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- Englisch (8)
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- Concrete (2)
- Construction materials (2)
- GPR (2)
- Ground penetrating radar (2)
- Ground penetrating radar (GPR) (2)
- Reinforcement corrosion (2)
- Accelerated steel corrosion in concrete (1)
- Chloride (1)
- Chloride contamination (1)
- Corrosion (1)
Using ground penetrating radar and time-frequency analysis to characterize construction materials
(2011)
For decades, applications of nondestructive evaluation-civil engineering (NDE-CE) focus on object identifications (such as steel bars, tendon ducts and backwall reflections) in infrastructures. Because of the advantage of efficient visualization of internal structure, utilization of these methods can probably be extended to material characterization (MC) of aging and adversely exposed infrastructures. However, two factors yield a big gap between NDE and MC. First, for the ease of visualization, the primary focus of NDE-signal processing is object identification, which usually alters the originality of the signal. Second, there is lack of relationship and inverse models bridging the NDE-derived and conventional material properties compared to other disciplines of science, such as geophysics. These disadvantages make laboratory and field-scale NDE-MC still a far-reaching holy grail and is possibly the greatest hurdle to be regularly adopted in CE structures. This paper attempts to address this gap from object identification to MC using ground penetrating radar (GPR) as one of the most frequently used NDE-CE methods, and signal processing with joint timefrequency domain (JTFA) analysis. Three examples of material property characterization regarding the individual effects of steel bar corrosion in concrete, hydration and moisture content distribution of construction materials are given.
This paper studies the dielectric dispersion of high frequency radar wave in concrete in early-aged and hardened concrete specimens. Frequency-dependent spectra of phase velocity ν(ω) were measured to deduce the spectra of real part of dielectric permittivity ε'(ω). The dispersion was measured by three high nominal ground penetrating radar frequencies (1.5, 1.6 and 2.6 GHz), experimenting on two steel bars with concrete cover 50 and 100 mm. It was found that ν(ω) and ε'(ω) dispersed at lower frequency, but became stable at high frequency regions, which agrees with the classical GPR plateau. The same frequency components at different nominal antenna frequencies show a close range of ν(ω) and ε'(ω) in concrete of different ages. The results in this paper warrant further investigation of using GPR wave to study material properties.
A new approach is presented to evaluate corrosion of steel bars in concrete by 1.5- and 2.6-GHz ground-penetrating radar (GPR) and a modified half-cell potential method. Changes in time-lapsed travel times, amplitudes, and peak frequencies that are associated with short-time Fourier transform spectrograms of the bar reflections were continuously measured. The year-long corrosion process of the reinforcement bar rapidly accelerated within a few days by impressing direct current across a pair of embedded reinforcement bars, which served as the anode and cathode. When corrosion started, the travel times, amplitudes, and frequency spectra of the bar reflection changed. The results were analyzed by dividing the material's response into three phases (NaCl contamination, depassivation, and corrosion). The writers attribute the phenomena of the first two phases to the ionic conduction and interfacial polarization effect, described in the low-frequency regime of complex dielectric permittivity outlined in the Maxwell-Wagner effect. The remaining phase corresponds with the appearance of large and multiple interfaces among steel, concrete, corrosion product, and cracks, in addition to the upward movement of the corrosion product to the concrete surface that intercepts wider radar footprints. The findings, based on time lapse measurements, provide a basis to further apply the GPR technique to spatial measurements in laboratory and field studies.
Periodic mapping of reinforcement corrosion in intrusive chloride contaminated concrete with GPR
(2014)
This paper presents an experimental effort for developing a novel reinforcement corrosion monitoring technique based on Ground Penetrating Radar (GPR). Experiments were carried out to periodically monitor the accelerated reinforcement corrosion process with GPR. The data were processed in both time and timefrequency domains to investigate the tendencies of GPR signal attribute changes related with corrosion, moisture and chloride contamination. Data processing methods were proposed to visualize the reinforcement corrosion and chloride distribution with target specified signal attribute mapping. Half-Cell Potential (HCP) and Laser-Induced Breakdown Spectroscopy (LIBS) methods were employed to verify the GPR observations.
This paper studies the spatial and temporal spectral absorption of reflector signals of a 1.5 GHz ground penetrating radar (GPR) during a drying process of a brickwall from initial wet to later dry state. The non-stationary GPR signals were processed with short time-Fourier transform (STFT) and wavelet transform (WT) in a novel spatial-timefrequency (STF) domain. Spatial distribution of peak frequency at the direct wave (DW) across the antenna and a backwall reflection was studied to characterize the mechanism of spectral absorption of GPR wave. Results from WT were shown to be more preferred to those from STFT because the WT offers multiple resolutions to cope with both low and high frequency components in GPR wavelets but STFT does not. In addition to the traditional GPR signal interpretation in time-domain and our previous works on time–frequency domain, the analysis method operated in the STF domain provides another possibility of material characterization by GPR in large and field scale.
Monitoring accelerated corrosion in chloride contaminated concrete with ground penetrating radar
(2012)
Ground penetrating radar (GPR) was used to characterize the frequency-dependent dielectric relaxation phenomena in ordinary Portland cement (OPC) hydration in concrete changing from fresh to hardened state. The study was experimented by measuring the changes of GPR A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT) in joint time-frequency analysis (JTFA) domain rather than a conventional time or frequency domain alone. The signals of the direct wave traveled at the concrete surface and the reflected wave from an embedded steel bar were transformed with STFT, in which the changes of peak frequency over ages were tracked. The peak frequencies were found to increase with ages and the patterns were found to match closely with primarily the well-known OPC hydration process and secondarily, the evaporation effect. The close match is contributed to the simultaneous effects converting free to bound water over time, on both conventional OPC hydration and dielectric relaxation mechanisms.