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

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60 A p p e n d i x C Standard Practice for Identification of Water Reducing, Accelerating, and Retarding Chemical Admixtures in Fresh Portland Cement Concrete by Attenuated Total Reflection Infrared Spectrometer AASHTO Designation SP XX-12 1. SCOPE 1.1 This method covers the qualitative identification of the type of a chemical admixture for portland cement concrete (PCC). The method is based on the qualitative analysis of the infrared absorbance spectra of a pure admixture sample. A pure admixture sample is obtained from the storage or feeding tank in a concrete plant. A pure admixture sample is scanned by attenuated total reflection (ATR) infrared spectrometer to obtain its absorbance spectrum. Next, the type of admixture is determined based on characteristic absorption bands associated with particular admixture type. Last, a fresh PCC sample is scanned by the ATR spectrometer, and the absorption bands associated with presence of the admixture are identified. 1.2 It is desired to perform ATR testing of an admixture sample immediately after sampling. Long exposure of an admixture to air can result in the evaporation of water or oxidation of an organic content of the admixture, which would alter its chemical composition. 1.3 It is required that PCC sample be tested by the ATR spectrometer within 5 minutes after its removal from framework. Furthermore, the ATR scanning should occur within 2 minutes after its placement on the ATR sampling plate. This is to avoid the damage to the testing apparatus due to fast drying of a thin PCC paste sample. 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 before use. 2. REFERENCED DOCUMENTS 2.1 ASTM Standards: • C494, Standard Specification for Chemical Admixtures for Concrete • C1017, Standard Specification for Chemical Admixtures for Use in Producing Flowing Concrete • C260, Standard Specification for Air-Entraining Admixtures for Concrete Proposed AASHTO Standards of Practice

61 3. APPARATUS 3.1 Sampling equipment 3.2 Pipette for sampling liquid admixture 3.3 Spoon for sampling PCC 3.4 Spectroscopic equipment 3.5 Infrared spectrometer equipped with diamond single reflection ATR accessory and load applicator 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 Pure chemical admixtures. Normally, no sample preparation is required for liquefied chemicals when the horizontal ATR sampling plate is used. 4.2 Fresh PCC. A PCC sample with maximum particle size of 1 mm is collected from a mixer or from the formwork with using a sampling spoon. Special care should be taken to avoid particles bigger than 2 mm and to preserve representative moisture content in a PCC sample. 5. SPECTROSCOPIC EQUIPMENT SETUP 5.1 The ATR spectrometer should be placed on a firm horizontal surface to avoid any vibrational interference with the instrument signal. 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 Pure Admixture 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 admixture sample using a pipette and place 3 to 5 drops of a sample on the ATR sampling plate. 6.1.4 Operate ATR spectrometer in accordance to the instrument manual to obtain infrared absorbance spectrum of a sample. Use accompanied data acquisition software to subtract background spectrum, correct baseline, and remove

62 atmosphere- and water vapor-related absorption bands from the sample spectrum. Store the ATR absorbance spectrum in numerical format for further processing as needed. 6.1.5 Repeat steps described in 6.1.1 through 6.1.4 two more times to establish standard deviation, as explained in Section 8.X of this standard. 6.1.6 Interpret the absorbance spectrum of the admixture sample and determine the type of admixture as explained in Sections 7.XX and 7.XXX of this standard. 6.2 ATR Testing of Fresh PCC Sample 6.2.1 Clean up the surface of the ATR sampling plate by applying soft tissue wetted in 99% acetone. 6.2.2 Collect and store the background spectrum in accordance with the ATR spectrometer manual. 6.2.3 Collect PCC sample using a sampling spoon and place enough of a sample to entirely cover ATR sampling plate. Ensure sample to be as explained in Section 4.2. Apply pressure to a sample using load applicator supplied with an instrument. Note: If no load applicator is supplied with the ATR instrument, it is recommended to: (a) ensure sample particle size is not larger than 0.3 mm to avoid increased variability in results, and (b) apply pressure to a sample through the flat surface of a sampling spoon. 6.3 Operate ATR spectrometer in accordance to the instrument manual to obtain infrared absorbance 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. 6.4 Repeat steps described in 6.2.1 through 6.2.3 four more times to establish standard deviation, as explained in Section 8.XX of this standard. 6.5 Interpret the absorbance spectrum of the admixture sample and verify presence of the admixture as explained in Sections 7.XXXX and 7.XXXXX of this standard. 7. SPECTRAL DATA PROCESSING 7.1 Identification of absorption bands in simple compounds such as chemical admixtures to PCC is normally done using software supplied with an infrared spectrometer by a manufacturer. The software generates an output in both tabular and graphic formats. In both formats, the reciprocal wavelength, or wave number, at the center of an identified band is reported along with the corresponding intensity of infrared absorption at that wave number. Alternatively, user can identify the absorption peaks from visual analysis of a spectrum. 7.2 The absorbance is directly proportional to the concentration of particular component of a compound or a mixture. The concentration of the admixtures in a PCC sample is expected to range between as low as 0.05% to 1%, which may make visual analysis of its spectrum difficult. In addition, the default sensitivity of the instrument software may not be sufficient to identify weak but narrow absorption bands associated with the admixture. However, a relatively simple mathematical manipulation of a spectrum using second-derivative method may be used for extraction of absorption peaks of any intensity. This method is documented elsewhere and it is beyond the scope of this standard practice.

63 8. INTERPRETATION OF RESULTS This section provides guidelines for the interpretation of the absorbance spectra of a pure admixture and a PCC sample. The class of admixture is determined based on the characteristic infrared absorption bands on a spectrum. The unique absorption bands are attributed to specific chemical components (functional groups) within an admixture. Those characteristic spectral features are used to verify the presence of the admixture in a resultant PCC mix sample. Appendix E briefly discusses classification of chemical admixtures to PCC and provides an example list of characteristic spectral features for the admixtures along with spectral graphs. 8.1 Identification of the Type of Admixture by Infrared Absorption Bands 8.1.1 Nonchloride Accelerators (ASTM C494, Type C). 8.1.1.1 Sodium thiocyanate is identified by the weak to medium band centered on 2,070 ±5 cm-1 wave numbers. When in aqueous solution, it can additionally give rise to strong and wide band centered around 1,330 ± 5 cm-1 with distinctive shoulder at 1,410 ± 5 cm-1. 8.1.1.2 Calcium nitrate is identified by a strong and wide band at 1,330 ± 5 cm-1 with distinctive shoulder at 1,410 ± 5 cm-1 attributable to NO2 and two medium and sharp peaks at 1,047 ± 5 cm-1 and 826 ± 5 cm-1 associated with nitrate anion NO3. 8.1.2 Water Reducers (ASTM C494, Types A and D). 8.1.2.1 Polycarboxylate ether is identified by a very strong absorption band centered around 1,086 ± 5 cm-1 with distinctive shoulder at about 1,140 cm-1 associated with polyether backbone. 8.1.2.2 Carbohydrates are typically identified by the coupled C–O–C vibrations yielding medium peaks at 1,300 and 1,250 cm-1 as well as by C–OH vibrations with a strong corresponding peak at 950 cm-1. 8.1.3 Retarders (ASTM C494, Type B). 8.1.3.1 Sodium gluconate is identified by a prominent terminal carboxylate in its structure, which yields characteristic split of the water band (1,649 and 1,592 cm-1) and a strong band split at 1,084 and 1,038 cm-1 because of vibrations of the multiple OH groups. 8.1.3.2 Carbohydrates—See 8.1.2.2. 8.2 Verification of Presence and Type of Admixture in Fresh PCC Sample 8.2.1 On the spectrum of a fresh PCC sample, identify characteristic peaks described in 8.1. 8.2.2 Assign characteristic peaks in accordance with 8.1. Note: Positive verification of the presence of a particular admixture is limited to those added in minimum 0.5% of the total PCC batch weight or 2% of the cement weight. 9. PRECISION 9.1 This method is based on the qualitative evaluation of the ATR spectra in regards to location of characteristic infrared absorption bands. It cannot be used for quantitative assessment of the admixture content in PCC. 9.2 Location of the characteristic peaks on an ATR spectrum can vary within ±10 cm-1 from the values given in this method.

64 Standard Practice for Standard Method of Test for Determination of Titanium Content in Traffic Paints by Field-Portable X-Ray Fluorescence Spectroscopy AASHTO Designation SP XX-12 1. SCOPE AND OVERVIEW 1.1 This guide covers the use of field-portable X-ray fluorescence (XRF) spectroscopy for the determination of titanium content traffic paints and pavement markings. 1.2 XRF spectroscopy is a proven analytical technique for measuring elemental concentrations. Increased sophistication of XRF technology has led to the development of field-portable devices that can be used for rapid, nondestructive analyses for on-site quality control in a variety of industrial settings. 1.3 The XRF spectrometer determines the concentrations of metals by measuring the intensity of the fluorescent radiation emitted by atoms at their characteristic energies upon bombardment by high-energy X-rays. 1.4 Because the specific operation varies greatly among the available XRF devices, no specific instructions are provided herein, and the user should refer to the operating instructions provided by the manufacturer. 1.5 The specific elements able to be detected by XRF depend on the type and calibration of the analyzer. In general, organic compounds cannot be detected using XRF and so this guide is applicable only for inorganic substances. 2. REFERENCED DOCUMENTS 2.1 ASTM Standards: • D3925, Sampling of Liquid Paints and Pigment Coatings • D4764, Titanium Dioxide Content in Paint by XRF • D5381, XRF of Pigments and Extenders 3. SIGNIFICANCE AND USE 3.1 The method described herein is effective for the rapid, nondestructive, on-site determination of titanium in traffic paints and related coatings by XRF for quality control purposes. 3.2 The method is suitable for measurements of liquid paint samples and in situ measurements of pavement markings. 4. SAFETY 4.1 XRF spectrometers produce ionizing radiation, which can damage biological tissue. Thus, necessary precautions must be followed to ensure safety and minimize exposure. 4.2 XRF spectrometers should be used only by trained operators in accordance with the instructions issued by the manufacturer and applicable occupational safety regulations. 4.3 Engineered safety features, such as trigger locking mechanisms and sample proximity sensors, are specific to the device. Consult the technical manual supplied by the manufacturer for device-specific safety practices and operating instructions.

65 4.4 The dangers involved with X-ray devices, and mitigation thereof, are well documented and, as such, this manual is not intended to be a reference to all the hazards associated with X-ray devices. 5. APPARATUS 5.1 Portable XRF Spectrometer—This is typically designed as a handheld device that is easily transported to and from field sites and measurement locations therein. The detectable elements depend on the instrument and manufacturer. Typical accessories include batteries, charging adapters, and a personal digital assistant (PDA) installed with the necessary measurement software. 5.2 Sampling Containers—Containers should be selected based on manufacturer recommendations. These are required when the material of interest must be sampled before analysis (i.e., for ex situ XRF measurements). 5.3 X-Ray Transparent Tape or Film—The sample containers should be covered by an X-ray transparent tape or film, such that X-rays can penetrate the sample in close proximity without damaging the instrument. 6. SAMPLE 6.1 Sampling of liquid paints should be conducted in accordance with ASTM Method D3925. 7. POTENTIAL INTERFERENCES 7.1 Moisture Effects—Caution must be exercised when analyzing and comparing XRF results obtained for paints that have variable moisture content. Titanium in the paint is necessarily concentrated as paint dries. 7.2 Sample Preparation—Steps should be taken to ensure that samples are uniform, homogenous, and randomly sampled, such that the results obtained are representative of the bulk of the material. 7.3 Spectral Overlap—When interpreting XRF results, one must be aware of potential overlap of signals from different elements with similar characteristic energies. This phenomenon is well documented and is likely addressed by the manufacturer. 7.4 Penetration Depth—X-rays penetration depth is usually on the order of micrometers to millimeters and is a complicated function of X-ray energy and the properties of the material. If the sample is thinner than the depth of X-ray penetration, the results will include contribution from the substrate. 8. STANDARDIZATION 8.1 Follow the instructions for device start-up and standardization as described by the manufacturer. 8.2 Typically, this is performed using a standardization material (e.g., Alloy 316) after a specified instrument warm-up period. Most devices have a digital screen or PDA that will prompt the user to perform the specific method for internal standardization. 9. PROCEDURE 9.1 For in situ measurements of pavement coatings: 9.1.1 Select a coated pavement surface that is smooth, clean, and of representative thickness. 9.1.2 Gently apply the XRF spectrometer directly to the clean coating, such that it is flush against the device and away from the adjacent exposed pavement.

66 9.2 For ex situ measurements: 9.2.1 Place a uniform, homogenized, and representative amount of the liquid paint into a sample container such that it is at least halfway filled. 9.2.2 Cover the opening of the container with X-ray transparent film and fasten into place. 9.3 Perform the measurement in accordance with the operating instructions for the device. Typically, data are collected on a continuously averaged basis for 1 to 2 minutes and repeated as necessary to obtain a sufficient sample size. 9.4 The results will be displayed in the form in concentration units. 9.5 Quality assurance can be addressed by periodically re-standardizing the instrument, verifying the standardization by measuring a known standard, and performing a blank measurement. If necessary and possible, collect a sample for labo- ratory analysis to verify measurement accuracy or identify possible matrix effects, or both. 10. REPORT 10.1 The report shall include the following: 10.1.1 The titanium content in units of percent concentration or parts per million by mass. 10.1.2 The mean and standard deviation associated with each sample. 10.1.3 Proof of verified instrument calibration (e.g., by ASTM Method D4764) if absolute concentration is reported. 10.1.4 Limits of detection.