Evaluating Applications of Field Spectroscopy Devices to Fingerprint Commonly Used Construction Materials (Phase IV–Implementation) (2014)

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Standard Practice for Evaluation of Oxidation Level of Asphalt Mixtures by Attenuated Total/Diffused Reflection Infrared Spectrometer AASHTO Designation SP XX-14 1. SCOPE 1.1 This method covers the semi-quantitative evaluation of the oxidation level in an asphalt mixture by measuring its carbonyl content. The method is based on the quantitative analysis of the infrared absorbance/ log (Reflectance) spectrum of an asphalt mixture sample. This sample can be obtained from the pavement surface and may be modified by adding recycled asphalt pavement or shingles (RAP and RAS, respectively). The carbonyl content of a sample in question is compared with predetermined carbonyl content of a non-oxidized (freshly paved) and fully oxidized (milled/removed) samples of asphalt mix. Those samples are obtained from an asphalt plant and a recycled asphalt stockpile, respectively. The asphalt mix samples are scanned by attenuated total reflection (ATR)/ diffused reflection (DR) infrared spectrometer to obtain their corresponding absorbance/ log(Reflectance) spectra. Next, the oxidation level in the samples is calculated based on the absorbance/ log(Reflectance) intensity in the infrared region of frequencies associated with carbonyl content. 1.2 The asphalt mix samples must be in a loose state (not compacted), while the maximum size of aggregate in a sample should pass U.S. sieve #30 (600 µm). 1.3 It is desired to perform ATR/DR testing of an asphalt mix sample at a temperature not exceeding 40°C. 1.4 This procedure may involve hazardous materials, operation, and equipment. This procedure does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this procedure to consult and establish appropriate safety and health practices and to determine the applicability of regulatory limitation prior to use. A-17

2. REFERENCED DOCUMENTS 2.1. ASTM Standards:  To be updated  Yut, I., and Zofka, A., Spectroscopic Evaluation of Recycled Asphalt Materials, Paper 12-1259, In: CD-ROM, 91st Annual TRB Meeting Compendium, January 2012  Yut I., Bernier A., and Zofka A., Development of a Compact Laboratory Aging Procedure for Asphalt Binders, Journal of Association of Asphalt Pavement Technologists, Vol. 81, 2012 3. APPARATUS 3.1 Sampling equipment 3.2 Hammer drill, scoop, and brush for sampling from pavement surface 3.3 Standard AASHTO sieves #8, #16, and #30 for sifting a sample of the loose mix 3.4 Spectroscopic equipment 3.5 Infrared spectrometer equipped with diamond single reflection ATR accessory and load applicator/diffused reflection infrared fourier transform (DRIFT) spectrometer 3.6 Cleaning tools 3.7 99% acetone for cleaning ATR sampling plate after sample is removed. 3.8 Soft cloth or tissue for sample removal. 4. SAMPLE PREPARATION 4.1 Loose Mix Sample. Sieve about 1 kilogram of loose mix through standard US #8, #16, and #30 sieves. Use passing #30 fraction for spectroscopic testing. 4.2 Field Pavement Sample. A sample of powdered asphalt mix from the in-situ pavement surface can be obtained by following procedures: 4.2.1 Drill a ½-in deep and ½-in diameter hole in pavement surface. Use brush and scoop to collect the asphalt powder residue. 4.2.2 Use sampling spoon to scrub binder mastic sample from the in-situ pavement surface. 5. SPECTROSCOPIC EQUIPMENT SETUP 5.1 The ATR/DRIFT spectrometer should be placed on a firm horizontal surface to avoid any vibrational interference with the instrument signal. A-18

5.2 A reliable source of electric power (AC or DC) should be provided to ensure no interference with the spectrometer signal. 5.3 It is recommended to follow the instrument manual in regards to the ambient temperature and moisture. 5.4 The ATR spectrometer should be connected to a data acquisition system (normally, a computer with an accompanying software) all the time during a test. 6. PROCEDURE 6.1 ATR testing of asphalt mix sample 6.1.1 Clean up the surface of the ATR sampling plate by applying soft tissue wetted in 99% acetone. 6.1.2 Collect and store the background spectrum in accordance with the ATR spectrometer manual. 6.1.3 Collect asphalt mix sample using a sampling spoon and place the sample on the ATR sampling plate in amount sufficient for covering the entirety of diamond reflection window. 6.1.4 Apply pressure to the sample by using load applicator attached to the instrument. 6.2 Note: If no load applicator is supplied with the ATR instrument, it is recommended to: (a) ensure sample particle size be not larger than 0.15 mm to avoid increased variability in results, and (b) apply pressure to a sample through the flat surface of a sampling spoon. 6.2.1 Operate ATR spectrometer in accordance to the instrument manual to obtain infrared absorbance/log(Reflectance) spectrum of a sample. Use accompanied data acquisition software to subtract background spectrum, correct baseline, and remove atmosphere- and water-vapor-related absorption bands from the sample spectrum. Store the ATR absorbance spectrum in numerical format for further processing as needed. 6.2.2 Repeat steps described in 6.1.1 through 6.1.4 four (4) more times to establish standard deviation, as explained in Section 9 of this standard. 6.2.3 Interpret the absorbance spectrum of the asphalt mix sample and determine the level of oxidation, as explained in Section 8 of this Standard. 7. SPECTRAL DATA PROCESSING 7.1 Normalization and smoothing of the absorbance spectrum 7.1.1 The absorbance spectrum of a sample should be normalized to the absorbance intensity A at 2920 cm-1 wavenumbers (A2920) by subtracting minimum intensity A-19

value for the given spectrum (Amin) from each reported intensity and dividing the result by difference between A2920 and Amin, as in Equation [1]. 7.1.2 min2920 min AA AAAnorm − − = [1] 7.1.3 The normalized absorbance spectra can be smoothed to reduce noise along the spectral line and thus facilitate determination of relevant absorbance peaks. This can be done using Savitzki-Golay algorithm. 7.2 Note: Both normalization and smoothing of a spectrum can be performed with an accompanied to the ATR/DRIFT instrument software or by an external computational software. 8. DETERMINATION OF OXIDATION LEVEL 8.1 The extent of oxidation is defined as a relative concentration of carbonyl(C=O) and sulfoxide(S=O) chemical functional groups within the sample. The relative concentration, or index of C=O and S=O, is defined as a value of absorbance/log(Reflectance) intensity at 1700 cm-1 and 990 cm-1 wavenumbers, correspondingly. 8.2 To evaluate level of oxidation, the relative concentrations of C=O and S=O in the sample in question should be compared with those in the fully oxidized and non-oxidized samples as shown in Figure A.8.1. Figure A.8.1 Comparison of oxidation levels between oxidized and non-oxidized asphalt samples. A-20

9. PRECISION 9.1 The coefficient of variation (C.O.V.) in measured oxidation indices for one sample is established as a ratio of standard deviation (std) over the mean index value for at least 5 probes from the sample. If the C.O.V. exceeds 25 percent, additional probes should be taken to achieve this threshold. 9.2 Location of the characteristic peaks on an ATR/DRIFT spectrum can vary within ± 10 cm-1 from the values given in this method. A-21