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.
KEYWORDS: Bridges, Nondestructive evaluation, Robotics, Robotic systems, General packet radio service, Global Positioning System, Inspection, Corrosion, Cameras, Data fusion
More economical management of bridges can be achieved through early problem detection and mitigation. The paper describes development and implementation of two fully automated (robotic) systems for nondestructive evaluation (NDE) and minimally invasive rehabilitation of concrete bridge decks. The NDE system named RABIT was developed with the support from Federal Highway Administration (FHWA). It implements multiple NDE technologies, namely: electrical resistivity (ER), impact echo (IE), ground-penetrating radar (GPR), and ultrasonic surface waves (USW). In addition, the system utilizes advanced vision to substitute traditional visual inspection. The RABIT system collects data at significantly higher speeds than it is done using traditional NDE equipment. The associated platform for the enhanced interpretation of condition assessment in concrete bridge decks utilizes data integration, fusion, and deterioration and defect visualization. The interpretation and visualization platform specifically addresses data integration and fusion from the four NDE technologies. The data visualization platform facilitates an intuitive presentation of the main deterioration due to: corrosion, delamination, and concrete degradation, by integrating NDE survey results and high resolution deck surface imaging. The rehabilitation robotic system was developed with the support from National Institute of Standards and Technology-Technology Innovation Program (NIST-TIP). The system utilizes advanced robotics and novel materials to repair problems in concrete decks, primarily early stage delamination and internal cracking, using a minimally invasive approach. Since both systems use global positioning systems for navigation, some of the current efforts concentrate on their coordination for the most effective joint evaluation and rehabilitation.
Graphene films grown by chemical vapor deposition of hydrocarbon gases on metal surfaces have been integrated with single-walled carbon nanotube (SWNT) films. Using simple thin film fabrication methods and the sequential deposition of these two components we obtained graphene/SWNT hybrid films with good structural quality. Obtained graphene/SWNT films possess opto-electrical properties better than that of pure graphene or SWNT films, making them promising for transparent conductive film (TCF) applications. The hybrid films have been tested as a transparent electrode in electrochromic (EC) devices to replace indium tin oxide (ITO) TCFs.
A passive, wireless sensor has been developed at the University of Texas at Austin to monitor the insitu conductivity of
concrete within civil infrastructure systems. Electrical conductivity is one possible indicator of corrosion of embedded
reinforcement and thereby provides information on structural performance. The sensors would be attached to the
reinforcement cages before placement of the concrete and interrogated as part of a routine inspection over the service
life. A new sensor design, a non-contact conductivity sensor, is being developed to minimize the likelihood of damage to
the sensor during placement of the concrete; a metal element is positioned above the sensor body but is not connected to
the resonant circuit within the sensor. In order to verify the response of the non-contact conductivity sensors, they were
submerged in liquids of increasing conductivity. Analysis of the measured data demonstrated that the noncontact
conductivity sensors successfully detected conductivity variations in liquids.
A passive, wireless and inexpensive sensor has been developed to monitor the conductivity of concrete and thereby
provide information on the progress of chloride-induced corrosion of the embedded reinforcement in concrete structures.
Sensors are designed to be attached to the reinforcement cages before placement of the concrete in new construction or
in portions of rehabilitated structures. Sensors will then be interrogated intermittently over the service life during routine
inspections. The results of two experimental investigations are discussed in this paper. In the first, conductivity sensors
were submerged in liquids of increasing conductivity. In the second, conductivity sensors were embedded in concrete
cylinders and interrogated over a 25-week period during initial set and curing of the concrete. Analysis of the measured
data shows that the passive conductivity sensors were successful in detecting a variety of conductivity levels in the
concrete.
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