Distribution of calcium carbonate in the process of concrete self-healing

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.     

土豆脲酶提取及基于酶诱导碳酸钙沉淀技术对风积沙改良的方法

基于酶诱导碳酸钙沉淀（EICP）技术,使用植物脲酶对沙漠风积沙进行改良加固试验。为寻求价格低廉和操作简单的脲酶提取方法,以土豆为原材料,去离子水、甘油水溶液和乙醇水溶液为提取液,通过破碎冷藏及高速离心方法成功地从土豆中分离提取出植物脲酶,分析提取过程中不同提取液对脲酶提取效果的影响,基于EICP技术,利用土豆脲酶液对风积沙进行改良处理。结果显示,在3种提取液中,效果最优的是乙醇溶液,甘油水溶液次之,去离子水提取效果最差。而当固液比为1:6、乙醇溶液浓度为30%时,脲酶活性值最高且提取效果最佳。在风积沙改良试验中,试件表面形成了坚硬的结皮层并具有较高的抗压强度,随着浸泡脲酶次数的增加,无侧限抗压强度逐渐增强。     

沥青路面损伤分析及实验开发

利用粘弹性与损伤的分析理论,对含表面裂缝沥青路面进行了有限元分析,计算了损伤区半径和裂缝长度的改变量随温度和加载时间的变化,得到不同加载时间和不同变温的损伤区和断裂区的分布情况,模拟了损伤区的演化和裂缝的扩展过程;通过复合材料理论和劈裂实验的比较,确定了含纤维沥青混凝土的劲度模量,同时对含纤维和不含纤维沥青混凝土路面的疲劳寿命进行了计算、分析和比较,提出了新型抗损伤沥青路面.     

Living concrete with self-healing function on cracks attributed to inclusion of microorganisms: Theory,technology and engineering applications—A review

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.

     

Self-healing of cracks in concrete with various crystalline mineral additives in underground environment

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.     

大体积毛石混凝土在控制温度裂缝方面的应用

针对重庆市南川神童镇污水处理厂工程C20混凝土挡土墙绝热温升（60．19℃）和内外温差（17．76℃）过高造成温度裂缝的问题,考虑到当地多阴雨、湿度大的气候特点,在比较其他控制裂缝方法的基础上,采用大体积毛石混凝土,毛石体积掺量为20％,热工计算后发现,结构的绝热温升值（48．15℃）和内外温差（14．20℃）明显下降,温度应力为0．76N／mm2,有效控制了由于温度应力造成的温度裂缝．在未采取其他措施的情况下,实施效果良好．通过工程实践进一步验证了大体积毛石混凝土在控制温度裂缝方面的作用．     

复合白云石表面链状纳米CaCO_3的制备

在Ca(OH)_2-H_2O-CO_2反应体系中,根据非均匀成核原理,通过调整体系反应温度、Ca(OH)_2浓度、ZnSO_4添加量等反应参数,控制在白云石颗粒表面生成具有链状结构的纳米Ca-CO_包覆层.利用SEM,XRD等检测表征手段,分析了不同反应参数对纳米CaCO_3晶形的影响.结果表明:当反应温度为25℃,ZnSO_4加入量为Ca(OH)_2的4%,Ca(OH)_2浓度为0.3mol/L时,在白云石颗粒表面生成了长径比为7:1的链状纳米CaCO_3.提高体系的反应浓度能够减少ZnSO_4的加入量.     

机场道面贯通裂缝产生的原因及整治方法

本文论述了厦门高崎国际机场水泥混凝土道面存在的病害,运用近年来发展起来的混凝土损伤力学与混凝土断裂力学理论,对混凝土道板贯通裂缝机制、温度应力,裂缝尖端附近应力场强度作了分析,并采用早强膨胀钢纤维混凝土对贯通裂缝做了修补加固,使机场混凝土道板符合安全飞行要求。     

温州泽雅水库大坝混凝土面板缺损分析及修复

泽雅水库自1998年建成后,主体部分运行基本正常,但水库坝体的混凝土面板由于受坝体不均匀沉降、面板温度应力、表面冲刷等诸因素的影响,出现了不同程度的裂缝.急需采取措施修复坝体面板裂缝,以消除可能的安全隐患.有关专家通过对水库混凝土面板裂缝成因的分析,对裂缝进行科学检测,提出了针对性的整治修复方案.     

纳米多孔类碳糊电极的制备工艺改进 及其电化学行为

以纳米碳酸钙微球为模板,吡咯为前驱体,石墨粉为填料直接诱导合成,廉价简便地制备出一种高灵敏的纳米多孔类碳糊电极,讨论了石墨粉与纳米碳酸钙微球质量比对电极性能的影响。结果表明,选用粒径最小的60~80 nm碳酸钙为模板,当纳米碳酸钙微球与石墨粉的质量比为1:1.5时,纳米多孔碳糊类电极的比表面积可高达923.5 m2/g。以循环伏安法(CV)和交流阻抗(EIS)研究其电化学行为,结果表明,纳米多孔类碳糊电极较纯碳糊电极电性能好,灵敏度高,稳定性和重现性好。     

碳酸钙微球合成、修饰及作为基因载体的研究

采用聚苯乙烯磺酸钠（PSS）作为调控剂,将其加入到氯化钙和碳酸钠溶液反应体系中成功制备出表面粗糙的碳酸钙微球（粒径平均约为510nm）,采用场发射扫描电镜（FE-SEM）、红外光谱（FTIR）、X-射线衍射（XRD）和动态光散射（DLS）等对碳酸钙微球颗粒进行表征。MTT实验显示碳酸钙微球毒性具有浓度依赖性,在终浓度〈1mg/mL时,细胞存活率都可达60%以上,显示出很低的细胞毒性,具有良好的生物相容性。不同pH值条件下碳酸钙微球的降解实验结果显示碳酸钙微球在酸性pH下能够更快速地降解,说明碳酸钙微球能够响应酸性pH值,具有pH依赖性。将碳酸钙微球经PEI表面修饰后用于负载质粒DNA,通过琼脂糖凝胶电泳及体外转染实验结果证实碳酸钙微球能够有效负载质粒DNA,并可在癌细胞内成功表达发出绿色荧光。这些研究结果显示将碳酸钙微球作为一种安全的非病毒基因载体用于基因治疗领域具有潜在的应用价值。     

不同电流密度下混凝土裂缝电沉积产物的分布特性

选用ZnSO₄作为电沉积溶液,以混凝土裂缝处电阻及裂缝填充深度为评价指标,研究电流密度对电沉积修复钢筋混凝土裂缝效果的影响及对沉积物矿物成分和微观形貌的影响。研究结果表明：经过电沉积修复36 d,混凝土试件电阻显著增加,电阻增加速率随着通电时间增加而减小,电流密度越大,早期电阻增加速率越快,但裂缝填充深度越小。X射线衍射结果表明,沉积物主要矿物成分为ZnO。电镜扫描结果表明,沉积物颗粒大小随着电流密度增大而变大,电流密度越小,沉积物排列越有序,结构越致密。     

水泥混凝土路面板开裂原因及设计建议

针对重庆地区普遍存在的水泥混凝土路面板开裂现象,分析了荷载、温度、路面板板长、板胀缝等因素对路面板开裂的影响,提出了相应的设计建议。     

Evolution and characterization of damage of concrete under freeze-thaw cycles

To study the internal damage of concrete under freeze-thaw cycles, concrete strains were measured using embedded strain gauges. Residual strain and coefficients of freezing expansion (CFE) derived from strain-temperature curves were used to quantify the damage degree. The experimental results show that irreversible residual strain increases with the number of freeze-thaw cycles. After 50 cycles, residual strains of C20 and C35 concretes are 320με and 100με in water, and 120 με and 60 με in saline solution, respectively. In lower temperature range (-10 ℃ to -25 ℃) CFE of C20 and C35 concretes decrease by 9.82×10-6/K and 8.44×10-6/K in water, and 9.38×10-6/K and 5.47×10-6/K in saline solution, respectively. Both residual strains and CFEs indicate that during the first 50 freeze-thaw cycles, the internal damage of concrete in saline solution is less than that of concrete in water. Thus residual strain and CFE can be used to measure the frost damage of concrete.     

某工程大体积混凝土温度场的试验研究

为了控制大体积混凝土的水化热温度,对控制混凝土早期裂缝提供依据,了解温度对混凝土早期力学性能的影响,采用镍铬-镍硅型热电偶传感器对混凝土内部温度场进行了实测.结果表明,混凝土浇筑初期内部温度场沿深度呈抛物线分布,最高温度为58℃,在浇筑后3 d出现,持续1 d左右,混凝土中心与表面最大温差19℃.通过实测的温度场分布情况,可以直接了解混凝土内部温度变化趋势,对控制水化热温度和温度裂缝起指导作用.     

基于微生物矿化沉积的混凝土裂缝修复研究进展

针对混凝土开裂工程难题,提出采用微生物矿化沉积材料进行裂缝修复的方法.详细讨论微生物矿化沉积的机理、修复剂各组分与混凝土基体的相互作用、修复后混凝土的强度和耐久性能这3个在裂缝修复中的关键技术问题,并探讨相应的最新进展.分析结果表明,沉积产物主要为碳酸钙矿物,且其修复的首要方面为改善混凝土的耐久性.当前亟待解决的问题包括微生物的有效保护、修复效率、经济性以及环境影响方面.结合实际应用前景,可预见智能化自修复是微生物修复技术未来重要的研究方向之一.     

不同强度混凝土静态破碎试验研究

将静态破碎剂在相同用量及相同拌合水温条件下,倒入强度等级分别为C20、C30、C40的混凝土预留孔中进行静态破碎试验,观察混凝土表面裂缝的扩展情况并记录反应过程中混凝土外表面应变变化规律。结果表明：随着混凝土强度等级的提高,混凝土外表面开始出现裂缝的时间逐渐推迟,裂缝扩展的宽度以及混凝土外表面出现裂缝的条数都随着混凝土强度等级的提高而逐渐缩小和减少。在反应过程中,随着混凝土强度等级的提高,混凝土外表面的应变出现明显波动的时间逐渐滞后,不同强度等级的混凝土的四个侧面中,始终有一个侧面产生拉应变,其余三个侧面产生压应变。     

基于双向电迁移的开裂混凝土除氯阻锈效果

采用双向电迁移（BIEM）方法对沿海环境下的开裂混凝土进行修复,以排除裂缝附近富集的氯离子,并对钢筋进行阻锈防护. 通过测定阻锈剂浓度、氯离子质量分数以及钢筋极化曲线,研究不同裂缝宽度下BIEM的作用效应,并通过氯离子迁移特征试验对氯离子的迁移规律加以验证. 试验结果表明：开裂混凝土双向电迁移后,钢筋腐蚀电位均能恢复至较高水平;当裂缝宽度较小时,混凝土保护层中氯离子的迁移规律与未裂混凝土相近;当裂缝宽度大于0.3 mm时,裂缝处的氯离子排出效率随裂缝宽度的增加有所提高,但离裂缝较远处的氯离子排出效率有所降低.     

微波加热与传统加热下混凝土的热力学响应

传统混凝土破碎技术存在粗骨料损伤大、机械磨损严重和能耗高等弊端,这些问题可以通过在破碎前对混凝土进行微波处理来解决。为了评价微波处理技术的工业适用性,通过不同功率微波对混凝土试件进行加热,并与传统加热方式相比较,研究混凝土的加热效率和宏观裂纹扩展规律,而后进行单轴抗压强度试验,得到混凝土在不同热处理条件下的强度弱化规律。结果表明：与传统加热方式相比,微波加热技术能有效促进混凝土内部和表面裂纹扩展,削弱混凝土的强度,并且高功率微波下效率更高,能量消耗更少。此外,微波加热时未完全烘干的混凝土容易出现低温爆裂现象,爆裂时间与功率水平呈负幂函数关系,与烘干时间呈正幂函数关系。     

大体积承台混凝土早期表面开裂控制措施

针对大体积混凝土浇筑时因水化热作用引起的早期表面开裂问题,对比分析浇筑温度、环境温度、保温材料以及位移约束条件4种因素对混凝土表面应力的影响程度.以宁波象山港公路大桥承台为实例建立有限元模型,选取6个开裂关键部位的节点,分析这些节点的应力数值在28d龄期内随4种影响因素变化的规律.模拟分析分层浇筑和水管冷却2种降温措施对于减小混凝土表面拉应力的作用.结果表明,混凝土表面拉应力与浇筑温度呈正比,与环境温度呈反比;保温层对承台表面中心部位拉应力的影响大于边缘部位;提高模板的刚度对抗裂有利;分层浇筑和水管冷却可以不同程度地改善表面开裂状况.