Installation and Calibration of M oisture Probes

1. Installation and Calibration of Moisture Probes Ben Worel ben.worel@state.mn.us Len Palek leonard.e.palek@state.mn.us Minnesota Department of Transportation (MnROAD) More details contact Len for the full presentation & written documentation

2. MnROAD Moisture Probes(Experience With)

3. Installation of Moisture Probes at MnROAD • Bore Hole • Separate Materials • Install Sensors • Flat installation • 1” Sieve #4 Material - Lite Compaction • 3” Material – Heavy Compaction • May add water as needed • Check void ratio – cup sampler

4. Installation of Moisture Probes at MnROAD Sensor Protection to Cabinet Cabinet Setup Campbell CR1000 data logger and multiplexer

5. Calibration Experience with Moisture Probes • Calibration efforts prior to 2012 • 2006 calibrations for TE (manufacturer’s process) • 2009 generic calibration equations are found not useable • 2010 and 2011 experimented with small scale calibrations • 2012 Calibration approach • Procedures developed by Starr and Paltineanu (2002) and refined by Decagon Devices (2010) • MnROAD Experience (Need calibration for each sensor and materials type)

6. Moisture Probe Calibration Lab Equipment • Soil drying containers • Scale or mass balance • Drying oven • Volumetric soil sampler • Calibration containers • Sensors (MnROAD started with Decagon TE and 5TE) • Data collection and storage system

7. Moisture Probe Calibration Procedure • Sample Preparation • Air dry material - Sieve material with #4 (2-5mm) sieve • Preliminary Calibration Procedure • Recording mass and volumes of calibration containers, volumetric samplers, and sensors with wire • Programming the data logger - Create spreadsheet templates • Calibration Procedure • Start with air-dry material • Fill calibration containers with sensors (Compact in 5 lifts – 20% of Max Density) • Weigh containers to determine density • Record sensor output (1 hour of 1 minute intervals) • Sample volumetric moisture content • Record moisture content • Repeat procedure for next moisture content (6 Data Points Required)

8. Moisture Probe Calibration Functions

9. Moisture Probe Calibration Functions Next sensor types - Moisture Block (851) and CS616 (58) calibrations

10. Moisture Probe Generic and Calibration Functions Applied to MnROAD Data With Calibration With (top base) - ~.50 VMC With (bottom base) - ~.35 VMC With Generic Calibration Without (top base) - ~1.30 VMC Without (bottom base) - ~.80 VMC

11. Moisture Gauge - Installation Discussion • Vertical (with forks) or Horizontal (without fork) • Collect Raw data only (no factors) – apply later • Use sieved material around sensor • Sensor Lead Length effect (50’ vs 500’) • Frequency of measurements (MnROAD 15 minutes) • Excitation Voltage (MnROAD 12 volts) • Data Collection Temperature Ranges (Cabinet Temps)

12. Moisture Gauge – Calibration Discussion • Role of material density and moisture measurements? • Differences – maybe soil sampler field? • Does a generic calibration function work for other types of non-capacitance sensors used in pavement research? • Does every sensor installed need a calibration? • Discussion on the process (manufacture vs modified) • Manufacture use same volume of soil compacted in a calibration container • Modified working to get maximum density (minimize voids)

13. Moisture Probe – Data Use Discussion • Can moisture sensors detect bound and unbound water in fine-grained clay materials? • Observe variation in the data • (6 hour running average used) – why? • Observed manufacture calibration factored data above 100% and negative data (why we did a calibration) • Flat vs vertical (eliminate potential of condensation) • Installation of sensor at a material interface • Do the readings vary with temperature extreams • Sensor Recommendations • Capacitance sensors seem the best • Moisture blocks have been improved (not fully tested)