Experiments were conducted to evaluate the healing of drying cracks in air-dried bentonite-sand blocks after hydration and swelling in groundwater,providing justifications to simplify the protection of blocks prior to...Experiments were conducted to evaluate the healing of drying cracks in air-dried bentonite-sand blocks after hydration and swelling in groundwater,providing justifications to simplify the protection of blocks prior to installation in a high-level radioactive waste repository.Synthetic groundwater was prepared to represent the geochemistry of Beishan groundwater,and was used to hydrate the blocks during the swelling pressure and swelling strain measurements,as Beishan is the most promising site for China's repository.Healing of the surface cracks was recorded by photography,and healing of the internal cracks was visualized by CT images and hydraulic conductivity of air-dried blocks.The results indicate that the maximum swelling pressure and swelling strain are primarily affected by the geochemistry of Beishan groundwater,but not affected by the drying cracks.The maximum swelling pressure and swelling strain of air-dried blocks are comparable to or even higher than the pressure and strain of fresh blocks.The maximum swelling pressure measured in strong(i.e.high ion strength)Beishan groundwater was 44%of the pressure measured in deionized(DI)water,and the maximum swelling strain was reduced to 23%of the strain measured in DI water.Nevertheless,the remained swelling of the blocks hydrated in strong Beishan groundwater was sufficient to heal the surface and internal drying cracks,as demonstrated by the pictures of surface cracks and CT images.The hydraulic conductivity of the air-dried block permeated with strong groundwater was comparable(3.7×higher)to the hydraulic conductivity of the fresh block,indicating the self-healing of drying cracks after hydration and swelling in groundwater.A simplified method of protecting the block with plastic wraps before installation is recommended,since the remained swelling of the block hydrated in Beishan groundwater is sufficient to heal the drying cracks.展开更多
Cracks can deteriorate mechanical properties and/or durability of concrete. A few studies have shown that, cracks can autogenously heal under a certain conditions besides the traditional passive repair with a delibera...Cracks can deteriorate mechanical properties and/or durability of concrete. A few studies have shown that, cracks can autogenously heal under a certain conditions besides the traditional passive repair with a deliberate external intervention. For underground concrete structures, the presence of water, as a necessity for chemical reactions of the healing additives, is beneficial to healing concrete. In this paper, a natural healing method by mineral additives was developed according to the chemical and physical characteristics of underground environment. The healing capacity of three different crystalline mineral materials classified namely, carbonate, calcium sulphoaluminate expansive agent and natural metakaolin due to permeation- crystallization, expansion and pozzolanic reaction, has been assessed from the mechanical properties, referring to the relative elastic modulus, the strength restoration, and the water permeability of the healed specimens. In addition, the morphology of the healing products in the vicinity of the crack was observed. The results indicate that the specimens incorporated with the three mineral additives show different healing capacity according to the improved mechanical properties and permeability. The permeability of the host matrix decreased a lot after crack healing by natural metakaolin followed by carbonate whereas no noticeable improvement of water permeability has been observed for the specimens mixed with expansive agent. The specimens incorporated with carbonate show the best mechanical restoration in terms of relative elastic modulus and compressive strength. Although the dominate element is CaCO3 by reaction of CO32-, either from the dissolved CO2 or from the additives, and Ca2＋ in the cementitious system to fill the cracks, the healing capacity depends greatly on the morphology and the properties of the newly formed products.展开更多
Advances in machine learning(ML)methods are important in industrial engineering and attract great attention in recent years.However,a comprehensive comparative study of the most advanced ML algorithms is lacking.Six i...Advances in machine learning(ML)methods are important in industrial engineering and attract great attention in recent years.However,a comprehensive comparative study of the most advanced ML algorithms is lacking.Six integrated ML approaches for the crack repairing capacity of the bacteria-based self-healing concrete are proposed and compared.Six ML algorithms,including the Support Vector Regression(SVR),Decision Tree Regression(DTR),Gradient Boosting Regression(GBR),Artificial Neural Network(ANN),Bayesian Ridge Regression(BRR)and Kernel Ridge Regression(KRR),are adopted for the relationship modeling to predict crack closure percentage(CCP).Particle Swarm Optimization(PSO)is used for the hyper-parameters tuning.The importance of parameters is analyzed.It is demonstrated that integrated ML approaches have great potential to predict the CCP,and PSO is efficient in the hyperparameter tuning.This research provides useful information for the design of the bacteria-based self-healing concrete and can contribute to the design in the rest of industrial engineering.展开更多
The complete deposition distribution process of calcium carbonate is summarized in three directions of cracks. Distribution of calcium carbonate in the self-healing process of microbial concrete is studied in detail, ...The complete deposition distribution process of calcium carbonate is summarized in three directions of cracks. Distribution of calcium carbonate in the self-healing process of microbial concrete is studied in detail, with the help of a variety of analytical techniques. The results show that carbonate deposits along the x-axis direction of the cracks. The farther from the crack surfaces of concrete matrix in x-axis direction, the more the content of the substrate, the less content of calcium carbonate. Gradual accumulation of calcium carbonate along the y-axis direction is like building a house with bricks. Different repair points are gradually connected, and ultimately the whole of cracks are completely filled. In the z-axis direction, calcium deposits on the surface of fracture direction, when the crack is filled on the surface, because the internal crack hypoxia in the depths of cracks hardly produces calcium carbonate.展开更多
Cement-based materials are brittle and crack easily under natural conditions.Cracks can reduce service life because the transport of harmful substances can cause corrosion damage to the structures.This review discusse...Cement-based materials are brittle and crack easily under natural conditions.Cracks can reduce service life because the transport of harmful substances can cause corrosion damage to the structures.This review discusses the feasibility of using microbial self-healing agents for crack healing.Tubular and spherical carriers can be used to load microbial self-healing agents and protect microbes,which prolongs the self-healing time.The area self-healing ratio,permeability,mechanical strength,precipitation depth method,numerical modeling,and ultrasonic method can be employed to identify the self-healing effect of cracks.Moreover,the self-healing mechanism is systematically analyzed.The results showed that microbial self-healing agents can repair cracks in cement-based materials in underground projects and dam gates.The difficulties and future development of self-healing cracks were analyzed.A microbial selfhealing agent was embedded in the cement-based material,which automatically repaired the developing cracks.With the development of intelligent building materials,self-healing cracks have become the focus of attention.展开更多
The brittleness of cement composites makes cracks almost inevitable,producing a serious limitation on the lifespan,resilience,and safety of concrete infrastructure.To address this brittleness,self-healing concrete has...The brittleness of cement composites makes cracks almost inevitable,producing a serious limitation on the lifespan,resilience,and safety of concrete infrastructure.To address this brittleness,self-healing concrete has been developed for regaining its mechanical and durability properties after becoming cracked,thereby promising sustainable development of concrete infrastructure.This paper provides a comprehensive review of the latest developments in self-healing concrete.It begins by summarizing the methods used to evaluate the self-healing efficiency of concrete.Next,it compares strategies for achieving healing concrete.It then discusses the typical approaches for developing self-healing concrete.Finally,critical insights are proposed to guide future studies on the development of novel self-healing concrete.This review will be useful for researchers and practitioners interested in the field of self-healing concrete and its potential to improve the durability,resilience,and safety of concrete infrastructure.展开更多
Mechanical as well as durability properties are pivotal for any type of concrete which gets adversely affected due to cracks that may form due to loading beyond its capacity.Concrete has the intrinsic property to heal...Mechanical as well as durability properties are pivotal for any type of concrete which gets adversely affected due to cracks that may form due to loading beyond its capacity.Concrete has the intrinsic property to heal itself to some extent but not fully as the passive form of autogenous healing plays an inferior role for a complete repair of a cementitious material.The self-healing capabilities can be enhanced by adding chemical admixtures,polymers,and bacteria strains induced calcium carbonate precipitation,etc.In this paper,the advancements in the development and performance of self-healing concrete using chemical admixtures,polymers,and bacteria strains are reviewed.This systematic review includes the available experimental tests and methodologies investigating self-healing efficiency over the last decade.Further,this review focussed on self-healing materials,the ideology,and opinions of those in the construction field on the direction of self-healing concrete for future applications.It is yet not possible to predict the most appropriate technique,however,a generalized opinion about the effectiveness of the different approaches has been illustrated.展开更多
Concrete is the most widely used composite material in civil engineering.Microbial induced calcium carbonate precipitation(MICP)is a green and environmental friendly technology,which has received extensive attention i...Concrete is the most widely used composite material in civil engineering.Microbial induced calcium carbonate precipitation(MICP)is a green and environmental friendly technology,which has received extensive attention in repair of concrete cracks.This paper introduces the research progress in Southeast University research in past 16 years.In the early stage,MICP technology of urea hydrolyzed by Bacillus pasteurii was mainly investigated to repair the surface cracks and to fill large-size cracks with grouting.However,aiming at the hidden cracks that were difficult for human intervention,a new mineralization route of Bacillus mucilaginosus was proposed,which could repair faster than Bacillus alcalophilus,and the problem of ammonia emission in the repair process of Bacillus pasteurii was also solved.In addition,in order to improve the protection of bacteria and the self-healing efficiency of the later age cracks,the methods of fiber immobilization,carrier uniformly immobilization and core-shell structural immobilization had been compared and studied.The results showed that core-shell structural immobilization had good protection ability and strong designability.What’s more,the paper also summarized the characteristics of spore germination,cell activity,nucleation and biological calcium carbonate in crack zone,and introduced the application experience of microbial self-healing concrete in water conservancy projects and subway stations.展开更多
This paper presents the effect on compressive strength and self-healing capability of bacterial concrete with the addition of calcium lactate.Compared to normal concrete,bacterial concrete possesses higher durability ...This paper presents the effect on compressive strength and self-healing capability of bacterial concrete with the addition of calcium lactate.Compared to normal concrete,bacterial concrete possesses higher durability and engineering concrete properties.The production of calcium carbonate in bacterial concrete is limited to the calcium content in cement.Hence calcium lactate is externally added to be an additional source of calcium in the concrete.The influence of this addition on compressive strength,self-healing capability of cracks is highlighted in this study.The bacterium used in the study is bacillus subtilis and was added to both spore powder form and culture form to the concrete.Bacillus subtilis spore powder of 2 million cfu/g concentration with 0.5%cement was mixed to concrete.Calcium lactates with concentrations of 0.5%,1.0%,1.5%,2.0%,and 2.5%of cement,was added to the concrete mixes to test the effect on properties of concrete.In other samples,cultured bacillus subtilis with a concentration of 1×10^cells/mL was mixed with concrete,to study the effect of bacteria in the cultured form on the properties of concrete.Cubes of 100 mm×100 mm×100 mm were used for the study.These cubes were tested after a curing period of 7,14,and 28 d.A maximum of 12%increase in compressive strength was observed with the addition of 0.5%of calcium lactate in concrete.Scanning electron microscope and energy dispersive X-ray spectroscopy examination showed the formation of ettringite in pores;calcium silicate hydrates and calcite which made the concrete denser.A statistical technique was applied to analyze the experimental data of the compressive strengths of cementations materials.Response surface methodology was adopted for optimizing the experimental data.The regression equation was yielded by the application of response surface methodology relating response variables to input parameters.This method aids in predicting the experimental results accurately with an acceptable range of error.Findings of this investigation indicated the influence of added calcium lactate in bio-concrete which is quite impressive for improving the compressive strength and self-healing properties of concrete.展开更多
Maintaining the health and reliability of civil facilities is of strategic importance.In highway engineering,pavement cracking impairs the road service and travel comfort level,while structure cracking can cause catas...Maintaining the health and reliability of civil facilities is of strategic importance.In highway engineering,pavement cracking impairs the road service and travel comfort level,while structure cracking can cause catastrophic damage.Microcapsule-based self-healing materials offer solutions to auto-recovery micro-cracks and maintain structural health.Such solution has become available by laboratory synthesis and proved effective in addressing the cracking problem during long-term mechanical,thermal,and hydraulic conditions.However,full-scale applications of this technique are not prevalent,showing its potential limitations in highway engineering.Crack healing in highways is a big topic,therefore,this review has two insertion points.(1)We focus on the cracking issues on two specific materials:asphalt and concrete,which account for the vast majority of all the materials used in pavement and structures in highways.(2)Instead of the laboratory studies,we pay more attention to the practical applications,the meaning of healing performance,and the adverse effects of microcapsules to the main structural components(i.e.,tunnel lining,bridge piers and beams)and pavement in highways.The practical significance of self-healing materials in highway projects was discussed from the three aspects:strength,durability,and stress redistribution.The difficulty in applying this new technique is also discussed from economic perspective.For future-proofing,a material evaluation system that fits the load condition is required.The self-healing technique brings composites a chance to interact with the environment,showing high potential for contributing to the development of various types of long-lasting infrastructures.展开更多
Self-healing polymers represent a class of materials with built-in capability of rehabilitating damages. The topic has attracted increasingly more attention in the past few years. The on-going research activities clea...Self-healing polymers represent a class of materials with built-in capability of rehabilitating damages. The topic has attracted increasingly more attention in the past few years. The on-going research activities clearly indicate that self-healing polymeric materials turn out to be a typical multi-disciplinary area concerning polymer chemistry, organic synthesis, polymer physics, theoretical and experimental mechanics, processing, composites manufacturing, interfacial engineering, etc. The present article briefly reviews the achievements of the groups worldwide, and particularly the work carried out in our own laboratory towards strength recovery for structural applications. To ensure sufficient coverage, thermoplastics and thermosetting polymers, extrinsic and intrinsic self-healing, autonomic and non-autonomic healing approaches are included. Innovative routes that correlate materials chemistry to full capacity restoration are discussed for further development from bioinspired toward biomimetic repair.展开更多
Five complete caverns were discovered in Longyou in 1992.They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago.When they were un-watered,their integrity was maintained completel...Five complete caverns were discovered in Longyou in 1992.They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago.When they were un-watered,their integrity was maintained completely,and their interior rock surfaces were free of old cracks.Since then,however,the rock's interior faces have initiated and propagated more and more cracks.This paper attempts to address the question of why the rock interior faces were free of old cracks once they were unearthed.To address this question,this paper proposes a hypothesis that the argillaceous siltstone has the ability of self-healing its cracks over a short period of time under weak acid water environment.Data and evidence are presented herewith to prove the hypothesis.They include observations and measurements in the field and test results in the laboratory.Specifically,a three-point bending test is used to form a tensile crack in a rectangular rock specimen and a deadload test for the specimen immersed in initially weak acid water is used for self-healing its crack.The results have shown that the argillaceous siltstone is in a state of weak alkalinity and the rain water at the site is in a state of weak acidity.Therefore,when it is immersed in weak acid water for some time,the argillaceous siltstone would be able to make chemical reactions to generate new minerals such as calcite.The new minerals would be able to infill the cracks and then heal the crack within a few years.Once the crack is self-healed,the rock can regain its strength and integrity.Consequently,the rock interior surfaces could be free of old cracks when the water was pumped out of the caverns.展开更多
Three strategies were proposed to prolong the service life of continuous fiber-reinforced silicon carbide ceramic matrix composite(CMC-SiC),which served as thermal-structure components of aeroengine at thermo-mechanic...Three strategies were proposed to prolong the service life of continuous fiber-reinforced silicon carbide ceramic matrix composite(CMC-SiC),which served as thermal-structure components of aeroengine at thermo-mechanical-oxygenic coupling environment.As for some thermal-structure components with low working stress,improving the degree of densification was crucial to prolong the service life,and the related process approaches were recited.If the thermal-structure components worked under moderate stress,the matrix cracking stress(σ^(mc))should be improved as far as possible.The fiber preform architecture,interface shear strength,residual thermal stress,and matrix strengthening were associated withσ_(mc)in this review.Introducing self-healing components was quite significant with the appearance of matrix microcracks when CMC-SiC worked at more severe environment for hundreds of hours.The damage can be sealed by glass phase originating from the reaction between self-healing components and oxygen.The effective self-healing temperature range of different self-healing components was first summarized and distinguished.The structure,composition,and preparation process of CMC-SiC should be systematically designed and optimized to achieve long duration target.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.41972265)the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2021-57)+1 种基金the Gansu Province Science Foundation(Grant No.20JR10RA492)Special thanks to the Environmental Research and Education Foundation for supporting the first author(Y.Tan)through a fellowship for his study at the University of Wisconsin-Madison.
文摘Experiments were conducted to evaluate the healing of drying cracks in air-dried bentonite-sand blocks after hydration and swelling in groundwater,providing justifications to simplify the protection of blocks prior to installation in a high-level radioactive waste repository.Synthetic groundwater was prepared to represent the geochemistry of Beishan groundwater,and was used to hydrate the blocks during the swelling pressure and swelling strain measurements,as Beishan is the most promising site for China's repository.Healing of the surface cracks was recorded by photography,and healing of the internal cracks was visualized by CT images and hydraulic conductivity of air-dried blocks.The results indicate that the maximum swelling pressure and swelling strain are primarily affected by the geochemistry of Beishan groundwater,but not affected by the drying cracks.The maximum swelling pressure and swelling strain of air-dried blocks are comparable to or even higher than the pressure and strain of fresh blocks.The maximum swelling pressure measured in strong(i.e.high ion strength)Beishan groundwater was 44%of the pressure measured in deionized(DI)water,and the maximum swelling strain was reduced to 23%of the strain measured in DI water.Nevertheless,the remained swelling of the blocks hydrated in strong Beishan groundwater was sufficient to heal the surface and internal drying cracks,as demonstrated by the pictures of surface cracks and CT images.The hydraulic conductivity of the air-dried block permeated with strong groundwater was comparable(3.7×higher)to the hydraulic conductivity of the fresh block,indicating the self-healing of drying cracks after hydration and swelling in groundwater.A simplified method of protecting the block with plastic wraps before installation is recommended,since the remained swelling of the block hydrated in Beishan groundwater is sufficient to heal the drying cracks.
基金Funded by National Basic Research Program of China(973 Program)(No.2011CB013805)National Natural Science Foundation of China(Nos.51278360,51478348,51308407)National Key Project of Scientific and Technical Supporting Programs of China(No.2014BAL03B02)
文摘Cracks can deteriorate mechanical properties and/or durability of concrete. A few studies have shown that, cracks can autogenously heal under a certain conditions besides the traditional passive repair with a deliberate external intervention. For underground concrete structures, the presence of water, as a necessity for chemical reactions of the healing additives, is beneficial to healing concrete. In this paper, a natural healing method by mineral additives was developed according to the chemical and physical characteristics of underground environment. The healing capacity of three different crystalline mineral materials classified namely, carbonate, calcium sulphoaluminate expansive agent and natural metakaolin due to permeation- crystallization, expansion and pozzolanic reaction, has been assessed from the mechanical properties, referring to the relative elastic modulus, the strength restoration, and the water permeability of the healed specimens. In addition, the morphology of the healing products in the vicinity of the crack was observed. The results indicate that the specimens incorporated with the three mineral additives show different healing capacity according to the improved mechanical properties and permeability. The permeability of the host matrix decreased a lot after crack healing by natural metakaolin followed by carbonate whereas no noticeable improvement of water permeability has been observed for the specimens mixed with expansive agent. The specimens incorporated with carbonate show the best mechanical restoration in terms of relative elastic modulus and compressive strength. Although the dominate element is CaCO3 by reaction of CO32-, either from the dissolved CO2 or from the additives, and Ca2＋ in the cementitious system to fill the cracks, the healing capacity depends greatly on the morphology and the properties of the newly formed products.
文摘Advances in machine learning(ML)methods are important in industrial engineering and attract great attention in recent years.However,a comprehensive comparative study of the most advanced ML algorithms is lacking.Six integrated ML approaches for the crack repairing capacity of the bacteria-based self-healing concrete are proposed and compared.Six ML algorithms,including the Support Vector Regression(SVR),Decision Tree Regression(DTR),Gradient Boosting Regression(GBR),Artificial Neural Network(ANN),Bayesian Ridge Regression(BRR)and Kernel Ridge Regression(KRR),are adopted for the relationship modeling to predict crack closure percentage(CCP).Particle Swarm Optimization(PSO)is used for the hyper-parameters tuning.The importance of parameters is analyzed.It is demonstrated that integrated ML approaches have great potential to predict the CCP,and PSO is efficient in the hyperparameter tuning.This research provides useful information for the design of the bacteria-based self-healing concrete and can contribute to the design in the rest of industrial engineering.
基金Funded by the National Natural Science Foundation of China(No.51178104)333 Project of JiangsuPhD Program’s Foundation of Ministry of Education of China(No.20110092110033)
文摘The complete deposition distribution process of calcium carbonate is summarized in three directions of cracks. Distribution of calcium carbonate in the self-healing process of microbial concrete is studied in detail, with the help of a variety of analytical techniques. The results show that carbonate deposits along the x-axis direction of the cracks. The farther from the crack surfaces of concrete matrix in x-axis direction, the more the content of the substrate, the less content of calcium carbonate. Gradual accumulation of calcium carbonate along the y-axis direction is like building a house with bricks. Different repair points are gradually connected, and ultimately the whole of cracks are completely filled. In the z-axis direction, calcium deposits on the surface of fracture direction, when the crack is filled on the surface, because the internal crack hypoxia in the depths of cracks hardly produces calcium carbonate.
基金the National Natural Science Foundation of China(Grant No.51808483)the Natural Science Foundation of Jiangsu Province(No.BK20180930)Opening Funds of the Jiangsu Key Laboratory of Construction Materials(No.CM2018-02).
文摘Cement-based materials are brittle and crack easily under natural conditions.Cracks can reduce service life because the transport of harmful substances can cause corrosion damage to the structures.This review discusses the feasibility of using microbial self-healing agents for crack healing.Tubular and spherical carriers can be used to load microbial self-healing agents and protect microbes,which prolongs the self-healing time.The area self-healing ratio,permeability,mechanical strength,precipitation depth method,numerical modeling,and ultrasonic method can be employed to identify the self-healing effect of cracks.Moreover,the self-healing mechanism is systematically analyzed.The results showed that microbial self-healing agents can repair cracks in cement-based materials in underground projects and dam gates.The difficulties and future development of self-healing cracks were analyzed.A microbial selfhealing agent was embedded in the cement-based material,which automatically repaired the developing cracks.With the development of intelligent building materials,self-healing cracks have become the focus of attention.
文摘The brittleness of cement composites makes cracks almost inevitable,producing a serious limitation on the lifespan,resilience,and safety of concrete infrastructure.To address this brittleness,self-healing concrete has been developed for regaining its mechanical and durability properties after becoming cracked,thereby promising sustainable development of concrete infrastructure.This paper provides a comprehensive review of the latest developments in self-healing concrete.It begins by summarizing the methods used to evaluate the self-healing efficiency of concrete.Next,it compares strategies for achieving healing concrete.It then discusses the typical approaches for developing self-healing concrete.Finally,critical insights are proposed to guide future studies on the development of novel self-healing concrete.This review will be useful for researchers and practitioners interested in the field of self-healing concrete and its potential to improve the durability,resilience,and safety of concrete infrastructure.
文摘Mechanical as well as durability properties are pivotal for any type of concrete which gets adversely affected due to cracks that may form due to loading beyond its capacity.Concrete has the intrinsic property to heal itself to some extent but not fully as the passive form of autogenous healing plays an inferior role for a complete repair of a cementitious material.The self-healing capabilities can be enhanced by adding chemical admixtures,polymers,and bacteria strains induced calcium carbonate precipitation,etc.In this paper,the advancements in the development and performance of self-healing concrete using chemical admixtures,polymers,and bacteria strains are reviewed.This systematic review includes the available experimental tests and methodologies investigating self-healing efficiency over the last decade.Further,this review focussed on self-healing materials,the ideology,and opinions of those in the construction field on the direction of self-healing concrete for future applications.It is yet not possible to predict the most appropriate technique,however,a generalized opinion about the effectiveness of the different approaches has been illustrated.
基金supported by the National Natural Science Foundation of China(Grant No.51738003).
文摘Concrete is the most widely used composite material in civil engineering.Microbial induced calcium carbonate precipitation(MICP)is a green and environmental friendly technology,which has received extensive attention in repair of concrete cracks.This paper introduces the research progress in Southeast University research in past 16 years.In the early stage,MICP technology of urea hydrolyzed by Bacillus pasteurii was mainly investigated to repair the surface cracks and to fill large-size cracks with grouting.However,aiming at the hidden cracks that were difficult for human intervention,a new mineralization route of Bacillus mucilaginosus was proposed,which could repair faster than Bacillus alcalophilus,and the problem of ammonia emission in the repair process of Bacillus pasteurii was also solved.In addition,in order to improve the protection of bacteria and the self-healing efficiency of the later age cracks,the methods of fiber immobilization,carrier uniformly immobilization and core-shell structural immobilization had been compared and studied.The results showed that core-shell structural immobilization had good protection ability and strong designability.What’s more,the paper also summarized the characteristics of spore germination,cell activity,nucleation and biological calcium carbonate in crack zone,and introduced the application experience of microbial self-healing concrete in water conservancy projects and subway stations.
文摘This paper presents the effect on compressive strength and self-healing capability of bacterial concrete with the addition of calcium lactate.Compared to normal concrete,bacterial concrete possesses higher durability and engineering concrete properties.The production of calcium carbonate in bacterial concrete is limited to the calcium content in cement.Hence calcium lactate is externally added to be an additional source of calcium in the concrete.The influence of this addition on compressive strength,self-healing capability of cracks is highlighted in this study.The bacterium used in the study is bacillus subtilis and was added to both spore powder form and culture form to the concrete.Bacillus subtilis spore powder of 2 million cfu/g concentration with 0.5%cement was mixed to concrete.Calcium lactates with concentrations of 0.5%,1.0%,1.5%,2.0%,and 2.5%of cement,was added to the concrete mixes to test the effect on properties of concrete.In other samples,cultured bacillus subtilis with a concentration of 1×10^cells/mL was mixed with concrete,to study the effect of bacteria in the cultured form on the properties of concrete.Cubes of 100 mm×100 mm×100 mm were used for the study.These cubes were tested after a curing period of 7,14,and 28 d.A maximum of 12%increase in compressive strength was observed with the addition of 0.5%of calcium lactate in concrete.Scanning electron microscope and energy dispersive X-ray spectroscopy examination showed the formation of ettringite in pores;calcium silicate hydrates and calcite which made the concrete denser.A statistical technique was applied to analyze the experimental data of the compressive strengths of cementations materials.Response surface methodology was adopted for optimizing the experimental data.The regression equation was yielded by the application of response surface methodology relating response variables to input parameters.This method aids in predicting the experimental results accurately with an acceptable range of error.Findings of this investigation indicated the influence of added calcium lactate in bio-concrete which is quite impressive for improving the compressive strength and self-healing properties of concrete.
基金The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China(51978066)the Construction Science and Technology Project of Xi'an(SZJJ2019-23)+1 种基金the Funding Project for Innovation Ability Training of Doctoral Candidates of Chang'an University(300203211217)the National Key R&D Program of China(2018YFC0808706).Enlin Ma acknowledges the financial support by China Scholarship Council for the Joint-PhD Training Program at Aalto University。
文摘Maintaining the health and reliability of civil facilities is of strategic importance.In highway engineering,pavement cracking impairs the road service and travel comfort level,while structure cracking can cause catastrophic damage.Microcapsule-based self-healing materials offer solutions to auto-recovery micro-cracks and maintain structural health.Such solution has become available by laboratory synthesis and proved effective in addressing the cracking problem during long-term mechanical,thermal,and hydraulic conditions.However,full-scale applications of this technique are not prevalent,showing its potential limitations in highway engineering.Crack healing in highways is a big topic,therefore,this review has two insertion points.(1)We focus on the cracking issues on two specific materials:asphalt and concrete,which account for the vast majority of all the materials used in pavement and structures in highways.(2)Instead of the laboratory studies,we pay more attention to the practical applications,the meaning of healing performance,and the adverse effects of microcapsules to the main structural components(i.e.,tunnel lining,bridge piers and beams)and pavement in highways.The practical significance of self-healing materials in highway projects was discussed from the three aspects:strength,durability,and stress redistribution.The difficulty in applying this new technique is also discussed from economic perspective.For future-proofing,a material evaluation system that fits the load condition is required.The self-healing technique brings composites a chance to interact with the environment,showing high potential for contributing to the development of various types of long-lasting infrastructures.
基金supported by the National Natural Science Foundation of China (20874117, 50903095, 51073176 and U0634001)Doctoral Fund of Ministry of Education of China (20090171110026)the Science and Technology Program of Guangdong Province (2010B010800021)
文摘Self-healing polymers represent a class of materials with built-in capability of rehabilitating damages. The topic has attracted increasingly more attention in the past few years. The on-going research activities clearly indicate that self-healing polymeric materials turn out to be a typical multi-disciplinary area concerning polymer chemistry, organic synthesis, polymer physics, theoretical and experimental mechanics, processing, composites manufacturing, interfacial engineering, etc. The present article briefly reviews the achievements of the groups worldwide, and particularly the work carried out in our own laboratory towards strength recovery for structural applications. To ensure sufficient coverage, thermoplastics and thermosetting polymers, extrinsic and intrinsic self-healing, autonomic and non-autonomic healing approaches are included. Innovative routes that correlate materials chemistry to full capacity restoration are discussed for further development from bioinspired toward biomimetic repair.
基金The authors would like to thank financial supports from the National Natural Science Foundation of China(Grant Nos.42272122 and 40902088).
文摘Five complete caverns were discovered in Longyou in 1992.They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago.When they were un-watered,their integrity was maintained completely,and their interior rock surfaces were free of old cracks.Since then,however,the rock's interior faces have initiated and propagated more and more cracks.This paper attempts to address the question of why the rock interior faces were free of old cracks once they were unearthed.To address this question,this paper proposes a hypothesis that the argillaceous siltstone has the ability of self-healing its cracks over a short period of time under weak acid water environment.Data and evidence are presented herewith to prove the hypothesis.They include observations and measurements in the field and test results in the laboratory.Specifically,a three-point bending test is used to form a tensile crack in a rectangular rock specimen and a deadload test for the specimen immersed in initially weak acid water is used for self-healing its crack.The results have shown that the argillaceous siltstone is in a state of weak alkalinity and the rain water at the site is in a state of weak acidity.Therefore,when it is immersed in weak acid water for some time,the argillaceous siltstone would be able to make chemical reactions to generate new minerals such as calcite.The new minerals would be able to infill the cracks and then heal the crack within a few years.Once the crack is self-healed,the rock can regain its strength and integrity.Consequently,the rock interior surfaces could be free of old cracks when the water was pumped out of the caverns.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.92060202,51632007,51872229,and 51521061)the 111 Project of China(Grant No.B08040)National Science and Technology Major Project(Grant No.2017-VI-0007-0077).
文摘Three strategies were proposed to prolong the service life of continuous fiber-reinforced silicon carbide ceramic matrix composite(CMC-SiC),which served as thermal-structure components of aeroengine at thermo-mechanical-oxygenic coupling environment.As for some thermal-structure components with low working stress,improving the degree of densification was crucial to prolong the service life,and the related process approaches were recited.If the thermal-structure components worked under moderate stress,the matrix cracking stress(σ^(mc))should be improved as far as possible.The fiber preform architecture,interface shear strength,residual thermal stress,and matrix strengthening were associated withσ_(mc)in this review.Introducing self-healing components was quite significant with the appearance of matrix microcracks when CMC-SiC worked at more severe environment for hundreds of hours.The damage can be sealed by glass phase originating from the reaction between self-healing components and oxygen.The effective self-healing temperature range of different self-healing components was first summarized and distinguished.The structure,composition,and preparation process of CMC-SiC should be systematically designed and optimized to achieve long duration target.
