Determining the electrical resistivity of concrete offers valuable insights into its long-term durability. Concrete resistivity is directly related to its ability to resist the penetration of harmful water-borne chlorides.
水在溶液中含有各种盐，很容易渗透透水混凝土. 氯离子迁移到孔隙系统中, decreasing freeze-thaw resistance and kicking off the cycle of corrosion in the reinforcing steel. Permeability (resistance to fluid penetration) and chloride diffusion rates are critical measurements that predict performance and identify durable concrete.
The electrical resistivity measurement of saturated concrete has a very good correlation to permeability and chloride diffusion values. The ASTM C1202/AASHTO T 277 rapid chloride permeability (RCP) method can measure these values effectively, 但这只是一个严格的实验室测试. RCP样品的固化时间从几天到几周不等, 而且需要进行大量的准备工作，才能将标本准备好进行测试. The ASTM C1556 test for chloride diffusion coefficient also has complex sample preparation and test procedures.
Bulk resistivity and surface resistivity tests are two recognized and increasingly popular methods to estimate permeability and establish durability predictions.
Bulk resistivity is performed by placing a metal electrode plate with conductive foam inserts at each end of a 4in (102mm) diameter test cylinder or core and measuring potential values between opposite ends. 与RCP方法相比，该测试快速且直接. However, the test still requires some sample preparation and is limited to cylindrical samples in the lab.
Surface resistivity tests employ the proven four-probe Wenner electrode array to measure electrical resistance. This practice was first used for geological applications in the early part of the 20th century and is now a reliable alternative to the RCP method for measuring concrete electrical resistivity. 的AASHTO T 358 test method, published in 2011, describes the procedure, and an ASTM test method is pending. 温纳阵列由四个等间距的电极组成. The external electrodes apply low-frequency alternating current on the moist concrete surface, 而内部的探头测量电阻. Qualitative terms express the electrical resistance to chloride-ion penetration.
The Resipod quickly determines surface electrical resistivity and can be used on lab specimens or areas of any form factor in the field. Measurements are fast, require little sample preparation, and are completely nondestructive.
- Permeability and chloride diffusion estimates are quickly determined on lab specimens or structures in the field using the same instrument.
- Performing a series of tests on-site assesses uniformity of the structure and locates areas with higher rates of permeability.
- Correlation of resistivity readings to rapid chloride permeability values allows fast and efficient estimation of the rate and likelihood of reinforcing steel corrosion.
- Surface tests performed on concrete strength specimens before testing correlates resistivity values with curing rates and strength development.
- Surface resistivity readings can indicate variations in relative water/cementitious materials ratios.
- Areas of concrete with inconsistent resistivity readings are easily located and noted for follow-up examinations with half-cell 腐蚀米, 混凝土水分检测设备, or 混凝土强度检测设备.
Aggregate particles are often non-conductive relative to the concrete mix as a whole, 所以探针间距必须超过最大粒子的尺寸. 同时, the presence of highly conductive reinforcing steel also has a significant impact on results, 因此，最佳间距应该小于棒之间的已知距离.
AASHTO T 358指定探针间距为38.1mm (1.5in) for their method, but other procedures have settled upon 50mm as the best compromise. The Resipod Meter has two fixed-probe model variants that meet each of these requirements. Their 几何配件 (Note: loveBet爱博 product listing needs a photo) is an optional probe attachment with probe spacing variables from 40 to 70mm (1.57 to 2.76in)，以适应不同的骨料尺寸和钢筋间距.
Sample preparation for concrete test cylinders tested in the laboratory is very straightforward. 试样表面需要潮湿以进行测试, 与抗压强度测试的要求相同. Simple straightedges and markers plot the sample surfaces for positioning of the instrument. 为了更好的电接触，表面材料被刮掉, 如果需要, 读数的最大分辨率可以提高使用 泡沫接触垫.
在确保探测水库充满水后, 用力将仪器压在样品表面. Stable readings are displayed on the LCD and saved for later upload to a PC through a USB connection and included software. The Resipod detects insufficient electrical connections and displays relevant coded alerts to help correct them.
For field testing applications, reinforcing steel is located using an accurate 钢筋定位器或盖表. Surface moisture conditions should be similar when comparing field resistivity tests to laboratory results. 通常，这意味着在读数时测试区域应该是潮湿的. Optimum orientation when positioning the probe array is diagonally within the space between reinforcing bars, 如下所示:
如果杆的紧密间距不允许这样做, 仪器可以垂直于杆放置, 如有必要，跨越他们的头寸:
We hope this blog post on resistivity testing of concrete has provided some insight into methods and equipment. 要讨论您的特定应用程序，请联系 测试专家 今天在吉尔松.