Application Note 82: Calibration of Penetration and Softening point in Bitumen using an FOP-38 Fibre Optic Probe Analyser.

July 2006.

Introduction:

Bitumen is used in many fields through out the world and is most notably used from the manufacture of roadways.

This study was undertaken to demonstrate the feasibility of measuring penetration and softening point properties of bitumen. The FOP-38 Fibre Optic Probe Analyser was used for the purpose of this study.

Procedure:

6 samples of bitumen were supplied. The samples were allowed to cool to room temperature and solidify. After experimentation with several sampling methods it was determined that the use of a FOP-38 Fibre Optic Probe analyser gave the only reproducible results. The samples were placed under the probe and scanned over the wavelength range of 720nm to 1100nm in reflectance. A number of scans were collected and each sampling was repeated and presented to the instrument twice. The spectra was collected and then uploaded into NTAS (NIR Technology Australia Software) and Partial Least Squares Regression (PLS) was used to develop a calibration for penetration and softening point.

Results:

Figure 1, below, shows the NIT spectra of the 6 samples of bitumen.

Figure 1: Plot of NIR Spectra for scanned bitumen samples.

Figure 2, below, shows the calibration statistics for the NIR moisture versus reference moisture. The Standard Error of Prediction is 0.03 with a correlation(R²) of 0.95.

Figure 2: Plot NIR penetration value vs. Reference penetration value.

Figure 2 above shows the Standard Error of Prediction is 0.45 with a correlation (R²) of 0.99 for the penetration values.

Figure 3, below, shows the calibration statistics for the softening point values versus the reference values. The Standard Error of Prediction is 0.08 with a correlation (R²) of 0.99.

Figure 3: Plot NIR Predicted FFA value vs. Reference FFA value.

Conclusion:

It can be seen in figures two and three that the FOP-38 used in reflectance can be calibrated to determine the penetration and softening point values in bitumen. Whilst the sample sets are to small for a true calibration they do clearly demonstrate the potential of the analyser.

In figure 1 it can be seen that the absorbance levels of the bitumen are quite high. This is not usual for substances of this nature when measured in reflectance.