Jones Owusu Twumasi

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.

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...

Forward and inverse dielectric modeling of oven-dried cement paste specimens in the frequency range of 1.02 GHz to 4.50 GHz

The use of radar non-destructive evaluation (NDE) technique for condition assessment of deteriorated civil infrastructure systems is an effective approach for preserving the sustainability of these systems. Radar NDE utilizes the interaction between radar signals (electromagnetic waves) and construction materials for surface and subsurface sensing based on dielectric properties and geometry. In the success of radar inspection, it is imperative to develop models capable of predicting the dielectric properties of the materials under investigation. The dielectric properties (dielectric constant and loss factor) of oven-dried cement paste specimens with water-to-cement (w/c) ratios (0.35, 0.40, 0.45, 0.50, 0.55) in the frequency range of 1.02 GHz to 4.50 GHz were studied and modeled using modified Debyes models. An open-ended coaxial probe and a network analyzer were used to measure dielectric properties. Forward models are proposed and inversed for predicting the w/c ratio of a given oven-dried cement paste specimen. Modeling results agreed with the experimental data. The proposed models can be used for predicting the dielectric properties of oven-dried cement paste specimens. Also, the modeling approach can be applied to other cementitious materials (e.g., concrete) with additional modification.

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.

Electromagnetic characterization of white spruce at different moisture contents using synthetic aperture radar imaging

Detection and quantification of moisture content inside wood (timber) is key to ensuring safety and reliability of timber structures. Moisture inside wood attracts insects and fosters the development of fungi to attack the timber, causing significant damages and reducing the load bearing capacity during their design life. The use of non-destructive evaluation (NDE) techniques (e.g., microwave/radar, ultrasonic, stress wave, and X-ray) for condition assessment of timber structures is a good choice. NDE techniques provide information about the level of deterioration and material properties of timber structures without obstructing their functionality. In this study, microwave/radar NDE technique was selected for the characterization of wood at different moisture contents. A 12 in-by-3.5 in-by-1.5 in. white spruce specimen (picea glauca) was imaged at different moisture contents using a 10 GHz synthetic aperture radar (SAR) sensor inside an anechoic chamber. The presence of moisture was found to increase the SAR image amplitude as expected. Additionally, integrated SAR amplitude was found beneficial in modeling the moisture content inside the wood specimen.

Corrosion current level estimation of rust samples using inverse dielectric spectroscopy

Dielectric spectroscopy is a standard technique used for characterizing the energy storage and dissipation properties of dielectrics and has been applied for a wide range of fields in science and engineering. In civil engineering, dielectric properties of construction materials can be used for quality assurance (e.g., mechanical strength) and structural health monitoring (e.g., corrosion detection). In the corrosion detection problem of reinforced concrete structures, level of corrosion current is crucial to the accurate estimation of corrosion level (amount of rust) and is typically challenging to measure without destructively damaging the integrity of concrete. In this paper, a new technique based on inverse dielectric spectroscopy is proposed to estimate the current level in artificial corrosion. To achieve the goal, artificially accelerated corrosion products (rust samples) were developed. In artificially accelerated corrosion experiment, three externally supplied corrosion current levels (0.25 A, 0.50 A, and 0.75 A) were applied to steel specimens inside a corrosion reactor, and the rust samples were collected for dielectric spectroscopy measurement (dielectric constant and loss factor) in the microwave frequency range of 0.5 ∼ 4.5 GHz using a dielectric coaxial probe (Agilent 85070E) and a network analyzer (Agilent E5071C). An inverse dielectric spectroscopy model incorporating loss factor, measurement frequency and corrosion current level was developed from the artificially corroded rust samples. From our experimental result, it is found that i) the higher the corrosion current level, the lower the dielectric constant and loss factor of artificial rust in the measured frequency range; and ii) corrosion current level inside artificial rust can be estimated by using an inverse dielectric spectroscopy model

Condition assessment of corroded steel rebar in free space using synthetic aperture radar images

Synthetic aperture radar (SAR) imaging of construction materials offers civil engineers an opportunity to better assess the condition of aging civil infrastructures such as reinforced concrete (RC) structures. Corrosion of steel rebar in RC structures is a major problem responsible for their premature failure and unexpected collapse. In this paper, SAR imaging is applied to the quantitative assessment of corroded steel rebar in free space as the first step toward the use of SAR imaging for subsurface sensing of aging RC structures. A 10 GHz stripmap SAR system was used inside an anechoic chamber. The bandwidth of the radar system was 1.5 GHz. Steel rebar specimens were artificially corroded to different levels by regularly applying a mist of 5% NaCl solution for different durations of time in order to simulate the condition of natural corrosion. Two sizes (No. 3 and No. 4) of steel rebar were used in this research. Different orientations of steel rebar were considered. Corrosion level was determined by measuring the mass loss of corroded steel rebar specimens. From our results, feasibility of SAR images for the condition assessment of corroded steel rebar was experimentally demonstrated. It was found that the presence of surface rust on corroded steel rebar reduces the amplitude in SAR images. The SAR image of corroded steel rebar also exhibited a distribution of SAR amplitudes different from the one of intact steel rebar. In addition, it was also found that there is an optimal range for the condition assessment of corroded steel rebar in free space. In our experiment, the optimal range was determined to be 30.4 cm.

Roadside IED detection using subsurface imaging radar and rotary UAV

Modern improvised explosive device (IED) and mine detection sensors using microwave technology are based on ground penetrating radar operated by a ground vehicle. Vehicle size, road conditions, and obstacles along the troop marching direction limit operation of such sensors. This paper presents a new conceptual design using a rotary unmanned aerial vehicle (UAV) to carry subsurface imaging radar for roadside IED detection. We have built a UAV flight simulator with the subsurface imaging radar running in a laboratory environment and tested it with non-metallic and metallic IED-like targets. From the initial lab results, we can detect the IED-like target 10-cm below road surface while carried by a UAV platform. One of the challenges is to design the radar and antenna system for a very small payload (less than 3 lb). The motion compensation algorithm is also critical to the imaging quality. In this paper, we also demonstrated the algorithm simulation and experimental imaging results with different IED target materials, sizes, and clutters.