Reproducibly reversible fiber loop ringdown water sensor embedded in concrete and grout for water monitoring

Abstract A novel fiber optic water sensor based on the evanescent field-fiber loop ringdown (EF-FLRD) technique is described. After removal of the plastic jacket of a section of single mode fiber, followed by chemical etching of the fiber cladding partially, this section of bare fiber (sensor head) was placed inside a concrete mixture. Presence of water in the concrete changes the optical refractive index of the medium that is the interface between the bare etched fiber surface and the concrete, and a change in ringdown time is recorded due to a change in EF scattering loss occurred in the sensor head. Continuous monitoring of ringdown time, the water sensors read diligent data about variations of the water inside the concrete after tens of ml water is poured on the surface of a concrete bar. Eight EF-FLRD water sensor units were constructed and the sensors were embedded in different concrete bars to detect presence of water inside the concrete. The EF-FLRD water sensors show instant response. The demonstrated detection sensitivity is 10 ml water when it is poured to the surface of a concrete bar with approximate dimensions of 30 cm × 5 cm × 5 cm and the signal-to-noise ratio is 86, corresponding to a detection sensitivity limit of 0.12 ml. In addition to fast response, high sensitivity, additional unique advantage of the EF-FLRD water sensor over its counterparts, such as polymer-coated FBG water sensors, is high reversibility. The EF-FLRD water sensors embedded in concrete demonstrate to be highly reversible when tested in water–dry–water–dry duty cycles for as long as 43 h. Free of using temperature sensitive optical components in the sensor head, the EF-FLRD water sensor is immune to temperature variations in the concrete. This new type of fiber optic water sensor will have broad applications in long-term monitoring of presence/absence of water inside concrete as well as in concrete property characterization.

[1]  P. Rastogi,et al.  Relative humidity sensor with optical fiber Bragg gratings. , 2002, Optics letters.

[2]  Kenneth T. V. Grattan,et al.  Demonstration of a fibre-optic sensing technique for the measurement of moisture absorption in concrete , 2006 .

[3]  Mohammod Ali,et al.  Concrete Moisture Content Measurement Using Interdigitated Near-Field Sensors , 2010, IEEE Sensors Journal.

[4]  T. L. Yeo,et al.  Optical fiber sensors for monitoring ingress of moisture in structural concrete , 2006 .

[5]  Max B. Reid,et al.  Temperature dependence of fiber optic Bragg gratings at low temperatures , 1998 .

[6]  Kenneth T. V. Grattan,et al.  Monitoring Ingress of Moisture in Structural Concrete Using a Novel Optical-Based Sensor Approach , 2006 .

[7]  T. L. Yeo,et al.  Characterisation of a polymer-coated fibre Bragg grating sensor for relative humidity sensing , 2005 .

[8]  Tong Sun,et al.  Development and Longer Term In Situ Evaluation of Fiber-Optic Sensors for Monitoring of Structural Concrete , 2009, IEEE Sensors Journal.

[9]  Shiquan Tao,et al.  Optical fiber humidity sensor based on evanescent-wave scattering. , 2004, Optics letters.

[10]  Hans-Peter Loock,et al.  Chemical Sensing Using Fiber Cavity Ring-Down Spectroscopy , 2010, Sensors.

[11]  R Aneesh,et al.  Zinc oxide nanoparticle based optical fiber humidity sensor having linear response throughout a large dynamic range. , 2011, Applied optics.

[12]  Jiong Hu,et al.  Use of a Moisture Sensor for Monitoring the Effect of Mixing Procedure on Uniformity of Concrete Mixtures , 2005 .

[13]  I. Ioannou,et al.  In-situ measurement of liquid phase moisture in cement mortar , 2012 .

[14]  T. L. Yeo,et al.  Optical fibre sensors for the measurement of concrete sample properties following exposure to freeze/thaw tests , 2009 .

[15]  D. Cleland,et al.  Assessment of the durability of concrete from its permeation properties: a review , 2001 .

[16]  A. Mendez,et al.  Applications Of Embedded Optical Fiber Sensors In Reinforced Concrete Buildings And Structures , 1990, Other Conferences.

[17]  Kenneth T. V. Grattan,et al.  Fibre optic chemical sensor systems for internal concrete condition monitoring , 2004, European Workshop on Optical Fibre Sensors.

[18]  James J. Beaudoin,et al.  Modeling ion and fluid transport in unsaturated cement systems in isothermal conditions , 2005 .

[19]  Chuji Wang,et al.  Fiber Loop Ringdown — a Time-Domain Sensing Technique for Multi-Function Fiber Optic Sensor Platforms: Current Status and Design Perspectives , 2009, Sensors.

[20]  P. Radhakrishnan,et al.  A fiber optic smart sensor for studying the setting characteristics of various grades of cement , 2006 .

[21]  T. L. Yeo,et al.  Fibre-optic sensor technologies for humidity and moisture measurement , 2008 .

[22]  Banshi D. Gupta,et al.  A novel probe for a fiber optic humidity sensor , 2001 .

[23]  Chuji Wang,et al.  Fiber ringdown pressure sensors. , 2004, Optics letters.

[24]  Sunil K. Khijwania,et al.  An evanescent-wave optical fiber relative humidity sensor with enhanced sensitivity , 2005 .

[25]  Chamini Herath,et al.  High-sensitivity fiber-loop ringdown evanescent-field index sensors using single-mode fiber. , 2010, Optics letters.

[26]  Zhongjun Zhao,et al.  A low cost fiber-optic humidity sensor based on silica sol–gel film , 2011 .

[27]  Determining the moisture content in concrete with a fibre optic Mach-Zehnder interferometer: a feasibility study , 2001 .

[28]  Chuji Wang,et al.  Fiber loop ringdown for physical sensor development: pressure sensor. , 2004, Applied optics.

[29]  Chamini Herath,et al.  Fabrication and characterization of fiber loop ringdown evanescent field sensors , 2010 .

[30]  Chuji Wang,et al.  Fiber loop ringdown DNA and bacteria sensors. , 2011, Journal of biomedical optics.

[31]  Hiroyuki Sasaki,et al.  A humidity sensor based on a hetero-core optical fiber , 2010 .

[32]  Alan D. Kersey,et al.  Fiber optic sensors in concrete structures: a review , 1996 .

[33]  Gangbing Song,et al.  Recent applications of fiber optic sensors to health monitoring in civil engineering , 2004 .