海洋环境下混凝土中钢筋锈蚀机理及监测技术概述

2014年我国由于腐蚀产生的损失约为21 278亿元,占国家GDP的3.34%。海洋环境中氯离子渗透至混凝土内部导致钢筋锈蚀是海洋环境下混凝土结构损伤的重要原因。海洋不同腐蚀区域的离子浓度、氧气浓度及海水干湿循环作用时间各不相同,这使得海洋不同腐蚀区域中暴露混凝土的氯离子传输速度和分布规律、钢筋锈蚀产物及锈蚀模式、钢筋锈蚀速率存在显著差异。其中海洋浪溅区和高潮位区域因氧气充足、海水干湿循环作用剧烈及浪溅作用导致钢筋混凝土更易破坏。钢筋锈蚀产物体积是原始体积的2~6倍,持续增加的锈蚀产物将导致混凝土开裂、保护层剥落并进一步加速钢筋锈蚀;考虑钢筋非均匀锈蚀、锈蚀产物填充效应、钢筋及混凝土性能的钢筋混凝土锈胀开裂模型将更加精确。根据海洋不同腐蚀区带特点、钢筋混凝土性能及受荷情况,建立不同腐蚀区域中混凝土的氯离子传输模型,钢筋锈蚀速率模型和混凝土锈胀开裂模型有助于准确预测海洋环境下钢筋混凝土的服役寿命。 通过对混凝土中钢筋锈蚀的检测与监测有助于实时了解混凝土的服役状态。采用线性极化、电化学噪声和电化学阻抗谱等电化学方法可以较好地检测钢筋锈蚀状态、获得混凝土中钢筋的锈蚀速率。基于电化学原理开发的阳极梯和环形电极、基于钢筋锈胀应力测试的光纤监测技术以及基于数字图像技术获得混凝土中钢筋锈蚀应力应变场,有助于实现对混凝土中钢筋锈蚀的监测,并且部分已应用于海洋工程。相比于普通钢筋,锈蚀钢筋的导电率和导磁率均显著降低,采用电磁感应原理开发钢筋锈蚀装置实现了暴露在海水中的普通钢筋和耐蚀钢筋磁通量变化值与钢筋质量损失线性关系的建立。这也为更精确监测混凝土中钢筋锈蚀全过程、实现混凝土中钢筋锈蚀源定位及损伤程度识别提供可能。因此,综合利用氯离子、pH微电极等实现混凝土内部微环境监测,开发先进的钢筋锈蚀监测传感器实现混凝土中钢筋锈蚀源和锈蚀速率监测,通过图像监测技术实现钢筋锈蚀诱导混凝土开裂过程监测。综合上述措施将实现对钢筋混凝土结构腐蚀的全过程监测,并为海洋钢筋混凝土服役寿命预测模型的验证与修正提供依据,同时为海洋环境混凝土的耐久性评估系统提供预警机制。     

受荷混凝土中钢筋锈蚀速率计算方法

为研究荷载对钢筋锈蚀速率及结构耐久性的影响,在潮汐区与盐雾区开展不同荷载条件下氯离子扩散试验,荷载大小分别为无荷载、0.3倍和0.5倍混凝土抗折强度.在混凝土中掺入氯盐,开展不同浓度氯盐条件下的钢筋锈蚀试验.通过氯离子扩散试验得到荷载对氯离子扩散影响系数与荷载大小的关系,修正菲克第二定律中的氯离子扩散系数.钢筋锈蚀试验中测试不同时间下混凝土构件中钢筋的锈蚀电流密度,拟合出钢筋锈蚀电流密度与氯盐浓度和锈蚀时间之间的关系.结合混凝土中考虑荷载影响的氯离子扩散模型与钢筋锈蚀模型,给出荷载作用下混凝土中钢筋锈蚀速率的计算方法.该方法对于海洋环境中荷载作用下钢筋混凝土结构耐久性寿命计算具有重要意义.     

锈蚀-疲劳耦合作用下钢筋混凝土梁挠度计算方法研究

为探究锈蚀-疲劳耦合作用下钢筋混凝土梁的结构力学行为及刚度退化规律，设计了3组不同应力幅作用的钢筋混凝土梁锈蚀-疲劳耦合持荷试验，分析了各试验梁的疲劳寿命及刚度演化规律。结果表明，钢筋、混凝土疲劳和钢筋的锈蚀耦合作用下，钢筋混凝土构件的疲劳寿命显著降低，疲劳梁和锈蚀疲劳耦合梁的挠度发展曲线均呈现“突增-稳定-突增”的变化规律，且锈蚀疲劳耦合梁在第二阶段的挠度发展速率要远大于同应力幅下的疲劳加载梁。该方法在既有规范基础上分别改进了现有疲劳梁和锈蚀疲劳耦合作用下结构的挠度计算方法，可以有效考虑钢筋疲劳作用、外荷载应力幅、混凝土模量退化、钢筋锈蚀等因素的影响，其计算值与试验值吻合较好，验证了该文提出的刚度计算模型的有效性。     

往复荷载下锈蚀钢筋与混凝土粘结性能的试验研究

针对钢筋混凝土结构在服役过程中钢筋锈蚀以及承受往复荷载工况下引起的钢筋混凝土材料耐久性能劣化会对钢筋混凝土间的粘结性能产生影响，设计并制作了48根粘结区带裂缝的钢筋混凝土梁式试件，以研究在承受不同往复荷载工况(往复荷载幅度分别为极限荷载的0%、10%、20%及30%)、四种钢筋锈蚀率(0%、3%、5%及7%)以及往复荷载与钢筋锈蚀耦合工况下钢筋与混凝土粘结性能的变化情况。结果表明：钢筋锈蚀会影响试件破坏状态；施加往复荷载过程中残余滑移的增长主要发生在前六个循环，且残余滑移随着钢筋锈蚀率以及往复荷载幅度的增加而增大；耦合工况会进一步促进粘结性能的劣化，且粘结强度损失率随着钢筋锈蚀率和往复荷载幅度的增加而增大。该研究可为对应工况下钢筋混凝土构件的现状评估提供理论参考依据。     

弯曲荷载与氯盐侵蚀共同作用下的预应力混凝土梁耐久性能研究

当前在进行海工混凝土结构受氯盐侵蚀的耐久性研究时往往忽略了混凝土力学损伤的影响,这可能会导致高估结构的耐久性能。该文提出了在数值分析中引入损伤因子实现综合考虑结构损伤影响及氯盐侵蚀共同作用的分析方法,通过干湿循环的氯盐侵蚀试验与数值模拟分析,研究遭受氯盐腐蚀且受到长期荷载作用的预应力混凝土梁的耐久性能。结果表明,数值分析结果和试验结果吻合良好。参数分析结果表明:0.2mm宏观裂缝的出现对氯离子浓度有着较为显著的影响,未出现宏观裂缝时,拉应力对氯离子输运的影响较为有限;荷载比的大小影响结构的损伤范围和程度,进而影响氯离子在混凝土内的传输;梁构件施加预应力后,在15%和30%两种低荷载比状态下延缓其力学损伤（裂缝）的开展,减小荷载作用对氯离子扩散系数的增大效应,有效提高构件的抗氯盐侵蚀性能,当荷载比增加到45%以上,普通钢筋混凝土梁相对于预应力梁的氯离子浓度增比降至10%以内,这表明较高应力比下预应力对梁抗氯盐侵蚀能力的影响减弱。     

应力-化学介质-冻融循环协同作用下水泥基材料失效机理及寿命预测的研究

针对水泥基材料在应力-化学介质-冻融循环协同作用下的耐久性进行了研究,并开发了多种材料失效试验方法和装置。砂浆试件应力-化学腐蚀协同作用试验装置的特点是加载稳定,克服了应力松弛;协同作用耐久性试验装置可以用于监测协同作用下钢筋混凝土试件性能的衰减过程。研究发现:矿物掺合料改善抗渗性的能力依次是矿渣粉、活化煤矸石粉、粉煤灰;随应力比加大和冻融循环次数增加,水泥基材料中钢筋锈蚀加速、化学介质的渗透速度和深度增大,协同作用加速了水泥基材料的失效;可以用一元二次函数来近似预测氯盐-冻融循环-弯曲荷载协同耦合作用下的寿命。     

荷载与氯离子耦合作用下混凝土耐久性试验方法与装置的研究进展

20世纪20年代初,随着设计理论和施工技术的不断成熟,钢筋混凝土开始被大规模应用于基础建设中。钢筋混凝土兼具钢与混凝土的优点——坚固又耐用,但是人们却低估了环境因素对它的影响并为此付出了巨大的代价,氯离子、碳化、冻融、硫酸盐、化学侵蚀等环境因素均可导致钢筋混凝土的耐久性劣化。其中,氯离子引起的钢筋锈蚀问题最为突出,空气或水中的氯离子可穿透混凝土保护层到达钢筋表面,从而引起钢筋锈蚀。针对这一问题,学者们集中研究了氯离子如何穿透混凝土,并取得了相当丰硕的成果。然而,服役中的钢筋混凝土需时刻承受荷载的作用,复杂的应力状态会引起混凝土材料内部细观结构的变化,从而影响甚至改变氯离子的扩散行为。上述研究忽略了荷载因素,难以应用于实际工程。此外,氯离子扩散行为还与应力在材料内累积的损伤有关。因此,近年来,荷载与氯离子侵蚀耦合的耐久性研究越来越受到重视,且已成为重大工程项目中不可缺少的一部分。针对实际工程中钢筋混凝土的荷载形式,研究人员开发了大量耦合试验方法与装置,较为成熟的有单轴拉伸、单轴压缩、静力弯曲分别与氯离子耦合。但研究人员在运用上述方法时所采用的实验制度不同,导致其结果没有可比性。此外,还有部分研究人员探索了更为复杂的耦合因素(劈裂拉伸、偏心压缩、疲劳弯曲、静力剪切分别与氯离子耦合),复杂耦合因素更符合实际工程状态,也是近年来研究的趋势,但关于它的研究仍处在起步阶段。本文归纳了拉伸、压缩、弯曲、剪切荷载作用下混凝土的抗氯离子侵蚀耐久性试验方法,对存在的问题进行了讨论,并提出了改进建议和进一步的研究方向,以期为制定统一、标准化的耦合耐久性试验方法与装置提供参考。     

钢筋混凝土梁受弯破坏及尺寸效应的细观模拟分析

钢筋混凝土构件破坏的尺寸效应取决于混凝土材料的非均质性以及钢筋/混凝土相互作用。该文借助混凝土细观结构特征,基于非线性弹簧单元来描述钢筋与混凝土之间的相互作用,建立了钢筋混凝土梁破坏行为模拟的三维细观数值模型。在模拟结果与试验结果吻合良好的基础上,拓展模拟了更大尺寸梁的弯曲大变形破坏行为,并分析了单调及循环加载模式对不同尺寸悬臂梁受弯破坏及名义抗弯强度影响规律。模拟结果分析表明:1)该文工况下钢筋混凝土悬臂梁的弯曲破坏存在尺寸效应,弯曲强度随梁深增大而减小; 2)循环加载下,混凝土、钢筋以及两者间的粘结性能由于低周疲劳而使得梁的弯曲破坏呈现出脆性特征; 3)相比于单调加载,循环加载条件下,悬臂梁的破坏具有更强的脆性,名义抗弯强度尺寸效应更明显。     

锈蚀钢筋混凝土梁动态抗弯性能细观数值研究EI北大核心CSCD

为研究锈蚀对钢筋混凝土(reinforced concrete,RC)梁动态力学性能的影响,考虑钢筋锈蚀和应变率效应及混凝土内部结构的非均质性,建立锈蚀钢筋混凝土梁两阶段三维细观尺度数值模型。钢筋的非均匀锈蚀膨胀以施加非均匀径向位移的方式模拟,并以保护层开裂“最终状态”作为之后混凝土梁动载模拟的“初始输入条件”,获得锈蚀后的动态力学行为。在验证了数值模型合理性的基础上,分析了钢筋锈蚀引起的保护层锈胀开裂行为及不同应变率下构件力学性能的变化。结果表明:钢筋锈蚀使混凝土梁产生了明显的纵向裂缝,梁的承载力随钢筋锈蚀率增加而降低;高应变率下,混凝土梁发生冲切破坏,梁的承载力显著提高;锈蚀混凝土梁承载力损失与锈蚀后梁频率降低系数(反映刚度损失)近似呈线性规律,且低应变率下的承载力对频率变化更加敏感。最后,基于模拟结果回归分析,发展建立了考虑锈蚀及应变率耦合影响的混凝土梁动态抗弯承载力预测公式。     

盐冻作用下混凝土受弯构件承载力的计算

为了探究混凝土构件在除冰盐作用下承载能力的衰减规律,采用快冻法进行了混凝土构件在浓度(质量分数)为3.5%的NaCl溶液中的盐冻循环试验后,对构件进行静力加载试验。结果表明,盐冻损伤后,荷载—挠度曲线的初裂点不明显,随着相对动弹性模量的下降,混凝土构件弯曲刚度和承载能力的极限值也随之下降,跨中挠度增大。因此,在盐冻作用下,混凝土构件的承载力极限值及荷载挠度的变化与动弹性模量的变化是相关联的,相对动弹性模量值可以作为混凝土构件耐久性设计时间限值参数。基于合理的假定,参照现行《混凝土结构设计规范》(GB 50010-2010)中受弯构件承载力的计算方法,引进盐冻作用下以相对动弹性模量为设计参数的钢筋混凝土结构耐久性设计公式,计算值与试验值吻合较好,可供实际工程耐久性设计时参考。     

钢筋及其锈蚀对混凝土构件阻尼的影响

钢筋及其锈蚀将显著影响混凝土构件的动力特征参数。以纵筋配筋率、纵筋表面形式、箍筋间距、钢筋锈蚀率为主要参数,采用简支梁三点弯曲动态阻尼测试,研究各因素对弯曲小变形混凝土梁弹性阶段损耗因子与耗散模量的影响,探讨其作用机理,并对比分析构件刚度退化、阻尼演变随钢筋锈蚀率的变化规律。结果表明:损耗因子与耗散模量随配筋率增加先增加后减小,在配筋率为1%时达到峰值;损耗因子与耗散模量随钢筋锈蚀率增加先减小后增大,在锈蚀率为0.4%时达到最小值;损耗因子与耗散模量随箍筋间距的增大而减小;损耗因子与耗散模量按纵筋表面形式从大到小依次为月牙肋、光圆、方钢。随钢筋锈蚀率增加,阻尼比增长比刚度退化更显著,用阻尼参数探测钢筋混凝土构件的锈蚀损伤具有可行性。     

Lokale Last- und Eigenspannungsverteilungen an rißbehafteten Oberflächen nach Korrosionsermüdung von vergütetem Ck 45

Distributions of Loading and Residual Stresses in Cracked Surfaces of Corrosion Fatigued Quenched and Tempered Steel Ck 45 Corrosion fatigue in the active state leads to a great number of short cracks and corrosion pits in the surface of metallic materials. This paper deals with the resulting distributions of loading and residual stresses in the case of bending fatigue. The material investigated was the quenched and tempered CBN-ground steel Ck 45. Results presented clearly indicate that stress distributions around cracks and corrosion pits are very inhomogeneous. Corrosion pits lead to a relaxation of manufacturing induced residual stresses. In the loaded state as a consequence of notch effects, maximum stresses are observed, which explains the importance of corrosion pits as crack initiation sites.     

Deterioration of fracture toughness of concrete under acid rain environment

Deterioration of fracture toughness of concrete caused by acid rain attack was investigated through laboratory-accelerated corrosion tests. Fracture toughness of the corroded concrete with different corrosion period was obtained by three point bending tests, and meanwhile the P-COMD curves and elastic modulus E of the corroded specimens with different corrosion degrees were also obtained. The experimental results showed that the deterioration of concrete surface is large and the corrosion depth increases with corrosion duration. The observation by scanning electron microscopy showed that the microstructures of crack tip are porous and loose due to acid corrosion, and many crisscross cracks appear at corrosion layer. Based on the experimental results, equivalent crack length in the fracture process zone and the effective fracture toughness K_IC were also obtained by theoretical analysis. Under the impact of acid corrosion, the concrete material physical and chemical properties changed significantly, which made the corresponding resistance stresses to crack propagation decrease. The curves of fracture toughness versus corrosion depth were obtained in this study.     

应力状态下离心成型钢纤维混凝土耐硫酸腐蚀研究

对1组未受侵蚀和4组不同初始拉应力状态下经受侵蚀后的离心成型钢纤维混凝土环形截面试件进行了侧压力学试验,对经受侵蚀后的试件进行了化学分析研究.结果表明硫酸的腐蚀降低了构件的极限荷载和极限变形,降低了钢纤维混凝土的弹性模量,初始拉应力的增加使腐蚀破坏进一步加剧,受拉区的硫酸根含量和中性化深度随之增加.根据试验结果分析,推导了应力状态下离心成型钢纤维混凝土中性化深度与硫酸根含量的数学预测模型.     

Effects of mechanical properties of concrete constituents including active mineral admixtures on fatigue behaviours of high performance concrete

In order to explore the links between the macroscopic and microstructural characteristics of concrete with admixtures of active mineral additions, four series of concrete prisms, of mortar matrix prisms and mortar-aggregate Interfacial Transition Zone (ITZ) are prepared and tested under monotonic and cyclic loads. Five static mechanical parameters (compressive and bending strength, fracture energy, elastic modulus, Poisson ratio) and bending fatigue performance (fatigue life, critical maximum displacement and strain, fatigue damage) of such materials are experimentally evaluated. The results show that degradation laws of concrete properties under both monotonic and cyclic loads vary with the different cohesive strength ratio and elastic modulus ratio of ITZ and mortar matrix. The single or double additions of ground slag and fly ash with optimized mass fractions remarkably enhance the static and bending fatigue properties as well as change the failure mechanisms of concrete.     

A finite macro-element for corroded reinforced concrete

This paper proposes a model of the mechanical behaviour of corroded reinforced concrete members subjected to bending under service load. The model is based on the formulation of a macro-element to be used in FEM analysis, having a length equal to the distance between two consecutive flexural cracks and a cross-section equal to the member cross-section. The mechanical formulation is directly written in generalized variables (bending moment and curvature) and is based on the concept of the transfer length necessary for the transmission of tensile load from re-bar to tensile concrete thanks to the bond. It is thus possible to take into account the effect of reinforcement corrosion on the bond between re-bar and concrete, by increasing the transfer length versus intensity of corrosion. The variation of the transfer length versus corrosion is expressed using a scalar damage parameter. A first experimental validation is performed on a 17-year-old beam kept in a chloride environment under its service load.     

非均质混凝土材料破坏的三维细观数值模拟

在随机骨料模型的基础上,采用特征单元尺度对网格进行剖分,建立了非均质混凝土材料损伤破坏及宏观力学特性研究的三维细观单元等效化模型。对单轴拉伸、单轴压缩条件下湿筛混凝土试件的破坏过程及宏观力学性能进行了模拟分析;研究了混凝土梁的三分点弯拉力学特性,并与平面模型结果作了对比。研究表明:1) 与平面计算模型相比,三维模型更真实地模拟混凝土材料在外荷载作用下的损伤破坏过程,更准确的描述非均质混凝土材料的宏观力学性能,且与实验结果吻合;2) 骨料空间分布形式基本不影响混凝土材料的宏观弹性模量及强度,但影响其破坏过程和破损路径;3) 与随机骨料模型等细观力学方法相比,该方法具有高效性。     

WS2软涂层刀具的材料优选及涂层制备

运用有限元软件分析了不同基体材料和过渡层的基体表面WS2软涂层的残余热应力。结果表明弹性模量和热膨胀系数等参数是影响涂层残余热应力大小的主要因素。采用中频磁控溅射、多弧离子镀外加离子束辅助沉积工艺制备了4种WS2软涂层刀具并对其性能进行了测试,分析结果符合有限元计算的结论,发现残余热应力对WS2软涂层刀具的性能产生很大的影响,并发现Zr过渡层能有效促进WS2Ⅱ型织构的生长。     

Effects of reinforcement configuration and sustained load on the behaviour of reinforced concrete beams affected by reinforcing steel corrosion

Corrosion of reinforcing steel bars in concrete is one of the main causes of early deterioration and reduction of service life of reinforced concrete (RC) structures. This paper reports on the results of an experimental programme that was carried out to study the effect of reinforcement corrosion on the serviceability behaviour of RC beams under load. The main parameters investigated were the effects of reinforcement arrangement and the magnitude of the sustained load. Four series of scaled beams were tested, each series containing six beams, three of which were subjected to reinforcement corrosion while the other three were used as un-corroded control beams. All these beams carried the same sustained load during the process of reinforcement corrosion. The reinforcement arrangement for the fourth test series was identical to the first series but these beams carried a higher sustained test load. All the beams were subjected to a four-point bending load arrangement. Corrosion of the tension reinforcement was accelerated using an impressed current while the soffits of the beams were immersed in a 3% sodium chloride solution. The evolution of reinforcement corrosion and central deflection under simultaneous load and corrosion is given. The deflections of the beams increase with progressive corrosion of the reinforcement especially during the early stages of corrosion as a result of propagation of transverse cracks and the expansive stresses induced by the corrosion products. The importance of the arrangement of the steel in the section of concrete on the performance in terms of deflection was also clarified.     

Role of anisotropic behaviour of Sn on thermomechanical fatigue and fracture of Sn-based solder joints under thermal excursions

Solder joints experience thermomechanical fatigue (TMF) as a consequence of thermal stresses that arise from coefficient of thermal expansion (CTE) mismatches between various entities present in the joint under thermal excursions. Sn present in solder joints made with alloys containing significant amounts of Sn, exists in a body centred tetragonal (BCT) structure, under normally realized thermal excursion regimes encountered during service. BCT Sn exhibits significant anisotropic behaviour in its physical and mechanical properties as a consequence of its highly unusual c/a ratio of about 0.5. Such severe anisotropy causes significant stresses at the Sn grain boundaries present within the solder joints during thermal excursions, resulting in damage accumulation within the solder. Stresses resulting from this anisotropy can be much larger than those that can arise from CTE mismatches between entities such as solder/substrate, solder/intermetallics etc. Damage accumulation under TMF progresses in the severely constrained region of the solder/substrate interface, and causes the initiation and propagation of the catastrophic crack. This crack propagates within the solder in a region very close to the solder/substrate interface and results in the TMF failure of the joint.