摘要
为探究微生物固化月壤作为建筑材料的潜力,通过微生物诱导碳酸钙沉淀(MICP)对模拟月壤CQU-L1和CQU-L2进行加固,对不同加固次数和不同胶结液(CS)浓度的固化模拟月壤进行无侧限抗压试验、剪切波速试验及扫描电镜SEM微观观测。结果表明:随着MICP加固次数和胶结液浓度的增加,固化模拟月壤强度提升显著。相同加固次数下,固化模拟月壤的强度随胶结液浓度的提升而提升,用浓度为2.0 mol/L的胶结液加固12次的试样峰值强度可达1.303 MPa。土体剪切波速与无侧限抗压强度增加的趋势相似,最大剪切波速可达508 m/s。微生物注浆加固对模拟月壤CQU-L1的加固效果较CQU-L2差,原因在于模拟月壤CQU-L1颗粒较细,在相同加固次数下,其渗透性下降更显著,使得有效加固次数降低。SEM试验结果表明:随着加固次数和胶结液浓度的增加,固化模拟月壤孔隙中形成更为明显的致密结构,并且碳酸钙以球霰石为主。微生物加固有望为月球建造提供一种新的方式,但需要根据月壤的级配以及月壤的物理化学特性对加固方法进行改进。
随着全球人口的持续增长以及太空探索活动的加速,月球栖息地建设已成为许多国家和国际航天组织的重要目标。根据国务院新闻办发布的《2021中国的航天》白皮
月壤是由微小的玻璃珠、矿物碎片和细小的岩石颗粒组成的粉末状物
月球建造需要对月壤进行成形处理,并使其具备一定强度。针对月壤固化,学者们提出了黏
微生物诱导碳酸钙沉淀(MICP)技术目前被广泛研究并应用于加固地表
鉴于月壤的特点,笔者利用MICP技术对模拟月壤CQU-L1和CQU-L2进行加固。通过无侧限抗压试验、剪切波速测试试验和酸洗试验对不同加固次数和不同胶结液(CS)浓度的MICP固化模拟月壤的力学特性进行研究,通过环扫电子显微镜对破裂面的MICP固化模拟月壤样品进行分析。
模拟月壤选用吉林龙岗火山群黑色玄武岩样品进行制备。利用球磨机将原位开采的玄武岩进行研磨,以获得小颗粒玄武岩样品,玄武岩样品如

图1 模拟月壤粒径级配曲线及玄武岩颗粒形貌
Fig. 1 Particle size gradation of regolith simulant and morphology of basalt
试验选用的矿化菌为巴氏芽孢杆菌。每升去离子水液体培养基中含20 g酵母提取物、15 g氯化铵和1 mL氯化镍溶液,利用1 mol/L的NaOH调节pH值至9.2~9.3,氯化镍溶液浓度为0.1 mol/L。对液体培养基进行高压高温灭菌,冷却后通过接种环将琼脂固体培养皿中的菌种接种至液体培养基。将液体培养基在35 °C的摇床中以200 r/min培养20 h,如

图2 微生物培养基与加固液材料
Fig. 2 Materials for microbial culture media and cementation solution
注: (a)酵母提取物;(b)氯化铵;(c)氯化镍;(d)固体培养皿;(e)尿素;(f)氯化钙。
为保证不同加固次数下的菌液浓度,通过721型可见分光光度计进行OD600测试。试验过程中共培养液体培养基12次,不同的液体培养基OD600值介于1.247~1.301之间,菌液浓度如

(a) 细菌浓度

(b) 微生物活性

(c) CQU-L1固化菌电导率变化

(d) CQU-L2固化菌电导率变化
图3 细菌活性检测
Fig. 3 Bacterial activity examination
试样采用的针筒直径为39.1 mm,制样密度为1.302 g/c

图4 微生物注浆示意图
Fig. 4 Microbial grouting scheme
针对含细粒较多的模拟月壤CQU-L1,设置的注浆次数分别为1、2、3次;针对颗粒尺寸较大的CQU-L2模拟月壤,设置的注浆次数分别为4、8和12次。注浆完成后,利用去离子水清洗试样表面盐溶液。将制备好的试样放入80 ℃的烘箱中干燥48 h,利用热熔刀切开试样进行后续试验。对加固完成后的试样,采用弯曲元进行剪切波检

(a) 加固1次

(b) 加固2次

(c) 加固3次

(d) 无侧限强度对比
图5 不同加固次数下固化CQU-L1模拟月壤应力-应变曲线
Fig. 5 Stress-strain curve of solidified CQU-L1 lunar soil under different reinforcement cycles
剪切波在土体中的传递时间与土体种类、制样密度、粒径级配以及胶结等因素有

(a) 加固4次

(b) 加固8次

(c) 加固12次

(d) 无侧限强度对比
图6 不同加固次数下固化CQU-L2月壤应力-应变曲线
Fig. 6 Stress-strain curve of solidified CQU-L2 lunar soil under different reinforcement cycles

(a) 剪切波形图

(b) 微生物加固CQU-L1剪切波速

(c) 微生物加固 CQU-L2剪切波速
图7 不同加固次数下固化模拟月壤的剪切波及剪切波速
Fig. 7 Shear wave velocity of solidified regolith simulant under different biotreatment cycles

(a) CQU-L1

(b) CQU-L2

(c) UCS与碳酸钙含量关系

(d) 剪切波速与碳酸钙含量关系
图8 不同加固次数下固化模拟月壤碳酸钙含量与力学特性关系
Fig. 8 Calcium carbonate content in solidified lunar regolith simulant under different reinforcement cycles

图9 不同加固次数下模拟月壤试样破坏形貌
Fig. 9 Failure pattern of solidified lunar simulant under different biotreatment cycles
为了更好地观察模拟月壤孔隙内的碳酸钙沉淀,对MICP加固的月壤样品进行SEM微观观测。

(a) 1.0 mol/L加固8次

(b) 1.0 mol/L加固12次
图10 MICP固化模拟月壤扫描电镜图
Fig. 10 Scanning electron microscopy of of MICP reinforced regolith simulant
随着人类对月球和火星等地外空间的探索,地外建造技术成为近年来学者们研究的热点。Santomartino

图11 月表照片(亚利桑那州立大学拍摄)(左
Fig. 11 Lunar surface (from Arizona State University) and lunar simulant brick by MICP
为了探究微生物加固月壤成形的可行性,使用火山玄武岩制备模拟月壤CQU-L1和CQU-L2,并利用微生物注浆加固方式对模拟月壤进行加固成形。通过对模拟月壤CQU-L1、CQU-L2进行无侧限抗压试验、剪切波速试验和碳酸钙含量测试,获得了不同加固次数和不同CS浓度条件下的微生物固化模拟月壤的强度、波速以及碳酸钙沉淀胶结特性。探索性地将微生物加固技术用于月壤成型,有望为月球建造建筑材料的选择提供参考。主要结论如下:
1)MICP加固次数和CS浓度对模拟月壤CQU-L1和CQU-L2的无侧限抗压强度有较大影响。在相同加固次数下,CS浓度越高,固化模拟月壤的无侧限抗压强度越大。相同CS浓度条件下,加固次数越多,固化模拟月壤的无侧限抗压强度提升越显著,CS浓度为2.0 mol/L加固12次试样峰值强度可达1.303 MPa,具有作为月球建材的潜力。
2)相同加固次数下,随着CS浓度的提高,剪切波速提高。相同CS浓度条件下,加固次数越多,剪切波速提高越显著。CS浓度为2.0 mol/L加固12次模拟月壤的剪切波速可达508 m/s,土体峰值抗压强度与剪切波速的增加趋势相似。
3)随着CS浓度和加固次数的增加,固化模拟月壤中的碳酸钙含量显著提升,固化土内部孔隙减小,碳酸钙填充紧密。碳酸钙含量分别与无侧限抗压强度及剪切波速呈近似的变化规律。MICP能在模拟月壤颗粒之间形成碳酸钙胶结,并在模拟月壤表面形成涂层分布。碳酸钙形貌以球形为主,推测为球霰石,表明细菌浓度过高,钙离子不足。
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