Evaluating Applications of Field Spectroscopy Devices to Fingerprint Commonly Used Construction Materials (2013)

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56 A p p e n d i x B This appendix presents generic procedures for the proposed spectroscopic methods. Those procedures were first imple- mented in the laboratory and then re-evaluated under field conditions. As a result, field operation manuals for the most successful spectroscopic methods, attenuated total reflec- tance (ATR) and X-ray fluorescence (XRF), were developed (see Appendix D). Generic FTiR Testing procedure Scope This test method covers sample preparation, acquisition of infrared (IR) spectra, and comparison of the sample IR spectra with reference (standard) spectra. The concentration of each chemical component is determined by analyzing IR spectra on the basis of the Beer-Lambert law. Apparatus The apparatus includes the following: • Spatula (for solids and extremely viscous liquids) and pipette (for mobile liquids); • ATR gas cell (for volatile liquids) (optional); • Solvent (for solutions); • Acetone (for removal of test material from the ATR crystal surface); • Fourier transform infrared (FTIR) spectrometer with IR transmission window or horizontal ATR module; and • Personal computer (desktop or laptop) with MS Excel or similar spreadsheet analysis software (optional). Sample Preparation Liquid Sample The following methods are used: • IR Transmission Method. Use sealed or semipermanent transmission cell for nonvolatile or semivolatile liquids. Use gas cell for volatile liquids. Use salt optic (e.g., KBr or NaCl) windows for viscous liquids. Do not use salt optics when water is present in a sample. • ATR Method. Use pipette to draw the mobile liquid into and put enough material to cover the entire ATR diamond sur- face. Use a sealed ATR cell for volatile liquids and solutions with volatile solvent. The heated ATR gas cell is optional for extremely volatile liquids. Use small spatula or screwdriver for extremely viscous materials (e.g., asphalt binder) to place enough material to cover the entire ATR diamond surface. It should be noted that the transmission method will be used over the ATR method only for material–method combinations that do not yield useful results using the ATR method, which is more amenable to field use. This applies to all sample types. Paste, Emulsion, and Slurry Sample The following methods are used: • IR Transmission Method. Use KBr or NaCl optics, as done for viscous liquids. • ATR Method. Use small spatula or screwdriver to place enough material to cover the entire ATR diamond surface. Solid Sample Preparation The following methods are used: • IR Transmission Method. For grindable powders, prepare a compressed KBr or KCl pellet or a mineral oil mull. For coarse or hard organic powders, mix sample with KBr/KCl in 1:10 proportion (use 1:50 proportion for inorganic samples). For amorphous solids, mold or hot-press the sample to pre- pare self-supporting film. Minimize the thickness of sample for highly absorptive materials. • ATR Method. For grindable powders and fibrous and elastomeric materials, place enough material to cover the Generic Spectroscopic Testing Procedures

57 entire ATR diamond surface and apply pressure to ensure full contact between the sample and the ATR diamond surface. For moldable materials, prepare self-supporting film before placing sample on the ATR diamond surface. For soluble solids, use volatile solvent for soluble materials to cast the material into a film. Heat the sample to remove all residual solvent. Be sure to record the solvent used in the preparation in case residual solvent remains. Control Sample Preparation The control sample is a sample of material with the designated chemical composition that is to serve as a reference for com- parison to test samples. If the concentration of a chosen component in the designated mixture or solution is analyzed, several control samples should be prepared by mixing the component of interest with the neat/original material in different proportions. The mixing procedure should com- ply with the original procedure used by a manufacturer to produce the designated material. In some cases, it may be necessary to dissolve a solid (or liquid) sample in a solvent to obtain a satisfactory spectrum. Common solvents, such as acetone, methanol, n-hexane, or water, will be used as necessary. Testing Procedure The testing procedure is as follows: • Prepare control sample, if required. • Obtain infrared spectrum of the control sample as specified by the FTIR equipment user manual. • Collect test material according to an ASTM/AASHTO pro- cedure, if applicable. • Prepare test sample as specified above. • Obtain infrared spectrum as specified in the FTIR equip- ment user’s manual. • Compare the test sample spectrum with that of the control sample by using an appropriate method of analysis, as described below. Data Reduction and Analysis The data for the FTIR spectroscopic analysis are collected in absorbance units over the typical wavelength number range (4,000 cm-1 to 400 cm-1 for FTIR spectroscopes). The tabu- lated data may be plotted for graphical representation (absor- bance on the y-axis versus wavelength number on the x-axis). Several methods of analysis are available depending on the objectives of the test. Confirmation of a known chemical composition is a primary objective of the quality control procedure. For this purpose, the infrared spectrum of a test sample can be compared with that of a control sample in terms of correlation (R2) or in terms of significance of the difference (Student’s t-test). To analyze an unknown material, other statistical methods, such as multiple regression and principle component analysis, can be used concurrently with spectra libraries available in the literature. Generic Raman Testing procedure Scope This test method covers preparing samples of the designated material, obtaining Raman spectra of the samples, and comparing the spectra to reference (standard) spectra of the material and components of the material. The concentrations of specific chemical components are determined from the analysis of Raman spectra of each pure (100%) component using the same measurement conditions. Apparatus The apparatus includes the following: • Spatula (for solids and extremely viscous liquids) and pipette (for mobile liquids); • Mortar and pestle to grind course solids; • Disposable 2-mL glass vials or 1-in. × 3-in. glass slides; • Solvents (for preparing solutions or performing simple extractions); • Portable Raman analyzers with 785-, 976-, and 1,064-nm laser excitation; and • Laptop computer with Raman VISTA spectral analysis software. Sample Preparation Liquid Sample For liquids, a pipette sample is prepared in 2-mL glass vials. Paste, Emulsion, and Slurry Sample For the paste, emulsion, and slurry samples, use a small spatula to cover ~½-in. square glass slides. Solid Sample Preparation The solid sample preparation includes the following: • Fine Powders. Use small spatula to place samples into 2-mL glass vials. • Course Powders. Use mortar and pestle to grind to reason- able powder, then small spatula to place into 2-mL glass vials.

58 Control Sample Preparation The control sample is a sample of material with the designated chemical composition that is to serve as a reference for com- parison to test samples. If the concentration of a chosen component in the designated mixture or solution is analyzed, several control samples should be prepared by mixing the component of interest with the neat (original) material in different proportions. The mixing procedure should comply with the original procedure used by a manufacturer to produce the designated material. In some cases, it may be necessary to dissolve a solid (or liquid) sample in a solvent to obtain a satisfactory spectrum. Common solvents, such as acetone, methanol, n-hexane, or water, will be used as necessary. Testing Procedure The testing procedure is as follows: • Prepare control sample, if required. • Place the glass vial or slide containing the control sample onto the Raman sample holder. • Measure the Raman spectrum as specified in the user’s manual (e.g., set laser to 400 maw and acquisition time to 1 min). • Collect test material according to an ASTM/AASHTO procedure, if applicable. • Prepare test sample as specified above. • Place the glass vial or slide containing the test sample onto the Raman sample holder. • Measure the Raman spectrum as specified in the user’s manual. • Compare the test sample spectrum to the control sample using the ChemID software described below. Data Reduction and Analysis Raman spectra typically consist of peaks distributed between 0 and 4,000 cm-1 shifted from the laser excitation wavelength, which are attributable to molecular vibrations. The peak position corresponds to the energy of the vibration, while the peak intensity corresponds to the concentration of the vibra- tion (or the chemical). Material Identification Real-Time Analyzers’ (RTA’s) ChemID software employs four different library search algorithms to identify an unknown chemical. In essence, the measured spectrum is subtracted from all of the spectra in a stored library (database), where a perfect match equals zero. After subtraction, all of the library spectra are ranked with the lowest value (closest to zero) representing a match. Successful analysis requires populating the library with spectra of chemicals or materials likely to be analyzed. Consequently, highway materials must be measured as references. Material Quantification RTA’s S-Quant software can be used to quantify up to five components in a mixture. If the components are known, their spectra are loaded and weighted by percent until the mea- sured spectrum is recreated (based on peak intensities). If the components are unknown, they can be identified using the ChemID program. Generic xRd/xRF Testing procedure Scope This test method covers preparing a sample of the designated material (the sample) and performing X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis of the sample. XRD analysis is used to identify chemical structure of the sample on the basis of the comparison of the diffraction peaks against a library of known crystalline materials. XRF analysis is used to quantify sample components on the basis of the intensity of their characteristic fluorescent radiation. Apparatus The apparatus used includes the following: • Bruker D5005 X-ray diffractometer, • inXitu XRD/XRF Terra analyzer and laptop computer with custom software, and • Innov-X Systems portable XRF analyzer with custom software and personal digital assistant. Sample Preparation The methods of sample preparation are as follows: • XRF Method. No sample preparation is required. This method can be conducted on any surface and type of material. • XRD Method. Oven-dry or air-dry liquid sample. Grind or pulverize solid, powder, and extracted pigments samples to reduce particle size. If only qualitative evaluation of material components is required, samples may remain wet. There are no control samples required for XRD and XRF analyses.

59 XRD Testing Procedure The XRD testing procedure is as follows: • Prepare test sample as specified above. • Place sample into a sample holder. Alternatively, smear uniformly onto a glass slide, assuring a flat upper surface, pack into a sample container, or sprinkle on double sticky tape. • Place sample holder or container into an X-ray diffractometer. • Obtain diffractogram of the sample as specified in the equipment user’s manual. • Reduce and analyze the data, as described below. XRD Data Reduction and Analysis Qualitative and quantitative analysis of the diffractograms will be performed using the Jade v.8.5 software with reference to the International Centre for Diffraction Data database and the American Mineralogist Crystal Structure Database. XRF Testing Procedure The XRF testing procedure is as follows: • Turn on portable XRF device. • Attach the X-ray tube of the device to the sample surface. • Obtain the fluorescence energy spectrum of the test sample. • Reduce and analyze the data, as described below. XRF Data Reduction and Analysis The software provided with the Innov-X portable analyzer automatically reduces the data and provides a list of metal concentrations that can be downloaded in Excel format.