The application of the microbially induced carbonate precipitation(MICP)method for remediating heavy metals(i.e.,HMs)has recently garnered significant attention.Nevertheless,the inhibition of urease activity by toxic ...The application of the microbially induced carbonate precipitation(MICP)method for remediating heavy metals(i.e.,HMs)has recently garnered significant attention.Nevertheless,the inhibition of urease activity by toxic Cd^(2+),Pb^(2+),Zn^(2+),and Cu^(2+)poses a challenge for MICP-based remediation of HMs contamination.This study:(1)first performed the traditional MICP tests(in which the bacterial solution,urea solution,and HMs were mixed simultaneously),and investigated the toxic effect of HMs on the urease activity and the immobilization efficiency,(2)analyzed the toxicity and immobilization mechanism during the MICP process by combining the simulation and XRD tests,(3)conducted the two-step MICP tests(which initially mixed the bacterial solution and urea solution to promote urea hydrolysis,then added the HMs solutions for HMs precipitation)to improve the immobilization efficiency.The tube experiments and simulations were investigated in the HMs concentration range from 1 to 10 mmol/L.Indicators including am-monium concentration,HMs concentrations,and pH were measured/recorded during the tests.The results show that soluble HMs exhibit a concentration-dependent inhibition of urea hydrolysis during the traditional MICP process,resulting in a decreasing immobilization efficiency.The two-step MICP method can effectively immobilize almost the Cd^(2+)and Zn^(2+)when the initial urea hydrolysis period exceeds 1-2 h.In addition,a high immobilization rate of over 90% can be achieved for Cu-contaminated solutions at the optimal first-step reaction time.Compared with the traditional MICP procedure,the effective two-step MICP method exhibits more promising application prospects for the immobilization of soluble HMs in aquatic environments.展开更多
The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated s...The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions.Furthermore,the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented.Moreover,the effect of wetting-drying(WD)cycles on the cyclic characteristics of MICP-treated sand is not readily available,which may contribute to the limited adoption of MICP treatment in field applications.In this study,strain-controlled consolidated undrained(CU)cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains:Sporosarcina pasteurii and Bacillus subtilis.The treatment durations of 7 d and 14 d were considered,with an interval of 12 h between treatments.The cyclic characteristics,such as the shear modulus and damping ratio,of the MICP-treated sand with the different bacterial strains have been estimated and compared.Furthermore,the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5–15 cycles and aging of samples up to three months.The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand,considering the influence of different bacterial strains,treatment duration,and WD cycles.展开更多
Soil desertification and salinization are the main environmental disasters in arid and semi-arid areas.It is of great significance to study the water-salt migration law of saline soil and propose corresponding water-s...Soil desertification and salinization are the main environmental disasters in arid and semi-arid areas.It is of great significance to study the water-salt migration law of saline soil and propose corresponding water-salt regulation and control measures.Microbial-induced calcite precipitation(MICP)technology was proposed to improve saline soil based on salt inhibition,and the water–salt–heat coupling migration law and salt-frost heave deformation law of saline soil before and after improvement were studied using soil column model tests.XR1#,XR2#(Saline-alkali-tolerant mineralization bacteria isolated from saline soil)and Sporosarcina pasteurii were used in the MICP improvement and the effect of XR1#was the best.Under high-temperature evaporation,the water migration change rate,water loss rate,accumulated evaporation amount,and accumulated salt content of the improved soil columns within a depth range of 0–40 cm were reduced by an average of 53.6%,47.3%,69.5%,and 40%,respectively,compared with the untreated soil column.During low-temperature cooling,the characteristics of water-salt migration changed significantly,and the deformation of salt-frost heave decreased significantly.The water-salt content at the freezing point(−4.5°C)changed from a cliff-like steep drop(untreated saline soil)to a slow decrease at environmental temperature(MICP-treated saline soil),and the amount of water crystallization decreased from 81%to 56.7%at−5°C.At the end of the cooling process,the amount of salt-frost heaving on the surface of the soil columns decreased by an average of 62.7%.Based on the measured data,a numerical simulation was conducted using the HYDRUS-1D model,which had good reliability and accurately simulated and predicted the law of water-salt migration in saline soil under the conditions of microbial solidification and improvement.MICP technology significantly reduced the change rate of water-salt migration and water evaporation in saline soil,hindered salt accumulation,and reduced salt-frost heave deformation,which effectively improved saline soil.The research results provide an important innovation and theoretical basis for the improvement of saline soil.展开更多
Sporosarcina pasteurii(S.pasteurii)is widely used in microbial-induced carbonate precipitation(MICP)due to its high urease activity.In this paper,the effects of nutrients on the metabolic mechanism and mineralization ...Sporosarcina pasteurii(S.pasteurii)is widely used in microbial-induced carbonate precipitation(MICP)due to its high urease activity.In this paper,the effects of nutrients on the metabolic mechanism and mineralization ability of S.pasteurii were studied by comparing the bacteria's growth,gene expression,and mineralized sand column under different nitrogen sources.The results showed that urea and soy peptone replacing the inorganic and organic nitrogen sources in ammonium sulfate-yeast extract(NH4-YE)medium can increase the urease activity of S.pasteurii by 11.43%and 17.10%,respectively.In the composite nitrogen source medium composed of urea and soy peptone,the urease activity of S.pasteurii increased by 25.30%.The transcriptome sequencing results showed that the modified medium of urea and soy peptone could promote the basic life activity and metabolism of S.pasteurii and is beneficial to urease expression.Among them,the gene difference between the modified urea medium and the primary medium was more obvious,and the urea medium could promote the ATP synthase related to urease expression and urea hydrolysis.The unconfined compressive strength(UCS)of sand columns reinforced with S.pasteurii cultured in Urea-YE,NH4-Soy peptone and Urea-Soy peptone increased by 27.6%,36%and 58.1%respectively.The permeability decreased by 14.8%,20.1%and 81.3%respectively compared with that of sand columns reinforced with S.pasteurii cultured in NH4-YE.The higher the urease activity of cultured bacteria,the more calcium carbonate produced after mineralization reaction.In addition,the urease activity of bacteria has an influence on the morphology of calcite crystals.This study can facilitate our understanding of optimizing the culture medium of S.pasteurii and the artificial regulation of urease activity in the process of MICP.展开更多
Microbial-induced carbonate precipitation(MICP)and enzyme-induced carbonate precipitation(EICP)are two bio-cementation techniques,which are relatively new methods of ground improvement.While both techniques share some...Microbial-induced carbonate precipitation(MICP)and enzyme-induced carbonate precipitation(EICP)are two bio-cementation techniques,which are relatively new methods of ground improvement.While both techniques share some similarities,they can exhibit different overall behaviours due to the differences in urease enzyme sources and treatment methods.This paper presented 40 unconfined compressive strength(UCS)tests of MICP and EICP treated sand specimens with similar average calcium carbonate(CaCO3)content subjected to cycles of wetting-drying(WD),freezing-thawing(FT)and elevated temperature(fire resistance test e FR and thermogravimetric analysis e TG).The average CaCO3 content after a certain number of WD or FT cycles(ACn)and their corresponding UCS(qn)reduced while the mass loss increased.The EICP treated sand specimens appeared to exhibit a lower resistance to WD and FT cycles than MICP treated specimens possibly due to the presence of unbonded or loosely bonded CaCO3 within the soil matrix,which was subsequently removed during the wetting(during WD)or thawing(during FT)process.FR test and TG analysis showed a significant loss of mass and reduction in CaCO3 content with increased temperatures,possibly due to the thermal decomposition of CaCO3.A complete deterioration of the MICP and EICP treated sand specimens was observed for temperatures above 600C.The observed behaviours are complex and theoretical understanding is far behind to develop a constitutive model to predict qn.Therefore,a multi-objective evolutionary genetic algorithm(GA)that deals with pseudo-polynomial structures,known as evolutionary polynomial regression(EPR),was used to seek three choices from millions of polynomial models.The best EPR model produced an excellent prediction of qn with a minimum sum of squares error(SSE)of 2.392,mean squared error(MSE)of 0.075,root mean square error(RMSE)of 0.273 and a maximum coefficient of determination of 0.939.展开更多
The microbially cemented sand(MCS)material is a new building material with a broad research prospect,although the nationwide cold wave affects the mechanical properties of the material in the practical application.The...The microbially cemented sand(MCS)material is a new building material with a broad research prospect,although the nationwide cold wave affects the mechanical properties of the material in the practical application.The microstructure of MCS is obtained by computed tomography(CT)and scanning electron microscope(SEM);the thermodynamic mathematical model is established by considering the particle shapes and bonding state based on direct element method(DEM).By studying the damage of temperature drop amplitude and cooling duration to MCS material under the effect of cold wave,the following conclusions are drawn.For a given temperature drop range,an increased cooling time can aggravate the material damage.In addition,a rapid drop in temperature can cause serious damage to the material.The cracks generated by the temperature stress propagate in the direction of the weaker component of the material.The DEM model can be better used to analyze the damage of the MCS structure induced by cold wave.展开更多
Filtration is a prevalent treatment modality in the domain of wastewater management.Depending on the materials and properties of the filtration media,filtration can be classified into four main categories:microfiltrat...Filtration is a prevalent treatment modality in the domain of wastewater management.Depending on the materials and properties of the filtration media,filtration can be classified into four main categories:microfiltration,ultrafiltration,nanofiltration,and reverse osmosis.The present study focuses on the preparation of a novel porous CaCO_(3)microfiltration membrane,which is based on the microbial-induced calcium carbonate precipitation(MICP)biomineralization process.Initially,CaCO_(3) crystal particles with urease activity are prepared by controlling the MICP mineralization process.Secondary microbial mineralization is used to cement the loose calcium carbonate particles,forming a continuous porous solid CaCO_(3)membrane with certain mechanical strength.Filtration tests on bacterial cells,extracellular proteins,and polysaccharides show that the MICP-driven porous CaCO_(3) membrane effectively removes Escherichia coli,Brachybacterium sp.,and activated sludge,with removal rates of 99.998%,99.983%,and 99.996%,respectively.Compared to conventional filter paper,this porous CaCO_(3) membrane demonstrates superior capability in removing extracellular polymers(EPS).Furthermore,the CaCO_(3) microfiltration membrane prepared using the MICP process also exhibits ideal pore space,non-blocking characteristics,and high permeability.展开更多
Microbially induced carbonate precipitation(MICP)is a promising technique for the autonomous healing of concrete cracks.In this study,the effect of pH on MICP was investigated.The results indicate that the MICP proces...Microbially induced carbonate precipitation(MICP)is a promising technique for the autonomous healing of concrete cracks.In this study,the effect of pH on MICP was investigated.The results indicate that the MICP process was inhibited when the pH was higher than 11.Both vaterite and calcite were produced when the pH was<8,whereas only calcite was produced when the pH was>8.Recycled concrete aggregates(RCA)coated with sodium silicate have been proposed as protective carriers for microbial healing agents.Although the presence of the coated RCA resulted in a loss of the splitting tension strength of the concrete,the loaded healing agents were highly efficient in self-healing cracks.Concrete incorporated with 20%RCA loaded with healing agents exhibited the best self-healing performance.When the initial crack widths were between 0.3 and 0.4 mm,the 7-d mean healing rate was approximately 90%.At 28 d,the crack area filling ratio was 86.4%,while its water tightness recovery ratio was 74.4%and 29.8%,respectively,for rapid and slow absorption.This study suggests that RCA coated with sodium silicate is an effective method for packaging microbial healing agents and has great potential for developing cost-effective self-healing concrete.展开更多
Microbial-induced carbonate precipitation(MICP)has emerged as a promising eco-friendly and cost-effective alternative for improving the strength and stability of low-cohesion soils.This review provides an in-depth ana...Microbial-induced carbonate precipitation(MICP)has emerged as a promising eco-friendly and cost-effective alternative for improving the strength and stability of low-cohesion soils.This review provides an in-depth analysis of the microscopic mechanisms,implementation methods,and macroscopic properties of MICP in soil enhancement.The biogeochemical processes underlying MICP,including urea hydrolysis,denitrification,sulfate reduction,photosynthesis,and iron reduction,are discussed in detail.Various MICP implementation methods,such as two-phase treatment,one-phase treatment,and ex-situ mixing,are reviewed,highlighting their respective advantages and limitations in reinforcing low-cohesion soils.The review also addresses the performance of MICP-treated soils,including improvements in strength,stiffness,permeability,and durability.Furthermore,the key challenges and future prospects for microbial soil reinforcement technologies are summarized.Future research should focus on optimizing nutrient supply,enhancing bacterial retention and activity,controlling the crystallization process,conducting pilot projects,and reducing treatment costs.These efforts are crucial for advancing the practical application of MICP in sustainable infrastructure construction.This review aims to advance the understanding of MICP and its potential for sustainable soil improvement,offering valuable insights for geotechnical engineers.展开更多
基金supported by the Key research and development project of Hubei Province(No.2022BAA068)the National Natural Science Foundation of China(NSFC)(No.52122806,51978303)+1 种基金the Fundamental Research Funds for the Central Universities(No.2042023kfyq03)Joint fund of the technical R&D program of Henan Province(No.225200810005).
文摘The application of the microbially induced carbonate precipitation(MICP)method for remediating heavy metals(i.e.,HMs)has recently garnered significant attention.Nevertheless,the inhibition of urease activity by toxic Cd^(2+),Pb^(2+),Zn^(2+),and Cu^(2+)poses a challenge for MICP-based remediation of HMs contamination.This study:(1)first performed the traditional MICP tests(in which the bacterial solution,urea solution,and HMs were mixed simultaneously),and investigated the toxic effect of HMs on the urease activity and the immobilization efficiency,(2)analyzed the toxicity and immobilization mechanism during the MICP process by combining the simulation and XRD tests,(3)conducted the two-step MICP tests(which initially mixed the bacterial solution and urea solution to promote urea hydrolysis,then added the HMs solutions for HMs precipitation)to improve the immobilization efficiency.The tube experiments and simulations were investigated in the HMs concentration range from 1 to 10 mmol/L.Indicators including am-monium concentration,HMs concentrations,and pH were measured/recorded during the tests.The results show that soluble HMs exhibit a concentration-dependent inhibition of urea hydrolysis during the traditional MICP process,resulting in a decreasing immobilization efficiency.The two-step MICP method can effectively immobilize almost the Cd^(2+)and Zn^(2+)when the initial urea hydrolysis period exceeds 1-2 h.In addition,a high immobilization rate of over 90% can be achieved for Cu-contaminated solutions at the optimal first-step reaction time.Compared with the traditional MICP procedure,the effective two-step MICP method exhibits more promising application prospects for the immobilization of soluble HMs in aquatic environments.
基金the financial support provided by the Ministry of Education(MoE),Government of IndiaThe second author acknowledges Coal India Limited for providing financial assistance for the research(Project No.CIL/R&D/01/73/2021).
文摘The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions.Furthermore,the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented.Moreover,the effect of wetting-drying(WD)cycles on the cyclic characteristics of MICP-treated sand is not readily available,which may contribute to the limited adoption of MICP treatment in field applications.In this study,strain-controlled consolidated undrained(CU)cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains:Sporosarcina pasteurii and Bacillus subtilis.The treatment durations of 7 d and 14 d were considered,with an interval of 12 h between treatments.The cyclic characteristics,such as the shear modulus and damping ratio,of the MICP-treated sand with the different bacterial strains have been estimated and compared.Furthermore,the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5–15 cycles and aging of samples up to three months.The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand,considering the influence of different bacterial strains,treatment duration,and WD cycles.
基金funded by grants from the National Natural Science Foundation of China(No.51968057),(No.52378348),(No.12262031)Natural Science Foundation of Inner Mongolia Autonomous Region of China(No.2023QN04016),(No.2019LH05028)+1 种基金Basic scientific research business fees for universities directly under the Inner Mongolia Autonomous Region of China(No.JY20220204)Doctoral Research Foundation of Inner Mongolia University of Technology of China(No.DC2300001265).
文摘Soil desertification and salinization are the main environmental disasters in arid and semi-arid areas.It is of great significance to study the water-salt migration law of saline soil and propose corresponding water-salt regulation and control measures.Microbial-induced calcite precipitation(MICP)technology was proposed to improve saline soil based on salt inhibition,and the water–salt–heat coupling migration law and salt-frost heave deformation law of saline soil before and after improvement were studied using soil column model tests.XR1#,XR2#(Saline-alkali-tolerant mineralization bacteria isolated from saline soil)and Sporosarcina pasteurii were used in the MICP improvement and the effect of XR1#was the best.Under high-temperature evaporation,the water migration change rate,water loss rate,accumulated evaporation amount,and accumulated salt content of the improved soil columns within a depth range of 0–40 cm were reduced by an average of 53.6%,47.3%,69.5%,and 40%,respectively,compared with the untreated soil column.During low-temperature cooling,the characteristics of water-salt migration changed significantly,and the deformation of salt-frost heave decreased significantly.The water-salt content at the freezing point(−4.5°C)changed from a cliff-like steep drop(untreated saline soil)to a slow decrease at environmental temperature(MICP-treated saline soil),and the amount of water crystallization decreased from 81%to 56.7%at−5°C.At the end of the cooling process,the amount of salt-frost heaving on the surface of the soil columns decreased by an average of 62.7%.Based on the measured data,a numerical simulation was conducted using the HYDRUS-1D model,which had good reliability and accurately simulated and predicted the law of water-salt migration in saline soil under the conditions of microbial solidification and improvement.MICP technology significantly reduced the change rate of water-salt migration and water evaporation in saline soil,hindered salt accumulation,and reduced salt-frost heave deformation,which effectively improved saline soil.The research results provide an important innovation and theoretical basis for the improvement of saline soil.
基金support of National Natural Science Foundation of China(Grant Nos.52178334 and 52374171)Guiding Project of Science and Technology Department of Fujian Province(Grant No.2024Y0014).
文摘Sporosarcina pasteurii(S.pasteurii)is widely used in microbial-induced carbonate precipitation(MICP)due to its high urease activity.In this paper,the effects of nutrients on the metabolic mechanism and mineralization ability of S.pasteurii were studied by comparing the bacteria's growth,gene expression,and mineralized sand column under different nitrogen sources.The results showed that urea and soy peptone replacing the inorganic and organic nitrogen sources in ammonium sulfate-yeast extract(NH4-YE)medium can increase the urease activity of S.pasteurii by 11.43%and 17.10%,respectively.In the composite nitrogen source medium composed of urea and soy peptone,the urease activity of S.pasteurii increased by 25.30%.The transcriptome sequencing results showed that the modified medium of urea and soy peptone could promote the basic life activity and metabolism of S.pasteurii and is beneficial to urease expression.Among them,the gene difference between the modified urea medium and the primary medium was more obvious,and the urea medium could promote the ATP synthase related to urease expression and urea hydrolysis.The unconfined compressive strength(UCS)of sand columns reinforced with S.pasteurii cultured in Urea-YE,NH4-Soy peptone and Urea-Soy peptone increased by 27.6%,36%and 58.1%respectively.The permeability decreased by 14.8%,20.1%and 81.3%respectively compared with that of sand columns reinforced with S.pasteurii cultured in NH4-YE.The higher the urease activity of cultured bacteria,the more calcium carbonate produced after mineralization reaction.In addition,the urease activity of bacteria has an influence on the morphology of calcite crystals.This study can facilitate our understanding of optimizing the culture medium of S.pasteurii and the artificial regulation of urease activity in the process of MICP.
文摘Microbial-induced carbonate precipitation(MICP)and enzyme-induced carbonate precipitation(EICP)are two bio-cementation techniques,which are relatively new methods of ground improvement.While both techniques share some similarities,they can exhibit different overall behaviours due to the differences in urease enzyme sources and treatment methods.This paper presented 40 unconfined compressive strength(UCS)tests of MICP and EICP treated sand specimens with similar average calcium carbonate(CaCO3)content subjected to cycles of wetting-drying(WD),freezing-thawing(FT)and elevated temperature(fire resistance test e FR and thermogravimetric analysis e TG).The average CaCO3 content after a certain number of WD or FT cycles(ACn)and their corresponding UCS(qn)reduced while the mass loss increased.The EICP treated sand specimens appeared to exhibit a lower resistance to WD and FT cycles than MICP treated specimens possibly due to the presence of unbonded or loosely bonded CaCO3 within the soil matrix,which was subsequently removed during the wetting(during WD)or thawing(during FT)process.FR test and TG analysis showed a significant loss of mass and reduction in CaCO3 content with increased temperatures,possibly due to the thermal decomposition of CaCO3.A complete deterioration of the MICP and EICP treated sand specimens was observed for temperatures above 600C.The observed behaviours are complex and theoretical understanding is far behind to develop a constitutive model to predict qn.Therefore,a multi-objective evolutionary genetic algorithm(GA)that deals with pseudo-polynomial structures,known as evolutionary polynomial regression(EPR),was used to seek three choices from millions of polynomial models.The best EPR model produced an excellent prediction of qn with a minimum sum of squares error(SSE)of 2.392,mean squared error(MSE)of 0.075,root mean square error(RMSE)of 0.273 and a maximum coefficient of determination of 0.939.
基金Foundation item:the National Natural Science Foundation of China(No.51621096)
文摘The microbially cemented sand(MCS)material is a new building material with a broad research prospect,although the nationwide cold wave affects the mechanical properties of the material in the practical application.The microstructure of MCS is obtained by computed tomography(CT)and scanning electron microscope(SEM);the thermodynamic mathematical model is established by considering the particle shapes and bonding state based on direct element method(DEM).By studying the damage of temperature drop amplitude and cooling duration to MCS material under the effect of cold wave,the following conclusions are drawn.For a given temperature drop range,an increased cooling time can aggravate the material damage.In addition,a rapid drop in temperature can cause serious damage to the material.The cracks generated by the temperature stress propagate in the direction of the weaker component of the material.The DEM model can be better used to analyze the damage of the MCS structure induced by cold wave.
基金Jiangsu Province Key Project of Research and Development Plan(No.BE2020676)Nantong Science and Technology Project(No.MS22021006)。
文摘Filtration is a prevalent treatment modality in the domain of wastewater management.Depending on the materials and properties of the filtration media,filtration can be classified into four main categories:microfiltration,ultrafiltration,nanofiltration,and reverse osmosis.The present study focuses on the preparation of a novel porous CaCO_(3)microfiltration membrane,which is based on the microbial-induced calcium carbonate precipitation(MICP)biomineralization process.Initially,CaCO_(3) crystal particles with urease activity are prepared by controlling the MICP mineralization process.Secondary microbial mineralization is used to cement the loose calcium carbonate particles,forming a continuous porous solid CaCO_(3)membrane with certain mechanical strength.Filtration tests on bacterial cells,extracellular proteins,and polysaccharides show that the MICP-driven porous CaCO_(3) membrane effectively removes Escherichia coli,Brachybacterium sp.,and activated sludge,with removal rates of 99.998%,99.983%,and 99.996%,respectively.Compared to conventional filter paper,this porous CaCO_(3) membrane demonstrates superior capability in removing extracellular polymers(EPS).Furthermore,the CaCO_(3) microfiltration membrane prepared using the MICP process also exhibits ideal pore space,non-blocking characteristics,and high permeability.
基金financial support provided by the National Key Research and Development Program of China(2019YFC1906203).
文摘Microbially induced carbonate precipitation(MICP)is a promising technique for the autonomous healing of concrete cracks.In this study,the effect of pH on MICP was investigated.The results indicate that the MICP process was inhibited when the pH was higher than 11.Both vaterite and calcite were produced when the pH was<8,whereas only calcite was produced when the pH was>8.Recycled concrete aggregates(RCA)coated with sodium silicate have been proposed as protective carriers for microbial healing agents.Although the presence of the coated RCA resulted in a loss of the splitting tension strength of the concrete,the loaded healing agents were highly efficient in self-healing cracks.Concrete incorporated with 20%RCA loaded with healing agents exhibited the best self-healing performance.When the initial crack widths were between 0.3 and 0.4 mm,the 7-d mean healing rate was approximately 90%.At 28 d,the crack area filling ratio was 86.4%,while its water tightness recovery ratio was 74.4%and 29.8%,respectively,for rapid and slow absorption.This study suggests that RCA coated with sodium silicate is an effective method for packaging microbial healing agents and has great potential for developing cost-effective self-healing concrete.
基金supported by the National Key Science and Technol-ogy Projects in Transportation Industry(Grant number 2021-MS5-127)the Research Program of the Hubei Department of Transportation(Grant number 2020-186-1-3).
文摘Microbial-induced carbonate precipitation(MICP)has emerged as a promising eco-friendly and cost-effective alternative for improving the strength and stability of low-cohesion soils.This review provides an in-depth analysis of the microscopic mechanisms,implementation methods,and macroscopic properties of MICP in soil enhancement.The biogeochemical processes underlying MICP,including urea hydrolysis,denitrification,sulfate reduction,photosynthesis,and iron reduction,are discussed in detail.Various MICP implementation methods,such as two-phase treatment,one-phase treatment,and ex-situ mixing,are reviewed,highlighting their respective advantages and limitations in reinforcing low-cohesion soils.The review also addresses the performance of MICP-treated soils,including improvements in strength,stiffness,permeability,and durability.Furthermore,the key challenges and future prospects for microbial soil reinforcement technologies are summarized.Future research should focus on optimizing nutrient supply,enhancing bacterial retention and activity,controlling the crystallization process,conducting pilot projects,and reducing treatment costs.These efforts are crucial for advancing the practical application of MICP in sustainable infrastructure construction.This review aims to advance the understanding of MICP and its potential for sustainable soil improvement,offering valuable insights for geotechnical engineers.
