Concrete Imaging and Scanning are used to assess the location and extent of sub-surface defects. Different non-destructive test methods have been developed and used over the past few decades. The following article briefly describes some of these methods, and their application in the structure inspection and structural condition assessment.
什么是混凝土成像和扫描？
Concrete Imaging and Scanning通常称为一组非破坏性测试（NDT.) that can locate, and quantify sub-surface anomalies and defects (targets). Several Imaging and Scanning technologies have been developed over the past few decades:
- Ground Penetrating Radar (based on Electromagnetic Field),
- 超声波断层扫描（基于超声波的传播），
- 电阻率和半电池腐蚀映射（基于电气和电化学性质）和X射线
此外，已经开发出固体中超声波和电磁波传播的潜在物理学以解决特殊结构中的某些挑战，例如大规模混凝土坝和基础。
Why Do We Need Concrete Scanning?
在不同情况下，具体扫描可能是必要的：
- structure inspection and condition survey of existing buildings,
- 定位steel rebar in slabs and walls,
- 定位defectssuch as voids and discontinuities in concrete slab on grades
- 定位live conduits ahead of coring and drilling
- Corrosion inspection and monitoring
用于混凝土成像和扫描的NDT方法
Different non-destructive testing methods have been developed forconcrete imaging and scanning。In this article, we will review some of the most famous NDT methods for concrete imaging and scanning.
1. Ground Penetrating Radar – GPR
Ground penetrating radar (GPR) is a widely used non-destructive method for scanning concrete. GPR uses pulsed electromagnetic radiation to scan concrete. GPR consists of a transmitter antenna and a receiver antenna, and a signal processing unit. GPR emits electromagnetic pulses (radar pulses) with specific central frequency to scan the subsurface medium. The reflected waves from subsurface layers, and objects are captured by the receiver antenna.
Applications and Use
Ground Penetrating Radar provides a cost-effective approach for scanning large areas. GPR scans can be performed at traffic speed (ideal for large areas, such as bridge deck scanning).
- 在混凝土元件中定位钢筋
- determine rebar location and spacing
- estimate concrete cover thickness
- 找到实时导管和管道
- 确定混凝土板中的主要空隙和不连续性
- Inspection of tunnel lining
Limitations of Use
- GPR scans不要provide information on the mechanical properties of concrete (i.e. concrete strength)
- GPR scans不要提供有关的腐蚀状况的信息steel bars
2. Ultrasonic Tomography – Pulse Echo
超声波断层扫描可用于扫描子表面空隙和混凝土中的缺陷。断层扫描采用超声剪切波来研究混凝土的多层性能。
The concept behind this method relies on the propagation of stress waves through materials. A transmitter introduces a stress pulse into the object at an accessible surface. The pulse propagates into the test object and is reflected at the interface of internal targets (air voids, steel bars, boundaries). The emitted impulse and the reflected acoustic waves are monitored at the receiving transducer. Mathematical solvers are used to reconstruct the location and extent of internal anomalies.
Applications and Use
- Estimate the thickness of concrete elements (thin elements through mid-range thickness)
- 检测内部空隙和缺陷。
- 检测浅深度裂解和分层
Limitations of Use
- Concrete scanning using tomography or UPE requires small spacing, making it time-consuming for scanning large areas.
- 粗糙混凝土表面上的测试可能是具有挑战性的（传感器 - 混凝土耦合）
3. X-Ray Scanning of Concrete
混凝土中的X射线想象非常类似于成像实验室中使用的X射线。使用X射线的混凝土扫描和成像可以使用常规方法或数字介质来完成。主要区别是他们如何处理图像。X射线扫描可用于定位钢筋在重强化元件中。
Limitations of Use
- 由于该技术正在使用高能X射线，因此在进行测试之前通常需要间隙。这意味着对于测试目的，应观察到明显的距离约为15米至25μm。大多数X射线成像项目计划在夜班或后工作时间，以降低准备安全间隙和进行测试所需的成本和努力。
- X-Ray attenuates as it travels through concrete; therefore, it is strongly recommended to limit the scan depth to appx 200 mm or thinner elements.
- The test results should be processed and interpreted by an experienced technician to map the images on the concrete slab.
- Another limitation of the method is that it does not provide information about the depth of sub-surface targets.
4.半细胞腐蚀潜在映射
半细胞腐蚀映射is an effective method for assessing the likelihood of corrosion activity in concrete structures. Half-Cell test works based on measuring the potential difference (electrochemical) of an arbitrary point on the concrete surface and a standard portable half-cell, typically a Cu/CuSO4 (CSE) standard reference electrode. The test is usually performed on a systematic grid, and measurements are often displayed as spatial distribution (2D contour maps) of potential value.
Applications and Use
- 评估混凝土元件腐蚀的可能性;
- Evaluate the effectiveness of concrete repair
Limitations of Use
- The test cannot be performed over asphalt toppings;
- 测试对混凝土湿度和温度敏感
- 通过环氧涂层钢筋的元素不能对测试进行测试
5. Seismic Tomography for Mass Concrete
地震断层扫描是基于非常概念的特殊测试设置Ultrasonic Pulse Velocity。在该方法中，将多个接收换能器阵列放置并固定在测试位置，而发送换能器沿着系统网格移动。通过接收换能器接收发射器产生的脉冲。测量每个轨迹处的脉冲速度。结果在2D或3D地震断层摄影等高图中证明，该轮廓图显示了混凝土元件的状况。地震断层扫描是测试大型混凝土元件的理想选择。
Applications and Use
- 检测质量混凝土元件的主要空隙和内部缺陷（即水坝，质量基础块等）
- 识别弱的位置（与混凝土强度的相关 - 间接波速度）
About Author
Dr. Hamed Layssi, PEngis the CEO and structural engineer at FPrimeC Solutions. He has been involved with the Concrete industry for over 15 years as a professional engineer, industrial research and development specialist, researcher and scholar. Dr. Layssi is a registered professional engineer in Ontario since 2014, hold a PhD from McGill University, Canada, and have received the 2018 entrepreneurship award from the PEO, Ottawa Chapter.
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我的教授告诉我，我应该对非破坏性测试进行介绍，因此我正在研究通常的应用程序的混凝土建筑物的研究。感谢您阐述超声波断层扫描通常用于检测结构中的缺陷。我想我会考虑更多地提出一个关于这个的专家，所以我可以在下个月展示我的研究。
Dear Angela,
Please feel free to reach out to one of our experts, Dr. Hamed Layssi or Dr. Farid Moradi (co-founders at FPrimeC). They are both experts in concrete structures, testing, and NDT. All the best. FPrimeC
Am currently researching on the use of thermal infrared camera as a NDT method of bridge integrity test, with the light you have xray on the thermography its quiet appreciated and also a pointer to what it seems i want to do. Thanks
Engr Musa
嗨musa。
Please find the following research by TRB and FHAW :http://onlinepubs.trb.org/onlinepubs/shrp2/SHRP2_S2-R06A-RR-1.pdf
There are sections that are relevant to your questions.
问候，
If you have any PPT on NDT, I need it make familiar the field staff. If possible please mail it to me.
谢谢和regads.
Methods shared for concrete imaging, and scanning are informative. People who are looking for such information would find it useful. Thanks for sharing this with us!
Hi,
I’m working in a society that managed important infrastructures in my city as an intern in research and development. During the construction of one of our bridges, about 90 years ago, a time capsule was introduced in one of the piles. We lost track of it and we are now looking to find a method to detect steel object in massive concrete/stone structure. We already tried a ground penetrating radar without any result. The box is in lead (about 46 cm3).
Do you have more information on the other method?
I appreciated it when you shared that GPR is a widely used non-destructive method for scanning concrete that uses pulsed electromagnetic radiation. It emits pulses at a specific central frequency to scan the subsurface medium. I would like to think if a company needs to hire a GPR service, it should consider hiring the one that is reliable and experienced.
很高兴知道有无损methods for scanning concrete and that ground penetrating radar is one of them. I head it can be quite useful. Glad to see how it works from another source.
Thank you for including a section on what concrete scanning is used for. My brother-in-law is a contractor and him and my dad were talking about concrete scanning the other day and I was super lost. Now I know that it can be used for a ton of different things including locating steel rebar in concrete!
What is a practical method of finding embedded objects in concrete that is more accurate/(provides for less misses) than GPR?