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A new method for periodically monitoring reinforcement corrosion in concrete with Ground-Penetrating Radar (GPR) is proposed and a ten-year long-term corrosion periodic monitoring experiment is reported. GPR historical data was taken in different years, under different conditions. In order to align and normalize the obtained images properly prior to effectively performing any automatic defect detection, image registration techniques based on mutual-information are employed, and a new signal processing scheme is proposed for normalizing the intensity of GPR images. Then, the processed image results can be used to compare and find out the change of GPR detection due to corrosion.
In this article, we present a laboratory experiment to monitor the accelerated corrosion in concrete using ground-penetrating radar (GPR). Four concrete test specimens were cast with rebars of different size and placed at different depths. The lifetime decades of reinforcement corrosion process were accelerated into 18 days by using the impress current technique. The electrochemical corrosion process was periodically monitored with GPR. Two control specimens were also prepared to investigate the influence of chloride contamination on GPR signal. The measured data were analysed both in time and frequency domains. In time domain, the peak-to-peak amplitude of a wave reflected by a rebar was calculated to investigate the relationship between an increase in signal amplitude and the degree of corrosion. In frequency domain, the time–frequency representations of the signal were computed by using S-transform. The results show that reinforce corrosion increased the amplitude of reflected signal in time domain but did not change the peak frequency in frequency domain while chloride contamination attenuates the signal to smaller amplitude and lower peak frequency. Based on the results, a novel process is finally proposed for GPR-based corrosion detection.
For almost 15 years, carbon fibre-reinforced polymer (CFRP) plates and sheets have been used for strengthening and repair of civil engineering structures. CFRP plates were applied to upgrade structures for change in use or increasing traffic load. CFRP laminates have also been used to repair deteriorated structures such as multi-storey parking or bridges. The execution quality and condition of the strengthening measure in terms of bond integrity were neither monitored nor tested systematically. Inspectors eventually applied simple hammer knocking during regular main inspection for subjective noise distinction as a measure for eventual insufficient bond. This paper presents the feasibility and the limitations of low-frequency transversal ultrasonic waves with dry-coupling point-contact sensors for inspection and defect detection between CFRP laminate and concrete surfaces. The German Centre of Competence in Civil Engineering (DIBt) has initiated a national research project [Helmerich et al. (2012). Condition analysis of bonded CFRP-applications on concrete structures by means of non-destructive testing [in German: Zustandsuntersuchung von CFK-Klebeverstärkungen an Betonbauteilen mittels zerstörungsfreier Prüfung (ZfP)]. Final, internal project report], carried out at the Federal Institute for Materials Research and Testing (BAM), Germany. The aim of the project was to present a potential non-destructive testing method for bond defect detection as a measure for the durability of the strengthening system more than 10 years after application.
Trans-European corridors for transport of people and goods require strengthening of bridges to carry increased axle loads in terms of absolute axle loads and of their frequency. Most of the bridges along highways are reinforced or prestressed concrete bridges.
Since the late 1990s, CFRP laminates have been applied to box girder and T-beam bridges to increase the overall capacity. Although regular inspections are carried out, no special method was available to test the bond condition of CFRP laminates after being in Service for more than ten years. The German Center of Competence in Civil Engineering is aware of this need and funded a research project to investigate the bond condition by means of advanced non-destructive testing (NDT).
Within the presented research project, experimental and numerical investigations were performed to develop a thin-shelled, modular, mobile element system made of a micro-reinforced ultra-high-performance ductile concrete (DUCON®). Material parameters were experimentally determined to adapt the material model within the numerical analysis applying the Drucker-Prager relationship. Afterwards, for validation of the numerical models, quasi-static and high-velocity impact tests were performed on plate-like structures. Finally, a suitable geometry of transportable barrier elements will be designed, which provides a maximum of resistance against impact by a minimum of weight and a maximum of mobility.
The vulnerability of low-quality concrete of some bridges to ageing and deterioration while they are exposed to environmental conditions during their service life, influence of growing population and climate changes, is a well-known effect and requires survey. For survey, the development of a low cost, cost-efficient sensor network to be embedded for continuous or attached to the surface for periodic monitoring is essential.
Changing ground water conditions, flood or even leakage in fresh or disposal of waste water can lead to in-creased moisture content in building materials and structural elements as walls or floors. Moisture allows the transport of other adverse chemicals that might reduce the durability of structures. The paper presents a feasibility study about the capability of microwave modules as bluetooth® or ZigBee with frequency range at 2,4 GHz to create advanced Wireless Sensor Networks (WSN) for estimation and visualization of moisture distribution in infrastructure assets. It was found that the value of the received signal strength indication (RSSI) depends on the moisture content and can be the basis for the moisture distribution inside a massive structure.
The microwave modules may be used to compose networks outside and inside of building materials or structural elements. The higher the number of connections between BLE modules, the more precise and the more distant information can be obtained from the network. Mesh networking was applied to increase the quantitative information.
Structural health monitoring contributes to early damage detection in the built infrastructure. During the last two decades, sensor networks transferred from wired to wireless sensor networks. Several methods exist to measure moisture in building materials. Most of the introduced commercial moisture measurement methods provide information about the local or near surface moisture. A feasibility study is presented to demonstrate, how the Received Signal Strength Indicator (RSSI) of a Bluetooth Low Energy (BLE) signal, transmitted from the BLE-module embedded in building materials, correlate with changing moisture content. The feasibility of this influence was investigated in the presented study. The maximum and minimum RSSI were systematically recorded and analysed.
The European infrastructure asset has developed historically and is characterized by nation-specific construction processes. Inspection, condition assessment, and maintenance procedures differ from country to country. Because of historical and political circumstances, national infrastructure assets are maintained at different levels, too. Since the budget for maintaining the bridge infrastructure less and less meets the demands of a growing bridge stock, bridge inspection, maintenance, and life-cycle considerations gain higher importance. The need exists to develop effective diagnosis tools for early detection of construction faults, defects, and deterioration processes during inspection, to keep the bridge infrastructure at an acceptable level, from structural safety and economic viewpoints. An overview on the latest research projects and integrated bridge management systems in Europe is given. The potentials of nondestructive testing (NDT) are presented, with special focus on technical advances of NDT applications to reinforced concrete (RC) and posttensioned concrete bridges. Although NDT is not regularly integrated in these processes, the application brings valuable information on the current condition of the inner structure in called-in special inspections. NDT-automation and the application of imaging echo methods, combined with advanced data processing, produce a surprising level of information about the inner structure of massive RC slabs up to a depth of about 60 cm. Detected inhomogeneity and scatterers of acoustic or electromagnetic waves can be visualized in vertical or horizontal slices through the structure or animations. The fusion of different three-dimensional data sets of processed data improves the interpretability and accuracy of the results.