Precast Solutions - May/June 2008 - (Page 22)

electrochemical process that produces an electric Typical Types of Sensors Sensor Type Technology What it can measure: current similar to that of a battery. This electric current spreads out from the rebar into the surrounding concrete, and the resulting voltage is measurable at the surface of the concrete. The amount of current flow is Optical Fiber System interferometric Structure strain/deformation directly proportional to the rate of loss of the steel mass. Optical Fiber System interferometric Acoustic emission There are no geophysical techniques that would indicate the amount of corrosion that had taken place and, therefore, reduce the quality of the rebar. However, Optical Fiber System interferometric Soil pressure monitoring numerous methods can be used to learn whether corrosion is currently active. If corrosion activity is Optical Fiber System polarimetric Weigh in motion of vehicular weights in motion and axial loading; traffic counting monitored and found to be active for a significant period of time, then the “quality” of the rebar will become degraded, and more will be known regarding the MEMS Based Fiber Optics Interferometric; miniaturization of optical Remote operations in harsh settings switch, couplers; power circuits; (electromagnetic and electrical optoelectronics and microprocessors. environments) Optical Time Domain Reflectometry (OTDR) Image Analysis. Automates ASTM C457 Determines the position and degree of damage along the sensor/structure length. Structural crack sensing. Air void analysis in hardened concrete. Resistivity to freeze/thaw cycles. Air content on fresh concrete (in situ). structure’s life cycle. Fiber Optic HOW SMART IS SMART? Smart concrete systems are structural systems with a certain level of autonomy relying on the embedded functions of sensors, actuators and processors. These systems can automatically adjust structural Automated Measurement System Fiber Optic Laser diode and photodetector optical apparatus Acoustic Emission characteristics in response to the change in external disturbance and environments toward structural safety and serviceability as well as the elongation of structural Non-Destructive Testing Prediction of compressive strength failure. service life. Today’s sensor technology is capable of recording Fiber Reinforced Polymer (FRP) Acoustic emission sensing rods Post tension; prestressing applications vibrations (harmonic motion and earthquakes), wind pressure, in-service loading, component creep, snow accumulation, integrity of components, stress-strain Conductivity Sensors Wireless sensor that measures subsurface conditions. single-sided pulse-echo-techniques Corrosive environment caused by carbon dioxide, salt and acid rain. Voids, thickness responses of components and effects of temperature extremes. There are even situations where nuclear, Ultrasound (UT) biological and chemical threat detection devices can be embedded that may prove to be of great significance for security. Eddy Current (ET) Coil impedance Locating rebar and coverage depth. Thermocouple Analog to digital conversion w/ algorithms Constant phase element Temperature CONCRETE COMES “SENSORS” TO ITS What is a sensor? A sensor is a device that converts physical, biological or chemical input into an electrical or Environmental conditions; delamination of CRFP from parent structure. Damage and damage progression. Electrochemical impedance spectroscopy (EIS) Piezoelectric Ceramic (PZT) optical signal. The signal must be measured and transformed into digital format that can be processed Electric Admittance and analyzed efficiently by computers. The information can be used by either a person or an intelligent device monitoring the activity to make decisions that maintain Shape Memory Alloy (SMA) Stress-strain relationships or change a course of action. What is a smart sensor? A smart sensor is simply 22 PRECAST SOLUTIONS | MAY/JUNE 2008

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Precast Solutions - May/June 2008 Contents Sustainability and Practicality Security Blanket A Frank Lloyd Wright Takes Shape Concrete Joins MENSA Precast Lightens Up

Precast Solutions - May/June 2008

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