Synthetic aperture focusing technique (SAFT) is one of the most-used ultrasonic imaging algorithms. However, by considering only the direct sound path (i.e., pulse-echo signals) for image reconstruction, this technique is unable to show steeply inclined interfaces and bottom boundaries of objects in concrete structures. To address this problem, the current study considered various sound paths when applying SAFT for concrete elements. The proposed hypothesis is that different sound paths will provide access and imaging opportunities to previously inaccessible areas of the inspected volume/region. As a proof of concept, the proposed method, namely the ray-based SAFT, was tested with ultrasonic shear wave data for two concrete slab specimens. The results indicated a significant improvement compared to conventional SAFT imaging for simulated rebar debonding, vertical boundaries of slabs, and bottoms/sides of tendon ducts.
Concrete delaminations are commonly-found defects in bridge decks and rigid pavements. While previous studies reported that ground-penetrating radar (GPR) could visualize those defects in many instances, it is still unclear about the factors that may affect such an application. For this reason, this study aimed to develop an understanding of the factors that influence the detectability of concrete delamination in GPR images/signals. Concerning the methodology, the study was conducted using both synthetic data generated from a GPR simulation program, and real data collected on a concrete bridge deck specimen. The analysis of such image data indicated the following. First, there is always some energy reflected from concrete delamination. However, its shape and strength are affected by the thickness of the delamination, the material (air or water) within it, and the peak (most energetic) frequency of the emitted signal. Second, the depth of delamination and its position relative to reinforcing steel bars might impact its visibility in GPR images.
KEYWORDS: Nondestructive evaluation, Bridges, Corrosion, Acoustics, Ground penetrating radar, General packet radio service, Data modeling, Signal attenuation, Robotics, Inspection
Reinforced concrete decks are in most cases the fastest deteriorating components of a bridge due to the multitude of influencing factors: direct traffic loading and environmental effects, maintenance activities (salting), etc. Among many deterioration types, corrosion-induced deterioration is the most common problem in reinforced concrete decks. The study concentrates on the condition assessment of bridge decks using complementary NDE techniques. The assessment has three main components: assessment of corrosive environment and corrosion processes, and assessment with respect to the deck delamination. The study concentrates on a complementary use of five NDE techniques: impact echo (IE) to detect and characterize delamination, ground penetrating radar (GPR) to describe the corrosive environment and detect delamination, and electrical resistivity (ER) to estimate the corrosion rate by measuring concrete resistivity. The ability of the NDE methods to objectively characterize deterioration progression is illustrated by the results from NDE surveys of 10 bridges of different ages in New Jersey during a period of one year. The deterioration progression is illustrated by condition maps and condition indices. As demonstrated in the paper, multiple deterioration models are developed utilizing the proposed methodology, which shows high potential for development of more realistic deterioration and life cycle cost models for bridge decks.
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