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  半电池电位与腐蚀速率测量方法的比较-现场评估钢筋腐蚀状况的经验
 
发 布 者:dt1718  添 加 时 间:2012/10/19  点 击 数:3012 

 
COMPARISON OF HALF-CELL POTENTIALS AND  CORROSION RATE MEASUREMENTS – A FIELD  EXPERIENCE WITH EVALUATION OF REINFORCEMENT  CORROSION 
半电池电位与腐蚀速率测量方法的比较-现场评估钢筋腐蚀状况的经验  
Thomas Frølund, COWI A/S, Parallelvej 2, DK-2800 Lyngby, TDF@cowi.dk  
Oskar Klinghoffer, FORCE Technology, Park Allé 345, DK-2605 Broendby,  
osk@force.dk
KEYWORDS: Half cell potential (HCP), Corrosion rate (Icorr), Galvanostatic Pulse Measurements (GPM), concrete structures 
关键词:半电池电位(HCP),腐蚀速率(Icorr),Galvanostatic脉冲测量(GPM),混凝土结构
1. BACKGROUND 
 
1、背景
Since 1978 Half Cell Potential (HCP) mapping [1] has been used for detecting corroding areas on concrete structures in Denmark. In the beginning (after balcony gangway has totally collapsed) this method was mainly used on carbonated structures and balconies exposed to de-icing salts. Later the method was used for all kind of structures and the experiences were discussed in Newsletters published by the Danish Corrosion Centre [2]. It was early recognised that the interpretation of the HCP results were difficult or misleading in wet and semi-wet structures where lack of oxygen as well as corrosion would lead to potential gradients.  
早在1978年,丹麦就开始使用半电池电位图法来确定混凝土结构的被侵蚀范围。一开始,这种方法主要用于碳化混凝土结构和容易受到除冰盐侵蚀的阳台检测使用,后来,这种方法推广用于所有的结构,而且使用经验在丹麦腐蚀中心的刊物上做了讨论。对于缺少氧气而且潮湿或者半潮湿的混凝土结构,腐蚀会导致产生电势差,半电池电位结构的解释很难,半电池电位的结果很难解释或者很容易引起误解。
A typical potential map of a highway bridge pillar is shown in fig.1. The pillar is exposed to de-icing salts splashed from the passing cars up to a level of 2 meters, but also has a high humidity at the ground level caused by capillary suction. The water filled pore system in the concrete makes the potential drop because the oxygen necessary to maintain the passive film will not be able to diffuse into the concrete fast enough.    
图1显示了一个高速公路桥梁柱子的典型电位图,2米高的柱子暴露于容易受到过往车辆飞溅冰盐的环境,而且由于虹吸作用,地表处的湿度很大,混凝土孔隙充满了水,使得保养必须的钝化薄膜不能够很快的弥散充满到混凝土结构里,导致混凝土结构的电势下降了。
 
Fig.1. Typical potential map of a high way concrete pillar exposed to de-icing  
salts  
The ongoing corrosion process is described by the chemical reaction: 
2Fe+O2+2H2O↔2Fe+++4OH-
The Fe++ forms at the high pH in concrete a complex protective film with oxygen. This film can be broken down by the chloride ions from de-icing salts or by neutralising of the high pH e.g. by carbonation.  
The interpretation problem is that the potential will drop either because the loss of passive film due to lack of oxygen (the corrosion process will not be able to proceed without oxygen) or because chlorides break down the passive film and start corrosion. 
正在进行的腐蚀进程可以用下面的化学反应公式来表述:
2Fe+O2+2H2O↔2Fe+++4OH-
高PH值的铁质氧化后行成复合钝化膜,这钝化膜会由于除冰盐的氯离子或者碳酸根离子中和作用而被破坏掉。
很难解释的是由于缺少氧气导致的钝化膜损坏同样会使得电势降低,而氯离子同样会破坏掉钝化膜导致钢筋开始腐蚀。
 
In 1994 it was decided to develop an equipment for concrete structures based on well know techniques for determination of corrosion rates to be able to distinguish between active corrosion and the lack of oxygen situation. 
1994年,决定开发一种成熟先进的设备用于确定混凝土结构的腐蚀速率,而且能够区分开是活跃的腐蚀状态还是缺少氧气的情况。
The results presented in this paper are all based on Galvanostatic Pulse Measurements (GPM). This polarisation technique makes it possible within a short time (typically 10 seconds) to calculate the corrosion rate [3,4]. The equipment gives both the corrosion rate and the half-cell potential as well as the resistance between the hand-held electrode placed on the examined concrete surface and the reinforcement. Four different examples from on-site investigations are described below, one where there is a good correlation between the HCP method and the GPM method and 3 where the HCP measurements are misleading. 
这篇论文所呈现的结果都是用Galvanostatic脉冲法测量得到的。极化技术使得能够在10秒的短时间内计算腐蚀速率。这仪器除了可以测试腐蚀速率外,还能测试半电池电位,还有放置于所测混凝土表面电极与钢筋间的电阻率。4个不同的现场测试案例将会在下文进行阐述,其中一个案例半电池电位(HCP)结果与脉冲电流测试(GMP)结果具有很有的相关性,其他三个案例半电池电位测量结果则容易让人误解。
 
2. EXAMPLES OF ON-SITE INVESTIGATIONS 
2、现场测试案例
2.1 Example no. 1   
2.1 案例一
Two parallel bridges were built in 1965-67 in the Copenhagen area, where the highway crosses over a railway line, a parking lot and two minor roads. The eastern bridge was rehabilitated extensively at a very high price in 1978, after which the western bridge have only received much less rehabilitation, but substantial inspection, test- loadings, probabilistic assessment etc., which essentially have kept the bridge in function at a much less cost that the eastern part. 
1965-1967年,哥本哈根区建造了两座平行的桥,公路线跨越了铁路线,有一个停车场和两条支线公路。1978年,东面的桥梁进行了费用昂贵的大修,而西面的桥梁经过检查测试评估后还比较牢固,所以只采用了费用较低的小幅简单修复。
Initial inspections, core investigations and chloride profiling in 1999 (fig. 2) pointed out column No.S303 to be suitable for corrosion rate measurements. 
1999年,进行了取芯和氯离子含量测试(图2),说明了No.S303圆柱体适合进行腐蚀速率测试。
 
Fig 2. Chloride profiles at level 0.3m and level 1 m 
图2.在0.3米和1米处的氯离子含量情况
Electrical continuity in the reinforcement was checked and a permanent connection was welded to the reinforcement. The vertical reinforcement (Ø35 mm) is typically in 60 mm depth and the horizontal (Ø14 mm) in 40 mm depth. Already in 1999 the chloride content in level 0.3 m is so high that active corrosion can be expected. In September 2000 and in April 
2001 corrosion rates were determined together with the half- cell potentials and resistance measurements [5] (fig 3). 
设备其中一端固定连接在钢筋上,并施加连续的脉冲电流。垂直的钢筋(Ø35 mm)在60mm深处,水平钢筋(Ø14mm)在40mm深处。在1999年,0.3米深处的氯离子含量已经非常高了,应该会存在积极的腐蚀情况。2000年的9月份和2001年的4月份,利用半电池电位和电阻率测试方法确定了腐蚀速率。(图3)
 
In this case there is a rather good correlation between resistance, half-cell potential and corrosion rate mapping. 
在这个案例里,腐蚀速率图、电阻率、半电池电位存在着很好的相关关系。
To verify the corrosion state a break-up was made at the position 90 degrees south near ground level, see fig. 4. 
为了验证腐蚀情况,在南面90度的方向,打开了靠近地面位置的结构。
 
Fig. 4 Corroding reinforcement.  Cross section loss: 1-2 mm 
图4.被腐蚀的钢筋,截面损失约为1-2mm
As the constructions have been examined close during the last 20 years it is possible to make a good estimate of the initiation of corrosion. Calculation of the average corrosion rate from the cross section loss of app. 2 mm and assuming the corrosion was initiated after app. 10 years gives an average corrosion rate of 9µA/cm22, which is with in the range of corrosion rates determined at this position by the GPM. The very low half-cell potentials agree with the high corrosion activity. 
在过去的20年时间里,由于建筑物进行了非常精密的检查测试,因此有可能对刚开始的腐蚀进行比较好的评估。计算得出的截面平均腐蚀速率接近2mm,假定差不多10年后平均腐蚀速率达到9µA/cm2,此时将开始腐蚀。该区域的腐蚀速率范围是由GPM方式测试得出的。非常低的半电池电位适合于高活跃的腐蚀状态测试。
2.2 Example 2 
2.2 案例2
The next two examples are from a bridge foundation and a bridge deck in Greenland. The foundation was investigated in the tidal zone as shown in fig. 5 [6]. 
接下来的两个案例是在格陵兰岛的一座桥的桥墩和桥面板。调研的桥墩处于潮间带,见图5.
 
Fig. 5. The investigated area and the location of the chloride profile. 
  图5. 调研区域与氯化物剖面位置
The chloride concentration in the depth of the reinforcement is in the range between 0,3% and 0,7% of the concrete weight. As indicated by the half-cell potential measurements corrosion should therefore be expected. However the measured corrosion rates are low and the verification by visual inspection (fig. 7) shows no damage to the reinforcement. 
钢筋处的混凝土氯含量大概是0.3%~0.7%之间。根据半电池电位测量,应该存在腐蚀情况,但是,测量得出的腐蚀速率非常地,而且通过直观观察钢筋,没有发生锈蚀或者破损。
 
Fig. 6 HCP and Icorr of bridge foundation  桥墩的半电池电位与腐蚀电流
Fig. 7 Photo of break-up  
图7 打开结构后的图片
2.3 Example 3
2.3 案例3  
The bridge deck from the same bridge in Greenland showed very different results as shown on fig. 8 and fig. 9. 
图8与图9显示了格陵兰岛同一座桥的桥面板完全不同的结果。
 
 
Fig.8. The investigated area and the location of the chloride profile. 
The typical dept of the reinforcement is here minimum 40-50 mm and the chloride concentration in this depth is near 0, 3% of the concrete weight. At this high chloride concentrations the half-cell potentials are expected to be low but the most negative values measured are all above -100 mV vs. Ag/AgCl (fig. 9). 
当钢筋处于保护层内至少40-50mm深处,而且氯离子含量接近0.3%时,半电池电位应该是比较低的,但是用Ag/AgCl参比电极测出来的电位值都在-100 mV以上(图9)。
 
Fig.9. The read circle indicates the location of the chloride profile and the break-up shown at fig. 11. 
  图9.圆形显示了氯化物轮廓面    图11是打开结构的图像
The corrosion rate map fig.10 shows a completely different picture and indicates active corrosion at several locations. 
图10的腐蚀速率图显示了完全不同的图片和指明了几处腐蚀活跃的区域。
Fig. 10. Corrosion rate of the bridge deck. The read circle indicates the location of the   
chloride profile and the break-up shown at fig. 11
图10 桥面板的腐蚀速率,圆形指出了氯化物轮廓面 图11则是打开结构后的图片
Fig.11. The first picture shows the corroded reinforcement and some water from cooling 
the diamond-cutting blade. The second picture shows the damage and the mortar repairs. 
图11.第一张照片显示了锈蚀的钢筋和一些冷却金刚石切割锯片的水。第二章照片显示了桥面板的破坏情况和砂浆修补情况。
 
General comments to examples 2 and 3 
案例2与案例3的概要注解
This bridge is located in a very cold environment. During the measurements described above the temperature was 15 °C at midday and this explains the rather high corrosion rates at the bridge deck. Further there were some damages to the concrete surface due to the traffic directly on the concrete surface and a lot of mortar repairs. 
这座桥处于非常寒冷的环境里,测量过程中,正午的温度是15 °C。在桥面板上会有更高的腐蚀速率,由于交通荷载直接作用在混凝土表面上,所以混凝土表面受到有更多的损害和存在很多的砂浆修补处。
2.4 Example 4 
2.4 案例4
In this example of swimming pool wall the conditions for performing corrosion rate measurements were not ideal. Tiles covered the inside of the swimming pool but preliminary performed GalvaPulse measurements showed that the joint filler was porous. Due to this fact it was possible to conduct the corrosion rate measurements by means of GalvaPulse equipment. The outside reinforcement was corroding at the casting joint between the pool floor and the pool walls and it was found necessary to investigate the inside reinforcement although no rust stains were visible. 
案例里的游泳池池壁的腐蚀速率测试环境不理想。游泳池内壁都采用瓷砖覆盖,但是最初使用GalvaPulse的测试结果显示接缝料多孔渗水。基于这样的事实,使用GalvaPulse测试腐蚀速率是可行的。游泳池池底与池壁接缝处的外部钢筋已经被腐蚀了,即使看不见锈斑,内部钢筋也很有必要进行量测。
The results were projected to a plane plot where the cast joint is in the centre of the plot fig. 12. 
测试结果反映在一张平面图上,图12的中央是结合处位置。
 
图12 沿着池底经过结合处再到池壁的腐蚀速率图
Even at these un-ideal measuring conditions the GalvaPulse pointed out the reinforcement corrosion points which was confirmed by visual inspections in breakups fig. 13. 
即使在不理想的测试环境里,GalvaPulse也能准确指出钢筋腐蚀地点,图13的实际照片证明了这点。
 
3. CONCLUSIONS: 
3、结论:
 
1.  Two techniques for evaluation of reinforcement corrosion, half-cell potential (HCP) and galvanostatic pulse measurements (GPM) are presented and discussed. 
1、目前有两种评价钢筋腐蚀的技术,半电池电位(HCP)和Galvanostatic脉冲电流测试(GPM)。
2.  The evaluation of corrosion by means of the traditional half-cell potential technique using the existing standards may lead to mistakes in cases where the concrete is water saturated, carbonated and also exposed to the very low temperature. 
2、在低温、碳酸化作用和饱水环境下的混凝土结构,如果只用目前标准的半电池电位方法进行腐蚀评估的话,容易导致错误的结果。
3.  Complimentary measurements by means of galvanostatic pulse technique determining the corrosion rate contribute to the unambiguous evaluation of reinforcement corrosion also under conditions where the results obtained by the HCP technique could be misleading. 
用Galvanostatic脉冲电流测试(GPM)测试腐蚀速率是一种令人赞赏的测试方法,即使在用HCP半电池电位方法容易获得不准确结果的情况下,也能很明确的评估钢筋的腐蚀情况。
4.  Four examples from on-site measurements are presented. Three of them show the need of using corrosion rate measurements together with half-cell potential for reliable evaluation of the actual corrosion state. 
文中介绍的四种现场测试的案例,其中三个案例说明了要正确评估腐蚀状况,除了使用HCP半电池电位法外,同时进行腐蚀速率测试是非常必要的。
5.  Passive areas are defined by galvanostatic pulse measurements as areas where the potential curve on the instruments computer screen has not reached a steady-state after pulsing over 5-10 seconds. In areas with active corrosion, areas where the potential curve exhibit a steady-state potential after 5-10 seconds, the corrosion current is measured as accurate as it can be expected from an on-site measurement taking into account the variation of the area of the reinforcement polarized over, the actual corroding area of the reinforcement and the inherent variations in moisture condition of the concrete and the temperature.
使用GPM方法对一个区域脉冲时间超过5-10秒后,仪器电脑屏幕上显示的电压曲线到达不了一个稳定不变的水平时,说明了该区域是腐蚀不活跃区域。在腐蚀活跃区域,施加脉冲时间5-10秒后,电压曲线将会达到稳定,此时测量的腐蚀电流会被精确测量。现场测量时应该重视钢筋极化区域的变化,实际的钢筋腐蚀区域和潮湿混凝土环境下固有的温度变化。
6.  It is not possible to estimate the actual loss of cross sectional area of the reinforcement from a single GPM measurement. If multiple GPM measurements are taken over a period of time, an average value can be estimated. Alternatively the reinforcement must be exposed in the most corrosion active areas as done in these 4 examples. 
在钢筋交叉组合区域仅仅使用一次GMP测量来评估实际损失是不可能和不足够的。如果在一段时间内进行多次GPM测量,利用平均值就可以进行评估了。测量过程中,就像在4个案例中,钢筋必须暴露于腐蚀活跃区域。
 
4.  REFERENCES:  
[1] American Society of Testing and Materials: “Standard Test Method for Half-Cell Potentials of uncoated Reinforcing Steel in Concrete” ASTM C876, 1987. 
[2] H. Arup: "Potential Mapping of Reinforced Concrete Structures", The Danish Corrosion Centre Report, January 1984 
[3] B. Elsener, O. Klinghoffer, T. Frølund, E. Rislund, Y. Schiegg and H. Böhni: "Assessment of Reinforcement Corrosion by Galvanostatic Pulse Technique, Proc. Int. Conf. on Repair of Concrete Strictures, Svolvaer, Norway, pp 391 - 400,1997.  
[4] J. Mietz and B. Isecke: "Electrochemical Potential Monitoring on Reinforced Concrete Structures using Anodic Pulse Technique", in "Non destructive Testing in Civil Engineering" ed. Bungey, H., The British Institute of NDT, 2, 567,1993. 
[5] T. Frølund.  F.M. Jensen and R. Bässler: "Determination of corrosion rate by means of the galvanostatic pulse technique”, First International Conference on Bridge Maintenance, Safety and Management, IABMAS 2002, Barcelona 2002.  
[6] H. E. Sørensen and T. Frølund: "Monitoring of Reinforcement Corrosion in Marine Concrete Structures by the Galvanostatic Pulse Method", Proceedings of International Conference on Concrete in Marine Environments, Hanoi-Vietnam, October 2002.

 
 
 
 

 
   
 
   
   
 
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