges in Zhejiang Province is demonstrated. Finally, durability regulations are provided accordingly to zonation.
基金supported by the Project on Excellent Post-Graduate Dissertation of Hohai University,Nanjing,China(422003508)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(SJCX23_0187+2 种基金422003287)the National Natural Science Foundation of China(52250410359)Young Elite Scientists Sponsorship Program by Jiangsu Provincial Association for Science and Technology(TJ-2023-043).
文摘When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on the design of the tensioning plans and selection of control measures for the BSS.In order to accurately obtain the bending stiffness of CFST beam and clarify its impact on the mechanical properties of composite BSS during con-struction,the influence of some factors such as height-width ratio,wall thickness of steel tube,elasticity modulus of concrete,and friction coefficient on the bending stiffness are analyzed parametrically by the numerical simula-tion technology based on an actual project.The calculation formula of the equivalent bending stiffness of CFST is also established through mathematical statistical simulation.Then,the equivalent bending stiffness is introduced into the construction and use stages of the composite BSS,respectively,and the mechanical properties such as prestress-tensioning control value,structural deformation,and internal force of key members are comparatively analyzed when adopting two different construction plans.Moreover,the optimal construction plan of concrete placementfirst and then prestress-tensioning is proposed.
文摘The construction industry faces significant challenges due to the inherent brittleness and cracking tendency of traditional concrete,which compromises structural durability and necessitates frequent,costly repairs.This paper explores the groundbreaking development of self-healing concrete as a transformative material technology for sustainable architecture.We examine three primary autogenous healing mechanisms:encapsulated polymer/microbial healing agents,vascular networks,and shape memory alloys.Through a review of recent laboratory experiments and pilot projects,this study analyzes the crack-sealing efficiency,recovery of mechanical properties,and long-term durability of these materials.A comparative case study of a demonstration building facade incorporating microbial self-healing concrete is presented,showing a potential 30%reduction in maintenance costs over a 20-year lifecycle.The findings indicate that self-healing concrete not only enhances structural resilience but also significantly reduces the carbon footprint associated with building maintenance,aligning with the core principles of sustainable development.The paper concludes by discussing current limitations in mass production and cost-effectiveness and proposes directions for future research to facilitate widespread adoption in architectural engineering.
基金funded by the National Natural Science Foundation of China(No.52278429)the Key R&D Program in Shaanxi Province(Nos.2023-ZDLGY-25,2025SF-YBXM-537)+1 种基金the Fundamental Research Funds for the Central Universities,CHD(No.300102315203)Transportation Science and Technology Project in Shaanxi Province(Nos.23-91K,24-14K,24-39K).
文摘The plateau environment not only affects the development of concrete's early strength but also damages its durability during its service life.This paper summarized and analyzed the impact of plateau environments on concrete’properties and proposed methods to improve the performance of concrete in plateau environment.The results indicated that low humidity and high evaporation rates in plateau regions inhibit the hydration of cement in concrete,leading to an increased content of micro-pores ranging from 500 to 1000 nm and raising the risk of early-stage cracking,thus reducing the impermeability of concrete.The low atmospheric pressure(AP)condition of 60 kPa decreases the entrained air content in concrete by over 20%,diminishes the pores under 200μm,and increases the average air-voids diameter and spacing factor,resulting in a decrease of more than 5%in the 28 d compressive strength of concrete.Consequently,the durability of concrete is compromised.Saponin and rosinbased air-entraining agents are recommended to improve the performance of concrete in plateau environments.Nanoparticles also aid in stabilizing bubbles in such conditions.Selecting low-heat specialty cements,increasing the amount of cement used,and extending the curing period are also vital measures to enhance the performance of plateau concrete.
文摘Computed tomography(CT)can inspect the internal structure of concrete with high resolution,but improving the accuracy of measurements remains a key challenge due to the reliance on complex image processing and significant manual intervention.This study aims to optimize CT scanning parameters to enhance the accuracy of measuring crack widths and rebar volumes in reinforced concrete.Nine sets of specimens,each with varying rebar diameters and concrete cover thicknesses,were scanned before and after corrosion using an Optima CT scanner,followed by three-dimensional reconstructions using Avizo software.The effects of threshold values and“Erosion”coefficients on measurement accuracy were evaluated.The results demonstrated that an optimal lower threshold of 2950,combined with an‘Erosion’coefficient of 6,effectively limits the measurement error of rebar volumes to within 1%.The optimal threshold for measuring crack widths was influenced by the crack width,rebar diameter,and concrete cover thickness.Additionally,an optimized formula for determining crack measurement thresholds was proposed.This study significantly improves the accuracy of CT-based non-destructive testing(NDT)techniques,providing valuable insights for structural health monitoring(SHM).
基金Projects(42477162,52108347,52178371,52168046,52178321,52308383)supported by the National Natural Science Foundation of ChinaProjects(2023C03143,2022C01099,2024C01219,2022C03151)supported by the Zhejiang Key Research and Development Plan,China+6 种基金Project(LQ22E080010)supported by the Exploring Youth Project of Zhejiang Natural Science Foundation,ChinaProject(LR21E080005)supported by the Outstanding Youth Project of Natural Science Foundation of Zhejiang Province,ChinaProject(2022M712964)supported by the Postdoctoral Science Foundation of ChinaProject(2023AFB008)supported by the Natural Science Foundation of Hubei Province for Youth,ChinaProject(202203)supported by Engineering Research Centre of Rock-Soil Drilling&Excavation and Protection,Ministry of Education,ChinaProject(202305-2)supported by the Science and Technology Project of Zhejiang Provincial Communication Department,ChinaProject(2021K256)supported by the Construction Research Founds of Department of Housing and Urban-Rural Development of Zhejiang Province,China。
文摘This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.
文摘Squat reinforced concrete(RC)shear walls are essential structural elements in low-rise buildings,valued for their high strength and stiffness.However,research on their seismic behavior remains limited,as most studies focus on tall,slender walls,which exhibit distinct failure mechanisms and deformation characteristics.This study addresses this gap by conducting an extensive review of existing research on the seismic performance of squat RC shear walls.Experimental studies,analytical models,and numerical simulations are examined to provide insights into key factors affecting wall behavior during seismic events,including material properties,wall geometry,reinforcement detailing,and loading conditions.The review aims to support safer design practices by identifying current knowledge gaps and offering guidance on areas needing further investigation.The findings are expected to aid researchers and practitioners in refining seismic design codes,ultimately contributing to the development of more resilient squat RC shear walls for earthquake-prone regions.This research underscores the importance of improving structural resilience to enhance the safety and durability of buildings.
基金supported by the National Natural Science Foundation of China(51708188).
文摘Semantic segmentation of concrete bridge defect images frequently encounters challenges due to insufficient precision and the limited computational capabilities ofmobile devices,thereby considerably affecting the reliability of bridge defect monitoring and health assessment.To tackle these issues,a concrete defects dataset(including spalling,crack,and exposed steel rebar)was curated and multiple semantic segmentation models were developed.In these models,a deep convolutional network or a lightweight convolutional network were employed as the backbone feature extraction networks,with different loss functions configured and various attention mechanism modules introduced for conducting multi-angle comparative research.The comparison of results indicates that utilizing VGG16 as the backbone network of U-Net for semantic segmentation of multi-class concrete defects images resulted in the highest recognition accuracy,achieving a Mean Intersection over Union(MIoU)of 80.37%and a Mean Pixel Accuracy(MPA)of 90.03%.The optimal combination of loss functions was found to be Focal loss and Dice loss.The lightweight convolutional network Mobile NetV2-DeeplabV3 slightly reduced recognition accuracy but significantly decreased the number of parameters,resulting in a faster detection speed of 71.87 frames/s,making it suitable for real-time defect detection.After integrating the SE(Squeeze-and-Excitation),CBAM(Convolutional Block Attention Module),and Coordinate Attention(CA)modules,both VGG16-U-Net and MobileNetV2-DeeplabV3 achieved improved recognition accuracy.Among them,the CAmodule(Coordinate Attention)effectively guides the model to accurately identify subtle concrete defects.The improved VGG16-U-Net can identify previously the new untrained concrete defect images in the concrete structural health monitoring(SHM)system,and the recognition accuracy can meet the demand for intelligent defect image recognition for structural health monitoring of concrete structures.
基金Funded by the Natural Science Foundation of Shaanxi Province(No.2023-JC-QN-0553)。
文摘To examine the influences of waste polypropylene fiber(PPF)on the strength and internal pore structure of recycled aggregate concrete incorporating iron ore tailings,both the cubic compressive strength and axial compressive strength of the concrete were measured.Additionally,the microstructure was analyzed using scanning electron microscopy.The evolution of pore structure parameters,including pore size distribution,pore type distribution,and nuclear magnetic resonance spectral area in the concrete,was investigated through nuclear magnetic resonance(NMR)analysis.A model correlating the concrete's pore structure with its macroscopic performance was subsequently developed based on fractal theory.The results demonstrate that an appropriate amount of PPF created a bridging effect that decelerated the progression of macro cracks,enhanced the ductility of the concrete's failure mode,and increased both cubic compressive strength and axial compressive strength,with the most effective dosage being approximately 0.6%.An appropriate amount of PPF(ranging from 0.3%to 0.6%)facilitated the formation of harmless pores and shifted the pore size distribution towards medium and small sizes.Specifically,a fiber content of 0.6%resulted in the most significant reduction in the T2 spectral area.Furthermore,the pore structure of concrete exhibits distinct fractal characteristics.As the PPF content increased,the fractal dimension initially rose and then declined,demonstrating a strong correlation with the mechanical properties.
文摘The main purpose of this paper is to investigate the effect of core eccentricity on the structural behavior of concrete tall buildings.Concrete buildings of 55 floors with plan dimensions 48.0×48.0 m2 were investigated.Three cases of main core locations are studied:centric(A),eccentric by one sixth(B)and one third(C)of building width.The three-dimensional finite element method has been used in conducting structural analysis through ETABS software.Gravity and lateral(wind and seismic)loadings are applied to all building cases.It has been concluded that the core location is the prime parameter governing the structural behavior of tall buildings.Although the first two cases(A,B)have acceptable and similar structural behaviors conforming to code limits,in the third case(C),the building behavior came beyond code limits.The author introduced remedial action by adding two secondary cores in the opposite direction of the main core(C-R)to restore the building behavior to the code limits.The results of this action were satisfactory.
基金Funded by the Western China Communication Science & TechnologyProjects (No.200632800003)
文摘The influence of binder composition and pore structure of concrete on chloride diffusion coefficient in concrete were investigated by the natural immersion test, MIP test, SEM and EDS test, respectively. The experimental results showed that the effect of binder composition on chloride diffusion coefficient was the comprehensive result of concrete pore structure and binder hydration products, and the porosity and pore size distribution were the main factors that influence the changes of diffusion coefficient. The chloride diffusion coefficient decreased with increasing the curing temperature and the relative humidity. The hydration degree were promoted by improving curing temperatures, and then the porosity of concrete decreased and the proportion of gel pore and transitional pore increased, respectively. But the water evaporation decreased with increasing the relative humidity and then decreased porosity and increased the proportion of gel pore and transitional pore. Additionally, The chloride diffusion coefficient of concrete got the lower value when the appropriate replacement of fly ash in the ranges of 10%-20%, when the double-adding fly ash and slag content was 50%. The porosity increased and the ratio of C/S in C-S-H decreased with further increasing the fly ash content, which led to increase the chloride diffusion coefficient in concrete.
基金Funed by the National Key R&D Program of China(No.2017YFB0309903)
文摘To study the effect of atmospheric pressure on the properties of fresh and hardened airentrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus(Lhasa, 61 kPa) and the plains(Beijing, 101 kPa). Air content, slump, compressive strength and pore structure of the three air-entrained concretes were tested in these two places. It is found that the air content of concrete under low atmospheric pressure(LAP) is 4%-36% lower than that of concrete under normal atmospheric pressure(NAP), which explaines the decrease of slump for air-entrained concrete under LAP. Pore number of hardened concrete under LAP is reduced by 48%-69%. While, the proportion of big pores(pore diameter >1 200 μm) and air void spacing factor are increased by 1.5%-7.3% and 51%-92%, respectively. The deterioration of pore structure results in a 3%-9% reduction in the compressive strength of concrete. From the results we have obtained, it can be concluded that the increase of critical nucleation energy of air bubbles and the decrease of volumetric compressibility coefficient of air in the concrete are responsible for the variation of air content and pore structure of concrete under LAP.
基金Funded by the Western Transportation Construction of Communication Ministry (No. 200331882008)
文摘Structure characteristics of three kinds of ceramsite with different water absorption and the influence on microstructure of interfacial zone as well as performance of chloride permeabil-ity and frost resistance of combined aggregate concrete were investigated. The results show that, dense shell and closed internal pore have sharp effects on lowering water absorption of ceramsite. However, the ceramsite with high water absorption has obvious effect on the densification of interfa-cial paste which would develop a structure with lower porosity, finer aperture and higher microhard-ness. Furthermore, the impermeability and frost-resistance of concrete can be improved due to the ef-fect of water absorption and releasing by ceramsite with higher water absorption.
