Improved Test Methods for Specific Gravity and Absorption of Coarse and Fine Aggregate (2015)

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TS-1c B-1 AASHTO A P P E N D I X B Revised AASHTO T 84

TS-1c B-2 AASHTO Standard Method of Test for Specific Gravity and Absorption of Fine Aggregate AASHTO Designation: T 84-XX1 ASTM Designation: C 128-XX American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001

TS-1c B-3 AASHTO Standard Method of Test for Specific Gravity and Absorption of Fine Aggregate AASHTO Designation: T 84-XX1 ASTM Designation: C 128-XX 1. SCOPE 1.1. This method covers the determination of bulk and apparent specific gravity, 23/23°C (73.4/73.4°F), and absorption of fine aggregate. 1.2. This method determines (after 15–19 h of soaking in water) the bulk specific gravity and the apparent specific gravity, the bulk specific gravity on the basis of mass of saturated surface-dry aggregate, and the absorption. 1.3. The values stated in SI units are to be regarded as the standard. 1.4. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of whomever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 6, Fine Aggregate for Hydraulic Cement Concrete M 231, Weighing Devices Used in the Testing of Materials T 2, Sampling of Aggregates T 11, Materials Finer Than 75-µm (No. 200) Sieve in Mineral Aggregates by Washing T 19M/T 19, Bulk Density (“Unit Weight”) and Voids in Aggregate T 85, Specific Gravity and Absorption of Coarse Aggregate T 100, Specific Gravity of Soils T 133, Density of Hydraulic Cement T 209, Theoretical Maximum Specific Gravity and Density of Hot Mix Asphalt (HMA) T 248, Reducing Samples of Aggregate to Testing Size T 255, Total Evaporable Moisture Content of Aggregate by Drying 2.2. ASTM Standards: C 128, Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of Fine Aggregate C 670, Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials

TS-1c B-4 AASHTO 2.3. IEEE/ASTM Standards: SI 10, American National Standard for Metric Practice D 5550, Standard Test Method for Specific Gravity of Soil Solids by Gas Pycnometer 3. TERMINOLOGY 3.1. Definitions: 3.1.1. Absorption—the increase in the mass of aggregate due to water in the pores of the material, but not including water adhering to the outside surface of the particles, expressed as a percentage of the dry mass. The aggregate is considered “dry” when it has been maintained at a temperature of 110 ± 5°C for sufficient time to remove all uncombined water by reaching a constant mass. 3.1.2. Specific Gravity—the ratio of the mass (or weight in air) of a unit volume of a material to the mass of the same volume of gas-free distilled water at stated temperatures. Values are dimensionless. 3.1.2.1. Apparent Specific Gravity—the ratio of the weight in air of a unit volume of the impermeable portion of aggregate at a stated temperature to the weight in air of an equal volume of gas-free distilled water at a stated temperature. 3.1.2.2. Bulk Specific Gravity—the ratio of the weight in air of a unit volume of aggregate (including the permeable and impermeable voids in the particles, but not including the voids between particles) at a stated temperature to the weight in air of an equal volume of gas-free distilled water at a stated temperature. 3.1.2.3. Bulk Specific Gravity (SSD)—the ratio of the mass in air of a unit volume of aggregate, including the mass of water within the voids filled to the extent achieved by submerging in water for 15–19 h (but not including the voids between particles) at a stated temperature, compared to the weight in air of an equal volume of gas-free distilled water at a stated temperature. 4. SIGNIFICANCE AND USE 4.1. Bulk specific gravity is the characteristic generally used for calculation of the volume occupied by the aggregate in various mixtures containing aggregate including portland cement concrete (PCC), bituminous concrete, and other mixtures that are proportioned or analyzed on an absolute volume basis. Bulk specific gravity is also used in the computation of voids in aggregate in T 19M/T 19. Bulk specific gravity determined on the saturated surface-dry basis is used if the aggregate is wet; that is, if its absorption has been satisfied. Conversely, the bulk specific gravity determined on the oven-dry basis is used for computations when the aggregate is dry or assumed to be dry. 4.2. Apparent specific gravity pertains to the relative density of the solid material making up the constituent particles not including the pore space within the particles that is accessible to water. This value is not widely used in construction aggregate technology. 4.3. Absorption values are used to calculate the change in the mass of an aggregate due to water absorbed in the pore spaces within the constituent particles, compared to the dry condition, when it is deemed that the aggregate has been in contact with water long enough to satisfy most of the absorption potential. The laboratory standard for absorption is that obtained after soaking dry aggregate in water. Aggregates mined from below the water table may have a higher absorption when used, if not allowed to dry. Conversely, some aggregates when used may contain an amount of absorbed moisture less than that achieved by the required amount of soaking time: For an aggregate that has been in contact with water and that has free moisture on the particle surfaces,

TS-1c B-5 AASHTO the percentage of free moisture can be determined by deducting the absorption from the total moisture content determined by T 255 by drying. 5. APPARATUS 5.1. Balance, conforming to the requirements of M 231, Class G 2. 5.2. Pycnometer—A flask or other suitable container into which the fine aggregate test sample can be readily introduced and in which the volume content can be reproduced with ±100 mm3. The volume of the container filled to mark shall be at least 50 percent greater than the space required to accommodate the test sample. A volumetric flask of 500-mL capacity or a fruit jar fitted with a pycnometer top is satisfactory for a 500-g test sample of most fine aggregates. A Le Chatelier flask as described in T 133 is satisfactory for an approximately 55-g test sample. 5.3. Mold—A metal mold in the form of a frustum of a cone with dimensions as follows: 40 ± 3 mm inside diameter at the top, 90 ± 3 mm inside diameter at the bottom, and 75 ± 3 mm in height, with the metal having a minimum thickness of 0.8 mm. 5.4. Tamper—A metal tamper having a mass of 340 ± 15 g and having a flat circular tamping face 25 ± 3 mm in diameter. 6. SAMPLING 6.1. Sampling shall be accomplished in general accordance with T 2. 7. PREPARATION OF TEST SPECIMEN 7.1. Obtain approximately 1 kilogram of the fine aggregate from the sample using the applicable procedures described in T 248. 7.1.1. Dry it in a suitable pan or vessel to constant mass at a temperature of 110 ± 5°C (230 ± 9°F). Allow it to cool to comfortable handling temperature. Remove the material finer than 75 µm from the test sample by dry sieving. Subsequently, cover the sample with water, either by immersion or by the addition of at least 6 percent moisture to the fine aggregate and permit to stand for 15– 16 h. Note 1—The removed material finer than 75 µm can be assumed to have the same specific gravity as the fine aggregate. Alternatively, the specific gravity of the material finer than 75 µm may be determined using T 100 (with ethyl alcohol), T 133 (with ethyl alcohol), or D5550; however, these test methods determine the apparent specific gravity and not the bulk specific gravity. The apparent specific gravity of the material finer than 75 µm can be combined with the bulk specific gravity of the material coarser than 75 µm using the weighted average calculation shown in Appendix X.3. Note 2—As an alternative to Section 7.1.1, for aggregate with absorption less than 2 percent, the requirement for initial drying to constant mass may be eliminated. Also, a vacuum soaking method using the testing apparatus arrangement described in AASHTO T 209 may be used in place of the 15-h soaking. Remove the material finer than 75 µm from the test sample by dry sieving or washing. Place the test sample into a vacuum container. Add sufficient water to cover the sample completely. Remove entrapped air and saturate the aggregate surface voids by applying gradually increased vacuum until the residual pressure manometer reads 3.7 ± 0.3 kPa (27.5 ± 2.5 mm Hg). Maintain this residual pressure for 10 ± 0.5 min. Agitate the container and contents during the vacuum period using a mechanical device or by vigorously shaking at intervals of about 2 min. At

TS-1c B-6 AASHTO the end of the vacuum period, release the vacuum by increasing the pressure at a rate not to exceed 8 kPa (60 mm Hg) per second. 7.1.2. As an alternative to Section 7.1.1, where the absorption and specific gravity values are to be used in proportioning concrete mixtures with aggregates used in their naturally moist condition, the requirement for initial drying to constant mass may be eliminated and, if the surfaces of the particles have been kept wet, the required soaking may also be eliminated. Note 3—Values for absorption and for specific gravity in the saturated surface-dry condition may be significantly higher for aggregate not oven dried before soaking than for the same aggregate treated in accordance with Section 7.1.1. 7.2. Decant excess water with care to avoid loss of fines, spread the sample on a flat, nonabsorbent surface exposed to a gently moving current of warm air, and stir frequently to secure homogeneous drying. If desired, mechanical aids such as tumbling or stirring may be employed to assist in achieving the saturated surface-dry condition. As the material begins to dry sufficiently, it may be necessary to work it with the hands in a rubbing motion to break up any conglomerations, lumps, or balls of material that develop. Continue this operation until the test specimen approaches a free-flowing condition. Follow the procedure in Section 7.2.1 to determine whether or not surface moisture is present on the constituent fine aggregate particles. It is intended that the first trial of the cone test will be made with some surface water in the specimen. Continue drying with constant stirring, and if necessary, work the material with a hand-rubbing motion, and test at frequent intervals until the test indicates that the specimen has reached a surface-dry condition. If the first trial of the surface moisture test indicates that moisture is not present on the surface, it has been dried past the saturated surface-dry condition. In this case, thoroughly mix a few milliliters of water with the fine aggregate and permit the specimen to stand in a covered container for 30 min. Then, resume the process of drying and testing at frequent intervals for the onset of the surface-dry condition. 7.2.1. Cone Test for Surface Moisture—Hold the mold firmly on a smooth nonabsorbent surface with the large diameter down. Place a portion of the partially dried fine aggregate loosely in the mold by filling until overflow occurs and heaping additional material above the top of the mold by holding it with the cupped fingers of the hand holding the mold. Lightly tamp the fine aggregate into the mold with 25 light drops of the tamper. Each drop should start about 5 mm (0.2 in.) above the top surface of the fine aggregate. Permit the tamper to fall freely under gravitational attraction on each drop. Adjust the starting height to the new surface elevation after each drop and distribute the drops over the surface. Remove loose sand from the base and lift the mold vertically. If surface moisture is still present, the fine aggregate will retain the molded shape. When the fine aggregate slumps slightly, it indicates that it has reached a surface-dry condition. Some angular fine aggregate or material with a high proportion of fines may not slump in the cone test upon reaching a surface-dry condition. This may be the case if fines become airborne upon dropping a handful of the sand from the cone test 100–150 mm onto a surface. For these materials, the saturated surface- dry condition should be considered as the point that one side of the fine aggregate slumps slightly upon removing the mold. Note 4—The following criteria have also been used on materials that do not readily slump: 1. Provisional Cone Test—Fill the cone mold as described in Section 7.2.1 except only use 10 drops of the tamper. Add more fine aggregate and use 10 drops of the tamper again. Then add material two more times using three and two drops of the tamper, respectively. Level off the material even with the top of the mold; remove loose material from the base; and lift the mold vertically. 2. Provisional Surface Test—If airborne fines are noted when the fine aggregate is such that it will not slump when it is at a moisture condition, add more moisture to the sand, and at the onset of the surface-dry condition, with the hand, lightly pat approximately 100 g of the material on a flat, dry, clean, dark, or dull nonabsorbent surface such as a sheet of rubber, a worn oxidized, galvanized, or steel surface, or a black-painted metal surface. After 1 to 3 s,

TS-1c B-7 AASHTO remove the fine aggregate. If noticeable moisture shows on the test surface for more than 1 to 2 s, then surface moisture is considered to be present on the fine aggregate. 3. Colorimetric procedures described by Kandhal and Lee, Highway Research Record No. 307, p. 44. 4. For reaching the saturated surface-dry condition on a single-size material that slumps when wet, hard-finish paper towels can be used to surface dry the material until the point is just reached where the paper towel does not appear to be picking up moisture from the surfaces of the fine aggregate particles. 8. PROCEDURE 8.1. Make and record all mass determinations to 0.1 g. 8.2. Partially fill the pycnometer with water. Immediately introduce into the pycnometer 500 ± 10 g of saturated surface-dry fine aggregate prepared as described in Section 7, and fill with additional water to approximately 90 percent of capacity. Manually roll, invert, and agitate or use a combination of these actions to eliminate all air bubbles in the pycnometer (Note 5). Accomplish mechanical agitation by external vibration of the pycnometer in a manner that will not degrade the sample. A level of agitation adjusted to just set individual particles in motion is sufficient to promote de-airing without degradation. A mechanical agitator shall be considered acceptable for use if comparison tests for each 6-month period of use show variations less than the acceptable range of two results (d2s) indicated in Table 1 from results of manual agitation on the same material. Adjust its temperature to 23.0 ± 1°C (73.4 ± 1.8°F), if necessary, by immersion in circulating water, and bring the water level in the pycnometer to its calibrated capacity. Determine total mass of the pycnometer, specimen, and water. Note 5—It normally takes about 15 to 20 min to eliminate air bubbles by manual methods. Dipping the tip of a paper towel into the pycnometer has been found to be useful in dispersing the foam that sometimes builds up when eliminating the air bubbles, or adding a few drops of isopropyl alcohol, after removal of air bubbles and just prior to bringing the water level to its calibrated capacity, has also been found useful in dispersing foam on the water surface. Do not use isopropyl alcohol when using the alternative method described in Section 8.2.1. Table 1—Precision Standard Deviation (1s)a Acceptable Range of Two Results (d2s)a Single-operator precision: Bulk specific gravity (dry) 0.011 0.032 Bulk specific gravity (SSD) 0.0095 0.027 Apparent specific gravity 0.0095 0.027 Absorption,b percent 0.11 0.31 Multilaboratory precision: Bulk specific gravity (dry) 0.023 0.066 Bulk specific gravity (SSD) 0.020 0.056 Apparent specific gravity 0.020 0.056 Absorption,b percent 0.23 0.66 a These numbers represent, respectively, the (1s) and (d2s) limits as described in ASTM C 670. The precision estimates were obtained from the analysis of combined AASHTO Materials Reference Laboratory reference sample data from laboratories using 15- to 19-h saturation times and other laboratories using 24 ± 4 h of saturation time. Testing was performed on aggregates of normal specific gravities, and started with aggregates in the oven-dry condition. b Precision estimates are based on aggregates with absorptions of less than 1 percent and may differ for manufactured fine aggregates having absorption values greater than 1 percent.

TS-1c B-8 AASHTO 8.2.1. Alternative to Determining the Mass in Section 8.2—The quantity of added water necessary to fill the pycnometer at the required temperature may be determined volumetrically using a buret accurate to 0.15 mL. Compute the total mass of the pycnometer, specimen, and water as follows: 0 9975 a C . V S W (1) where: C = mass of pycnometer with specimen and water to calibration mark, g; Va = volume of water added to pycnometer, mL; S = mass of saturated surface-dry specimen, g; and W = mass of the pycnometer empty, g. 8.2.2. Alternative to the Procedure in Section 8.2—Use a Le Chatelier flask initially filled with water to a point on the stem between the 0- and the 1-mL mark. Record this initial reading with the flask and contents within the temperature range of 23.0 ± 1°C (73.4 ± 1.8°F). Add 55 ± 5 g of fine aggregate in the saturated surface-dry condition (or other mass as necessary to result in raising the water level to some point on the upper series of graduation). After all fine aggregate has been introduced, place the stopper in the flask and roll the flask in an inclined position, or gently whirl it in a horizontal circle so as to dislodge all entrapped air, continuing until no further bubbles rise to the surface (Note 6). Take a final reading with the flask and contents within 1°C (1.8°F) of the original temperature. Note 6—When using the Le Chatelier flask method, slowly adding a small measured amount (not to exceed 1 mL) of isopropyl alcohol, after removal of air bubbles, has been found useful in dispersing foam appearing on the water surface. The volume of alcohol used must be subtracted from the final reading (R2). 8.3. Remove the fine aggregate from the pycnometer, dry to constant mass at a temperature of 110 ± 5°C (230 ± 9°F), cool in air at room temperature for 1.0 ± 0.5 h and determine the mass. Note 7—In lieu of drying and determining the mass of the sample that has been removed from the pycnometer, a second portion of the saturated surface-dry sample may be used to determine the oven-dry mass. This sample must be obtained at the same time and be within 0.2 grams of the mass of the sample that is introduced into the pycnometer. 8.3.1. If the Le Chatelier flask method is used, a separate sample portion is needed for the determination of absorption. Weigh a separate 500 ± 10 g portion of the saturated surface-dry fine aggregate, dry to constant mass, and reweigh. This sample must be obtained at the same time as the sample that is introduced into the Le Chatelier flask. 8.4. Determine the mass of the pycnometer filled to its calibration capacity with water at 23.0 ± 1°C (73.4 ± 1.8°F). 8.4.1. Alternative to Determining the Mass in Section 8.4—The quantity of water necessary to fill the empty pycnometer at the required temperature may be determined volumetrically using a buret accurate to 0.15 mL. Calculate the mass of the pycnometer filled with water as follows: 0.9975B V W (2) where: B = mass of flask filled with water, g; V = volume of flask, mL; and W = mass of the flask empty, g.

TS-1c B-9 AASHTO 9. BULK SPECIFIC GRAVITY 9.1. Calculate the bulk specific gravity, 23/23°C (73.4/73.4°F), as follows: bulk sp gr A B S C (3) where: A = mass of oven-dry specimen in air, g; B = mass of pycnometer filled with water, g; S = mass of saturated surface-dry specimen, g; and C = mass of pycnometer with specimen and water to calibration mark, g. 9.1.1. If the Le Chatelier flask method was used, calculate the bulk specific gravity, 23/23°C, as follows: 1 2 1 bulk sp gr 0.9975 S A S R R (4) where: S1 = mass of saturated surface-dry specimen used in Le Chatelier flask, g; R2 = final reading of water level in Le Chatelier flask; and R1 = initial reading of water level in Le Chatelier flask. 10. BULK SPECIFIC GRAVITY (SATURATED SURFACE-DRY BASIS) 10.1. Calculate the bulk specific gravity, 23/23°C (73.4/73.4°F), on the basis of mass of saturated surface-dry aggregate as follows: bulk sp gr saturated surface-dry basis ( )S B S C (5) 10.1.1. If the Le Chatelier flask method was used, calculate the bulk specific gravity, 23/23°C, on the basis of saturated surface-dry aggregate as follows: 1 2 1 bulk sp gr saturated surface-dry basis = 0.9975 – S R R (6) 11. APPARENT SPECIFIC GRAVITY 11.1. Calculate the apparent specific gravity, 23/23°C (73.4/73.4°F) as follows: apparent sp gr A B A C (7) 12. ABSORPTION 12.1. Calculate the percentage of absorption as follows: absorption, percent 100S A A (8) 13. REPORT 13.1. Report specific gravity results to the nearest 0.001 (Fine Aggregate meeting M 6 requirements may be reported to the nearest 0.01) and absorption to the nearest 0.1 percent. The appendix gives mathematical interrelationships among the three types of specific gravities and absorption. These

TS-1c B-10 AASHTO may be useful in checking the consistency of reported data or calculating a value that was not reported by using other reported data. 13.2. If the fine aggregate was tested in a naturally moist condition other than the oven dried and 15-h soaked condition, report the source of the sample and the procedures used to prevent drying prior to testing. 14. PRECISION AND BIAS 14.1. The estimates of precision of this test method (listed in Table 1) are based on results from the AASHTO Materials Reference Laboratory Reference Sample Program, with testing conducted by this test method and ASTM C 128. The significant difference between the methods is that ASTM C 128 requires a saturation period of 24 ± 4 h, and T 84 requires a saturation period of 15– 19 h. This difference has been found to have an insignificant effect on the precision indices. The data are based on the analyses of more than 100 paired test results from 40 to 100 laboratories. 14.2. Because there is no accepted reference material suitable for determining the bias for the procedure in T 84 for measuring specific gravity and absorption of fine aggregate, no statement on bias is being made. APPENDIX (Nonmandatory Information) X1. POTENTIAL DIFFERENCES IN BULK SPECIFIC GRAVITY AND ABSORPTION DUE TO PRESENCE OF MATERIAL FINER THAN 75 µM (NO. 200) X1.1. It has been found that there may be significant differences in bulk specific gravity and absorption between fine aggregate samples tested with the material finer than 75 µm (No. 200) present and not present in the samples. Samples from which the material finer than 75 µm is not removed usually give a higher absorption and a lower bulk specific gravity compared with testing the same fine aggregate from which the material finer than 75 µm is removed following the procedures of T 11. Samples with material finer than 75 µm may build up a coating around the coarser fine aggregate particles during the surface drying process. The resultant specific gravity and absorption that is subsequently measured is that of the agglomerated and coated particles and not that of the parent material. The difference in absorption and specific gravity determined between samples from which the material finer than 75 µm have not been removed and samples from which the material finer than 75 µm have been removed depends on both the amount of the material finer than 75 µm present and the nature of the material. When the material finer than 75 µm is less than about 4 percent by mass, the difference in specific gravity between washed and unwashed samples is less than 0.03. When the material finer than 75 µm is greater than about 8 percent by mass, the difference in specific gravity obtained between washed and unwashed samples may be as great as 0.13. X1.2. The material finer than 75 µm, which is removed, can be assumed to have the same specific gravity as the fine aggregate. Alternatively, the specific gravity of the material finer than 75 µm may be further evaluated using T 100; however, this test determines the apparent specific gravity and not the bulk specific gravity.

TS-1c B-11 AASHTO X2. INTERRELATIONSHIPS BETWEEN SPECIFIC GRAVITIES AND ABSORPTION AS DEFINED IN T 84 AND T 85 X2.1. Let: Sd = bulk specific gravity (dry basis), Ss = bulk specific gravity (SSD basis), Sa = apparent specific gravity, and A = absorption in percent. Then: 1 100s dS A S (X1.1) 1 1 1 100 100 d a d d SS A AS S (X1.2) Or: 1 1 100 1 1 100 100 s a s s SS A A A S S (X1.3) 1 100s d SA S (X1.4) 100 1 a s a s S SA S S (X1.5) 1 This method is technically equivalent to ASTM C 128-12. X1. X3. AVERAGE SPECIFIC GRAVITY VALUES X3.1. Average Specific Gravity Values—When the sample is tested in separate size fractions (retained on and passing the No. 200 sieve), the average value for bulk specific gravity, bulk specific gravity (SSD), or apparent specific gravity can be computed as the weighted average of the values as computed in accordance with Sections 9 through 11 using the following equation: (4) where: G = average specific gravity (all forms of expression of specific gravity can be averaged in this manner); P1, P2…Pn = mass percentages of each size fraction present in the original sample; and

TS-1c B-12 AASHTO G1, G2…Gn = appropriate specific gravity values for each size fraction depending on the type of specific gravity being averaged. Note 8—Some users of this method may wish to express the results in terms of density. Density may be determined by multiplying the bulk specific gravity, bulk specific gravity (SSD), or apparent specific gravity by the density of water (997.5 kg/m3 or 0.9975 Mg/m3 or 62.27 lb/ft3 at 23°C). Some authorities recommend using the density of water at 4°C (1000 kg/m3 or 1.000 Mg/m3 or 62.43 lb/ft3 ) as being sufficiently accurate. The density terminology corresponding to bulk specific gravity, bulk specific gravity (SSD), and apparent specific gravity has not been standardized.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation