Feasibility study on corrosion monitoring of a concrete column with central rebar using BOTDR

Yijie Sun 1, Bin Shi 1, Shen-en Chen 2, Honghu Zhu1, Dan Zhang 1 and Yi Lu 1

1 School of Earth Sciences and Engineering, Nanjing University, Nanjing, China

2 Department of Civil and Environmental Engineering, University of North Carolina Charlotte, NC 28223, USA

(Received May 20, 2012, Revised March 1, 2013, Accepted March 4, 2013)

Smart Structures and Systems, Vol. 13, No. 1 (2014) 041-053


Fulltext link: http://www.techno-press.org/?page=container&journal=sss&volume=13&num=1

Abstract. Optical fiber Brillouin sensor in a coil winding setup is proposed in this paper to measure the expansion deformation of a concrete column with a central rebar subjected to accelerated corrosion. The optical sensor monitored the whole dynamic corrosion process from initial deformation to final cracking. Experimental results show that Brillouin Optical Time Domain Reflectometer (BOTDR) can accurately measure the strain values and identify the crack locations of the simulated reinforced concrete (RC) column. A theoretical model is used to calculate the RC corrosion expansive pressure and crack length. The results indicate that the measured strain and cracking history revealed the development of the steel bar corrosion inside the simulated RC column.

Keywords: rebar corrosion; expansion pressure; BOTDR; optical fiber; distributed sensing monitoring

1. Introduction

Steel corrosion is one of the predominant factors for the degradation of steel reinforced concrete (RC) structures especially for structures exposed to aggressive environments. Corrosion of steel rebar is considered negligible when it is fully surrounded by the alkaline environment of concrete. However, corrosion can be introduced during penetration of chloride ions and carbon dioxide. To quantify the rate of corrosion, electro-chemical methods such as corrosion potential, AC impedance, half-cell and linear polarization methods have been suggested (Andrade et al. 2002, Cheng et al. 2004, Hussain et al. 2001, Ismail et al. 2006, Poursaee et al. 2009). However, most of these methods are difficult to set up for in-situ monitoring.

Corrosion of rebars typically results in expansion of ferric materials which in turn induces straining to the surrounding concrete through volumetric expansion. This paper suggests using fiber optic sensors (FOS) to monitor corrosion process within RC structures. FOS technologies are attracting considerable interests due to the apparent advantages including their immunity to electromagnetic interference, their resistance to chemical attack and their high sensitivity and accuracy. Also due to the low cost of the sensors, FOS is ideal for rebar corrosion detection for a large coverage area.


2. Working principle of BOTDR

3. Theoretical analysis of corrosion cracking

3.1 Calculation of crack length

3.2 Calculation of expansion pressure

4. Experiment

4.1 Materials and equipments

4.2 Specimen fabrication

4.3 Test procedure

5. Results and discussion

6. Conclusions


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