John Nieber, Professor, Bioproducts and Biosystems Engr
Subgrade materials provide the foundation for both asphalt and concrete pavements, and the compaction of these materials to optimum density is critical for the longevity of the overlying pavement. Current methods of measuring compaction density and moisture content include gravimetric sampling as well as nuclear (gamma attenuation for density and neutron scattering for moisture). Gravimetric methods are very time consuming, and there is a desire (expressed by the FHWA) to move away from nuclear methods for reasons of personal safety. There is now an interest to measure soil matric suction in compacted soils as this parameter is considered to more closely represent the mechanical strength performance of the compacted materials. There is also interest in developing or adapting methods for measurement of moisture content of compacted soil materials using more benevolent methods than those offered by nuclear-based technologies. This research project investigates several methods of measuring the moisture status of compacted unsaturated materials. The advantages and disadvantages of the various methods are described and quantified in terms of accuracy and precision of measurement, cost of measurement, rapidity of measurement, and the resilience of the measurement instruments/sensors to typical in situ conditions. Specifications for procedures in using these methods and interpreting results are included based on the results derived in this investigation with some reference to reports in the published research literature.