Qixiang Tang

All-Optical Photoacoustic Sensors for Steel Rebar Corrosion Monitoring

This article presents an application of an active all-optical photoacoustic sensing system with four elements for steel rebar corrosion monitoring. The sensor utilized a photoacoustic mechanism of gold nanocomposites to generate 8 MHz broadband ultrasound pulses in 0.4 mm compact space. A nanosecond 532 nm pulsed laser and 400 μm multimode fiber were employed to incite an ultrasound reaction. The fiber Bragg gratings were used as distributed ultrasound detectors. Accelerated corrosion testing was applied to four sections of a single steel rebar with four different corrosion degrees. Our results demonstrated that the mass loss of steel rebar displayed an exponential growth with ultrasound frequency shifts. The sensitivity of the sensing system was such that 0.175 MHz central frequency reduction corresponded to 0.02 g mass loss of steel rebar corrosion. It was proved that the all-optical photoacoustic sensing system can actively evaluate the corrosion of steel rebar via ultrasound spectrum. This multipoint all-optical photoacoustic method is promising for embedment into a concrete structure for distributed corrosion monitoring.

Finite element simulation of photoacoustic fiber optic sensors for surface corrosion detection on a steel rod

Structural steel members have become integral components in the construction of civil engineering infrastructures such as bridges, stadiums, and shopping centers due to versatility of steel. Owing to the uniqueness in the design and construction of steel structures, rigorous non-destructive evaluation techniques are needed during construction and operation processes to prevent the loss of human lives and properties. This research aims at investigating the application of photoacoustic fiber optic transducers (FOT) for detecting surface rust of a steel rod. Surface ultrasonic waves propagation in intact and corroded steel rods was simulated using finite element method (FEM). Radial displacements were collected and short-time Fourier transform (STFT) was applied to obtain the spectrogram. It was found that the presence of surface rust between the FOT and the receiver can be detected in both time and frequency domain. In addition, spectrogram can be used to locate and quantify surface rust. Furthermore, a surface rust detection algorithm utilizing the FOT has been proposed for detection, location and quantification of the surface rust.

Finite element simulation of ultrasonic waves in corroded reinforced concrete for early-stage corrosion detection

In reinforced concrete (RC) structures, corrosion of steel rebar introduces internal stress at the interface between rebar and concrete, ultimately leading to debonding and separation between rebar and concrete. Effective early-stage detection of steel rebar corrosion can significantly reduce maintenance costs and enable early-stage repair. In this paper, ultrasonic detection of early-stage steel rebar corrosion inside concrete is numerically investigated using the finite element method (FEM). Commercial FEM software (ABAQUS) was used in all simulation cases. Steel rebar was simplified and modeled by a cylindrical structure. 1MHz ultrasonic elastic waves were generated at the interface between rebar and concrete. Two-dimensional plain strain element was adopted in all FE models. Formation of surface rust in rebar was modeled by changing material properties and expanding element size in order to simulate the rust interface between rebar and concrete and the presence of interfacial stress. Two types of surface rust (corroded regions) were considered. Time domain and frequency domain responses of displacement were studied. From our simulation result, two corrosion indicators, baseline (b) and center frequency (fc) were proposed for detecting and quantifying corrosion.

Surface and Subsurface Remote Sensing of Concrete Structures Using Synthetic Aperture Radar Imaging

AbstractSurface and subsurface inspection of concrete structures provides useful information for the maintenance of these structures. Remote sensing techniques such as radar and microwave sensors e...

Finite element simulation for damage detection of surface rust in steel rebars using elastic waves

Steel rebar corrosion reduces the integrity and service life of reinforced concrete (RC) structures and causes their gradual and sudden failures. Early stage detection of steel rebar corrosion can improve the efficiency of routine maintenance and prevent sudden failures from happening. In this paper, detecting the presence of surface rust in steel rebars is investigated by the finite element method (FEM) using surface-generated elastic waves. Simulated wave propagation mimics the sensing scheme of a fiber optic acoustic generator mounted on the surface of steel rebars. Formation of surface rust in steel rebars is modeled by changing materials property at local elements. In this paper, various locations of a fiber optic acoustic transducer and a receiver were considered. Megahertz elastic waves were used and different sizes of surface rust were applied. Transient responses of surface displacement and pressure were studied. It is found that surface rust is most detectable when the rust location is between the transducer and the receiver. Displacement response of intact steel rebar is needed in order to obtain background-subtracted response with a better signal-to-noise ratio. When the size of surface rust increases, reduced amplitude in displacement was obtained by the receiver.

Finite element analysis for the damage detection of light pole structures

Failures of aging light poles can jeopardize the safety of residents and damage adjacent structures. The need for reliable and efficient damage detection methods is raised. Any change in structural properties (e.g., mass, stiffness and damping) can lead to differences in the dynamic response of structures (i.e., modal frequencies). As a result, changes in dynamic responses can be used as indicators for damage detection. In this study, relationships between artificial damages and modal frequencies are determined by investigating the modal frequencies of intact and damaged light pole models using the finite element method (FEM). Finite element (FE) models were built with 5,529 C3D8R elements in ABAQUSR. New parameters (sensitive and insensitive modes) were defined and used to evaluate the sensitivity of the first ten modes of FE models. It is found that combinations of sensitive and insensitive modes are unique for each damage location and can be used to locate artificial damages in light pole models. Empirical equations are proposed to quantify damage level and damage size.

Real time corrosion detection of rebar using embeddable fiber optic ultrasound sensor

Ultrasonic corrosion detection has been developed and widely applied in non-invasive tests in civil engineering. This paper demonstrates real time fiber optic ultrasonic corrosion detection on reinforcing rebar based on photoacoustic (PA) principle in non-invasive tests in civil engineering. The optical acoustic sensors are fabricated to monitoring the corrosion of rebar in concrete. This paper explores an approach to make an assessment for the level of rebar corrosion as well. From the experimental results, the trend of central frequency had a shift to lower based on the development of corrosion. Since the sensor can measure the rebar corrosion timely, it will have a significant step on structural health monitoring.

Characterization of steel rebar spacing using synthetic aperture radar imaging

Steel rebars is a vital component in reinforced concrete (RC) and prestressed concrete structures since they provide mechanical functions to those structures. Damages occurred to steel rebars can lead to the premature failure of concrete structures. Characterization of steel rebars using nondestructive evaluation (NDE) offers engineers and decision makers important information for effective/good repair of aging concrete structures. Among existing NDE techniques, microwave/radar NDE has been proven to be a promising technique for surface and subsurface sensing of concrete structures. The objective of this paper is to use microwave/radar NDE to characterize steel rebar grids in free space, as a basis for the subsurface sensing of steel rebars inside RC structures. A portable 10-GHz radar system based on synthetic aperture radar (SAR) imaging was used in this paper. Effect of rebar grid spacing was considered and used to define subsurface steel rebar grids. Five rebar grid spacings were used; 12.7 cm (5 in.), 17.78 cm (7 in.), 22.86 cm (9 in.), 27.94 cm (11 in.), and 33.02 cm (13 in.) # 3 rebars were used in all grid specimens. All SAR images were collected inside an anechoic chamber. It was found that SAR images can successfully capture the change of rebar grid spacing and used for quantifying the spacing of rebar grids. Empirical models were proposed to estimate actual rebar spacing and contour area using SAR images.

Sizing and ranging criteria for SAR images of steel and wood specimens

The use of microwave and radar sensors in the nondestructive evaluation (NDE) of damaged materials and structures has been proven to be a promising approach. In this paper, a portable imaging radar sensor utilizing 10 GHz central frequency and stripmap synthetic aperture radar (SAR) imaging was applied to steel and wood specimens for size and range determination. Relationships between range and properties of SAR images (e.g. maximum amplitude and total SAR amplitude) were developed and reported for various specimens including a steel bar (2.5 cm by 2.5 cm by 28.5 cm), a wood bar (2.5 cm by 2.5 cm by 28.5 cm), a steel plate (39.7 cm by 57.9 cm by 1.75 cm), and a wood board (30.5 cm by 30.5 cm by 1.8 cm). Various ranges from 30 cm to 100 cm were used on these specimens. In our experiment, attenuation of radar signals collected by the imaging radar system on different material specimens was measured and modeled. Change in the attenuation of maximum SAR amplitude was observed in different materials. It is found that SAR images can be used to distinguish materials of different compositions and sizes.

Ultrasonic transmission from fiber optic generators on steel plate

Fiber optic acoustic generators have generated a lot of interest due to its great potential in many applications including nondestructive tests. This paper reports four acoustic generation configurations. All the configurations are based on gold nanoparticles/polydimethylsiloxane (PDMS) composites. Since gold nanoparticles have high absorption efficiency to optical energy and PDMS has a high coefficient of thermal expansion, the composites can transfer optical energy to ultrasonic waves with high conversion efficiency. The strength and bandwidth of ultrasonic waves generated by the composites can be changed by different designs and structures of the composites. This paper explores the relation between the structure of fiber optic acoustic generators and the profile of generated ultrasonic waves. Experimental results also demonstrated that four ultrasonic generation configurations have similar features of ultrasonic transmission on a steel plate, which is important for future choices of ultrasonic receivers.