intrinsically smart cement-matrix composites topic 5
TRANSCRIPT
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Intrinsically smartcement-matrix composites
Topic 5
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Reading assignment
Chung, Composite Materials, Ch. 13. No. 130, under “Publications – cement” in
website http://www.wings.buffalo.edu/academic/department/eng/mae/cmrl
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Functions
Structural Strain/stress sensing Damage sensing Temperature sensing Electromagnetic interference (EMI) shielding Vibration reduction Self-heating
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Applications of strain-stress sensing
Structural vibration controlTraffic monitoringWeighing (including weighing in
motion)Building facility managementSecurity
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Strain/stress sensing
PiezoresistivityDirect piezoelectricity
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PiezoresistivityChange of electrical resistivity due to
strainGage factor = fractional change in
resistance per unit strain (more than 2)Gage factor up to 700 attained in
carbon fiber reinforced cement
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With carbon fiber
Tension
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With carbon fiber
Tension
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Without carbon fiber
Tension
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Applications of damage sensing
Structural health monitoringDamage/microstructural
evolution study
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Damage sensing methods
Acoutic emissionElectrical resistivity
measurementOptical fiber sensor
embedment
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Resistance measurement methods
Volume resistance (for sensing the damage of a volume)
Surface resistance (for sensing the damage of the surface)
Contact resistance (for sensing the damage of an interface)
Apparent volume resistance (for sensing the damage of an interface between dissimlar materials)
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A1 A2 A3 A4
B4B3B2B1
160
40
40
140
20 20 20 2080
Flexure
Dimensions in mm
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With carbon fiber
Flexure
Surface resistance at compression side
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Surface resistance at tension side
With carbon fiber
Flexure
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Through-thickness resistance
With carbon fiber
Flexure
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Oblique resistance
With carbon fiber
Flexure
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Oblique
Surface –tension
Through-thickness
Surface - compression
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Mortar (without fiber) during freeze-thaw cycling
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Without freezing
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Carbon fiber concrete under repeated
compression
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Interface between concrete and steel rebar under cyclic shear
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Interface between old and new mortar
under cyclic shear
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Interface between unbonded mortar elements
under cyclic compression
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Interface between concrete and its carbon fiber epoxy composite
retrofit
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Applications of temperature sensing
Thermal controlStructural operation controlHazard monitoring
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Temperature sensing methods
ThermocouplesThermistors
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Cement-based thermistor
Carbon fiber reinforced cementActivation energy = 0.4 eV
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Table 2.2 Resistivity, critical voltage and activation energy of five
types of cement paste.
Activation energy (eV) Formulation Resistivity at 20oC (.m)
Critical voltage
at 20oC (V) Heating Cooling
Plain Silica fume Carbon fibers + silica fume Latex Carbon fibers + latex
(4.87 ± 0.37) x 103
(6.12 ± 0.15) x 103
(1.73 ± 0.08) x 102
(6.99 ± 0.12) x 103
(9.64 ± 0.08) x 102
10.80 ± 0.45
11.60 ± 0.37
8.15 ± 0.34
11.80 ± 0.31
8.76 ± 0.35
0.040 ± 0.006
0.035 ± 0.003
0.390 ± 0.014
0.017 ± 0.001
0.018 ± 0.001
0.122 ± 0.006
0.084 ± 0.004
0.412 ± 0.017
0.025 ± 0.002
0.027 ± 0.002
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Cement-based thermocouple
Carbon fiber reinforced cement (p-type)
Steel fiber reinforced cement (n-type)pn-junction70 microvolts/degree C
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Thermoelectric cement-based materials
Absolute thermoelectric power tailored by using conductive admixtures
Carbon fiber for p-type behaviorSteel fiber for n-type behavior
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Effect of stainless steel fiber (60 micron diameter)
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Applications of electrically conducting cement-based materials
EMI shieldingElectrostatic protectionLightning protectionCathodic protectionSelf-heatingLateral guidance in automatic
highways
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Lane Lane
(a) (b)
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Cement pastes (with 1 vol.% conductive admixture)
Steel fiber (8 microns) 40 ohm.cm Carbon fiber (15 microns) 830 ohm.cm Carbon nanofiber (0.1 micron) 12,000 ohm.cm Graphite powder (0.7 micron) 160,000 ohm.cm Coke powder (less than 75 microns) 38,000 ohm.cm