In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. Fibre Bragg grating (FBG) sensors have emerged as a reliable, in situ, non-destructive tool for monitoring, diagnostics and control in civil structures. The versatility of FBG sensors represents a key advantage over other technologies in the structural sensing field. In this article, the recent research and development activities in structural health monitoring using FBG sensors have been critically reviewed, highlighting the areas where further work is needed. A few packaging schemes for FBG strain sensors are also discussed. Finally a few limitations and market barriers associated with the use of these sensors have been addressed.

Fibre Bragg gratings in structural health monitoring—Present status and applications

Properties and applications of foamed concrete; a review

Chloride threshold level for corrosion of steel in concrete

Mechanical properties of concrete at high temperature—A review

Use of recycled plastics in concrete: A critical review.

Performance of spalling resistance of high performance concrete with polypropylene fiber contents and lateral confinement

Chloride diffusivity of concrete cracked in flexure

In the previous studies on microcracks and rapid chloride permeability tests, microcracks were quantified in terms of total crack length. This was carried out by examining concrete slices after compression tests. No attempts have been made to characterise the microcracks during the compression test prior to the chloride permeability test. In the present study, concrete cylinders were loaded under uniaxial compression between 30% and 95% of the ultimate strength. A non-destructive method of microcrack evaluation was used to study the progressive microcracking in concrete cylinders during compression tests. After the compression test, a rapid chloride permeability test (RCPT) (ASTM C1202) was carried out on a specimen cut from the same cylinder. The total crack length was also determined from the same specimen to compare with the observed microcracking behaviour, assessed by the non-destructive testing. The characteristics of the microcracks in terms of the specific crack area are different when a concrete is under a load and when it is completely unloaded. The chloride permeability of a concrete (after it was unloaded) appears to be influenced by the occurrence of a certain stress level known as the critical stress. When the critical stress is exceeded in a concrete specimen, a comparatively large chloride permeability was measured. Where the critical stress in a specimen is not exceeded, the increase in the permeability is marginal in spite of the large increase in microcracks.

Microcracking and chloride permeability of concrete under uniaxial compression

The physical properties of reactive powder concrete (RPC) at early-age, i.e., the first 24 h from casting, and up to an age of 7 days is investigated experimentally using fibre Bragg gratings (FBGs), a type of fibre-optic sensors. A number of FBG sensors are multiplexed together and embedded directly into the RPC specimens, and the shrinkage and temperature change are measured directly and simultaneously. The final setting time and specimen size effect were also investigated. Results showed that there is an interplay between the shrinkage and temperature. The overall shrinkage for 7 days is 488 μe, with the early-age shrinkage contributing about 77% of this. The temperature curve exhibits a double peak behaviour, with the first peak appears at about 7 h, which is the final setting time. There is a size effect in that smaller prisms have a higher overall shrinkage and lower temperature change than larger prisms.

N Gowripalan

Papers

Performance of spalling resistance of high performance concrete with polypropylene fiber contents and lateral confinement

Chloride diffusivity of concrete cracked in flexure

Microcracking and chloride permeability of concrete under uniaxial compression

Simultaneous measurement of shrinkage and temperature of reactive powder concrete at early-age using fibre Bragg grating sensors

Chloride-ion induced corrosion of galvanized and ordinary steel reinforcement in high-performance concrete