Application of microbially induced carbonate precipitation to form biocemented artificial sandstone

It is difficult to collect and characterise well-preserved samples of weakly-cemented granular rocks as conventional sampling techniques often result in destruction of the cementation.An alternative approach is to prepare synthetic geomaterials to match required specifications.This paper introduces microbially induced carbonate precipitation(MICP)as a method to reliably deliver artificiallycemented specimens with customised properties,closely resembling those of soft carbonate sandstones.The specimens are generated from materials with two highly different particle size distributions(PSDs)to access a range of achievable combinations of strengths and porosities.The MICP parameters are kept constant across all samples to obtain similar calcium carbonate characteristics(size of individual crystals,type,etc.),while injected volume is varied to achieve different cementation levels.Although uniform cementation of very coarse sands has been considered very difficult to achieve,the results show that both the fine and coarse sand specimens present high degrees of uniformity and a good degree of repeatability.The unconfined compressive strengths(UCSs)(less than 3000 kPa)and porosities(0.25e0.4)of the artificial specimens fall in the same range of values reported for natural rocks.The strength gainwas greater in the fine sand than that in the coarse sand,as the void size in the latter was significantly larger compared to the calcium carbonate crystals’size,resulting in precipitation on less effective locations,away from contacts between particles.The strengths and porosities obtained for the two sands in this work fall within ranges reported in the literature for natural soft rocks,demonstrating theMICP technique is able to achieve realistic properties and may be used to produce a full range of properties by varying the grain sizes,and possibly the width of PSD.

Biotreatment of incinerated bottom ash and biocementation of sand blocks using soybean urease

Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation of sandy soil.We found the optimal soaking time and soybean-powder content to be 30 min and 130 g/L,respectively,based on a standard of 5 U of urease activity.The most efficient removal of nickel ions is obtained with an ideal mass ratio of urea to nickel ions to soybean-powder filtrate(SPF)of 1:2.4:20.The removal efficiency of nickel ions can reach 89.42%when treating 1 L of nickel-ion solution(1200 mg/L with the optimal mass ratio).In incinerated bottom ash(IBA),the removal efficiency of nickel ions is 99.33%with the optimal mass ratio.In biocemented sandy soil,the average unconfined compressive strength(UCS)of sand blocks cemented with soybean urease-based biocement can reach 118.89 kPa when the cementation level is 3.Currently,the average content of CaCO_(3)in sand blocks is 2.52%.As a result,the SUICP process can be applied to remove heavy metal ions in wastewater or solid waste and improve the mechanical properties of soft soil foundations.

Coupled bio-chemo-hydro-mechanical modeling of microbially induced calcite precipitation process considering biomass encapsulation using a micro-scale relationship

Geomaterials with inferior hydraulic and strength characteristics often need improvement to enhance their engineering behaviors.Traditional ground improvement techniques require enormous mechanical effort or synthetic chemicals.Sustainable stabilization technique such as microbially induced calcite precipitation(MICP)utilizes bacterial metabolic processes to precipitate cementitious calcium carbonate.The reactive transport of biochemical species in the soil mass initiates the precipitation of biocement during the MICP process.The precipitated biocement alters the hydro-mechanical performance of the soil mass.Usually,the flow,deformation,and transport phenomena regulate the biocementation technique via coupled bio-chemo-hydro-mechanical(BCHM)processes.Among all,one crucial phenomenon controlling the precipitation mechanism is the encapsulation of biomass by calcium carbonate.Biomass encapsulation can potentially reduce the biochemical reaction rate and decelerate biocementation.Laboratory examination of the encapsulation process demands a thorough analysis of associated coupled effects.Despite this,a numerical model can assist in capturing the coupled processes influencing encapsulation during the MICP treatment.However,most numerical models did not consider biochemical reaction rate kinetics accounting for the influence of bacterial encapsulation.Given this,the current study developed a coupled BCHM model to evaluate the effect of encapsulation on the precipitated calcite content using a micro-scale semiempirical relationship.Firstly,the developed BCHM model was verified and validated using numerical and experimental observations of soil column tests.Later,the encapsulation phenomenon was investigated in the soil columns of variable maximum calcite crystal sizes.The results depict altered reaction rates due to the encapsulation phenomenon and an observable change in the precipitated calcite content for each maximum crystal size.Furthermore,the permeability and deformation of the soil mass were affected by the simultaneous precipitation of calcium carbonate.Overall,the present study comprehended the influence of the encapsulation of bacteria on cement morphology-induced permeability,biocement-induced stresses and displacements.

Biomineralization and mineralization using microfluidics:A comparison study

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.

不同含水状态下微生物珊瑚砂桩单桩复合地基模型试验研究

微生物珊瑚砂桩复合地基是利用MICP技术固化珊瑚砂成桩与珊瑚砂组成复合地基,具有就地取材、对原状砂土扰动小及对岛礁生态环境影响小等优势,在岛礁工程建设中具有良好的应用前景。通过不同工况下的微生物珊瑚砂桩单桩复合地基模型试验,研究地基相对密实度(50%、65%、72%)、面积置换率(8%、14%、20%)、含水状态(干燥和饱和)和水位升降对复合地基承载特性的影响规律。结果表明:干燥状态下复合地基的承载力及桩侧摩阻力随地基相对密实度和面积置换率增大而增大;复合地基的桩身轴力和桩土应力比随地基相对密实度增大而减小,随面积置换率增大而增大;提高地基相对密实度和面积置换率可有效提高复合地基承载力。饱和状态下复合地基的承载力为干燥状态的49%~66%;饱和状态相对于干燥状态桩身最大轴力和桩侧摩阻力减小,桩土应力比增大。两次水位升降对微生物珊瑚砂桩单桩复合地基的承载特性影响较小。

微生物加固研究可视化试验系统的开发与应用

微生物加固是近十几年来兴起的绿色低碳建筑技术,在地基处理、边坡治理、混凝土裂缝修复等方面具有较好的应用前景。微生物加固涉及复杂的生物-物理-化学动态过程,需要开发实时可视化系统对其反应机理和加固机制进行研究。分析微生物加固可视化系统研发的必要性,提出微生物加固可视化试验系统由溶液输送系统、微反应器、观测系统、环境控制及监测系统组成的主要构造思路,其中溶液输送系统用于进样和控制流场边界条件,微反应器作为反应模具,观测系统用于反应过程的实时观测,环境控制及监测系统用于控制温度、光照等外部环境条件并获取流体压力等反馈数据。研究以图像处理为主,辅以环境监测的试验数据获取方法,提出相应的试验结果分析方法。结果表明:微生物加固可视化系统既能直接获取加固过程图像和渗透压力变化数据,亦能与扫描电镜等微观试验手段相结合进行材料表征和微观力学特性分析;开发的试验系统能用于微生物加固的微观实时研究,为微生物加固微观机制研究提供了新的手段,有利于揭示微生物加固机理。

胶结液浓度对微生物固化花岗岩残积土强度特性的影响规律

在分析花岗岩残积土物理特性的基础上,选用巴氏芽孢杆菌菌液和不同浓度的氯化钙与尿素的混合胶结液,利用设计的室内试验装置对花岗岩残积土开展不同灌注次数的微生物固化试验,并对不同工况的固化试样进行无侧限抗压强度(UCS)试验、碳酸钙生成率测试和崩解试验,同时开展X射线衍射(XRD)和扫描电子显微镜(SEM)等微观结构分析,以此探讨胶结液浓度和灌注次数对固化后花岗岩残积土强度特性的影响规律.结果表明:试验参数范围内,灌注次数相同时,胶结液浓度为1.0 mol/L时,试样的固化效果最好;胶结液浓度相同时,灌注次数越多,试样的固化效果越好;固化试样的崩解性大大降低,崩解系数均小于30%;微生物固化生成的方解石晶体呈现明显的簇状,填充、胶结在土颗粒之间,与砂土的微生物固化特性具有一定差异性,但两者的固化过程与机理具有相似性.

利用城市垃圾、污泥烧制生态水泥

综合评述了国内外城市垃圾、污泥等废弃物的处理现状 ,列举了它们在生态水泥生产中作为原料的应用情况 ,分析了水泥厂处理这些废弃物的优势。用城市垃圾和污泥来生产生态水泥既拓宽了原材料来源 ,减少了天然资源的消耗 ,降低了水泥生产的成本 ,又不需填埋场地 ,保护了自然环境 ,将是一条很有前途的。

产脲酶微生物诱导钙沉淀及其工程应用研究进展

产脲酶微生物诱导的碳酸钙沉淀是自然界生物矿化的重要组成部分,这一过程依靠微生物代谢产生的脲酶,高效催化尿素水解产生的碳酸根离子进而与钙离子形成碳酸钙沉淀.从产脲酶MICP矿化机理、微生物分布和工程应用三个方面,探讨了相应的最新进展,并对产脲酶MICP的进一步研究提出了思路和建议.MICP微生物属于氨化细菌的范畴,大都分布在厚壁菌门,然而在变形菌门、放线菌门和真菌界等亦发现了产脲酶菌,芽孢杆菌科的细菌是目前发现的具有前景的一类产脲酶微生物,如Bacillus和Sporosarcina属.产脲酶MICP在微生物建筑材料、土体性能的改善和重金属及放射性金属的治理方面有着广泛的应用前景.

珊瑚砂微生物固化体三轴压缩声发射试验研究

对不同干密度增量的珊瑚砂微生物固化体进行了三轴压缩声发射试验,研究不同围压条件下固化体的应力应变曲线特征及对应的声发射信号特征。试验结果表明,珊瑚砂微生物固化体的三轴压缩声发射曲线可分为三个阶段,在应力应变曲线的近似线弹性阶段声发射活动不频繁,屈服阶段声发射活动频度增大,延性流动阶段声发射活动频度降低,但仍有少量声发射振铃计数与能量高峰出现;累计振铃计数曲线呈直线型,反映了声发射活动在变形全过程均维持了一定的频度,说明内部的胶结断裂与颗粒破碎持续发生,颗粒发生错动并重新排列,导致固化体表现出延性流动特性。通过声发射试验,可以更好地理解珊瑚砂微生物固化体的宏观变形与破坏过程,为建立珊瑚砂微生物固化体损伤本构模型奠定基础。

珊瑚砂工程处理研究进展

珊瑚砂岛礁工程建设与国家海洋权益问题息息相关,开展相关研究具有重大战略意义。通过资料收集与分析,综述了珊瑚砂桩基地层勘探、承载特性与群桩效应方面的学术成果,总结了珊瑚砂混凝土的制作工艺、强度特性与耐久性研究的相关情况,并介绍了珊瑚砂微生物固化技术的试验研究进展,最后针对当前研究中的不足之处,简要提供了建议与展望。

菌液脲酶活性对珊瑚砂微生物固化效果的影响

使用不同脲酶活性的菌液对珊瑚砂进行微生物固化试验,分析了固化后试样的渗透特性、干密度增量分数、无侧限抗压强度与应力-应变曲线特征,研究了菌液脲酶活性对珊瑚砂微生物固化效果的影响。试验结果表明：脲酶活性为0.5 mmol/（L·min）的菌液,固化反应速率较慢、产物偏少;脲酶活性为1.0~1.5 mmol/（L·min）的菌液,固化后的珊瑚砂试样渗透系数降低了约2个数量级,固化生成的碳酸钙量多且分布较均匀,具有较高的抗压强度;脲酶活性为2.0-2.5 mmol/（L·min）的菌液,固化反应速率过快,导致试样上部易被碳酸钙堵塞,固化不均匀,应力-应变曲线形态不规则。菌液脲酶活性会影响珊瑚砂微生物固化生成的碳酸钙总量,试验中脲酶活性为1.5 mmol/（L·min）的菌液固化效果最好,珊瑚砂试样强度高、均匀性好,应力-应变曲线较为平滑。

β-磷酸钙-二水磷酸氢钙-水系统生物胶凝材料掺有机酸的研究

本文对β－磷酸钙（β－ＴＣＰ）－二水磷酸钙（ＤＣＰＤ）－水（Ｈ２Ｏ）系统钙磷酸盐胶凝材料（ＣＰＣ）掺加柠檬酸、丙二酸进行了研究。在接近生理条件（相对湿度１００％，温度３７±１℃）下养护，试样的抗压强度可达３６．２ＭＰａ，该系统胶凝材料的硬化时间为５～２０分钟。柠檬酸和丙二酸能有效地控制硬化时间。根据Ｘ－光衍射图谱、红外光谱、扫描电镜观察，羟基磷灰石对胶凝、硬化起了重要作用，柠檬酸钙有增强效应。

Field trial on use of soybean crude extract for carbonate precipitation and wind erosion control of sandy soil

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.

钙铝硅酸盐系生物材料的溶胶-凝胶法制备

采用Sol－Gel法制备了SiO2－Al2O3－P2O5－CaO－CaF2系生物无机粉末。运用DTA和XRD等研究手段对粉末的结构性能进行了研究。结果表明，粉末中含有与骨、牙齿成分相近的Ca3（PO4）2和有助于水泥硬化反应的AlPO4晶相，说明了该粉末可用于制备性能良好的生物无机水泥。

磷酸盐生物水泥劈裂强度和硬度改善的研究

本文主要以活性HAP(羟基磷灰石 :Ca5(PO4) 3OH)、磷酸盐生物水泥PBC为基础 ,研究了碳纤维、原蚕丝纤维和养护条件对水化试样的劈裂强度和表面硬度的改善。实验结果表明 ,生物纤维和适宜的养护条件使水化试体的劈裂强度有一定的提高 ,维氏硬度有较大的提高 ;用SEM和IR初步研究了纤维与水化产物之间的界面结构 ,发现纤维与生物水泥水化产物界面可能有不同程度的化学结合。

碳纤维对HAP-PAC-MPC基复合生物水泥的增强、增韧研究

研究了碳纤维对羟基磷灰石-磷铝酸盐-磷镁酸盐(HAP-PAC-MPC)复合生物水泥的增强、增韧作用,采用XRD、SEM和IR等测试方法分析和探讨了其作用机理。结果表明:(1)碳纤维对于复合生物水泥的增强效果明显,未经处理的碳纤维使复合生物水泥的劈裂强度提高13%,维氏硬度提高63%,而用碳纤维处理后分别提高了51%和近130%,碳纤维的最佳掺量为0.076%;(2)由于碳纤维处理后其表面含有的氧官能团—羟基和羧基的浓度显著提高,加强了它与水泥水化产物在界面处的结合力,形成了化学结合,从而使水泥基料水化、水化产物形成及结晶过程中产生的应力可以通过纤维与基料间的界面而被吸收;(3)碳纤维可以有效地阻止在外力作用下试件内裂纹的扩展或使其转向,从而导致复合材料增强、增韧。

靶向激活产脲酶微生物加固钙质砂试验研究

针对产脲酶微生物设计了6种不同的靶向激活方案,进行钙质砂的生物矿化加固试验。通过无侧限抗压测试、碳酸钙生成量测定、SEM和XRD试验分析,评价钙质砂的加固效果,得出最佳靶向激活方案,最后通过高通量测序的分析结果分析激活前后的钙质砂中微生物群落的变化情况。结果表明:(1)靶向激活方案中YE和NH4Cl的浓度会显著影响激活的效果,其中0.2 g/L的YE、100 mmol/L的NH4Cl、初始pH值为9.0的激活方案效果最好;(2)钙质砂中新生成的方解石含量越多、分布越均匀,则钙质砂的加固效果越好,在最佳的激活方案下矿化加固后砂柱的平均UCS值可提高至350 kPa;(3)靶向激活改变了微生物的群落组成,使产脲酶微生物成为优势物种。

混凝土开裂机理及其生物水泥修复评述

对于混凝土工程来说,裂缝一直是难以攻克的问题。综述了裂缝的机理、类型、危害及其修复方式,并专门介绍了诸如渗透结晶自修复技术,电解沉积自修复技术等混凝土裂缝自修复技术,另外还介绍了微生物诱导碳酸钙沉淀(MICP)修复技术,系统描述了基于此技术研制的生物水泥,包括其作用机理、生物固定载体、作用效果等内容。与传统的修复材料相比,生物水泥是更为绿色环保的新型胶凝材料,但与此同时,这种水泥仍存在一些不足,有待进一步的研究和改进。

微生物诱导碳酸钙沉积研究与应用

生物沉积在岩石表面是一种普遍的现象,对微生物诱导碳酸钙沉积(MICP)作用机理及其应用进行综述。在MICP过程中,微生物分解尿素产生CO3^2-,并在外加钙源条件下生成碳酸钙沉淀,从而把松散的颗粒胶结成一个整体。同时分析影响MICP性能的主要因素,分别为微生物种类及浓度、钙源种类、脲酶活性,并得出3个结论:一是各种微生物矿化机理一致,但沉淀形状出现差异,表现为微生物浓度越高,产生沉淀量越多;二是钙源差异影响沉积过程;三是脲酶活性影响沉淀速率,并涉及pH值和温度等环境因素的调控。此外,重点评述了MICP主要应用领域,分别为制作水泥、固化土壤、修复裂缝、混凝土的自修复和缓解温室效应等,并总结出微生物水泥对比传统水泥的突出优势。