Environmental Concrete Strain
Concrete Strain Transducer - KB/XB
Description
A "KB" sensor measures the strain in a PCC slab due to material shrinkage and environmental forces. A "XB" sensor, mounted within the KB sensor, is a thermocouple necessary for 17 temperature correction of the measured strain. Data is automatically collected once every 15 minutes. The KB sensor is a strain transducer, with an active gage length of 100 mm, and a low modulus case designed to measure strain in materials undergoing a transition from a compliant state to a hardened state (like concrete). The sensor is self-temperature compensated, having a linear thermal expansion coefficient similar to concrete. The attached "XB" thermocouple sensor permits temperature measurement at the exact location of the sensor.
Manufacturer
Tokyo Sokki KM-100BT.
Location and Quantity
KB sensors are embedded into the concrete surface layer near the top and bottom of the slab.
There are 4 KB sensors in MnROAD test cell 60.
Current Status
These sensors have performed very well and continue to report data.
MnROAD Database Table
Data has been collected automatically every 15 minutes over the life of each sensor. Data can be found in MnROAD database tables: MNR.KB_VALUES, MNR.XB_VALUES, MNR.KB_INITIAL_VALUES.
Concrete Vibrating Wire Strain Gauge [low modulus] - VM/XM
Description
A "VM" is a Geokon 4200L sensor, similar to a VW sensor except the metal case is constructed of a low modulus material. An attached thermistor "XM" sensor is used for temperature correction of the strain due to differences in coefficient of thermal expansion between the steel sensor and the concrete it is embedded into. See the description for VW more details. These sensors are only located in Test Cell 60.
Concrete Vibrating Wire Strain Gauge [short gauge length] - VG/XG
Description
A "VG" sensor measures the strain in a PCC slab due to material shrinkage and environmental forces. A "XG" sensor, mounted to the VG sensor, is a thermistor necessary for temperature correction of the measured strain. Data is automatically collected every 15 minutes. The VG sensor is a small (active gage length = 51 mm) vibrating wire stain gauge consisting of a taut wire that is anchored between two end flanges and surrounded by a protective tube. The wire is electro-mechanically excited, causing it to vibrate at its natural 18 frequency. The resonant frequency of the wire changes with the tension. Thus the strain exerted on the flanges by movement in the PCC slab changes the frequency of vibration, which can be correlated to strain. The attached thermistor (XG) sensor is used for temperature correction of the strain due to differences in coefficient of thermal expansion between the steel sensor and the concrete it is embedded into.
Manufacturer
Geokon 4202 Vibrating Wire Strain Gauges.
Location and Quantity
VG/XG sensors are embedded into the concrete surface layer near the top and bottom of a slab.
Current Status
These sensors continue to function.
MnROAD Database Table
Data has been collected automatically every 15 minutes over the life of each sensor. Data can be found in MnROAD database tables: MNR.VG_VALUES, MNR. XG_VALUES.
Concrete Vibrating Wire Strain Gauge [low modulus] - VW/XV
Description
A "VW" sensor measures the strain in a PCC slab due to material shrinkage and environmental forces. An attached thermistor "XV" sensor is used for temperature correction of the measured strain. Data is automatically collected every 15 minutes. The VW sensor is a medium (active gage length = 153 mm) vibrating wire stain gauge consisting of a taut wire that is anchored between two end flanges and surrounded by a protective tube. The wire is electro-mechanically excited, causing it to vibrate at its natural frequency. The resonant frequency of the wire changes with the tension. Thus the strain exerted on the flanges by movement in the PCC slab changes the frequency of vibration, which can be correlated to strain. Strain values from VW sensors are relative, in that one can only compare the change in value over time, or the change since the initial set of the concrete around the sensor. Initial VW values (at the time of concrete set) can be found in the database table MNR. VW_INITIAL_VALUES. The attached thermistor (XV) sensor is used for temperature correction of the strain due to differences in coefficient of thermal expansion between the steel sensor and the concrete it is embedded into.
Manufacturer
Geokon 4200 Vibrating Wire Strain Gauges.
Location and Quantity 19
VW/XV sensors are embedded into the concrete surface layer near the top and bottom of the slab at several locations in a test panel.
Current Status
These sensors have performed very well, and many original VW/XV sensors continue to function.
MnROAD Database Table
Data has been collected automatically every 15 minutes over the life of each sensor. Data can be found in MnROAD database tables: MNR.VW_VALUES, MNR.XV_VALUES, MNR.VW_INITIAL_VALUES.