Intrinsically smart cement-matrix compositesReading assignmentFunctionsApplications of strain-stress sensingStrain/stress sensingPiezoresistivitySlide 7Slide 8Slide 9Applications of damage sensingDamage sensing methodsResistance measurement methodsSlide 13Slide 14Slide 15Slide 16Slide 17Slide 18Mortar (without fiber) during freeze-thaw cyclingSlide 20Slide 21Without freezingSlide 23Carbon fiber concrete under repeated compressionSlide 25Slide 26Interface between concrete and steel rebar under cyclic shearSlide 28Interface between old and new mortar under cyclic shearSlide 30Interface between unbonded mortar elements under cyclic compressionSlide 32Slide 33Interface between concrete and its carbon fiber epoxy composite retrofitSlide 35Slide 36Applications of temperature sensingTemperature sensing methodsCement-based thermistorSlide 40Slide 41Slide 42Cement-based thermocoupleSlide 44Slide 45Thermoelectric cement-based materialsEffect of stainless steel fiber (60 micron diameter)Slide 48Slide 49Slide 50Applications of electrically conducting cement-based materialsSlide 52Slide 53Slide 54Slide 55Cement pastes (with 1 vol.% conductive admixture)Intrinsically smartcement-matrix compositesTopic 5Reading assignmentChung, Composite Materials, Ch. 13.No. 130, under “Publications – cement” in website http://www.wings.buffalo.edu/academic/department/eng/mae/cmrlFunctionsStructuralStrain/stress sensingDamage sensingTemperature sensingElectromagnetic interference (EMI) shieldingVibration reductionSelf-heatingApplications of strain-stress sensingStructural vibration controlTraffic monitoringWeighing (including weighing in motion)Building facility managementSecurityStrain/stress sensingPiezoresistivityDirect piezoelectricityPiezoresistivityChange of electrical resistivity due to strainGage factor = fractional change in resistance per unit strain (more than 2)Gage factor up to 700 attained in carbon fiber reinforced cementWith carbon fiberTensionWith carbon fiberTensionWithout carbon fiberTensionApplications of damage sensingStructural health monitoringDamage/microstructural evolution studyDamage sensing methodsAcoutic emissionElectrical resistivity measurementOptical fiber sensor embedmentResistance 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)A1A2A3A4B4B3B2B116040401402020 202080FlexureDimensions in mmWith carbon fiberFlexureSurface resistance at compression sideSurface resistance at tension sideWith carbon fiberFlexureThrough-thickness resistanceWith carbon fiberFlexureOblique resistanceWith carbon fiberFlexureOblique Surface –tensionThrough-thicknessSurface - compressionMortar (without fiber) during freeze-thaw cyclingWithout freezingCarbon fiber concrete under repeated compressionInterface between concrete and steel rebar under cyclic shearInterface between old and new mortar under cyclic shearInterface between unbonded mortar elements under cyclic compressionInterface between concrete and its carbon fiber epoxy composite retrofitApplications of temperature sensingThermal controlStructural operation controlHazard monitoringTemperature sensing methodsThermocouplesThermistorsCement-based thermistorCarbon fiber reinforced cementActivation energy = 0.4 eVTable 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 ± 0.002Cement-based thermocoupleCarbon fiber reinforced cement (p-type)Steel fiber reinforced cement (n-type)pn-junction70 microvolts/degree CThermoelectric cement-based materialsAbsolute thermoelectric power tailored by using conductive admixturesCarbon fiber for p-type behaviorSteel fiber for n-type behaviorEffect of stainless steel fiber (60 micron diameter)Applications of electrically conducting cement-based materialsEMI shieldingElectrostatic protectionLightning protectionCathodic protectionSelf-heatingLateral guidance in automatic highwaysLane Lane (a) (b)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