半电池腐蚀映射for Concrete

Half Cell corrosion mapping是评估混凝土结构中腐蚀活动严重程度的有效方法。它是最着名的方法，以确定活性腐蚀的可能性;但是，该测试不提供有关腐蚀活动动力学的任何信息。该测试的简单和经济效益的程序使其在工程师和结构检查员之间流行。该方法已用于桥式甲板检测，停车车库，钢筋混凝土梁，梁和墩的腐蚀监测。

什么是半细胞腐蚀映射

Half Cell corrosion mappingconsists of measuring the potential difference between a standard reference electrode, normally a copper/ copper sulfate (standard portable half-cell) placed on the surface of the concrete with the steel reinforcement underneath.半电池腐蚀映射为腐蚀评估提供了一种快速，经济效益和无损性的方式。该测试提供有关腐蚀可能性的有价值的信息，并有助于具体保障和康复的质量保证。几个标准关联已标准化了包括该的测试程序ASTM C 876,UNI 10174.andRilem TC 154.。根据测量的半电池腐蚀电位值，确定有源腐蚀的概率。

Half-Cell Potential Measurement (mV, CSE)	Likelihood of active corrosion (%)
> - 200	<10
-200到-350	uncertain
< -350	> 90
CSE：硫酸铜参比电极

When the half cell potential measurement is more negative than -350 mV (CSE electrode), then the chance of having active corrosion is more than 90%. When the measured value is more positive than -200 mV, the chance of active corrosion is less than 10%. For potential values between -200 mV and -350 mV, there is uncertainty in interpreting the test results.

如何执行半细胞腐蚀映射

在理想laboratory condition, performing half cell corrosion measurement is straight forward; however, performing the test in the field can become challenging. The following steps will help you perform an effective and reliable measurement in the field:

1-测量点

The first things first is to know the test locations. In general, a schematic grid will help you with smoothly taking the measurements, and managing test results. There is no general rule about the grid spacing. A finer mesh will be more precise, but also more expensive. Wide spacing can reduce the resolution of test results, and may result in inaccurate half cell potential measurements. A suitable spacing should be selected with regards to the area under investigation.

2- Rebar Connection / Connectivity Test

每个测试点处的半电池电位被测量到相同的参考点。在此参考位置需要与钢筋网络的电气连接。通常，应在本地拆下混凝土盖（这可以通过钻入混凝土），以建立与钢筋的声音电连接。为此，需要先找到钢筋（这可以通过使用钢筋定位器来完成）。钢筋网络通常提供连接的网格。然而，在较大的区域（例如甲板板）中，需要检查钢钢筋网络是否已连接。

3- Electrical Connection to Voltmeter

来自负端子的连接引线电缆应连接到参考电极，而其他引线应在参考位置连接到钢筋网络。电压表应该能够测量直流（DC）电压，并具有电池的电量。电压表应具有10至200mΩ的可变输入阻抗，可用于确定获得精度读数所需的输入阻抗。

4-预润湿表面

If the surface of concrete is too dry, the pre-wetting is required. Pre-wetting can either be achieved by spraying the water over the location to be tested, or through using a wet sponge.ASTM C 876describes how suitable pre-wetting condition can be achieved.

5- Perform Measurements

At each location, the value of half cell potential should be recorded to the nearest 0.01 V (ASTM C 876）。对于每个点，记录测试点的坐标，以及腐蚀潜在值。如果包括温度发生变化的天气状况，则应调整半电池测量值以进行温度变化。

How to Present Half Cell Potential Measurements

Half Cell potential maps are widely used to present the test results. The contour maps can show the gradient of the half cell potential values, can easily be interpreted. An example of this contour maps is illustrated in the figure below. Alternatively, results can be presented using cumulative frequency distribution.

半电池电位测量 - 影响参数

When it comes to half-cell potential values, one should take into account the effect of environmental conditions (such as moisture and humidity), as well as the properties of concrete materials (dense concrete versus porous concrete, carbonated concrete). According toping gu和J.J.Beaudoin（1998）以下参数可以影响腐蚀电位测量：

+混凝土电阻率
+混凝土密度
+ Cover thickness
+环氧涂料
+沥青覆盖的存在
+氧气可用性

关于半电池潜在测试的备注

+ Obtaining effective and reliable half cell potential measurement is difficult when the electrical resistivity of concrete cover is high. Wetting concrete surface can help reduce the impact of electrical resistivity on half cell measurements. Dense cover, as well as thick concrete cover may reduce the amount of oxygen, and results in more negative half cell potential values, without necessarily having active corrosion.

+在完全饱和混凝土中钢加强件表面的氧浓度降低将导致更负腐蚀潜在读数。

+另一个挑战是当混凝土表面覆盖有涂层或沥青时。在沥青覆盖中不可能进行有效测量。在这种情况下，一般的做法是钻入沥青层，以进入混凝土的表面。导电溶液可用于在电极和混凝土表面之间进行电连接。

+在进行半电池潜在测试时，应该记住，表面应没有涂料和化学环氧涂料。此外，对不锈钢加固和环氧涂层钢筋的测试将增加误差误差的可能性。