Using X-Ray Fluorescence to Assess Soil Subgrade Stabilization Competency During Construction Inspection

Abstract

A large portion of transportation corridor projects use lime and other calcium-based stabilizers to reduce soil plasticity, increase shear strength, reduce compressibility, and reduce volume changes when subjected to variations in water content. While design and construction practices for subgrade stabilization have been standardized, there is no extant quality control measures, particularly measures that are timely, cost effective, and accurate. Therefore, this study was undertaken to evaluate the ability of portable handheld X-ray fluorescence (PXRF) to detect calcium stabilizers in soil samples. The accuracy of Whole Rock XRF (WXRF) was evaluated and used to verify a variety of PXRF measurement techniques, including scan duration, particle size, and sample type. Additionally, the viability of PXRF in measuring soil sulfate content was investigated. It was concluded that the WXRF method is highly accurate in detecting both calcium and sulfate in soils, with average magnitude of deviation between WXRF-determined stabilizer content and actual stabilizer content of 0.3%. While the PXRF method found to be less accurate than WXRF, the average magnitude for clay samples was 2.1% and 10.6% for sand samples. Moreover, the existing calibration libraries do not require slope correction for calcium contents in lower ranges, but do not accurately measure calcium content in higher ranges. The calibration libraries for sulfate detection are able to accurately detect sulfate contents in the range of 0 to 8%, but require individual calibration coefficients.