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

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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-14 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. 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, non-destructive analyses for on-site quality control in a variety of industrial settings. 1.3. The XRF analyzer 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: • ASTM D3925-02: Standard Practice for Sampling Liquid Paints and Related Pigmented Coatings. In Annual Book of ASTM Standards, Vol. 06.01. West Conshohocken, PA, 2010. • ASTM D4764-01: Standard Test Method for Determination by X-ray Fluorescence Spectroscopy of Titanium Dioxide Content in Paint. In Annual Book of ASTM Standards, Vol. 06.01. West Conshohocken, PA, 2012. A-2

• ASTM D5381-93: Standard Guide for X-Ray Fluorescence (XRF) Spectroscopy of Pigments and Extenders. In Annual Book of ASTM Standards, Vol. 06.01. West Conshohocken, PA, 2009. 2.2. Radiation Safety Literature • EPA-402-K-07-006, Radiation: Risks and Realities, U.S. Environmental Protection Agency, 2007. • Shapiro, J. Radiation Protection. 4th ed., Harvard University Press, 2002. 2.3. Regulatory Standards: • OSHA 29 CFR 1910.1096, Ionizing Radiation: General Industry • OSHA 29 CFR 1926.53, Ionizing Radiation: Construction Industry 3. Significance and Use 3.1. The method described herein is effective for the rapid, non-destructive, 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 analyzers produce ionizing radiation, which damages biological tissue. Significant advancements in engineered safety features have reduced the risk of occupational exposure to ionizing radiation when using XRF devices. However, necessary precautions must be followed to further ensure safety and minimize radiation exposure (Shaprio, 2002; US EPA, 2007). 4.2. XRF analyzers should be used only by operators who have documented proficiency in radiation safety and have been trained by a representative of the instrument manufacturer. The XRF device must be used only as described in the instruction manual provided by the manufacturer. The instruction manual should be present anytime the instrument is in use. The operator should attend radiation safety training in accordance with the instructions issued by the manufacturer and applicable federal and state occupational safety regulations (e.g., OSHA 29 CFR 1910.1096 and 1926.53). 4.3. Safety should the primary objective when using portable XRF analyzers. The operator should avoid direct contact from the X-ray beam. Exposure from scattered X-rays should A-3

be minimized by measuring high-density samples, never performing measurements on handheld samples, and maximizing the distance between the operator and the sample. 4.4. The XRF operator is responsible for maintaining a safe environment during use of the XRF instrumentation. The XRF analyzer should never be pointed directly at another person. Nearby persons should be alerted of the radiation exposure hazards and kept at a safe distance from the XRF analyzer. 4.5. The XRF operator should wear a radiation dosimeter badge to monitor radiation exposure, in accordance with relevant state regulations. 4.6. Engineered safety features, such as trigger locking mechanisms and sample proximity sensors, are designed to minimize radiation exposure and should never be tampered with or altered in any way. 5. Apparatus 5.1. Portable XRF Analyzer—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. The XRF analyzer should have proof of calibration for absolute measurements. This method is only applicable to XRF instruments capable of detecting titanium. Typical accessories include batteries, charging adapters, and a personal digital assistant installed with the necessary measurement software. 5.2. Sampling containers—Sampling containers are typically cylindrical plastic cups and should be selected based on manufacturer recommendations. These are required when the material of interest must be sampled prior to 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 as Mylar or Kapton, 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. A-4

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 the dries. In situ measurements should be performed on dried paint coatings for consistency and to avoid damaging the XRF instrument. 7.2. Sample Preparation—Samples should be uniform, homogenized, 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 type of interference is usually resolved by the manufacturer in operating software of the XRF instrument. 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. Measurements performed on exceedingly thin coatings should be compared to measurements performed on an adjacent uncoated surface to evaluate the possibility of this type of interference. 8. Standardization 8.1. Follow the instructions for device startup and standardization as described by the manufacturer. This typically involves a warm-up period of 15 to 30 minutes prior to performing any analysis. 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. The measurement should be performed on an area of the coated pavement surface with thickness that is representative of the entire coating. The coating surface should be clean and smooth as to minimize potential interference from dirt or A-5

other debris and to ensure a close contact with the XRF instrument. The coating should be sufficiently dry as to not damage the XRF analyzer. 9.1.2. Quality control measurements should be performed on paint samples prior to the application of glass beads, which may potentially interfere with the measurements. 9.1.3. Follow the instructions for instrument warm-up and standardization. 9.1.4. Gently apply the XRF analyzer directly to the clean coating, such that it is flush against the device and away from the adjacent exposed pavement. Portable XRF analyzers are usually operated by depressing a trigger button. Once the trigger is released, the instrument stops emitting radiation. 9.1.5. Fluorescent X-ray counts are usually collected for a period of 1 to 2 minutes. The actually time required will depend on the instrument and desired level of accuracy. In general, the standard deviation of the measurement decreases with measurement time. 9.1.6. Measurements should be performed in multiple locations of larger coatings to ensure that results are representative of the entire desired coating surface. 9.1.7. The results will be displayed in the form of concentration units such as % total concentration or parts per million by mass. 9.2. For ex situ measurements: 9.2.1. The paint should be thoroughly mixed such that the sample is representative of the bulk material. 9.2.2. Place the uniform, homogenized, and representative amount of the liquid paint into a sample container such that it is at least halfway filled. 9.2.3. Cover the opening of the container with piece of X-ray transparent film. Sample containers generally come with a plastic fastener to hold the film in place and seal the container. Once sealed, check that the container is sealed and that the film window is as flat and straightened out as possible to ensure close contact with the X-ray source. 9.2.4. Perform the measurement in accordance with the operating instructions for the device. Some manufacturers provide an apparatus to house the XRF analyzer for A-6

bench-top measurements that do not require the instrument to be handheld and trigger-operated. 9.2.5. Fluorescent X-ray counts are usually collected for a period of 1 to 2 minutes. The actually time required will depend on the instrument and desired level of accuracy. In general, the standard deviation of the measurement decreases with measurement time. 9.2.6. The results will be displayed in the form of concentration units such as % total concentration or parts per million by mass. 9.3. Quality assurance can be addressed by restandardizing the instrument, as recommended by the manufacturer. This is typically performed before the first sample, after every 10 to 20 samples, and after the very last sample. The standardization can be verified by measuring a known standard and performing a blank measurement. If necessary and possible, collect a sample for laboratory analysis to verify the accuracy of in situ measurements and to identify possible matrix effects. 10. Report The report shall include the following: 10.1. The titanium content in units of percent concentration or parts per million by mass. 10.2. The mean and standard deviation associated with each sample. 10.3. Proof of verified instrument calibration (e.g. by ASTM Method D4764) if absolute concentration is reported. 10.4. Limits of detection. 10.5. Specify measurement increments and sample size. It is recommended that 5 readings per increment and 8 to 10 increments to represent a sample size of 1,000 linear ft. 11. Precision and Bias 11.1. Ti concentration may vary within ± 0.3% total concentration by mass between duplicate samples. A-7

Appendix A to Revised Draft ASHTO Methods: Portable XRF Manufacturers The following is a partial list of manufacturers of field portable XRF analyzers. • Olympus NDT, Inc. 48 Woerd Avenue Waltham, MA 02453 (781) 419-3900 • Bruker Optics 19 Fortune Drive Billerica, MA 01821 (978) 439-9899 • Thermo Scientific Portable Analytical Instruments 2 Radcliff Road Tewsbury, MA 01876 (978) 670-7460 • SPECTRO Analytical Instruments 160 Authority Drive Fitchburg, MA 01420 (978) 342-3400 A-8