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

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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-14 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 the particular admixture type. Lastly, 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 prior to use. A-9

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 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. A-10

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 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 of the test. 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 t o 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. 6.3 Note: If no load applicator supplied with the ATR instrument, it is recommended to: (a) ensure sample particle size be 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. 6.3.1 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- A-11

vapor-related absorption bands from the sample spectrum. Store the ATR absorbance spectrum in numerical format for further processing as needed. 6.3.2 Repeat steps described in 6.2.1 through 6.2.4 four more times to establish standard deviation of the test. 6.3.3 Interpret the absorbance spectrum of the admixture sample and verify presence of the admixture, as explained in Section 8 of this standard. 7. SPECTRAL DATA PROCESSING 7.1 Need in data processing for identification of characteristic absorption bands 7.2 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 wavenumber, at the center of an identified band is reported along with the corresponding intensity of infrared absorption at that wavenumber. Alternatively, the user can identify the absorption peaks from visual analysis of a spectrum. 7.3 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 a second- derivative method for extraction of absorption peaks of any intensity can be used. This method is documented elsewhere and it is beyond the scope of this standard practice. 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 A provides example chemical composition and list of characteristic spectral features for the admixtures, along with spectra graphs. 8.1 Identification of the Type of Admixture by Infrared Absorption Bands 8.1.1 Non-chloride Accelerators (ASTM C494, Type C). 8.1.1.1 Sodium thiocyanate is identified by the weak to medium band centered on 2070±5 cm-1 wavenumbers. When in aqueous solution, it can additionally give rise to a strong and wide band centered around 1330±5 cm-1 with distinctive shoulder at 1410±5 cm-1. A-12

8.1.1.2 Calcium nitrate is identified by a strong and wide band at 1330±5 cm-1 with distinctive shoulder at 1410±5 cm-1due to NO2 and two medium and sharp peaks at 1047±5 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 1086±5 cm-1 with distinctive shoulder at about 1140 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 1300 and 1250 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 (1649 and 1592 cm-1) and a strong band splitted at 1084 and 1038 cm-1 due to 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 8.3 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 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. A-13

Appendix A. Example of chemical composition and spectral features for PCC admixtures Table A-1 summarizes classification and chemical composition of the admixtures described in this standard. Figures A-1 through A-4 superimpose absorbance spectra of pure Portland cement concrete, an admixture, and their mix for each of the admixtures described in Table 1. Reference Yut I. and Zofka A., “Fingerprinting of Chemical Admixtures in Fresh Portland Cement Concrete by Portable Infrared Spectrometer,” Transportation Research Record: Journal of Transportation Research Board, No. 2290, pp.1-9, 2012 TABLE A-1. Chemical Composition of Admixtures (after Yut and Zofka, 2012) Admixture Class ASTM Type Chemical class Ingredients (Weight %) Chemical Functionalities High-Range Water Reducer (Superplasticizer) C494 Type A and F, ASTM C1017 Type I Acrylic co- polymer Water (90–99) Carboxylated polyether (1–10) H2O; -COO-; -CH2-O-CH2-; Air Entrainer AEA C260 Sodium abietate Water (>60) Tall oil, sodium salt (10– 30) 4-Chloro-3-methylphenol (<1) H2O; C19H29-,COOH, Na+; -C6H3OH; -CH3; -Cl Water Reducer/ Accelerator C494 Type C and E Calcium nitrate Water (40–70) Calcium nitrate (40–70) H2O; Ca(NO3)2 Water Reducer/ Retarder C494 Type D Sodium gluconate Water (>60) Sodium gluconate (30– 60) 4-Chloro-3-methylphenol (<1) H2O; -CHOH-; CH2OH; CONaO-C6H3OH; -CH3; -Cl A-14

FIGURE A-1. Composition of the ATR spectrum of PCC sample modified with High Range Water Reducer (HRWR) (after Yut and Zofka, 2012). FIGURE A-2. Composition of the ATR spectrum of PCC sample modified with Air Entraining Admixture (AEA). A-15

FIGURE A-3. Composition of the ATR spectrum of PCC sample modified with Water Reducer/Retarder (after Yut and Zofka, 2012). FIGURE A-4. Composition of the ATR spectrum of PCC sample modified with Water Reducer/Accelerator (after Yut and Zofka, 2012). . A-16