Hybrid optical-fibre/geopolymer sensors for structural health monitoring of concrete structures

Abstract

In this work, we demonstrate hybrid optical-fibre/geopolymer sensors for monitoring temperature, uniaxial strain and biaxial strain in concrete structures. The hybrid sensors detect these measurands via changes in geopolymer electrical impedance, and via optical wavelength measurements of embedded fibre Bragg gratings. Electrical and optical measurements were both facilitated by metalcoated optical fibres, which provided the hybrid sensors with a single, shared physical path for both voltage and wavelength signals. The embedded fibre sensors revealed that geopolymer specimens undergo 2.7 mε of shrinkage after one week of curing at 42 • C. After curing, an axial 2 mε compression of the uniaxial hybrid sensor led to impedance and wavelength shifts of 7×10 −2 and -2×10 −4 respectively. The typical strain resolution in the uniaxial sensor was 100 µε. The biaxial sensor was applied to the side of a concrete cylinder, which was then placed under 0.6 mε of axial, compressive strain. Fractional shifts in impedance and wavelength, used to monitor axial and circumferential strain, were 3×10 −2 and 4×10 −5 respectively. The biaxial sensor's strain resolution was approximately 10 µε in both directions. Due to several design flaws, the uniaxial hybrid sensor was unable to accurately measure ambient temperature changes. The biaxial sensor, however, successfully monitored local temperature changes with 0.5 • C resolution.

Self-Sensing Alkali-Activated Materials: A Review

“…Likewise, under tension the resistance of the specimen increases. This behaviour has been widely reported in both AAM [24][25][26]52,57,92] and OPC [106,[117][118][119][120]…”

“…Electrical impedance is frequency dependent, and so sweeping the frequency can lead to a rich dataset. The AC frequency can be selected to minimize or maximize the measurement of capacitive or resistive effects in the sample, depending on the application [24,26,57] and allows for the elimination of polarization if desired [26,52,86]. Overall, however, frequency tends to be selected to produce the highest sensitivity to measurands during characterization [24,55].…”

“…However, as the understanding and the technology of AAM progresses, the need for these additional sensing devices has diminished: interrogation of changes in the electrolytic conductivity of AAM allow them to be directly used as a sensing tool in their own right [22]. As a result, AAM have increased the number of supporting roles in structural health monitoring and maintenance, being used as both structural self-sensing elements (e.g., AAM concrete cubes and beams) [23][24][25], and as self-sensing coatings for OPC concrete substrates [26,27].…”

Crack Monitoring of Operational Wind Turbine Foundations

“…Each FBG strain gauge was installed running along the turbine tower axis, so that the strains caused by overturning moments could be captured. Thermometers were constructed in-house by encapsulating FBGs in two layers of copper capillaries, as outlined in previous work [ 31 ]. This provided a strain-isolated reference for the thermal compensation of nearby tower strains.…”

Smart cements: repairs and sensors for concrete assets

“…Chlorides and moisture are two leading causes of reinforced concrete degradation, and so form the measurands of interest in this work [5]. These degradation pathways are particularly important in a nuclear context, where concrete assets are usually coastal and may underpin safety-critical structures and radiation barriers.…”