S.K.T. Grattan

Monitoring of Corrosion in Structural Reinforcing Bars: Performance Comparison Using In Situ Fiber-Optic and Electric Wire Strain Gauge Systems

This work addresses the problems of effective in situ measurement of the initiation or the rate of steel corrosion in reinforced concrete structures through the use of optical fiber sensor systems. By undertaking a series of tests over prolonged periods, coupled with acceleration of corrosion, the performance of fiber Bragg grating-based sensor systems attached to high-tensile steel reinforcement bars (ldquorebarsrdquo), and cast into concrete blocks was determined, and the results compared with those from conventional strain gauges where appropriate. The results show the benefits in the use of optical fiber networks under these circumstances and their ability to deliver data when conventional sensors failed.

Development of a Bridge Weigh-in-Motion Sensor: Performance comparison using fibre optic and electric resistance strain sensor systems

This paper addresses the problems of effective in situ measurement of the real-time strain for bridge weigh in motion in reinforced concrete bridge structures through the use of optical fiber sensor systems. By undertaking a series of tests, coupled with dynamic loading, the performance of fiber Bragg grating-based sensor systems with various amplification techniques were investigated. In recent years, structural health monitoring (SHM) systems have been developed to monitor bridge deterioration, to assess load levels and hence extend bridge life and safety. Conventional SHM systems, based on measuring strain, can be used to improve knowledge of the bridges capacity to resist loads but generally give no information on the causes of any increase in stresses. Therefore, it is necessary to find accurate sensors capable of capturing peak strains under dynamic load and suitable methods for attaching these strain sensors to existing and new bridge structures. Additionally, it is important to ensure accurate strain transfer between concrete and steel, adhesives layer, and strain sensor. The results show the benefits in the use of optical fiber networks under these circumstances and their ability to deliver data when conventional sensors cannot capture accurate strains and/or peak strains.

In Situ Cross-Calibration of In-Fiber Bragg Grating and Electrical Resistance Strain Gauges for Structural Monitoring Using an Extensometer

This study addresses the direct calibration of optical fiber strain sensors used for structural monitoring and is carried out in situ. The behavior of fiber-Bragg-grating-based sensor systems when attached to metal bars, in a manner representative of their use as reinforcement bars in structures, was examined and their response calibrated. To ensure the validity of the measurements, this was done using an extensometer with a further calibration against the response of electrical resistance strain gauges, often conventionally used, for comparison. The results show a repeatable calibration generating a suitable geometric factor of extension to strain for these sensors, to enable accurate strain data to be obtained when the fiber-optic sensor system is in use in structural monitoring applications.

Fibre Bragg grating sensors for reinforcement corrosion monitoring in civil engineering structures

Fibre optic strain sensors offer a number of advantages over the current electrical resistance type gauges, yet are not widely used in civil engineering applications. The use of fibre optic strain sensors (with a cross comparison with the output of electrical resistance gauges) to monitor the production of corrosion by-products in civil engineering concrete structures containing reinforcement bars has been investigated and results reported.

Sensors Systems, Especially Fibre Optic Sensors in Structural Monitoring Applications in Concrete: An Overview

Reinforced concrete is the most popular construction material in the world due to its flexibility to make different complicated shapes, yet providing strength, long service life and structural integrity. However, a major issue for reinforced concrete structures is the corrosion of the reinforcement bars (rebars) when exposed to aggressive environmental conditions, such as those in marine or urban environments. The corrosion is normally caused by the ingress of chlorides, as in the case of marine environment, or carbon dioxide, as in the case of urban environment; the latter causes a reduction in the alkalinity of concrete through a process called carbonation and steel loses the protection provided by the concrete. Corrosion products (rust) occupy many times the volume of the original steel and as a consequence the integrity of the structure is severely compromised and occasionally leads to a catastrophic structural failure. Therefore, it is highly desirable to obtain information about factors which initiate the corrosion and the rate of corrosion once it has already started, both of which will help civil engineers to manage their reinforced concrete structures in a cost-effective manner.

Structural health monitoring - better solutions using fiber optic sensors?

This work focuses on results from recent research carried out to create and then investigate the performance of a number of different fiber optic sensor systems developed to monitor the changes occurring to civil engineering structures over time, both physical and chemical and which underpin their structural integrity.

Corrosion induced strain monitoring through Fibre Optic Sensors

The use of strain sensors is commonplace within civil engineering. Fibre optic strain sensors offer a number of advantages over the current electrical resistance type gauges. In this paper the use of fibre optic strain sensors and electrical resistance gauges to monitor the production of corrosion by-products has been investigated and reported.

Calibration of Optical Fiber Refractive Index Sensor with Potential for Structural Corrosion Monitoring

There is a need in industry for new devices for the monitoring of chloride ion ingress in structural concrete. This work reports on the development of a reflective, gold-coated long period grating-based sensor for the measurement of chloride ions in solution, with potential for evaluating the corrosion condition of concrete structures. The sensor scheme is based around a long period fiere grating (LPG)-based Michelson interferometer where the sensor was calibrated and evaluated in the laboratory using sodium chloride solutions, over a wide range of concentrations, from 0.01 M to 4.00 M. The grating response yields shifts in the spectral characteristic of the interferometer, due to the change of refracting index of the solution surrounding it. It was found that the sensitivity of the device could be enhanced over that obtained from a bare fiber by coating the LPG-based interferometer with gold nanoparticles.

Long period grating-based refractive index sensor for chloride concentration measurement

Effective devices for the monitoring of chloride ions are required in industry this work reports on the development of a reflective long period grating-based senor for the measurement of chloride ions in solution. The device is based around a long period fibre grating (LPG)-based Michelson interferometer where the sensor was calibrated and evaluated in the laboratory using sodium chloride solutions, over a wide range of concentrations, from 0.01 M to 4.00 M. The grating response yields shifts in the spectral characteristic of the interferometer, due to the change of refractive index of the solution surrounding it. The work was stimulated by the need for the more effective measurement of the ingress water-borne ions in structural concrete. It was found that the sensitivity of the device could be enhanced over that obtained from a bare LPG by coating the LPG-based interferometer with gold nanoparticles. Devices using this approach were also evaluated and their performance cross-compared.