Effect of Shrinkage Reducing Agent and Steel Fiber on the Fluidity and Cracking Performance of Ultra-High Performance Concrete

Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects of different types of cementitious materials,chemical shrinkage-reducing agents(SRA)and steel fiber(SF)were assessed.Compared with M2-UHPC and M3-UHPC,M1-UHPC was found to have better fluidity and shrinkage cracking performance.Moreover,different SRA incorporation methods,dosage and different SF types and aspect ratios were implemented.The incorporation of SRA and SF led to a decrease in the fluidity of UHPC.SRA internal content of 1%(NSRA-1%),SRA external content of 1%(WSRA-1%),STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%,8.3%,9.2%and 25%,respectively.However,SRA and SF improved the UHPC shrinkage cracking performance.NSRA-1%and STE-0.7 reduced the shrinkage value of UHPC by 40%and 60%,respectively,and increased the crack resistance by 338%and 175%,respectively.In addition,the addition of SF was observed to make the microstructure of UHPC more compact,and the compressive strength and flexural strength of 28 d were increased by 26.9%and 19.9%,respectively.

Introduction of a Japan Concrete Institute Guideline： Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures

There are many cracked concrete structures worldwide. Although there have been numerous efforts to eliminate cracks, some cracks are very harmful and should be repaired as soon as possible. On the other hand, some cracks are almost harmless. So, a good guideline regarding how to deal with cracks in concrete structures is needed. In this guideline, the practical investigation, repair and strengthening method of cracked concrete structures is discussed. And the detecting subjects are cracks generated immediately after casting and during the service time. This guideline targets on the owners （including managers） of concrete structure and the engineers working for the maintenance of concrete structure. JCI （Japan Concrete Institute） published first version of ＂Practical Guideline for Investigation and Repair of Cracked Concrete Structures＂ in 1980, and then the fourth version titled ＂Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures--2009＂ was published. This guideline is very practical when cracks are observed in existing concrete structures, in any other countries as well as in Japan. These three authors led the establishment of this guideline.

Introduction of a JCl Guideline： Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures

There are many cracked concrete structures, although there have been numerous efforts to eliminate cracks. Some cracks are very harmful and should be repaired as soon as possible. On the other hand, the other cracks are almost harmless. So, a good guideline about how to deal with cracks in concrete structures had been needed. JCI （Japan Concrete Institute） published the first version of ＂Practical Guideline for Investigation and Repair of Cracked Concrete Structures＂ in 1980, the second version in 1987, the third version in 2003, and then the fourth version titled ＂Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures-2009＂ was published. This Guideline is very practical, when cracks are observed in existed concrete structures, in any other countries as well as in Japan.

Corrosion Resistance of Steel in Cracked Reinforced Concrete after Electro-depositon Treatment

An electro-deposition method has been recently proposed to repair cracked reinforced concrete. To evaluate the corrosion resistance of the reinforcing steel in cracked concrete, three different parameters including type of auxiliary electrode, electrode distance, and current density were studied. Tafel polarization curve was used to evaluate the corrosion resistance of the steel. Self-corrosion potential and corrosion current of the steel were tested. The results indicate that the corrosion resistance improvement of the reinforcing steel is optimal as prism titanium mesh is applied as auxiliary electrode, followed by the flaky titanium mesh and the column titanium bar. When the electrode distance is 60 mm, the corrosion resistance improvement of the reinforcing steel is optimal, and with 80 mm electrode distance, the corrosion resistance improvement is the poorest. The property falls in between them when 40 mm electrode distance is used. Moreover, the corrosion resistance improvement of the reinforcing steel increases as the current density goes up.

Characterisation of Bacteria⁃Based Concrete Crack Rejuvenation by Externally Applied Repair

Microbiologically⁃induced calcite⁃precipitation(MICP)has been increasingly studied in structural repair including self⁃healing and external applications.Among various MICP pathways,enzymatic urea hydrolysis is suggested to be applied as external repair instead of self⁃healing.This study comprehensively characterised the enzymatic urea hydrolysis pathway in physical,impermeable,and mechanical rejuvenation of concrete cracks.The visual quality of repaired structures was presented,and the importance of humidity in the remediation of cracks was demonstrated.Moreover,this study investigated the differences in the effectiveness of repair between premixing bacteria with urea and without any premixing.With premixing,there was a concern that the accelerated reactions would precipitate calcite in the shallow spaces of the cracks and impede deeper healing.However,the observed results indicated that neither physical nor impermeable rejuvenation of concrete cracks repair would be detrimentally affected.The results obtained from this study will allow further development in commercialisation since the effectiveness of repair has been confirmed with an improvement in its efficiency.

水工混凝土矿化微生物固载及自修复试验研究

直接内掺方式制备微生物自修复混凝土会因拌合的机械挤压摩擦、生存环境受限等因素影响矿化微生物的长期活性。本文选择巴氏芽孢杆菌为矿化微生物,以膨胀珍珠岩和陶粒为微生物载体,以水泥浆和偏高岭土浆液为载体包覆材料,通过试验优选有助于微生物释放和保护的载体及其合理粒径、包覆材料,并研究微生物固载对裂缝自修复效果的影响。结果表明:掺入定量的膨胀珍珠岩的水工混凝土试样劈裂裂缝处拉裂面积比更大,作为水工混凝土微生物固载材料时较陶粒更能有效释放矿化微生物;偏高岭土浆液较水泥浆更适合作为载体的包覆材料,其包覆的微生物14 d存活率为86.63%,有效保证了固载微生物的长期活性;对微生物进行膨胀珍珠岩固载和偏高岭土浆液包覆,修复养护90d裂缝最大修复宽度为0.616mm,高于直接内掺的0.453mm,有效改善了混凝土试件的裂缝自修复效果。

城市轨道交通混凝土抗裂防渗技术研究与应用

抑制混凝土开裂渗漏是保障城市轨道交通地下结构建设质量的重点和难点。以城市轨道交通地下车站为例,分析了混凝土开裂的主要原因,介绍了施工期混凝土抗裂性评估与设计方法,提出了混凝土材料抗裂性能控制指标,以及保障指标实现的材料、施工控制措施,结合实际工程,介绍了成套技术应用效果,为类似工程抗裂防渗建设质量提升提供指导。

适宜水工混凝土内环境的矿化微生物梯度驯化优选

水工混凝土内部高碱性环境限制了微生物混凝土的自修复效能。利用梯度驯化方法可提高矿化微生物对高碱度的耐受性,优选出适宜混凝土孔隙内环境并具备高诱导矿化沉积能力的增强嗜碱型微生物。首先,在实验室高碱性环境下,对比巨大、科氏、枯草、巴氏等4种芽孢杆菌的活性及诱导矿化沉积量,初选耐碱性较好的微生物并对其开展耐碱性梯度驯化;随后,综合分析驯化微生物对混凝土力学性能、吸水性、渗透性和自愈能力的影响,通过扫描电子显微镜和X射线衍射对矿化产物微观形态和组成进行分析。结果表明:相较于巨大、科氏和枯草芽孢杆菌,巴氏芽孢杆菌在高碱性条件下表现出更强的活性,梯度驯化技术可进一步提高巴氏芽孢杆菌在高碱性环境中的活性,并证实通过该方法增强的耐碱性具有后代保留的特性;与掺未驯化微生物组试样相比,掺驯化微生物混凝土试样养护28 d的抗压强度提高了16.59%,吸水系数降低了37.74%,渗透系数减小了19.22%;掺驯化微生物混凝土试样的裂缝自修复试验得到裂缝最大修复宽度为0.57 mm,超过了未驯化微生物组的0.44 mm。本研究为基于微生物诱导矿化沉积技术的微生物水工混凝土研发和应用提供理论依据和技术支撑。

自密实高抗裂混凝土在盾构隧道工作井侧墙中的应用

采用明挖顺作法施工的盾构隧道工作井侧墙位于由维护结构、环框梁、底板及模板组成的密封空间内,其受到的约束作用强,施工难度大,容易因混凝土收缩开裂及浇筑不密实导致渗漏。依托在建的江阴靖江长江隧道工程,在室内研究的基础上,通过现场系列模型试验,比较了采用不同混凝土材料及施工工艺时混凝土结构的密实性。模型试验及工程应用结果表明,采用自密实高抗裂混凝土,结合布料工艺、浇筑速率、分层浇筑静置时间的控制,并辅以必要的振捣,可保证混凝土浇筑密实,进一步结合抗裂温控措施,可消除混凝土收缩裂缝,避免工作井侧墙出现渗漏。

矿用喷涂堵漏风自修复材料性能研究及工程应用

喷涂堵漏风是防止煤自燃的有效手段之一。针对传统水泥基喷涂堵漏风材料脆性大、易开裂、堵漏风效果差的弊端,提出以微生物及结晶矿物为自愈合剂,研制出生物胶囊和矿物胶囊以及一种生物–矿物–纤维协同自修复材料。研究了不同养护湿度和养护时间对材料裂缝自修复能力的影响。结果表明:当养护湿度为100%相对湿度、养护时间为35 d时,研制的生物胶囊和矿物胶囊可以将裂缝完全修复,裂缝最大修复宽度为1260μm。采用扫描电子显微镜(SEM)和X射线能谱仪(EDS)探究了自修复材料裂缝区域修复产物的晶型及元素组成,发现裂缝处的修复产物为球碳镁石、花瓣状的水菱镁矿以及大量由细菌矿化产生的球形方解石,这些修复产物在一定程度上起到了密闭裂缝的作用;EDS能谱分析证实了修复产物为MgCO_(3)和CaCO_(3)。当养护湿度为100%时,材料具有最高的堵漏风率(97.15%),比同养护条件的对照组试样高出73.62%。最后将自修复材料用于沿空煤柱喷涂堵漏风,结果显示该材料在6个月内未发现明显裂隙,与传统水泥砂浆相比,该材料具有更长的使用寿命和更好的预防效果。

土木工程建筑中混凝土裂缝的施工处理技术分析

混凝土裂缝是土木工程建筑中的常见问题,影响结构的稳定性和美观性,通过分析裂缝形成的多种因素,包括材料、施工、环境和设计等,以及针对性的解决方案,如裂缝修补技术、结构加固技术和预防性措施,并结合实际案例,评估这些技术在实际工程中的应用效果。文章的研究结果对于提高混凝土结构的安全性、稳定性和美观性具有重要的指导意义。

环氧树脂胶粘剂对混凝土裂缝修复性能的影响研究

研究使用环氧树脂胶粘剂修复混凝土裂缝问题,分析环氧树脂胶粘剂对于混凝土结构力学性能的影响,使用丁腈橡胶改性环氧树脂,增加环氧树脂韧性,并与稀释剂、固化剂混合制备修复混凝土的环氧树脂,将该环氧树脂灌注在预制裂缝的混凝土试件中,通过万能试验机等设备测试修复前后试件的抗压、抗折强度变化,并验证丁腈橡胶用量对于修复效果的影响。结果表明,使用改性环氧树脂修复混凝土多种形式的裂缝,能够提升混凝土抗压、抗折强度的恢复率,降低液体向混凝土入渗的速度,提升混凝土的性能,同时在环氧树脂中添加丁腈橡胶8 phr能够提升修复的耐水性。

城市轨道交通地下车站结构自防水关键技术及应用

抑制混凝土开裂是保障城市轨道交通地下车站结构自防水性能的关键。文章首先分析了混凝土抗渗性能以及出现开裂的主要原因,在此基础上,结合相关标准,介绍了包括抗裂性设计、混凝土材料、施工工艺、监测和检验在内的地下车站结构抗裂防渗成套技术以及工程实施效果。研究成果可以为提升地下车站结构自防水性能、解决工程渗漏难题提供有效的技术途径。

公路路面裂缝处治及小修保养技术创新与应用研究

为了解决日益突出的公路路面裂缝维修和保养问题,本文对公路路面裂缝的修补与小修保养技术创新及其应用进行了研究。通过对当前公路维修技术的深度解析,探讨并引入新的技术创新方法,包括高效的裂缝检测技术、自修复混凝土以及机器人维修技术等。研究结果表明,这些技术创新方法不仅提高了修补效率,而且大大延长了公路使用寿命。此外,还讨论了技术创新在公路修补和保养工作中的实际应用,以及如何推广这些新技术。

膨胀结晶法裂缝填充技术分析与评价

文中通过面积修复率和超声脉冲速度法评价了西卡膨胀结晶自修复剂的修复效果。试验结果表明,膨胀结晶自修复剂作用下生成的修复产物有效填充了裂缝区,提升了水泥砂浆内部的密实度,该膨胀结晶自修复剂的修复产物主要有Mg(OH)_(2)和CaCO_(3)。

高性能快速修补混凝土在公路养护工程中的应用

受交通量与汽车载重量日益剧增影响,很多公路路面结构出现不同程度的损坏。高性能快速修补混凝土能够有效修补路面结构损坏。为了进一步探究该混凝土在公路养护工程中的具体应用,结合国内某公路养护工程,对高性能快速修补混凝土的实际应用进行研究,通过研究得出高性能快速修补混凝土的高低温性能良好,且具备良好的变形能力,可满足路面抗反射裂缝变形的实际要求,并且修补后路面的行车舒适度、抗滑性以及耐久性均能够达到相应的要求。

镁质膨胀剂微胶囊对砂浆裂缝自修复效果的影响研究

混凝土呈脆性、内部易产生细小裂缝,从而影响混凝土的整体性和耐久性。以氧化镁膨胀剂、硅质材料和水泥为囊芯,硅酸盐材料为囊壁,制备了四种粒径的镁质膨胀剂微胶囊。研究了各粒径微胶囊掺量对砂浆试件抗压强度的影响;以强度恢复率和裂缝面积修复率作为评价指标,探讨了微胶囊对砂浆裂缝自修复性能的影响;采用X射线衍射(X-ray diffraction,XRD)和扫描电子显微镜(scanning electron microscopy,SEM)对裂缝处自修复物质进行物相和形貌分析,探讨了自修复机理。结果表明,当微胶囊掺量不超过10%时,微胶囊的掺入提升了砂浆试件的抗压强度。当微胶囊掺量为10%、粒径为1.18~2.36mm、二次养护14 d时,宽度0.3 mm以下的裂缝完全修复,裂缝面积修复率达到100%,远高于空白组。结合XRD和SEM分析可知,裂缝修复的主要机理是裂缝中C-S-H凝胶、Ca(OH)_(2)、CaCO_(3)、AFt和Mg(OH)_(2)等高强、微膨胀物质大量生成,有效填充了裂缝空间,促进了裂缝的愈合,从而显著提升了砂浆的耐久性与整体性能。

水电站大坝混凝土施工及裂缝防渗处理研究

在开展水电站大坝施工阶段,缺乏对混凝土工程的系统化研究,导致透水率难以达到施工要求,基于此,提出水电站大坝混凝土施工及裂缝防渗处理施工技术研究。将普通硅酸盐水泥P·O42.5作为主要材料,从性能角度出发,对大坝混凝土施工材料进行设计,采用多个单元墙段逐个施工的方式对大坝结构浇筑。对于大坝混凝土结构存在的裂缝问题,结合裂缝的具体状态设计了结构表面修补法和内部填充法两种防渗处理施工方式。从测试结果可以看出,施工大坝的透水率始终稳定在1.50 Lu以内,达到了施工管理要求。

公路桥梁裂缝修复用改性新材料性能测试及效果研究

针对传统混凝土桥梁裂缝修复困难的问题,提出通过改性石蜡、碳纤维布与内置钢丝网水泥砂浆板对混凝土桥梁裂缝进行协同修复。试验对工业石蜡的改性条件进行优化,研究了改性石蜡、碳纤维布与内置钢丝网水泥砂浆板对混凝土桥梁裂缝的修复效果。试验结果表明,工业石蜡∶石墨粉∶乳化剂∶环氧树脂=100∶1.5∶12∶12时,对工业石蜡的改性效果最好,在改性石蜡厚度为9 mm,侧面单面铺设2层碳纤维布,底面铺设一层内置钢丝网水泥砂浆板的条件下,桥梁混凝土开裂载荷提升至15.8 kN,破坏载荷提升至16.9 kN,裂缝的最终修复率约为32.1%,表现出良好的增韧效果和修复效果。

地库承台裂缝渗漏修补及抗浮分析

文中以贵州凯里畅达公馆项目为例,结合地库承台渗漏情况,分析渗漏修补施工难点,提出了具体修补技术。该项目经历多次暴雨,通过对修复位置监测发现,原渗漏位置未出现渗漏迹象,取得了良好的修复效果。