SENSOR BASED STRUCTURAL HEALTH MONITORING OF CONCRETE STRUCTURES

Othman Sidek, S.A.Quadri and Hassan bin AfzalCollaborative µ-electronic Design Excellence Centre

Universiti Sains Malaysia

Presented in Université de Sherbrooke

Problems Concerned

Heterogeneous multi sensor data fusion system • To find a simple and affordable monitoring strategy for Alkali-aggregate reaction (AAR), which is one of the root causes for

structural deterioration in concrete.

• To develop heterogeneous multi sensor data fusion system for improving evaluation of concrete structures.

• Fusion of heterogeneous data from acoustic system; electro-mechanical system; optical system and embedded sensors in an efficient way to increase the accuracy and consistency of the acquired data.

• Establishing correlation among surface damage level, internal damage level and the amount of gel concentration in the structure.

• To develop decision-level multi sensor data fusion system by integrating data fusion technology with ANN approach.

FOS Based Sensing Technology• To fabricate and design a novel and unique FOS based sensing technology to detect and measure the level of corrosion inside

concrete structures.

• Application of Polydimethylsiloxane (PDMS) as a coating of optical fiber cable and analysis of overall performance.

• Assessment of overall performance by verifying the output results with provided data.

• Enhancement of proposed sensor with PDMS coating and output analysis.

Terminology

Fiber Optic Sensors(FOS)

• A special kind of sensor that uses optical fiber either as the sensing element ("intrinsic sensors"), or as a means of relaying signals from a remote sensor to the electronics that process the signals ("extrinsic sensors").

Fiber Bragg grating (FBG)

• A type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others.

Polydimethylsiloxane (PDMS)

• Type of silicone elastomer or silicone rubber which contains very useful properties as a base material for various sensing applications.

Data fusion

• Process of combining inputs from various sensors to provide a robust and complete description of an environment or process of interest.

Decentralized Kalman filter

• Robust means to fuse heterogeneous data used as optimal solution to many tracking and data prediction.

National Building Research Institute (NBRI)

• Standard testing method employed to accelerate AAR expansion with different level of alkali concentrations.

Multi-layer perceptron (MLP) network

• Artificial neural network (ANN) which is ideally suited to identify non linear system dynamics.

Schematic Diagram of FOS

Corrosion Detection using FOS based Technology• In reinforced concrete infrastructure, the steel corrosion occurs due to penetration of chloride ions or carbon dioxide.

• The objective of the present investigation is to develop a low-cost FOS based sensing technology for detecting steel corrosion inside reinforced concrete infrastructures and also measure the level of the corrosion occurred in the specific section so necessary steps can be taken effectively.

• A novel FOS based sensing method for detecting the onset of steel corrosion inside reinforced concrete structure with particular application on concrete structures is being studied, developed and experimented in the laboratory.

• The specific sensing method developed will be tested in various conditions and also embedded in cement mortar to demonstrate the feasibility of corrosion sensing.

Source:J. Wu, W. Wu (2010)

Standard Electrical Wireless Sensing Method to Detect Corrosion

• The first and second figure shows the basic wireless sensors without and with switch technology for enhanced detection. After applying the switch (shown in figure-2), the detection accuracy has been improved(shown in the graph).

• There is only one switch in this sensor, which can only indicate whether the steel wire breaks or not and only two corrosion states of the reinforcement can be monitored. Whether or not more corrosion states of the reinforcement can be indicated when more switches with different diameters of steel wires are added into the sensor and how to obtain the relationship between the diameter of the steel wire and the loss of the weight of reinforcement need to be studied further.

Fig.1

Fig.2

Schematic Diagram of EFOCS

Here, the first figure represents Typical layout of corrosion sensors in reinforced concrete structure and the next figure shows the Photograph of fiber optic corrosion sensor.

Source: J. Gao et al.(2011)

Performance Enhancement by Applying PDMS Coating Material in FOS

• Polydimethylsiloxane (PDMS) is a very interesting and exceptional type of silicone elastomer or silicone rubber which contains very useful properties as a base material for various sensing applications.•In the recent years, FOS based fiber Bragg grating (FBG) sensors have been studied, researched and experimented extensively for sensing and measuring several types of physical parameters such as strain, bending, pressure, temperature, and chemicals•It has a unique ability of cross-linking without any sort of difficulty makes it one of the primary choices for numerous micro- and nano- cast applications as a base material or coating material. In case of fiber optic sensing technology, PDMS can be used as a coating material to enhance the sensing and measurement performance for corrosion detection in concrete structures.

• Proposed PDMS-coated FBG can be used as a simple, convenient, and durable chemical sensing element with a high sensitivity, compared with conventional FBG sensors requiring an evanescent wave coupling.

Source: Chang –sub Park et al.(2010)

Heterogeneous Multi sensor Data fusion system A novel integrated multi sensor data fusion approach in structural health monitoring is proposed to monitor AAR reaction in concrete structures

To assess :• Structural integrity of concrete structure.

• Damage at surface level.

• Damage at internal level.

To find :• Total amount of cracking in terms of length and width.

• Correlation between surface damage level with internal damage level.

• Correlation between overall damage level and AAR gel concentration.

Heterogeneous Sensor System Different sensor systems are used at surface and internal level.

• Acoustic sensor system

(Pulse-echo Method)

• Electro-mechanical system(LVDT Sensors)

• Optical systems

(CCD Camera) • Embedded sensors (PZT Piezo electric sensors)

Surface Damage Level

Internal Damage Level

Experimental setup

Data flow diagram

Current work and expected results

Extensive research using heterogeneous sensors to find affordable and sustainable monitoring strategy by applying

• Modified PDMS coated FOS • Multi sensor data fusion • Artificial neural network

Expected outcome • Improved accuracy• High precision • Establishing correlation among surface damage level, internal damage level and the

amount of gel concentration in the structure. • Evaluation of corrosion detection accuracy applying fiber optics sensors with PDMS

materials.