The C60 concrete blocks with surface crack damage under high temperature environment were soaked by adding appropriate amount of soybean urease into the CO(NH_(2))_(2)-CaCl_(2) solution,the soybean urease mineralized ...The C60 concrete blocks with surface crack damage under high temperature environment were soaked by adding appropriate amount of soybean urease into the CO(NH_(2))_(2)-CaCl_(2) solution,the soybean urease mineralized calcium carbonate were characterized,and the effect of repairing concrete surface crack damage were evaluated by the surface sedimentation of C60 concrete blocks in the study.The experimental results showed that the activity of soybean powder was statistically significant,and its productivity of urease was comparable with that of urease-producing bacteria.After immersion in a soybean solution,a layer of complete and continuous white sediment covered the concrete surface.The cracks on the concrete surface were completely shielded,and the rising temperature on infrared thermal image of the concrete after repair was lower than before.Besides,through analysis by SEM,EDS,and XRD,the products formed after repair were found to be calcite-type CaCO_(3) with high purity,and the crystals exhibited different morphological features.The above results indicate that soybean urease can regulate and induce the formation of calcium carbonate,and the precipitate is innocuous and harmless,suitable for a new type of concrete crack repair material.展开更多
Wind erosion is one of the significant natural calamities worldwide, which degrades around one-third of global land. The eroded and suspended soil particles in the environment may cause health hazards, i.e.allergies a...Wind erosion is one of the significant natural calamities worldwide, which degrades around one-third of global land. The eroded and suspended soil particles in the environment may cause health hazards, i.e.allergies and respiratory diseases, due to the presence of harmful contaminants, bacteria, and pollens.The present study evaluates the feasibility of microbially induced calcium carbonate precipitation(MICP)technique to mitigate wind-induced erosion of calcareous desert sand(Thar desert of Rajasthan province in India). The temperature during biotreatment was kept at 36℃ to stimulate the average temperature of the Thar desert. The spray method was used for bioaugmentation of Sporosarcina(S.) pasteurii and further treatment using chemical solutions. The chemical solution of 0.25 pore volume was sprayed continuously up to 5 d, 10 d, 15 d, and 20 d, using two different concentration ratios of urea and calcium chloride dihydrate viz 2:1 and 1:1. The biotreated samples were subjected to erosion testing(in the wind tunnel) at different wind speeds of 10 m/s, 20 m/s, and 30 m/s. The unconfined compressive strength of the biocemented crust was measured using a pocket penetrometer. The variation in calcite precipitation and microstructure(including the presence of crystalline minerals) of untreated as well as biotreated sand samples were determined through calcimeter, scanning electron microscope(SEM), and energydispersive X-ray spectroscope(EDX). The results demonstrated that the erosion of untreated sand increases with an increase in wind speeds. When compared to untreated sand, a lower erosion was observed in all biocemented sand samples, irrespective of treatment condition and wind speed. It was observed that the sample treated with 1:1 cementation solution for up to 5 d, was found to effectively resist erosion at a wind speed of 10 m/s. Moreover, a significant erosion resistance was ascertained in15 d and 20 d treated samples at higher wind speeds. The calcite content percentage, thickness of crust,bulk density, and surface strength of biocemented sand were enhanced with the increase in treatment duration. The 1:1 concentration ratio of cementation solution was found effective in improving crust thickness and surface strength as compared to 2:1 concentration ratio of cementation solution. The calcite crystals formation was observed in SEM analysis and calcium peaks were observed in EDX analysis for biotreated sand.展开更多
Wind erosion is a major cause of land desertification and sandstorm formation in arid and semi-arid areas.The objective of this study was to evaluate the potential of soybeans crude extract induced calcium carbonate p...Wind erosion is a major cause of land desertification and sandstorm formation in arid and semi-arid areas.The objective of this study was to evaluate the potential of soybeans crude extract induced calcium carbonate precipitation(SICP)on reducing wind erosion risk of sandy soil.Field tests were carried out in Ulan Buh Desert,Ningxia Hui Autonomous Region,China.Results showed that the SICP method could significantly enhance the surface strength and wind erosion resistance of the topsoil.The optimal cementation solution(urea-CaCl2)concentration and spraying volume,according to experiments conducted on sandy land,were 0.2 mol/L and 4 L/m^2,respectively.Under this condition,the CaCO3 content was approximately 0.45%,the surface strength of sandy soil could reach 306.2 kPa,and the depth of wind erosion was approximately zero,after 30 d completion of SICP treatment.Soil surface strength declined with the increase of time,and long-term sand fixation effects of SICP treatment varied depending on topography.Whereas wind erosion in the top area of the windward slope was remarkable,sandy soils on the bottom area of the windward slope still maintained a relatively high level of surface strength and a low degree of wind erosion 12 month after SICP treatment.Scanning electron microscopy(SEM)tests with energy dispersive X-ray(EDX)confirmed the precipitation of CaCO3 and its bridge effect.These findings suggested that the SICP method is a promising candidate to protect sandy soil from wind erosion in desert areas.展开更多
Biomineralization through microbial process has attracted great attention in the field of geotechnical engineering due to its ability to bind granular materials,clog pores,and seal fractures.Although minerals formed b...Biomineralization through microbial process has attracted great attention in the field of geotechnical engineering due to its ability to bind granular materials,clog pores,and seal fractures.Although minerals formed by biomineralization are generally the same as that by mineralization,their mechanical behaviors show a significant discrepancy.This study aims to figure out the differences between biomineralization and mineralization processes by visualizing and tracking the formation of minerals using microfluidics.Both biomineralization and mineralization processes occurred in the Y-shaped sandcontaining microchip that mimics the underground sand layers.Images from different areas in the reaction microchannel of microchips were captured to directly compare the distribution of minerals.Crystal size and numbers from different reaction times were measured to quantify the differences between biomineralization and mineralization processes in terms of crystal kinetics.Results showed that the crystals were precipitated in a faster and more uncontrollable manner in the mineralization process than that in the biomineralization process,given that those two processes presented similar precipitation stages.In addition,a more heterogeneous distribution of crystals was observed during the biomineralization process.The precipitation behaviors were further explained by the classical nucleation crystal growth theory.The present microfluidic tests could advance the understanding of biomineralization and provide new insight into the optimization of biocementation technology.展开更多
Microbial geoengineering technology,as a new eco-friendly rock and soil improvement and reinforcement technology,has a wide application prospect.However,this technology still has many deficiencies and is difficult to ...Microbial geoengineering technology,as a new eco-friendly rock and soil improvement and reinforcement technology,has a wide application prospect.However,this technology still has many deficiencies and is difficult to achieve efficient curing,which has become the bottleneck of large-scale field application.This paper reviews the research status,hot spots,difficulties and future development direction microbial induced calcium carbonate precipitation(MICP)technology.The principle of solidification and the physical and mechanical properties of improved rock and soil are systematically summarized.The solidification efficiency is mainly affected by the reactant itself and the external environment.At present,the MICP technology has been preliminarily applied in the fields of soil solidification,crack repair,anti-seepage treatment,pollution repair and microbial cement.However,the technology is currently mainly limited to the laboratory level due to the difficulty of homogeneous mineralization,uneconomical reactants,short microbial activity period and large environmental interference,incidental toxicity of metabolites and poor field application.Future directions include improving the uniformity of mineralization by improving grouting methods,improving urease persistence by improving urease activity,and improving the adaptability of bacteria to the environment by optimizing bacterial species.Finally,the authors point out the economic advantages of combining soybean peptone,soybean meal and cottonseed as carbon source with phosphogypsum as calcium source to induce CaCO3.展开更多
基金Funded by the National Natural Science Foundation of China(No.51478290)Key R&D Projects of Shanxi Province(No.201903D321113)Shanxi Province Excellent Postgraduate Innovation Project(No.2019BY055)。
文摘The C60 concrete blocks with surface crack damage under high temperature environment were soaked by adding appropriate amount of soybean urease into the CO(NH_(2))_(2)-CaCl_(2) solution,the soybean urease mineralized calcium carbonate were characterized,and the effect of repairing concrete surface crack damage were evaluated by the surface sedimentation of C60 concrete blocks in the study.The experimental results showed that the activity of soybean powder was statistically significant,and its productivity of urease was comparable with that of urease-producing bacteria.After immersion in a soybean solution,a layer of complete and continuous white sediment covered the concrete surface.The cracks on the concrete surface were completely shielded,and the rising temperature on infrared thermal image of the concrete after repair was lower than before.Besides,through analysis by SEM,EDS,and XRD,the products formed after repair were found to be calcite-type CaCO_(3) with high purity,and the crystals exhibited different morphological features.The above results indicate that soybean urease can regulate and induce the formation of calcium carbonate,and the precipitate is innocuous and harmless,suitable for a new type of concrete crack repair material.
基金Prestige Institute of Engineering, Management, and Research, Indore, India for their supportGuangdong Department of Science and Technology,China for"Overseas Famous Teacher Project"(Grant No.2020A1414010268)。
文摘Wind erosion is one of the significant natural calamities worldwide, which degrades around one-third of global land. The eroded and suspended soil particles in the environment may cause health hazards, i.e.allergies and respiratory diseases, due to the presence of harmful contaminants, bacteria, and pollens.The present study evaluates the feasibility of microbially induced calcium carbonate precipitation(MICP)technique to mitigate wind-induced erosion of calcareous desert sand(Thar desert of Rajasthan province in India). The temperature during biotreatment was kept at 36℃ to stimulate the average temperature of the Thar desert. The spray method was used for bioaugmentation of Sporosarcina(S.) pasteurii and further treatment using chemical solutions. The chemical solution of 0.25 pore volume was sprayed continuously up to 5 d, 10 d, 15 d, and 20 d, using two different concentration ratios of urea and calcium chloride dihydrate viz 2:1 and 1:1. The biotreated samples were subjected to erosion testing(in the wind tunnel) at different wind speeds of 10 m/s, 20 m/s, and 30 m/s. The unconfined compressive strength of the biocemented crust was measured using a pocket penetrometer. The variation in calcite precipitation and microstructure(including the presence of crystalline minerals) of untreated as well as biotreated sand samples were determined through calcimeter, scanning electron microscope(SEM), and energydispersive X-ray spectroscope(EDX). The results demonstrated that the erosion of untreated sand increases with an increase in wind speeds. When compared to untreated sand, a lower erosion was observed in all biocemented sand samples, irrespective of treatment condition and wind speed. It was observed that the sample treated with 1:1 cementation solution for up to 5 d, was found to effectively resist erosion at a wind speed of 10 m/s. Moreover, a significant erosion resistance was ascertained in15 d and 20 d treated samples at higher wind speeds. The calcite content percentage, thickness of crust,bulk density, and surface strength of biocemented sand were enhanced with the increase in treatment duration. The 1:1 concentration ratio of cementation solution was found effective in improving crust thickness and surface strength as compared to 2:1 concentration ratio of cementation solution. The calcite crystals formation was observed in SEM analysis and calcium peaks were observed in EDX analysis for biotreated sand.
基金Projects(51978244,51979088,51608169)supported by the National Natural Science Foundation of China。
文摘Wind erosion is a major cause of land desertification and sandstorm formation in arid and semi-arid areas.The objective of this study was to evaluate the potential of soybeans crude extract induced calcium carbonate precipitation(SICP)on reducing wind erosion risk of sandy soil.Field tests were carried out in Ulan Buh Desert,Ningxia Hui Autonomous Region,China.Results showed that the SICP method could significantly enhance the surface strength and wind erosion resistance of the topsoil.The optimal cementation solution(urea-CaCl2)concentration and spraying volume,according to experiments conducted on sandy land,were 0.2 mol/L and 4 L/m^2,respectively.Under this condition,the CaCO3 content was approximately 0.45%,the surface strength of sandy soil could reach 306.2 kPa,and the depth of wind erosion was approximately zero,after 30 d completion of SICP treatment.Soil surface strength declined with the increase of time,and long-term sand fixation effects of SICP treatment varied depending on topography.Whereas wind erosion in the top area of the windward slope was remarkable,sandy soils on the bottom area of the windward slope still maintained a relatively high level of surface strength and a low degree of wind erosion 12 month after SICP treatment.Scanning electron microscopy(SEM)tests with energy dispersive X-ray(EDX)confirmed the precipitation of CaCO3 and its bridge effect.These findings suggested that the SICP method is a promising candidate to protect sandy soil from wind erosion in desert areas.
基金We acknowledge the funding support from the National Natural Science Foundation of China(Grant Nos.51922024 and 52078085)Chongqing Talents Program,China(Grant No.cstc2021ycjhbgzxm0051).
文摘Biomineralization through microbial process has attracted great attention in the field of geotechnical engineering due to its ability to bind granular materials,clog pores,and seal fractures.Although minerals formed by biomineralization are generally the same as that by mineralization,their mechanical behaviors show a significant discrepancy.This study aims to figure out the differences between biomineralization and mineralization processes by visualizing and tracking the formation of minerals using microfluidics.Both biomineralization and mineralization processes occurred in the Y-shaped sandcontaining microchip that mimics the underground sand layers.Images from different areas in the reaction microchannel of microchips were captured to directly compare the distribution of minerals.Crystal size and numbers from different reaction times were measured to quantify the differences between biomineralization and mineralization processes in terms of crystal kinetics.Results showed that the crystals were precipitated in a faster and more uncontrollable manner in the mineralization process than that in the biomineralization process,given that those two processes presented similar precipitation stages.In addition,a more heterogeneous distribution of crystals was observed during the biomineralization process.The precipitation behaviors were further explained by the classical nucleation crystal growth theory.The present microfluidic tests could advance the understanding of biomineralization and provide new insight into the optimization of biocementation technology.
基金This work was financed by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK0904)the Key Research and Development Plan of Yunnan Province(Grant No.202103AA080013).
文摘Microbial geoengineering technology,as a new eco-friendly rock and soil improvement and reinforcement technology,has a wide application prospect.However,this technology still has many deficiencies and is difficult to achieve efficient curing,which has become the bottleneck of large-scale field application.This paper reviews the research status,hot spots,difficulties and future development direction microbial induced calcium carbonate precipitation(MICP)technology.The principle of solidification and the physical and mechanical properties of improved rock and soil are systematically summarized.The solidification efficiency is mainly affected by the reactant itself and the external environment.At present,the MICP technology has been preliminarily applied in the fields of soil solidification,crack repair,anti-seepage treatment,pollution repair and microbial cement.However,the technology is currently mainly limited to the laboratory level due to the difficulty of homogeneous mineralization,uneconomical reactants,short microbial activity period and large environmental interference,incidental toxicity of metabolites and poor field application.Future directions include improving the uniformity of mineralization by improving grouting methods,improving urease persistence by improving urease activity,and improving the adaptability of bacteria to the environment by optimizing bacterial species.Finally,the authors point out the economic advantages of combining soybean peptone,soybean meal and cottonseed as carbon source with phosphogypsum as calcium source to induce CaCO3.
