Hoda Azari

Validation of Benefits of Automated Depth Correction Method Improving Accuracy of Ground-Penetrating Radar Deck Deterioration Maps

Current ASTM specifications provide an approach for directly correlating the top rebar reflection amplitude from ground-penetrating radar (GPR) to deck condition when corrosion is the primary mechanism for concrete deterioration. However, current specifications do not offer an approach to compensate for geometric spreading losses caused by the inevitable variability in as-built concrete rebar cover. Even when cover thickness meets specified tolerances, significant errors may occur in mapping the location and quantity of deteriorated concrete when these amplitude variations are unaccounted for in air-coupled or ground-coupled GPR investigations. The significance of this correction is demonstrated by comparing mapped deterioration quantities that have been corrected and not corrected for depth variation, versus those quantities from independent methods such as half-cell corrosion potential, chain drag, or impact echo. One manual and two automated processes for depth correction are presented. These three processes compare favorably with one another on several mapped decks. One of the automated methods, which sets a deterioration threshold calibrated with half-cell and chain drag results, has been shown to be as accurate as manual methods on numerous decks. This approach is recommended for further evaluation and incorporation within ASTM D6087-08: Standard Method for Evaluating Asphalt-Covered Bridge Decks Using Ground-Penetrating Radar.

Nondestructive Testing of Steel Corrosion in Prestressed Concrete Structures using the Magnetic Flux Leakage System

The Magnetic Flux Leakage (MFL) method can be nondestructively used to disclose the location and extent of corrosion or fracture in prestressed strands in concrete structures. In this study, parameters with the greatest effect on the performance of the MFL system are investigated using numerical simulations. The MFL system under study is based on two permanent magnets to magnetize embedded strands and Hall-effect sensors to detect normal magnetic flux leakage. The system is assessed using magnetostatic and transient numerical analysis to effectively simulate the MFL system. Results have been verified by laboratory and field experiments. Both normal and axial Hall-effect sensors are modeled in simulations to better identify magnetic signals at the corrosion zone. The sensor lift-off and the magnetic field masking by lateral reinforcements on nearby pitting corrosion are addressed as two main drawbacks of using MFL systems to detect corrosion in prestressed concrete structures. To provide more details about the flux leakage interference between the pitting corrosion and lateral reinforcements in prestressed concrete structures, linear and oriented magnets/sensor arrays are proposed and analyzed numerically.

Reducing Thermal Reflections for Infrared Thermography Applications on Tunnel Liners with Reflective Finishes

Infrared thermography (IRT) has been employed as a non-destructive evaluation (NDE) method to detect delaminations in bridge decks by ASTM standards since 2003. Compared to other NDE methods, IRT is fast in data acquisition and processing. In addition to applications on bridge decks, IRT can be employed to detect defects in other structures such as roadway pavements and tunnel liners. Recent IRT applications on tunnel liners with reflective finishes such as ceramic tiles show that the IRT results can be severely contaminated by infrared reflections of the vehicles and the illuminating systems in the tunnels. In this study, an algorithm is developed to mitigate the contamination caused by the thermal reflections in the IRT results. The reflection is reduced by combining thermal data from multiple thermographs. Perspective projection is employed to map thermal data to the same coordinates if the thermographs are taken with an infrared camera moving in the space. The algorithm is proved to be successful by the results from the lab experiments and field tests. The algorithm can work with IRT data collected by vehicle-mounted infrared cameras to achieve high-speed IRT for tunnel liners with reflective finishes.

NDE application of air-coupled ultrasonic array system and f-k domain analysis for delamination-like defect detection in bridge deck

Recent development of the air-coupled sensing technique provides great potential for practical data measurement in the field; however, an improved data analysis method and careful design of test configuration are required to inspect structures appropriately. Impact-echo (IE) is an efficient method to evaluate delamination-like defects in concrete bridge decks. However, practical application of air-coupled IE is limited due to direct impact and ambient noises. Another practical problem is the difficultly in data interpretation associated with the dominant flexural mode frequency. Although IE analysis is able to estimate a depth of delamination-like defect from the thickness mode frequency, it is well known that the flexural mode frequency is dominant for shallow delaminations but cannot provide the depth information. The structural inspection needs of many data and conventional IE schemes possibly mislead data interpretation. New concepts for IE data measurement and analysis are needed to evaluate full-scale infrastructure in the field.

NDE application of air-coupled array for thickness measurement of concrete slab

In this paper, we describe the improvement of Impact-Echo (IE) using developed air-coupled array system. The air-coupled array system utilizes microelectromechanical systems (MEMS) to receive leaky waves in concrete-air media without physical coupling process. The air-coupled array system benefits of Lamb wave analysis. It is known that thickness mode frequency measured by IE test is emerged from S1-ZGV (zero group velocity at the first symmetric mode) among Lamb waves. Lamb wave analysis is experimentally evaluated through the aircoupled sensing and two-dimensional fast Fourier transform. The contour map of frequency-wave number domain (f-k domain) clearly provides thickness mode frequency of tested slab among noise components, indicating the thickness information of concrete slab with minimal error. The developed air-coupled array system has a great potential to provide thickness mode frequency of concrete slab, which has been practically limited at air-coupled IE.

Virtual Laboratory for Leveraging Technology for Bridges and Constructed Systems

The writers are exploring the development of an innovative and adaptive resource for highway bridge owners, managers, engineers as well as technicians from non-destructive testing (NDT) and structural health monitoring (SHM) industries and the public. The primary objective is an official Federal Highway Administration (FHWA) website offering guidance and training on how technology tools may be selected and applied with sufficient depth to generate reliable and actionable information. Currently a large number of technology tools in the realm of “information, communication, computing and data technology,” “software for modelling and analysis of multi-physics phenomena and civil engineering systems,” “sensing, imaging and non-destructive probing,” and, “uncertainty and risk analysis and decision-making” are available for off-the-shelf purchase or applications by consultants. However, there are very few institutions that offer an ability for an integrative leveraging of such tools and the resulting data in conjunction with engineering heuristics for meaningful, feasible and effective solutions to infrastructure performance problems.

Performance of Concrete Bridge Decks of Similar Construction and Environment, but Different Traffic Loads

Maintenance, rehabilitation, and replacement of reinforced concrete decks are the largest bridge component expenditures for most transportation agencies. Therefore, concrete bridge deck performance was identified as one of the key bridge performance issues in the Federal Highway Administration’s Long-Term Bridge Performance Program. To improve knowledge of bridge deck performance, high-quality quantitative performance data should be collected periodically through the use of complementary nondestructive evaluation (NDE) technologies, such as impact echo, ground penetrating radar, half-cell potential, ultrasonic surface waves, and electrical resistivity. This paper presents the condition change of a bridge deck in Virginia over a period of six years. The assessment covered corrosive environment and corrosion processes, concrete degradation, and deck delamination. Deterioration progression from periodic NDE surveys is illustrated qualitatively by condition maps and quantitatively by condition assessment numbers. The results demonstrate the ability of NDE technologies to capture and quantify the progression of deterioration. Strong agreement between different NDE technology results improves the confidence level of the condition assessment of the deck. The study also evaluated the similarities in performance of bridge decks of comparable age, similar construction, and similar environment, with different traffic loads. Multiple NDE technologies were used to assess two concrete decks of a similar design, construction, age, and environment, but with different traffic conditions. The complementary use of multiple NDE technologies identified corrosion as the primary cause of damage in both decks. The severity of deterioration differed at the time of the survey, which caused the estimated remaining life of the two decks to differ by about 10 percent.