| dc.description.abstract | Chemically stabilized subgrades increase the overall quality of pavements compared to non-treated subgrades. Currently, there is no efficient way to detect chemical stabilizers (CS) in pavement subgrades. Generally, only one test indicating the presence of stabilizers is used, however it is rarely mentioned in the design specifications and can only test the presence of stabilizer, not the concentration. Using X-ray fluorescence (XRF) can provide a quantitative measurement of stabilizer content in soils. Previous research at the University of Oklahoma using a Portable Handheld XRF (PHXRF) device showed the need for a unique calibration for chemical stabilizers in soils. Such a calibration can improve measurements of a PHXRF for determining stabilizer content. To create a new calibration, standard samples were made using different soils, chemical stabilizers, and a range of stabilizer content to create a large number of combinations. The method developed with the PHXRF uses the calcium oxide (CaO) concentration measured in raw soil (without CS), CS, and mixed soil (with CS) to determine the amount of CS in the mixed soil. Additionally, an independent laboratory measured the actual CaO content of each sample using the Whole Rock XRF Analysis, which is a validated technique to detect CS in soils. Samples were also subjected to CaO measurement with the PHXRF device for comparison. Through the calibration process, both values, actual (Whole Rock XRF) and experimental (PHXRF), were used to calculate the correction factor to modify the experimental values to best fit the actual ones. This correction factor was used to develop a new calibration. Two validation procedures were performed to determine the accuracy of the new calibration. First, standard samples were subjected to CaO measurement with the PHXRF device using the new calibration to compare to results of the previous values measured during the calibration. Results closer to the actual values mean that the new calibration improved the device measurement. Other samples not used for the calibration were also prepared and subjected to CaO measurement using the PHXRF device. Two new calibrations were made during this research, one for clay soils and one for sandy soils. The results showed that the PHXRF device provides better CaO content measurements when the coefficients of calibration were applied. The comparison between the new calibrations and the old ones for several samples demonstrated the improvement. The average difference between the SC measurements performed by the device and the actual SC were lower using the new calibrations. However, the new calibration was less accurate than another existing calibration for some high concentration clay samples. Therefore, more studies trying to explain this observation are recommended. Moreover, some additional experiments in the field using the new calibrations are recommended to assess the usability and the accuracy of the new calibrations for quality control purposes. Improving the measurement of SC in soil can significantly improve quality control measures and forensic investigations of pavements leading to increased confidence when stabilizing soils. | en_US |
