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AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values (2012)

Chapter: AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values

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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Suggested Citation:"AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values." National Academies of Sciences, Engineering, and Medicine. 2012. AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values. Washington, DC: The National Academies Press. doi: 10.17226/14640.
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Research Results Digest 369 February 2012 C O N T E N T S Background, 1 Objectives and Scope, 1 Survey of State DOT Laboratories, 2 Experiment Design, 2 Results and Analysis, 7 Findings and Conclusions, 23 BACKGROUND AASHTO T 209, Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures, describes a test method for determination of the theoretical maxi- mum specific gravity (Gmm) and density of uncompacted hot mix asphalt (HMA).1 The Gmm and the density of HMA are fundamen- tal properties whose values are influenced by the composition of the HMA mixtures in terms of types and amounts of aggre- gates and asphalt materials. Gmm is used to calculate percent air voids in compacted HMA and to provide target values for the compaction of HMA. Gmm also is essen- tial when calculating the amount of asphalt binder absorbed by the internal porosity of the individual aggregate particles in HMA. AASHTO T 209 requires application of a vacuum to a sample of HMA loose mix. The vacuum, combined with either manual or mechanical agitation, removes entrapped air in order to accurately determine the Gmm. The Gmm is then used to determine both the air void content and the in-place density of the HMA. In-place density is commonly used in the acceptance and pay-factor de- termination of HMA. Analysis of the AMRL Proficiency Sample Program data has demonstrated that mechanical agitation provides less variation in test results when compared to manual ag- itation. However, several types of mechan- ical vibratory shakers are commonly used to apply agitation. It was not known if these different devices provide significantly dif- ferent results when compared to one another. In addition, the effects on Gmm values of changes in vibration intensity from various settings of the vibrating devices had not been explored. OBJECTIVES AND SCOPE The goal of this research was to eval- uate the effect of using various devices and methods on measured values of Gmm. The specific objectives were to (1) compare the Gmm between manual and mechanical agitation; (2) investigate the relationship between the measured Gmm and the vibratory AASHTO T 209: EFFECT OF AGITATION EQUIPMENT TYPE ON THEORETICAL MAXIMUM SPECIFIC GRAVITY VALUES This digest summarizes key findings of research conducted in NCHRP Project 10-87(01), “Precision Statements for AASHTO Standard Methods of Test,” by the AASHTO Asphalt Materials Reference Laboratory (AMRL) under the direction of the principal investigator, Dr. Haleh Azari. The digest is an abridgement of the full final report, which is available for download at http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3049. Responsible Senior Program Officer: E. T. Harrigan NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM 1AASHTO T 209-10, Theoretical Maximum Spe- cific Gravity and Density of Hot Mix Asphalt (HMA). In Standard Specifications for Transpor- tation Materials and Methods of Sampling and Testing, 30th ed. American Association of State Highway and Transportation Officials, Washington, D.C., 2010.

parameters of the mechanical vibratory tables and determine an optimum vibration intensity of the vi- brating devices; and (3) evaluate the effect on Gmm measurements of several variables, such as the order of placing water and mixture and the period of vac- uum and agitation. The research was conducted in ten major steps: 1. Survey the state highway agencies to deter- mine what specific mechanical equipment and methods are currently being used for determining the Gmm of asphalt mixtures. 2. Identify, based on the results of the survey, the most commonly used and the most unique equipment and methods used for measuring Gmm. 3. Select a variety of laboratory-prepared and plant-produced asphalt mixtures for the study, including (a) a fine-graded, low traffic volume (< 1 million ESALs) Superpave mix; (b) a coarse-graded, high traffic volume (> 30 million ESALs) Superpave mix; and (c) a gap-graded or SMA high traffic volume Superpave mix. 4. Measure Gmm using manual agitation and at several settings of various mechanical agitators. 5. Evaluate the frequency, acceleration, and kinetic energy at various settings of the vi- brating devices. 6. Evaluate the practical and statistical signif- icance of the differences between Gmm values obtained using (a) various settings of each vibratory device, (b) zero vibration, and (c) manual agitation, and use this informa- tion to determine the optimum setting of the various devices. 7. Evaluate the practical and statistical signifi- cance of the differences between the highest Gmm values from various mechanical devices and manual agitation. 8. Examine the relationship between the vi- bration properties of the vibrating devices and the highest Gmm value produced by the device. 9. Investigate the effect on Gmm of the order in which mixture and water are placed in the vacuum flask or bowl. 10. Investigate the effect on Gmm of changing the duration of the vacuum and agitation process. SURVEY OF STATE DOT LABORATORIES The survey of the state DOTs included nine questions to identify the candidate devices for the study, how the devices are operated by each state, and whether any of the state’s test methods deviate from those prescribed by AASHTO T 209. The 35 responses to the survey are organized and presented in Appendix A of the project final report, which can be accessed at http://apps.trb.org/cmsfeed/ TRBNetProjectDisplay.asp?ProjectID=3049. Based on the results of the survey, the most com- monly used mechanical agitators were selected for the laboratory experiment so that the research find- ings would apply to the widest number of laborato- ries. Several unique setups also were selected to compare the application of non-typical methods to typical methods. EXPERIMENT DESIGN A laboratory experiment was designed to mea- sure Gmm of various mixture types using different de- vices and a variety of agitation levels. The experiment also investigated the effects on Gmm of factors such as the order in which water and mixture are placed in the pycnometer and the vacuum and agitation duration. Test Apparatus and Setup Seven devices were selected for investigation, as follows: 1. Humboldt Vibrating Table (H-1756); 2. Gilson Vibro-Deaerator (SGA-5R); 3. Syntron Vibrating Table (VP-51 D1); 4. Orbital Shaker Table (SHKE 2000); 5. HMA Vibrating Table (VA-2000); 6. Aggregate Drum Washer (with vacuum lid); and 7. Corelok Vacuum Sealing Device. Table 1 provides a brief description of each unit. The Humboldt, Gilson, and HMA tables were selected because together they make up more than 80% of the devices used by the state laboratories. Despite being less common, the Orbital shaker (similar to the Barnstead shaker), Aggregate washer, and Corelok offered unique features and thus the op- portunity to investigate differences between these devices and the more common setups. The Syntron shaker was selected because it is used with a unique setup by the Minnesota DOT. 2

The setup used for measuring Gmm includes an agitator, vacuum container, a vacuum bowl or vacuum flask (pycnometer), a balance, a vacuum pump, a moisture trap, a vacuum measurement device, a ma- nometer, a bleeder valve, a thermometric device, a water bath, and a drying oven that conforms to the re- quirements of Sections 6.2 to 6.11 of AASHTO T 209. Vibratory frequency and amplitude measure- ments were made using a triaxial accelerometer, a signal conditioner, and SignalView computer soft- ware. An accelerometer produces an electrical sig- nal that is a function of mechanical vibration. A sig- nal conditioner obtains the signal voltage and acts as an interface between the accelerometer and the com- puter, which processes and displays the signals. The accelerometer was attached to the top of the vacuum container lid with wax adhesive to capture the frequency and acceleration of vibration. The fre- quency measurements were recorded to the nearest 0.1 Hz and acceleration measurements were recorded to the nearest 0.01 m/s2 in vertical, horizontal, and perpendicular axes. Looking down at the container from the top, the x-axis extended from the left to the right of the device, the y-axis perpendicular to the x- axis forming a plane parallel to the table, and the z-axis perpendicular to the x-y plane. Specimen Preparation Test specimens were either prepared in the lab- oratory or acquired from the field. Dense-graded 4.75-mm, 12.5-mm, 25.0-mm, and 37.5-mm nomi- nal maximum aggregate size (NMAS) mixtures were prepared in the laboratory. Dense-graded 9.5-mm and 3 Table 1 Description of the devices selected for the refinement of AASHTO T 209 study. Device Manufacturer Agitation Type Description Humboldt Vibrating Table (H-1756) Gilson Vibro-Deaerator (SGA-5R) Syntron Vibrating Table (VP-51 D1) Orbital Shaker Table (SHKE 2000) HMA Vibrating Table (VA-2000) Aggregate Drum Washer (with vacuum lid) Corelok (vacuum sealing device) Humboldt Mfg. Co. Gilson Co., Inc. FMC Technologies, Inc. Thermofisher Scientific HMA Lab Supply Karol-Warner Co. InstroTek, Inc. Vibratory Vibratory Vibratory Orbital Vibratory Rotary No agitation (vacuum seal- ing method) The unit has a dial for adjusting the fre- quency and amplitude of vibration. Different intensities are indicated by numbers on the dial from 1 to 10. The unit has a dial for adjusting the fre- quency and amplitude of vibration. Different intensities are indicated by bars with different thicknesses. No number is associated with the bars. The unit comes with a dial-rheostat for adjusting the amplitude of the vibration. The dial-rheostat is part of a separate control box, which allows for remote control if desired. The unit has an adjustable knob that controls the speed of the shaker plat- form in an orbital pattern in the range of 0 to 350 rpm. The unit has a fixed intensity. This table was the most frequently used by the state DOTs. The unit rotates slowly at the rate of 25 rpm and tumbles the loose mixture while the vacuum is applied. The unit vacuum-seals the loose asphalt mixture in a plastic bag.

19.0-mm NMAS mixtures were obtained from con- struction sites at the National Institute of Standards and Technology, Gaithersburg, Maryland, and gap- graded stone matrix asphalt (SMA) 9.5-mm, 19.0-mm, and 25.0-mm NMAS mixtures were obtained at construction sites in Richmond, Virginia. The mix- ture designs of the dense-graded laboratory-prepared and plant-produced mixtures are provided in Table 2; however, the mixture designs for the SMA mixtures were not available from the contractor. Plant-produced samples were obtained in con- formance to the requirements of AASHTO T 168 and stored in sealed boxes until the time of testing.2 To prepare the plant mixtures for testing, they were first heated in their boxes at 135 ± 5°C (275 ± 9°F) for about 2 hours. The materials were then worked until a loose mixture condition was obtained. Me- chanical splitter and quartering methods were used to split the mixtures to the appropriate size for test- ing in accordance with AASHTO R 47.3 Mixtures were then dried in the oven at 105 ± 5°C (221 ± 9°F) to constant mass. HMA particles were further sepa- rated by hand so that the particles of the fine aggre- gate portion were no larger than 6.3 mm (1⁄4 in.). The mixtures were then cooled to room temperature before weighing and testing. The laboratory mixtures were designed accord- ing to the Superpave mix design procedure. Non- 4 Table 2 Mix designs of the dense-graded laboratory-prepared and plant-produced mixtures. Laboratory-Prepared Mixtures Plant-Produced Mixtures 4.75-mm 12.5-mm 25.0-mm 37.5-mm 9.5-mm 19.0-mm Percent Percent Percent Percent Percent Percent Sieve (mm) Passing (%) Passing (%) Passing (%) Passing (%) Passing (%) Passing (%) 50.00 100 100 100 100 100 100 37.50 100 100 100 97 100 100 25.00 100 100 97 91 100 100 19.00 100 100 86 78 100 98 12.50 100 92 71 59 100 87 9.50 100 78 63 45 94 74 4.75 93 52 45 29 53 37 2.36 67 34 29 19 33 27 1.18 44 22 18 12 22 20 0.60 23 15 11 8 14 15 0.30 16 11 7 5 10 10 0.15 11 7 5 4 7 7 0.075 8.0 4.4 4.4 3.6 6 5.1 AC % 5.8 5.2 4.0 3.6 5.2 4.4 D. B. Ratio 1.5 0.9 1.0 1.1 1.18 1.23 2AASHTO T 168-03, Sampling Bituminous Paving Mixtures. In Standard Specifications for Transportation Materials and Methods of Sampling and Testing, 30th Ed. (CD-ROM), Amer- ican Association of State Highway and Transportation Offi- cials, Washington, D.C., 2010. 3AASHTO R 47-08, Reducing Samples of Hot Mix Asphalt (HMA) to Testing Size. In Standard Specifications for Trans- portation Materials and Methods of Sampling and Testing, 30th ed. American Association of State Highway and Trans- portation Officials, Washington, D.C., 2010.

absorptive limestone-dolomite aggregate and PG 64-22 asphalt were mixed at 157°C (315°F) and short-term conditioned for 2 hours at 145°C (293°F) according to AASHTO R 30.4 The mixtures then were separated by hand so that the particles of the fine aggregate portion were not larger than 6.3 mm. Samples then were cooled to room temperature before weighing and testing. The 4.75-mm and 9.5-mm mixtures were pre- pared in 1,500-g batches. The 12.5-mm mixtures were prepared in 2,000-g batches, and the 19-mm and 25-mm mixtures were prepared in 2,500-g batches. The 37.5-mm mixture also was prepared in 2,000-g batches given that the 4,000-g batch weight required by AASHTO T 209 for 37.5-mm and larger mixes could not fit in the flask or pycnometer. In this respect, four 2,000-g specimens of 37.5-mm mixture were tested, combined into two pairs, and the weight measurements from each of the two specimens per pair were added and served as values for one replicate. Measurement of Test Data Gmm measurements using vibratory, orbital, and rotary devices were conducted following AASHTO T 209. The cooled, separated particles of asphalt mixture were placed in a tared vacuum container, and the dry mass of the sample was recorded. A suf- ficient amount of 25°C (77°F) distilled water then was added to cover the sample completely. A deviation from the AASHTO T 209 test method was conducted on several mixtures in which the specified weight of the dry sample was added to the flask or pycnometer after water was placed in the con- tainer. The purpose of this deviation was to examine the effect on the release of air—and thus on the Gmm—of the order of placement of mixture and water. After adding 0.001% of wetting agent, the container or flask was sealed and subjected to vibration at 27.5 ± 2.5 mm Hg of vacuum for 15 minutes. For three of the mixtures, agitation-vacuum times of 10 minutes, 20 minutes, and 25 minutes also were used with the Gilson vibratory device to examine the effect on Gmm of the duration of agitation. Subsequent to the release of the vacuum, the con- tainer was (a) immersed in a distilled-water bath for 10 minutes for mass measurement in water or (b) filled with distilled water, kept in the water bath for 10 min- utes, then dried and placed on the scale for mass de- termination in the air. The weight measurements were obtained to the nearest 0.1 g. In addition to the weight measurements, the acceleration and frequency in the x-, y- and z-axes of the vibrating tables were measured to the nearest 0.01 m/s2 and 0.1 Hz, respectively. Gmm was measured using the Corelok vacuum sealing device according to ASTM D6857-09, “Stan- dard Test Method for Maximum Specific Gravity and Density of Bituminous Paving Mixtures Using Automatic Vacuum Sealing Method.”5 The specified weight of loose asphalt mixture was placed in special plastic bags provided for the vacuum sealing device. The bags were sealed and subjected to a vacuum of 4 mm Hg. The weight of the dry sample in air, weight of the bag, and weight of the mixture and bag in water were used to calculate Gmm of the mixture. Table 3 presents the test factorial of the study. The effects of several variables on Gmm were evalu- ated. The effect of vibration intensity on Gmm was de- termined for four shaking devices with variable set- tings (Humboldt, Gilson, Syntron, and Orbital) and for all nine mixtures, yielding the 32 mixture–device test combinations designated as “a” in Table 3. The effect of measuring device on Gmm was evaluated using four of the devices (Corelok, Aggregate Drum Washer, HMA, and Humboldt) with all nine mix- tures, two of the devices (Gilson and Orbital) with eight mixtures, and one of the devices (Syntron) with seven mixtures. This evaluation yielded a total of 59 mixture-device test combinations, designated as “b” in Table 3. The comparison of manual and me- chanical agitation was performed using four of the devices (Humboldt, Gilson, Orbital, and HMA) with all nine mixtures, yielding the 34 mixture device com- binations designated as “c” in Table 3. The effect on Gmm of the order of placement of water and mixture in the pycnometer was conducted using three devices with seven mixtures, yielding the 21 mixture-device combinations designated as “d” in Table 3. Finally, the effect of vacuum-agitation duration was deter- 5 4AASHTO R 30-02, Mixture Conditioning of Hot Mix Asphalt (HMA). In Standard Specifications for Transportation Materi- als and Methods of Sampling and Testing, 30th Ed. American Association of State Highway and Transportation Officials, Washington, D.C., 2010. 5ASTM D6857-09, Standard Test Method for Maximum Spe- cific Gravity and Density of Bituminous Paving Mixtures Using Automatic Vacuum Sealing Method. In Annual Book of ASTM Standards, Vol. 4.03, ASTM International, West Conshohocken, PA, 2010.

Table 3 Experimental plan for evaluation of the effects of various factors on Gmm values. Mixtures Plant-Produced Dense-Graded Plant-Produced Gap-Graded Laboratory-Produced Dense-Graded 9.5-mm 19.0-mm 9.5-mm 12.5-mm 19.0-mm 4.75-mm 12.5-mm 25.0-mm 37.5-mm Percent Percent Percent Percent Percent Percent Percent Percent Percent Passing Passing Passing Passing Passing Passing Passing Passing Passing Device (%) (%) (%) (%) (%) (%) (%) (%) (%) Humboldt Vibrating a, b, c, d a, b, c, d a, b, c a, b, c a, b, c, d a, b, c a, b, c, d a, b, c a, b, c Table (H-1756) Gilson Vibro-Deaerator a, b, c, d a, b, c a, b, c, e a, b, c, d, e a, b, c, e a, b, c, d a, b, c — a, b, c (SGA-5R) Syntron Vibrating a, b a, b a, b, d a, b a, b, d a, b, d a, b, d — — Table (VP-51 D1) Orbital Shaker a, b, c, d a, b, c a, b, c a, b, c, d a, b, c a, b, c, d a, b, c a, b, c — Table (SHKE 2000) HMA Vibrating b, c b, c, d b, c, d b, c, d b, c b, c b, c, d b, c b, c Table (VA-2000) Aggregate Drum b b, d b, d b b, d b b b b Washer Corelok (vacuum b b b b b b b b b sealing device) a = Change in vibration b = Equipment evaluation c = Manual versus mechanical d = Order of placement (water and mixture) e = Vacuum/agitation duration

mined using one device (Gilson) and three mixtures, yielding the three mixture-device combinations des- ignated as “e” in Table 3. RESULTS AND ANALYSIS The experimental results were analyzed to de- termine the effects of the variables discussed in the previous section on Gmm. The variables included vibration settings of mechanical agitators, agitation type (manual or mechanical), brand of mechanical agitators, order of placement of water and mixture in pycnometer, and the duration of the vacuum/agitation process. The relationship between the vibration prop- erties of vibrating tables and the highest Gmm measured by them also was examined. The significance of the effects of these variables on Gmm was evaluated statistically, physically, and from a practical point of view. The physical signifi- cance was evaluated by visually observing the change in water cloudiness during agitation. The practical sig- nificance was evaluated by estimating the change in air void values resulting from the observed change in Gmm. The statistical significance was evaluated using either a Scheffé test for multivariate comparisons or a paired t-test for two-variable comparisons. Vibration Measurements Using an accelerometer, frequency and accelera- tion were measured in x, y, and z directions for the four vibratory devices (Humboldt, Gilson, Syntron, and HMA shaking tables). The frequency and acceleration data were collected for 10 seconds at 5 minutes into the 15-minute agitation period. Data was collected every 0.000605 seconds, providing 16,526 accelera- tion data points and 10 frequency data points. The ac- celeration data was used to calculate the kinetic energy of vibration using the kinetic energy equation, KE = 1⁄2 mv2, where m is the mass of the object and v is the velocity of vibration. The velocity was calculated by integrating the acceleration data over the 10-second period. The energy values in the three directions were then summed to calculate the total kinetic energy. The total energy of vibration of the various shaking tables was compared to examine whether the same energy of vibration would yield the same Gmm value. For the Humboldt device, at each vibration set- ting, the frequency was the same in the x, y, and z di- rections. However, the acceleration and energy were not the same in all directions; they were the highest in the z direction and the lowest in the y direction. No noticeable change in vibration occurred until Setting 5. The frequency, acceleration, and energy started to increase with the increase in the dial set- ting of the Humboldt device after Setting 4. A max- imum frequency of 53 Hz, a maximum acceleration of 5.0 m/s2, and a maximum kinetic energy of 50 micro- joules were achieved at Setting 8 and were maintained through Setting 10. As with the Humboldt device, for the Gilson de- vice the frequency was the same in the x, y, and z di- rections at each vibration setting. Also as with the Humboldt device, the acceleration and energy were most prominent in the z direction and least promi- nent in the y direction. The difference between the vibrations imparted by the Gilson and Humboldt devices was in the vibration trends. Although the Humboldt device did not provide any noticeable ac- celeration up to Setting 5, the acceleration of the Gilson device was noticeable starting at Setting 1, with a steady increase in frequency, acceleration, and energy afterward. A maximum frequency of 52 Hz, a maximum acceleration of 7.2 m/s2, and a maximum total kinetic energy of 90 microjoules were achieved at the highest setting (Setting 8). Unlike the previous devices, the Syntron device showed substantial differences in the directional fre- quencies. At Setting 3 and lower, the x and y direc- tions were fairly close in magnitude, and the magni- tude in the z direction was about half of this value. However, from Setting 4 until the peak at Setting 8, the increase in magnitude in the z direction was far greater than that of the x and y magnitudes. Although the frequency peaked at Setting 8 with frequencies of 63, 119, and 629 Hz in the x, y, and z directions, respectively, the maximum acceleration and energy occurred at Setting 9. The maximum acceleration and total energy at Setting 9 were 76.3 m/s2 and 4,307 microjoules, respectively. The HMA device operates at a fixed setting. Al- though the vibration frequencies in the x, y, and z di- rections were the same, differences occurred in the directional accelerations and energies. The acceler- ation and energy in y and z directions were relatively close in magnitude, but the magnitude in the x di- rection was considerably less. The maximum accel- eration and total energy for the HMA device were 26 m/s2 and 1,400 microjoules, respectively. As the above results show, the vibration proper- ties of the four devices are very different. As shown from the comparison of the total energy from the 7

Syntron and Humboldt devices, the total energy from one device could be as much as 10 times greater than that from another device. The next sections discuss the effect on Gmm of different vibration intensities. Gmm Measurements at Various Settings of the Vibrating Tables Four vibratory tables with variable settings were used to evaluate the effect of vibration intensity on Gmm: the Humboldt Vibrating Table, Gilson Vibro- Deaerator, Syntron Vibrating Table, and Orbital Shaker. Measurements of Gmm were made at several settings of the vibrating devices, as well as at zero agitation and manual agitation. A comparison of Gmm at various settings would indicate if there was a systematic change in Gmm and its variability with change in vibration setting. Although measurements at zero agitation were performed with all four mechanical devices, the manual agitation was only performed with three of the device setups. The Minnesota DOT setup with the Syntron device was not used for manual agitation because it was not prac- tical to strike or shake its bell-jar vacuum chamber. To examine the physical significance of the vi- bration intensity, changes in the clarity of water in which the HMA sample was immersed were ob- served in conjunction with the changes in intensity of vibration. Substantially cloudy water would indi- cate the occurrence of asphalt stripping due to in- tensive vibration of the shaking tables. The practical significance of the change in Gmm was examined using the equation where Va = air voids, Gmm = theoretical maximum specific gravity, and Gmb = bulk specific gravity. For calculating the air voids, a Gmb that would result in air voids equal to 4% ± 1% was assumed for each mixture. Although a change of more than ± 0.5% in air voids is typically significant, in this study a change greater than 0.2% in air voids was consid- ered practically significant, compensating for the po- tential variability in the measurement of Gmb, which here was assumed to be a constant for each mixture. Va = −G G G mm mb mm The statistical significance of the difference between values of Gmm was examined using a Scheffé test.6 Whenever multivariate analysis of variance (MANOVA) rejects the null hypothesis, the Scheffé test will find which comparison yielded the signifi- cant difference. A Scheffé test was conducted to compare the Gmm values that resulted from various set- tings of each device. The comparison of the computed F from the Scheffé test with the critical F values would determine whether the difference between Gmm of each pair of vibration settings was significant. To determine the optimum vibration setting, the results of both the physical evaluation and the sta- tistical analysis were taken into account. The setting that provided the highest Gmm without substantially clouding the water was considered the optimum set- ting for a device. The statistical tests on Gmm and the comparison of the computed air void values were used to select an optimum setting of a device that would result in a Gmm that was not significantly dif- ferent from the highest Gmm of the several mixtures. The significance of the difference between the Gmm from manual agitation and the highest Gmm ob- tained with a mechanical device also was evaluated statistically and from a practical standpoint. If this dif- ference was significant, use of manual agitation would not be recommended for that particular mixture. The following sections discuss the analysis of the results obtained from the four vibrating tables with variable settings. Humboldt Vibrating Table (H-1756) The Humboldt Vibrating Table has 11 discrete vibration settings marked 0 to 10. Based on the re- sults of the state DOT survey, Setting 5 (mid-range) and Setting 10 (maximum) are commonly used with the Humboldt device. The Gmm of field and labora- tory mixtures was measured at various settings of the Humboldt device, and the highest Gmm values were compared with the Gmm from manual agitation and from the settings commonly used by the states. Dense-Graded Field Mixtures. For the dense- graded 19.0-mm field mixture, measurements were conducted at all 11 settings of the device. For the dense-graded 9.5-mm field mixture, the measure- ments at Settings 1 through 4 were omitted from the 8 6NIST/SEMATECH e-Handbook of Statistical Methods, avail- able at http://www.itl.nist.gov/div898/handbook/.

analysis because the changes in Gmm at these settings with respect to the zero setting were very small. The Gmm of the mixtures increased with the increase in the device setting until Gmm reached a maximum. Further increases in vibration intensity resulted in decreases of Gmm. For the 9.5-mm mixture, the highest Gmm of 2.512 was achieved at Setting 8, and for the 19.0-mm mixture, the highest Gmm of 2.536 was achieved at Setting 7 of the Humboldt device. For the 9.5-mm mixture, Gmm from manual agitation (2.506) was equivalent to Gmm at Setting 5; for the 19.0-mm mix- ture, Gmm from manual agitation (2.525) was equiva- lent to Gmm from Setting 4. The change in water clarity was monitored to ex- amine the physical effect of vibration on the mixtures. Visual observation of the water indicated that for both mixtures the water remained clear up to Setting 6. At Setting 7 the water became slightly cloudy, and at Set- tings 8, 9, and 10 the water was substantially cloudy. The differences in replicate Gmm values at differ- ent settings would indicate if there is a relationship between vibration setting and measurement variabil- ity. The difference between replicate measurements of both mixtures at every setting of the device was smaller than 0.005, which is significantly smaller than the acceptable difference between two replicate mea- surements specified in AASHTO T 209. Calculated air void values were compared to ex- amine the practical significance of differences be- tween the highest Gmm and the Gmm at settings indi- cated as important by the state DOT survey. Gmb values of 2.404 and 2.422 were assumed for calcu- lating the air voids of the 9.5-mm and 19.0-mm mix- tures, respectively. The differences between the air voids from the highest Gmm and from the Gmm with manual agitation were 0.25% for 9.5-mm mixtures and 0.41% for 19.0-mm mixtures. The differences in air voids between the highest Gmm and Gmm at mid- range agitation (Setting 5) were 0.24% and 0.22% for 9.5-mm and 19.0-mm mixtures, respectively. Moreover, the differences between the air voids from the highest Gmm and the Gmm of the maximum setting (Setting 10) were 0.21% and 0.27% for 9.5-mm and 19.0-mm mixtures, respectively. Considering other possible sources of variability in measuring air voids, use of manual agitation and use of mid-range and maximum settings could result in significantly lower air voids than the actual air voids of the compacted 9.5-mm and 19.0-mm mixtures. The significance of the differences between Gmm measurements from various settings also was evalu- ated statistically using the Scheffé test. For the 9.5-mm mixture, the comparison of the computed F and the critical F value for a 5% level of significance indicated that the highest Gmm value from Setting 8 was signif- icantly different from those of Settings 0 through 5, Setting 10, and manual agitation. The Gmm of Setting 8 was not statistically different from those of Settings 6, 7, and 9. For the 19.0-mm mixture, comparison of the computed F with the critical F value indicated that the highest Gmm from Setting 7 was significantly greater than those of Settings 0 through 2. The rest of the settings provided Gmm that were statistically the same as that of Setting 7. Based on the results of the statistical analysis and the air voids comparison, manual agitation and the mid-range (Setting 5) and maximum (Setting 10) of the Humboldt device would most likely provide sig- nificantly lower air voids than the highest achieved air voids for the 9.5-mm mixture. However, for the 19.0-mm mixture, the statistical analysis indicated that the highest Gmm of Setting 7 was statistically the same as the Gmm from manual agitation and the mid- range and maximum settings. This suggests that man- ual agitation and lower agitation settings would be adequate for measuring Gmm of the coarser mixtures. Given that the water became substantially cloudy at Settings 8, 9, and 10, the possibility of using Set- ting 7 for the 9.5-mm mixture was investigated. The F values from comparison of Gmm at Settings 7 and 8 indicate that Settings 7 and 8 produced not signifi- cantly different values of Gmm for the 9.5-mm mix- ture. The difference between the calculated air voids at Settings 7 and 8 is 0.07%, which is not considered practically significant. Based on the small difference in the Gmm of the 9.5-mm mixture at Settings 7 and 8, Setting 7 of the Humboldt device is suggested as the optimum operational setting for measuring Gmm of 9.5-mm and 19.0-mm dense-graded field mixtures. Gap-Graded (SMA) Field Mixtures. The Gmm of the three gap-graded (SMA) mixtures (9.5-mm, 12.5-mm, and 19.0-mm NMAS) were measured using the Humboldt device. Because there was no notice- able change in the vibration level of the device up to Setting 4, the measurements were conducted at Set- tings 5 through 10. The highest Gmm of the 9.5-mm and 12.5-mm mix- tures (2.647 and 2.466, respectively) were achieved at Setting 8 and the highest Gmm of the 19.0-mm mixture (2.448) was achieved at Setting 9. The Gmm of the 9.5-mm and 12.5-mm mixtures with manual agitation 9

were equivalent to those from Setting 5 (2.641 and 2.459, respectively) and the Gmm of the 19.0-mm mix- ture with manual agitation was equivalent to that of Setting 6 (2.439). Visual observation of the water indicated that for all three mixtures the water remained clear up to Set- ting 6. At Settings 7 and 8, the water became slightly cloudy, and at Settings 9 and 10, the water became substantially cloudy. The differences in replicate Gmm values at dif- ferent settings would indicate if there is a relation- ship between vibration setting and measurement variability. The differences in Gmm of two replicates at various settings did not indicate a defined trend as a function of vibration setting. However, the dif- ferences between replicate measurements of the 19.0-mm mixture were larger than those of the 9.5-mm and 12.5-mm mixtures. Nevertheless, at every set- ting of the Humboldt device, the difference between replicate measurements of the three mixtures was less than 0.007, significantly smaller than the ac- ceptable difference between two replicate measure- ments specified in AASHTO T 209. The calculated air voids were compared to exam- ine the practical significance of the differences be- tween the highest Gmm and Gmm of the settings indi- cated as important by the state DOT survey. Gmb values of 2.532, 2.357, and 2.339 were assumed for calculating the air voids of the 9.5-mm, 12.5-mm, and 19.0-mm SMA mixtures, respectively. The difference between air voids from the highest Gmm and Gmm from manual agitation was in the range of 0.23% to 0.30%; the difference between the air voids from the highest Gmm and Gmm of mid-range agitation was in the range of 0.23% to 0.45%; and the difference between the air voids from the highest Gmm and Gmm from the maxi- mum setting (Setting 10) was in the range of 0.05% to 0.20%. Considering other possible sources of vari- ability in determining air voids, using the mid-range settings or manual agitation would most likely provide significantly lower air voids. However, operating the Humboldt device at the maximum setting would pro- duce Gmm practically the same as the highest Gmm. The significance of the differences between Gmm measurements from various settings was evaluated statistically. For the 9.5-mm mixture, comparison of the computed F and the critical F value indicates that, for a 5% level of significance, the Gmm values from manual agitation and those of various settings are statistically the same. For the 12.5-mm mixture, the highest Gmm of a 12.5-mm mixture from Setting 8 is significantly greater than the Gmm from Setting 0, Setting 5, and manual agitation. The rest of the settings provide statistically the same Gmm values as that of Setting 8. For the 19.0-mm SMA mixture, the highest Gmm of the 19.0-mm mixture from Setting 9 is only significantly greater than the Gmm obtained with zero agitation. Given that water became substantially cloudy at Setting 9, the possibility of using Setting 8 instead of Setting 9 for the 19.0-mm SMA mixture was ex- amined. The difference between the air voids from the two settings is 0.1%, which is practically in- significant. The computed F values also show that the Gmm values from Setting 8 and Setting 9 are sta- tistically the same. Therefore, conducting the Gmm measurement of the 19.0-mm mixture at Setting 8 is recommended. Based on the highest achieved Gmm of the 9.5-mm and 12.5-mm mixtures at Setting 8 and the small dif- ference between the Gmm from Settings 8 and 9 for the 19.0 mixtures, Setting 8 is suggested as the opti- mum operational setting of the Humboldt device for measuring Gmm of the SMA mixtures. Dense-Graded Laboratory Mixtures. The Gmm of 4.75-mm, 12.5-mm, 25.0-mm, and 37.5-mm dense- graded laboratory mixtures were measured at Set- tings 4 through 10 of the Humboldt device. The highest Gmm of the 4.75-mm mixture (2.557) was achieved at the maximum setting (Setting 10); the highest Gmm of the 12.5-mm mixture (2.580) was obtained at Setting 8; and the highest Gmm of the 25.0-mm and 37.5-mm mixtures (2.617 and 2.629, respectively) were achieved at Setting 9 of the Humboldt device. For the 4.75-mm and 12.5-mm mixtures, the Gmm from manual agitation (2.548 and 2.572, respectively) are equivalent to the Gmm from Setting 5, and for the 25.0-mm and 37.5-mm mix- tures, the Gmm from manual agitation (2.610 and 2.625, respectively) are equivalent to the Gmm from Setting 6. This finding suggests that, for coarser mixtures, manual agitation produces Gmm equivalent to those from higher agitation levels than are found for finer mixtures. The change in water clarity was monitored to examine the physical effect of vibration on the mix- tures. The water did not become substantially cloudy at any of the settings. For the four mixtures, water was slightly cloudy at the settings of the highest Gmm (Setting 10 for the 4.75-mm mixture, Setting 8 for the 12.5-mm mixture, and Setting 9 for the 25.0-mm and 37.5-mm mixtures). 10

The differences in replicate Gmm values at dif- ferent settings would indicate if there is a relation- ship between vibration setting and measurement variability. For these mixtures, the difference in Gmm of two replicates at various settings did not follow a defined trend as a function of vibration setting. At every setting of the device, the difference between replicate measurements was less than 0.005, which is significantly smaller than the acceptable differ- ence between two replicate measurements specified in AASHTO T 209. The practical significance of the difference be- tween the highest Gmm and the Gmm of the settings in- dicated as important by the state DOT survey was ex- amined by evaluating the differences between their corresponding air voids. Gmb of 2.444, 2.466, 2.502, and 2.515 were assumed for calculating the air voids of the 4.75-mm, 12.5-mm, 25.0-mm, and 37.5-mm mixtures, respectively. The difference between the air voids that resulted from the highest Gmm and those that resulted from manual agitation was 0.30% for the 4.75-mm and 12.5-mm mixtures and 0.24% and 0.15% for the 25.0-mm and 37.5-mm mixtures, re- spectively. Considering other possible sources of variability in measuring the air voids, these differ- ences could be significant. Therefore, from a practi- cal viewpoint, for obtaining the highest Gmm of mix- tures, use of manual agitation is not recommended for these dense-graded laboratory mixtures. For the 4.75-mm, 25.0-mm, and 37.5-mm mix- tures, the difference between the highest air voids and those from the mid-range setting (Setting 5) av- eraged 0.30%, which could be significant. The dif- ferences between the highest air voids and those from the maximum setting (Setting 10) averaged 0.03%, which was not practically significant. These numbers suggest that operation of the Humboldt device at its higher settings will achieve the highest Gmm for these dense-graded laboratory mixtures. The significance of the differences between Gmm measurements obtained from various settings also was evaluated statistically. Based on a comparison of the computed and critical F values, the differences between the highest Gmm and the Gmm from manual agitation, Setting 5, and Setting 10 were not statisti- cally significant. However, use of manual agitation and mid-range settings are not suggested for the dense- graded laboratory mixtures because of the potential significance of the differences in air voids. The possibility of using one vibration setting for all four dense-graded laboratory mixtures also was explored. The highest Gmm of each mixture was com- pared with Gmm at the settings that produced the high- est Gmm of other mixtures. The differences between the air voids of the mixtures resulting from the set- tings that yielded the highest Gmm were below 0.1%, which is considered not significant. Comparison of Gmm from Settings 8, 9, and 10 confirmed this finding statistically by providing F values that were smaller than the critical F value. Based on the highest achieved Gmm of the four laboratory mixtures at Settings 8, 9, and 10 and the similarity of the air voids from Settings 8, 9, and 10, Setting 8 is suggested as the optimum operational setting for the Humboldt device for measuring the Gmm of the dense-graded laboratory mixtures. At Setting 8, the water was only slightly cloudy. Gilson Vibro-Deaerator (SGA-5R) The Gilson device has an adjustable dial that per- mits a continuous increase of the vibration level. Eight marks, labeled 1 through 8, were made at ap- proximately equal intervals on the dial to represent eight discrete levels of vibration. Based on the re- sults of the state DOT survey, in the state laborato- ries the Gilson device is commonly operated in its middle to maximum range. The Gmm of field and lab- oratory mixtures were measured at various settings of the Gilson device, and the resulting highest Gmm values were compared with the Gmm from manual agitation and from the settings commonly used by the states. Dense-Graded Field Mixtures. The Gmm of the 9.5-mm and 19.0-mm dense-graded field mixtures were measured at Settings 1 through 8 of the Gilson device, as well as at zero agitation and using manual agitation. The highest Gmm (2.515 for the 9.5-mm mixture and 2.536 for the 19.0-mm mixture) were achieved at Settings 6 and 7, respectively. The Gmm values from manual agitation were equivalent to Gmm values from Setting 3 for both mixtures (2.507 for the 9.5-mm mixture and 2.527 for the 19.0-mm mixture). The change in water clarity was monitored to ex- amine the physical effect of vibration on the mixtures. Visual observation indicated that the water remained clear up to Setting 4. From Setting 5 through Setting 6, the water became slightly cloudy, and at Setting 7 and Setting 8 the water became substantially cloudy. The differences between two replicate Gmm values at various settings of the Gilson device were 11

examined. No defined trend existed between the variability of measurements and the intensity of vi- bration; however, higher variability was observed at high Gmm values for the 19.5-mm mixture. Neverthe- less, the difference between replicates at any setting was less than 0.005, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference be- tween the highest Gmm and the Gmm values obtained from the settings of importance identified in the state DOT survey was examined by comparing the calcu- lated air voids. Gmb of 2.404 and 2.422 were as- sumed for calculating the air voids of the 9.5-mm and 19.0-mm mixtures, respectively. The difference between air voids of the highest Gmm and the Gmm from manual agitation was 0.31% for the 9.5-mm mixture and 0.35% for the 19.0-mm mixture. Con- sidering other possible sources of variability in mea- suring air voids, use of manual agitation for either mixture would most likely result in significantly lower air voids than the actual air voids of the com- pacted mixture. The difference between air voids from the high- est Gmm and that of mid-range agitation (Setting 4) was 0.23% for the 9.5-mm mixture and 0.11% for the 19.0-mm mixture. This finding suggests that use of the mid-range setting would most probably result in significantly lower air voids for the 9.5-mm mixture; however, for the 19.0-mm mixture, the mid-range setting would produce air voids similar to Setting 7. The results also showed that the difference be- tween air voids from the highest Gmm and those from the maximum setting (Setting 8) is 0.07% for the 9.5-mm mixture and 0.24% for the 19.0-mm mix- ture. This suggests that for finer mixtures, the Gilson device can be operated at maximum setting to achieve air voids similar to those achieved at Setting 6. How- ever, for the 19.0 mm mixture, the maximum setting would most likely result in stripping of asphalt and provide significantly lower air voids than the actual air voids of the compacted mixture. The significance of the difference between Gmm measurements from various settings of the Gilson device also was evaluated statistically. The highest Gmm of the 9.5 mm mixture from Setting 6 is signif- icantly different from the Gmm at zero agitation and using manual agitation, and significantly different from the Gmm yielded by Settings 1 through 4, but it is statistically the same as the Gmm from Settings 5 through 8. For the 19.0-mm mixture, the highest Gmm from Setting 7 is only significantly different from the Gmm yielded by zero agitation and Setting 1. The rest of the settings provide statistically the same Gmm as that of Setting 7. This agrees with previous observations that manual and lower vibration levels might provide adequately high Gmm values for coarser mixtures. Given that water was substantially cloudy at Set- ting 7 and higher, the possibility of using Setting 6 for the 19.0-mm mixture was investigated. It was observed from both air voids values and from statis- tical results that for measuring the 19.0-mm mixture, lower settings (up to Setting 4) would result in Gmm not significantly different from the highest Gmm. Therefore, Setting 6 can be used for accurate mea- surement of Gmm for both the 9.5-mm and 19.0-mm dense-graded field mixtures. Gap-Graded (SMA) Field Mixtures. The three SMA mixtures of 9.5-mm, 12.5-mm, and 19.0-mm NMAS were tested using the Gilson device. The Gmm of the mixtures were measured at Settings 1 through 8. For all mixtures, measurements also were made at zero agitation and using manual agitation. The highest Gmm values (2.649, 2.463, and 2.447 for the 9.5-mm, 12.5-mm, and 19.0-mm mixtures, respectively) were achieved at Setting 7 of the Gilson device. For the SMA mixtures, the Gmm values from manual agita- tion were equivalent to the Gmm values in the range of Settings 3 through 5. Change in water clarity was monitored to examine the physical effect of vibra- tion on the mixtures. Observation of the water indi- cated that up to Setting 4, the water remained clear. From Setting 5 to Setting 7, the water became slightly cloudy, and at Setting 8, the water became substan- tially cloudy. The differences between two replicate Gmm val- ues at various settings of the Gilson device were ex- amined. No defined trend was found between the variability of measurement and the intensity of vi- bration; however, the differences between replicates were larger for the 19.0-mm mixtures. Nevertheless, the difference between replicates at any setting was smaller than 0.007, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference be- tween the highest Gmm and the Gmm from settings of importance identified in the state DOT survey was examined by comparing the calculated air voids. Gmb 12

values of 2.532, 2.357, and 2.339 were assumed for calculating the air voids of the 9.5-mm, 12.5-mm, and 19.0-mm SMA mixtures, respectively. The dif- ference between the air voids from the highest Gmm and the Gmm at the maximum setting (Setting 8) is in the range of 0.08 to 0.10, which is not practi- cally significant. At 0.25% for the 9.5-mm mixture and 0.28% for the 19.0-mm mixtures, the differ- ences between air voids from the highest Gmm and the Gmm from manual agitation could be significant. At 0.39% for the 19.0-mm mixture, the difference between using the highest Gmm and using the Gmm from mid-range agitation (Setting 4) also could be significant. The significance of the differences between Gmm measurements from various settings of the Gilson device also were evaluated statistically. Based on the computed F values, the highest Gmm of the SMA mixtures from Setting 7 was statistically the same as those from manual agitation, from the mid-range setting (Setting 4), and from maximum agitation (Setting 8). Thus, manual agitation, mid-range, and maximum settings would provide statistically the same Gmm as that from Setting 7. However, from a practical point of view, the differences between air voids from Setting 7 and those from the mid-range setting and from manual agitation could become sig- nificant if the variability of the Gmb measurements is considered. Given that the highest Gmm was produced at Set- ting 7 and water was only slightly cloudy at this set- ting, Setting 7 of the Gilson device is suggested as the optimum operational setting for the SMA mixtures. Dense-Graded Laboratory Mixtures. The Gmm of the 4.75-mm, 12.5-mm, and 37.5-mm dense-graded laboratory mixtures were measured at Settings 1 through 8, at zero agitation, and using manual agita- tion. The highest Gmm of 2.555, 2.580, and 2.631 of the 4.75-mm, 12.5-mm, and 37.5-mm mixtures were achieved at Settings 7, 6, and 6 of the Gilson device, respectively. For all three dense-graded laboratory mixtures, manual agitation resulted in Gmm values that were equivalent to or less than the Gmm values from Setting 2. For the 4.75-mm mixture, water be- came cloudy at Setting 8, and for the 12.5-mm and 37.5-mm mixtures, water became cloudy at Settings 7 and 6, respectively. The differences between the two replicate Gmm values at various settings of the Gilson device were examined. Although no defined trend was found be- tween the variability of measurement and the inten- sity of vibration, a smaller variability at the settings of higher Gmm was observed for the 12.5-mm mix- ture. The variability of the 37.5-mm mixture was less than those of the 4.75-mm and 12.5-mm mix- tures, which might be attributed to the better release of air from coarser mixtures. Nevertheless, the dif- ference between replicates at any setting was less than 0.005, significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference be- tween the highest Gmm and the Gmm from settings of importance identified in the state DOT survey was ex- amined by comparing the calculated air voids. Gmb values of 2.444, 2.466, and 2.515 were assumed for calculating the air voids of the 4.75-mm, 12.5-mm, and 37.5-mm mixtures, respectively. The difference between the air voids from the highest Gmm and the air voids from mid-range agitation (Setting 4) was in the range of 0.12% to 0.18%. The difference between the air voids from the highest Gmm and the air voids from the maximum setting (Setting 8) was in the range of 0.10% to 0.15%. The difference between the air voids from the highest Gmm and the air voids from manual agitation was in the range of 0.20% to 0.37%. There- fore, from a practical point of view, the use of Gmm from manual agitation could result in significantly lower air voids for compacted mixtures. The statistical significance of the difference between Gmm from various device settings was eval- uated using a Scheffé test. A comparison of the com- puted and critical F values showed that the differ- ence between the highest Gmm and the Gmm from manual agitation was significant for the 12.5-mm and 37.5-mm mixtures but not significant for the 4.75-mm mixture. Comparison of the highest Gmm with the Gmm of Settings 4 and 8 revealed that the highest Gmm values were statistically the same as those from the mid-range and maximum settings. Based on the results from statistical comparison and evaluation of the air void values, use of manual ag- itation for the dense-graded laboratory mixtures is not suggested. The possibility of selecting one optimum setting of the Gilson device for the dense-graded laboratory mixtures was investigated. As indicated earlier, for the 37.5-mm mixture, the water was substantially cloudy at Setting 6, so the possibility of using Set- ting 5 for the three mixtures was examined. The dif- ference between the air voids from Settings 5, 6, and 13

7 for the three mixtures was less than 0.11%, which is not considered practically significant. This finding is reinforced by the results of the statistical analysis, where the computed F values from comparison of Gmm of Settings 5, 6, and 7 were smaller than the crit- ical F value. Considering the small difference be- tween the air voids yielded from Setting 5 and those from Settings 6 and 7, Setting 5 is suggested for the 4.75-mm, 12.5-mm, and 25.0-mm mixtures. Syntron Vibrating Table (VP-51 D1) The Syntron device can be operated at ten discrete settings (Settings 1 through 10). Based on the results of the state DOT survey, the Syntron device is com- monly operated at Setting 5 in state laboratories. Dur- ing this study, the device was used following the setup used by the Minnesota DOT. Measurements at zero agitation were performed along other settings, but manual agitation was not performed with this device as it is impractical to strike or shake the bell- jar vacuum chamber given this setup. The following results are based on Gmm measurements. Dense-Graded Field Mixtures. The highest Gmm (2.513 and 2.534 for the 9.5-mm and 19.0-mm mix- tures, respectively) were achieved at Setting 7 of the Syntron device. Visual observation indicated that the water remained clear through Setting 4. At Set- tings 5 through 8 and at Setting 10, the water was slightly cloudy. At Setting 9, the water was substan- tially cloudy. Examination of differences between two repli- cate Gmm values at various settings of the Syntron de- vice yielded no defined trends between the variabil- ity of measurements and the intensity of vibration. The difference between replicate measurements at any setting was smaller than 0.004, which is sig- nificantly smaller than the acceptable difference be- tween two replicate measurements as specified in AASHTO T 209. The practical significance of the difference be- tween the highest Gmm and the Gmm from the settings of importance indicated by the state DOT survey was examined by comparing calculated air voids. Gmb values of 2.404 and 2.422 were assumed for cal- culating the air voids of the 9.5-mm and 19.0-mm mixtures, respectively. Air voids resulting from the highest Gmm (at Setting 7) were compared with air voids resulting from Setting 5, which is commonly used by the state laboratories. The difference was 0.07% for the 9.5-mm mixture and 0.08% for the 19.0-mm mixture; neither of these differences is considered practically significant. The significance of the difference between Gmm values from various settings also was examined sta- tistically using a Scheffé test. For the 9.5-mm mix- ture, the differences between Gmm values from vari- ous settings were not significant. For the 19.0-mm mixture, only the differences between the highest Gmm and the Gmm from Setting 10 and zero agitation are statistically significant. Based on achieving the highest Gmm and water clarity, Setting 7 is suggested as the optimum oper- ational setting of the Syntron device for measuring Gmm of the 9.5-mm and 19.0-mm dense-graded field mixtures. Gap-Graded (SMA) Field Mixtures. The Gmm of the 9.5-mm, 12.5-mm, and 19.0-mm SMA mix- tures were measured at Settings 1 through 10 of the Syntron device. Measurements also were conducted at zero agitation. The highest Gmm of the 9.5-mm (2.646), 12.5-mm (2.464), and 19.0-mm (2.448) mixtures were achieved at Settings 8, 7, and 9, re- spectively. The water appeared clear through Set- ting 5. At Settings 6 through 8 and at Setting 10, the water became slightly cloudy. At Setting 9, the water was substantially cloudy. The differences between two replicate Gmm val- ues at various settings of the Syntron device yielded no defined trend between the variability of mea- surement and the intensity of vibration. However, the differences between replicates of the 19.0-mm mixtures were larger than those of the other mix- tures. Nevertheless, the difference between repli- cates at any setting was less than 0.007, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the differences be- tween the highest Gmm and the Gmm from the settings of importance indicated in the state DOT survey was examined by comparing calculated air voids. Gmb of 2.532, 2.357, and 2.339 were assumed for calculating the air voids of the 9.5-mm, 12.5-mm, and 19.0-mm mixtures, respectively. The differences between the air voids yielded from the mid-range (Setting 5) and the highest Gmm were 0.40%, 0.15%, and 0.30% for the 9.5-mm, 12.5-mm, and 19.0-mm mixtures, re- spectively. Considering other possible sources of variability in measuring air voids, using Setting 5 14

would likely result in significantly lower air voids than the actual air voids of the 9.5-mm and 19.0-mm compacted mixtures. The statistical comparison indicated that the high- est Gmm of the 9.5-mm mixture (from Setting 8) is sig- nificantly different from the Gmm of Settings 0 through 5. For the 12.5-mm mixture, the only significant dif- ferences were found between the highest Gmm and the Gmm of Settings 0 and 1. For the 19.0-mm mixture, the highest Gmm differed significantly from the Gmm at Settings 0 through 4, but not significantly from the Gmm at Setting 5 and higher. These results suggest that for the 9.5-mm and 19.0-mm mixtures, if the Syntron device is operated at the mid-range setting, the result- ing Gmm would likely be significantly lower than the highest Gmm. The possibility of selecting one setting of the Syntron device for all three mixtures was explored. Comparing the air voids from the highest Gmm and the Gmm from Settings 7, 8, and 9, the smallest dif- ferences occurred between the air voids from the highest Gmm and from the Gmm of Setting 8 (a maxi- mum of 0.14%). Therefore, Setting 8 can be used for the SMA mixtures without a significant decrease in air voids. This finding is supported by the statistical analysis of the data. F values for comparison of Gmm from Setting 8 with Gmm from Settings 7 and 9 were lower than the critical F value. Based on these ob- servations, Setting 8 is suggested as the optimum operational setting of the Syntron device for mea- suring the Gmm of the SMA mixtures. Dense-Graded Laboratory Mixtures. Two of the four dense-graded laboratory mixtures were tested with the Syntron device. The Gmm of the 4.75-mm and 12.5-mm mixtures were measured at Settings 1 through 10 and at zero agitation. The highest Gmm (2.556 and 2.582, for the 4.75-mm and 12.5-mm mix- tures, respectively) were achieved at Setting 8. Visual observation indicated that the water remained clear through Setting 4. At Settings 5 through 7 and at Set- ting 10, the water was slightly cloudy. At Settings 8 and 9, the water was substantially cloudy. Comparison of the differences between two repli- cate Gmm values at various settings of the Syntron de- vice yielded no defined trend between the variability of measurement and the intensity of vibration. The difference between replicate measurements at any set- ting was less than 0.005, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the differences between the highest Gmm and the Gmm from the set- tings of importance indicated by the state DOT sur- vey was examined by comparing the calculated air voids. Gmb values of 2.444 and 2.466 were assumed for calculating the air voids of the 4.75-mm and 12.5-mm mixtures, respectively. The differences be- tween the air voids from the highest Gmm and the air voids from Setting 5, which is commonly used by the state laboratories, were 0.17% for the 4.75-mm mixture and 0.18% for the 12.5-mm mixture. From a practical point of view, these differences are not considered significant. The significance of the difference between Gmm measurements from various settings of the Syntron table also was evaluated statistically. The highest Gmm of the two dense-graded laboratory mixtures were not significantly different from the Gmm from Setting 5, which is commonly used by the state lab- oratories. Computed F values also indicated that, for measuring Gmm of the dense-graded laboratory mix- tures, any setting higher than Setting 3 would yield Gmm values that were not statistically different. Because water became substantially cloudy at Setting 8, the use of a lower setting as the optimum setting was evaluated. Comparing the air voids from Settings 7 and 8 yielded differences smaller than 0.1%, which is not practically significant. This find- ing also was supported by statistical analysis: Set- tings 7 and 8 were found to produce statistically the same Gmm values. Therefore, based on the clarity of the water and the non-significant differences between the air voids from Settings 7 and 8, Setting 7 is suggested as the optimum operational setting of the Syntron device for measuring the Gmm of the 4.75-mm and 12.5-mm dense-graded laboratory mixtures. Orbital Shaker (SHKE 2000) The Orbital Shaker has a digital dial for the con- tinuous increase of vibration in the range of 15 to 500 rpm. The measurement of Gmm of the dense- graded field mixtures was conducted at nine vibra- tion intensity levels at 30-rpm intervals between 90 and 330 rpm. Measurements also were conducted at zero agitation and using manual agitation. Based on the survey of the state laboratories, 270 rpm is the most commonly used vibration level. Dense-Graded Field Mixtures. For the dense-graded field mixtures, the highest Gmm (2.512 and 2.537, for 9.5-mm and 19.0-mm mixtures, respectively) were 15

obtained at vibration levels of 240 rpm and 210 rpm of the Orbital device. The Gmm values from manual agitation were equivalent to the Gmm values obtained at 150 rpm for the 9.5-mm mixture and at 90 rpm for the 19.0-mm mixture. Visual observation indicated that the water remained clear through 150 rpm. From 180 rpm through 240 rpm, the water became slightly cloudy. At 270 rpm and higher, the water became substantially cloudy. Examination of the differences between two repli- cate Gmm values at various settings of the Orbital de- vice showed no defined trend between the variabil- ity of measurement and the intensity of vibration for the 19.0-mm mixture. The difference between repli- cate values of the 9.5-mm mixture reached a maxi- mum at 180 rpm; nevertheless, for both mixtures, the difference at any setting was less than 0.005, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference between the highest Gmm and those from the set- tings of importance indicated from the state DOT survey was examined by comparing the calculated air voids. Gmb values of 2.404 and 2.422 were as- sumed for calculating the air voids of the 9.5-mm and 19.0-mm mixtures, respectively. Differences between the air voids from the highest Gmm and the air voids from manual agitation and at 270 rpm (the level commonly used by the state laboratories) were examined. For the 9.5-mm mixture, the differ- ence between the air voids from the highest Gmm and the air voids from manual agitation was 0.18%. For the 19-mm mixture, the difference was 0.27%. Con- sidering the possible variability of the Gmb measure- ments, use of manual agitation might result in signif- icantly lower air voids for the 19.0-mm compacted mixtures. The differences between the air voids from the highest Gmm and the air voids at a vibration level of 270 rpm is 0.11% for the 9.5-mm mixture and 0.16% for the 19.0-mm mixture. For 9.5-mm and 19.0-mm mixtures, vibration at 270 rpm produced air voids that were not significantly different from the highest air void values. The statistical significance of the difference be- tween the Gmm from various settings of the Orbital device was evaluated using a Scheffé test. The dif- ferences between the highest Gmm (from a vibration level of 240 rpm) and the Gmm from other vibration levels or from manual agitation were not significant for the 9.5-mm mixture. For the 19.0-mm mixture, however, the difference between the highest Gmm (from a vibration level of 210 rpm) and the Gmm from manual agitation was significant. The possibility of selecting one setting for the Orbital device for both the 9.5-mm and 19.0-mm mixtures was explored. The differences between the air voids at vibration levels of 210 rpm and 240 rpm were 0.05% and 0.11% for the 9.5-mm and 19.0-mm mixtures, respectively. These differences are not considered significant. Statistical analysis also indicated that, for both mixtures, the Gmm from vibration levels of 210 rpm and 240 rpm are sta- tistically the same. Therefore, a setting of either 210 rpm or 240 rpm could be selected. Based on observation of a slight level of cloudiness in the water at 240 rpm, use of the higher setting of 240 rpm is suggested as the optimum vibration level at which to set the Orbital device for dense-graded field mixtures. Gap-Graded (SMA) Field Mixtures. The three SMA mixtures (9.5-mm, 12.5-mm, and 19.0-mm NMAS) were tested with the Orbital shaker. Mea- surements were conducted at nine vibration inten- sity levels at 30-rpm intervals between 90 rpm and 330 rpm. Measurements also were conducted at zero agitation and using manual agitation. For the 9.5-mm mixture, the highest Gmm (2.649) was obtained at a vibration level of 270 rpm; for the 12.5-mm mixture, the highest Gmm (2.464) was obtained at 240 rpm; and for the 19.0-mm mixture, the highest Gmm (2.449) was obtained at 300 rpm. Manual agitation resulted in Gmm values that were equivalent to the values ob- tained at vibration levels in the range of 90 rpm to 150 rpm. Visual observation indicated that the water remained clear at vibration levels through 150 rpm. From 180 rpm through 240 rpm, water became slightly cloudy, and at 270 rpm and higher, the water became substantially cloudy. The differences between two replicate Gmm val- ues at various settings of the Orbital device showed no defined trend between the variability of measure- ment and the intensity of vibration. Differences between replicate values at any vibration level were less than 0.007, which is significantly smaller than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The practical significance of the difference be- tween the highest Gmm and the Gmm from the settings of importance identified in the state DOT survey was 16

examined by comparing calculated air voids. Gmb values of 2.532, 2.357, and 2.339 were assumed for calculating the air voids of the 9.5-mm, 12.5-mm, and 19.0-mm mixtures, respectively. The difference in air voids between the highest Gmm and the Gmm from manual agitation was 0.17%, 0.24%, and 0.53% for the 9.5-mm, 12.5-mm, and 19.0 mm mixtures, re- spectively. Considering other possible sources of vari- ability in measuring air voids, using manual agitation would probably provide significantly lower air voids than the actual air voids for the 12.5-mm and 19.0-mm compacted mixtures. For the 19.0-mm mixture, the difference in air voids between the highest Gmm and the Gmm at a vi- bration level of 270 rpm, which is the level commonly used by the states, was 0.03%. For the 12.5-mm mix- ture, the difference was 0.07%. These differences in air voids are not practically significant. The significance of the differences between Gmm values from various settings of the Orbital device also was examined statistically using F values from a Scheffé test. For the 9.5-mm mixture, the difference between the Gmm of any pair of vibration levels was not significant. For the 19.0-mm mixture, the highest Gmm from a vibration level of 300 rpm was only sig- nificantly different from the Gmm from zero agitation and from a vibration level of 90 rpm. For the 12.5-mm mixtures, however, the highest Gmm from a vibration level of 240 rpm was significantly different from the Gmm from zero agitation, at 90 rpm, and using manual agitation. In summary, based on differences between the air voids, manual agitation is not suggested for the 12.5-mm and 19.0-mm SMA mixtures. Water was observed to be substantially cloudy at vibration levels of 270 rpm and above. Therefore, the possibility of using a level of 240 rpm for the three SMA mixtures was examined on the basis of differ- ences in air voids between vibration levels at 240 rpm, 270 rpm, and 300 rpm. The differences (0.00% for the 9.5-mm mixture and 0.01% for the 19.0-mm mixture) were not practically significant. This finding was con- firmed by the results of statistical analysis. For the 9.5-mm and 19.0-mm mixtures, F values from com- parisons of Gmm from vibration levels of 240 rpm, 270 rpm, and 300 rpm were smaller than the criti- cal F values. This indicates that a vibration level of 240 rpm can be used for the SMA mixtures without a significant decrease in Gmm. Dense-Graded Laboratory Mixtures. Three out of four dense-graded laboratory mixtures were tested using the Orbital device. The Gmm of the 4.75-mm, 12.5-mm, and 25.0-mm dense-graded laboratory mixtures were measured at nine vibration intensity levels at 30-rpm intervals between 90 rpm and 330 rpm. Measurements also were conducted at zero agitation and using manual agitation. For the 4.75-mm, 12.5-mm, and 25.0-mm mixtures, the highest Gmm of 2.556, 2.580, and 2.616 were ob- tained at the 270, 240, and 300 rpm settings of the Orbital device, respectively. Visual observation indicated that the water remained clear through a vibration level of 150 rpm. From 180 rpm through 240 rpm, the water became slightly cloudy, and at levels of 270 rpm and above, the water became substantially cloudy. The differences between two replicate Gmm values at various settings of the Orbital device showed no de- fined trend between the variability of measurements and the intensity of vibration. Also, the difference be- tween replicate measurements at any setting was less than 0.005, which is significantly smaller than the ac- ceptable difference between two replicate measure- ments as specified in AASHTO T 209. The practical significance of the difference be- tween the highest Gmm and the Gmm from the vibra- tion levels identified as important from the state survey was examined by comparing calculated air voids. Gmb values of 2.444, 2.466, and 2.502 were assumed for calculating the air voids of the 4.75-mm, 12.5-mm, and 25.0-mm mixtures, respectively. The differences in air voids between manual agitation and the highest Gmm were in the range of 0.28% to 0.34%. Such differences suggest that manual agitation of the Orbital shaker flasks could result in significantly lower air voids than the actual air voids of compacted mixtures. The differences in air voids between the highest Gmm and the Gmm at a vibration level of 270 rpm are 0.04% and 0.10% for the 12.5-mm and 25.0-mm mixtures, respectively. These differences are not considered practically significant. The differences in Gmm of the dense-graded lab- oratory mixtures using various vibration levels of the Orbital device also were examined statistically using F values from a Scheffé test. For the 4.75-mm mixture, the highest Gmm at 270 rpm is statistically the same as the Gmm at every other setting. For the 12.5-mm mixture, the highest Gmm at 240 rpm dif- fers only from the Gmm at zero agitation. For the 25.0-mm mixture, the highest Gmm at 300 rpm is sig- nificantly different from the Gmm at zero agitation 17

through 150 rpm. For the three mixtures, manual ag- itation produced Gmm that were not significantly dif- ferent from Gmm using the mechanical settings. This finding regarding manual agitation disagrees with that based on the calculated air voids discussed in the previous paragraph. Given that water was substantially cloudy at vi- bration levels of 270 rpm and above, the possibility of using 240 rpm for the dense-graded laboratory mixtures was explored through an examination of the difference in air voids. Between the highest Gmm and the Gmm at 240 rpm, the difference in air voids was 0.17% for both the 4.75-mm and 25.0-mm mix- tures, which is considered not significant. Statistical analysis also confirmed no significant differences between the Gmm at 240 rpm and the Gmm at 210 rpm for the 4.75-mm mixture and at 300 rpm for the 25.0-mm mixture. Based on the above observations, a vibration level of 240 rpm is suggested as the op- timum setting of the Orbital device for the dense- graded laboratory mixtures. Selecting Optimum Device Settings Previously, the optimum setting of each agita- tion device was selected for each of the three mix- ture types. A summary of the settings that resulted in the highest Gmm and the device settings suggested for each mixture type are provided in Table 4. The suggested settings were selected based on the eval- uation of change in air voids, statistical significance of differences in Gmm, and observed substantial changes in water clarity. This section explores the possibility of choosing one setting of each device for all mixture types. As shown in Table 4, using the Humboldt device, the highest values of Gmm for the nine mixtures were produced over a range from Setting 7 to Setting 10. Based on the concern with water clarity at Settings 8 and 9, however, Setting 7 was recommended for the dense-graded field mixtures and Setting 8 was rec- ommended for the SMA and dense-graded laboratory mixtures. The possibility of using Setting 7 of the Humboldt device for all mixture types was evaluated by examining the computed F values for the compar- ison of Gmm from Settings 7 and 8. This difference was not significant for any of the mixtures. Therefore, Setting 7 of the Humboldt device can be suggested for all three mixture types. For the Gilson device, Settings 6 and 7 provided the highest Gmm for the three mixture types. Based on the increased cloudiness of the water at Settings 6 through 8, however, Settings 5, 6, and 7 were recom- mended for dense-graded laboratory, dense-graded field, and SMA mixtures, respectively. To explore if Setting 5 can be recommended for all three mixture types, the results of the Scheffé test comparing the Gmm values from Settings 5, 6, and 7 were examined. This analysis indicated that the computed F values for the comparisons of Gmm for Settings 5, 6, and 7 were all less than the critical F values. Therefore, Setting 5 of the Gilson device can be recommended for all three mixture types. For the Syntron device, Settings 7, 8, and 9 pro- vided the highest Gmm for the three mixture types. Based on the substantial water cloudiness at Settings 8 and 9, however, Setting 7 was suggested for dense- graded field and laboratory mixtures and Setting 8 was suggested for the SMA mixtures. To explore the possibility of using Setting 7 for all mixture types, the computed F values for the comparison of Gmm from Settings 7 and 8 were examined. These differ- ences were not significant for any of the mixtures. Therefore, Setting 7 of the Syntron device is sug- gested for measuring Gmm of all three mixture types. For the Orbital device, the highest Gmm values of the mixtures were obtained using vibration levels in the range of 210 rpm to 300 rpm. Based on the sub- stantial level of water cloudiness at vibration levels of 270 rpm and above, however, a vibration level of 240 rpm was selected for each mixture category. Table 5 summarizes the suggested settings for the four vibrating devices that have adjustable settings. The table also provides the vibration parameters of the vibrating devices at the suggested settings. The manufacturers can adjust the vibration settings of their devices to these suggested settings to minimize the between-laboratory variability that could result from differences in vibration intensity of the Gmm measuring devices. Comparison of Devices and Methods The seven devices and methods listed in Table 1, along with manual agitation, were compared in terms of the highest measured Gmm and the variability of the measurements. The highest Gmm values of the mixtures were compared statistically and from a practical point of view. The variability of each device was repre- sented by the pooled standard deviations of the Gmm measurements from various settings of the device. The variability of manual agitation was represented 18

Table 4 Settings yielding the highest Gmm of the vibrating devices with variable settings. Mixtures Plant-Produced Dense-Graded Plant-Produced Gap-Graded Laboratory-Produced Dense-Graded 9.5-mm 19.0-mm 9.5-mm 12.5-mm 19.0-mm 4.75-mm 12.5-mm 25.0-mm 37.5-mm Percent Percent Percent Percent Percent Percent Percent Percent Percent Passing Passing Passing Passing Passing Passing Passing Passing Passing Device (%) (%) (%) (%) (%) (%) (%) (%) (%) Humboldt Vibrating 8 7 8 8 9 10 8 9 9 Table (H-1756) Suggested for Humboldt 7 (Cloudy at 8) 8 (Cloudy at 9) 8 (No significant cloudiness) Gilson Vibro-Deaerator 6 7 7 7 7 7 6 — 6 (SGA-5R) Suggested for Gilson 6 (Cloudy at 7) 7 (Cloudy at 8) 5 (Cloudy at 8, 7, 6, respectively) Syntron Vibrating Table 7 7 8 7 9 8 8 — — (VP-51 D1) Suggested for Syntron 7 (Cloudy at 9) 8 (Cloudy at 9) 7 (Cloudy at 8) Orbital Shaker Table 240 210 270 240 300 270 240 300 — (SHKE 2000) Suggested for Orbital 240 (Cloudy at 270) 240 (Cloudy at 270) 240 (Cloudy at 270)

by the pooled standard deviations from manual agi- tations using different setups. The results of these comparisons are discussed below. Dense-Graded Field Mixtures For the 9.5-mm mixture, the largest difference between Gmm from the mechanical devices was 0.003 (between the Orbital and Gilson devices). This dif- ference corresponds to a 0.13% difference in air voids. For the 19.0-mm dense graded field mixture, the largest difference was 0.006, between the Corelok and Orbital devices. This difference in Gmm corre- sponds to a 0.24% difference in air voids. Consider- ing the potential variability due to measurement of Gmb, the difference between air voids for the 19.0-mm mixture could become significant. For both dense-graded field mixtures, manual ag- itation provided the lowest Gmm. For the 9.5-mm mixture, the largest difference was 0.008 with the Gilson device, which corresponds to a 0.29% differ- ence in air voids. For the 19.0-mm mixture, the largest difference was 0.010 with the Orbital device, which corresponds to a 0.38% difference in air voids. Con- sidering the potential variability due to measurement of Gmb, these differences between air voids of me- chanical devices and manual agitation could become significant. The F values from the Scheffé test were used to compare the highest Gmm of the 9.5-mm and 19.0-mm dense-graded field mixtures obtained from the vari- ous devices and methods. The differences between the Gmm values from the mechanical devices were not statistically significant. However, the differences in Gmm between manual agitation and the mechani- cal devices were significant in five out of seven com- parisons for the 9.5-mm mixture and in one out of seven comparisons for the 19.0-mm mixture. There- fore, the comparison of air voids and the results of statistical analysis suggest that the mechanical de- vices produce the same Gmm if they are operated at their optimum settings, but that manual agitation produces statistically lower Gmm values than the me- chanical devices. An analysis of the standard deviation of the Gmm measurements for the 9.5-mm and 19.0-mm dense- graded field mixtures using the various devices and methods found that the highest Gmm standard devia- tions of the mechanical devices were 0.002 and 0.003, which are below the acceptable 1s repeatabil- ity standard deviation for a single-operator test con- dition described in AASHTO T 209. Manual agita- tion provided either equivalent or smaller standard deviations than the majority of the devices. Between the two mixtures, none of the devices or methods was consistently more variable than the others. Gap-Graded (SMA) Field Mixtures For the 9.5-mm, 12.5-mm, and 19.0-mm SMA mixtures, the largest differences in the highest Gmm values of the various mechanical devices were 0.005, 0.003, and 0.003, respectively. These differences correspond to differences of 0.17%, 0.10%, and 0.12% between the air voids, which are not considered prac- tically significant. A comparison of the Gmm from mechanical and manual agitation shows that manual agitation pro- 20 Table 5 Suggested settings and associated vibration parameters of the four vibrating devices with variable settings. Optimum Frequency, Hz Acceleration, m/s2 Energy, microjoules Device Setting x y z x y z x y z Total Humboldt Vibrating 7 48.7 48.7 48.7 3.79 1.35 4.68 14.3 1.7 24.9 40.9 Table (H-1756) Gilson Vibro- 5 44.3 44.3 44.3 3.95 2.71 6.05 16.1 7.5 38.8 62.4 Deaerator (SGA-5R) Syntron Vibrating 7 83.8 91.4 612.2 19.13 21.67 72.32 217 268 2899 3384 Table (VP-51 D1) Orbital Shaker Table 240 rpm — — — — — — — — — — (SHKE 2000)

vides the lowest Gmm for the SMA mixtures. For the 9.5-mm mixture, the largest difference was 0.007, which corresponds to a 0.26% difference in air voids. For the 12.5-mm SMA mixture, the largest difference was 0.008, which corresponds to a 0.27% difference in air voids. For the 19.0-mm SMA mixture, the largest difference was 0.011, which corresponds to a 0.43% difference in air voids. Considering the potential vari- ability due to measurement of Gmb, the differences in Gmm between manual and mechanical agitation could be practically significant. The F values from the Scheffé test were used to compare the highest Gmm of the 9.5-mm, 12.5-mm, and 19.0-mm SMA mixtures for the various devices and methods, including manual agitation. The com- puted F values for comparison of the Gmm of the me- chanical devices were all below the critical F-value; therefore, the differences between values of Gmm for the seven devices and methods listed in Table 1 were not statistically significant. A comparison of manual agitation with the mechanical devices indicates that the differences between manual and mechanical Gmm also were not significant. Although the statistical re- sults do not support the significance of the difference between the air voids from manual and mechanical methods, the use of manual agitation for measuring the Gmm of SMA mixtures is not suggested. Dense-Graded Laboratory Mixes The Gmm of the 4.75-mm and 12.5-mm mixtures were measured using all seven Table 1 devices; the Gmm of 25.0-mm and 37.5-mm mixtures were mea- sured using five devices. The largest difference in the highest Gmm produced by the devices for the 4.75-mm, 12.5-mm, 25.0-mm, and 37.5-mm mixtures was 0.005, 0.006, 0.008, and 0.005, respectively. These differences translate into air voids differences of 0.18%, 0.23%, 0.30%, and 0.20%. Although the Gmm of the 4.75-mm and 37.5-mm mixtures from the various devices are not significantly different, for the 12.5-mm and 25.0-mm mixtures, the difference in Gmm between at least two devices could become practically significant. The F values from the Scheffé test were used to statistically compare the highest Gmm of the four dense-graded laboratory mixtures as produced by various devices and methods. These F values were all less than the critical F values, suggesting that if the Gmm measuring devices are operated at their optimum setting, they should all provide the same Gmm value. The F values for the comparisons of the values of Gmm between the seven mechanical devices and manual agitation were all less than the critical F val- ues for the 4.75-mm and 12.5-mm mixtures, indicat- ing that the differences are not statistically significant. For the 25.0-mm mixture, however, the differences between the Gmm from manual agitation and that from the HMA Vibrating Table and Orbital Shaker Table are significantly different; for the 37.5-mm mixture, the difference between the Gmm from manual agitation and the Gmm from the Aggregate Drum Washer is significantly different. In light of the prac- tical significance of the difference in air voids and the statistical significance of the differences between Gmm of manual agitation and the Gmm of the several mechanical devices, the use of manual agitation for measuring the Gmm of dense-graded laboratory mix- tures is not suggested. An analysis of the standard deviations of the Gmm measurements of the dense-graded laboratory mixtures using various devices and methods found that the largest standard deviation from the devices is less than 0.004, which is less than the acceptable 1s repeatability standard deviation for single-operator test condition described in AASHTO T 209. No one device consistently produced the highest or the low- est standard deviation. Relationship Between Vibration Properties of the Devices and Highest Gmm In previous sections, the agitation devices were compared in terms of the highest Gmm they produce and the variability of their measurements. It was shown that different mechanical devices produce statistically the same Gmm values at their optimum settings. The vibration properties of the devices at their optimum setting also were compared to deter- mine if the same vibration properties produce the same highest Gmm. This analysis showed that even though the high- est Gmm values from various devices and methods are very similar at the setting of the highest Gmm, the vi- bration properties of the devices at those settings are very different. For example, the highest Gmm of the 19.0-mm dense-graded field mixture measured by four vibratory devices (Humboldt, Gilson, Syntron, and HMA) are in the range of 2.533 to 2.536, while the total kinetic energy of the devices is in a range of 38.3 to 2,854 microjoules. This finding suggests that the energy produced by a device is not necessarily equiv- alent to the energy transferred to the mixture. 21

Relationship Between Gmm and Order of Placement of Water and Mixture The effect on Gmm of the order of placement of the mixture and water in the vacuum container was ex- amined. Seven mixtures were each tested twice with three of the devices: once by placing the water first (Water First) and once by placing the mixture first (Sample First). The significance of the difference between the Gmm values from the two orders of place- ment was evaluated by a comparison of the resulting air voids and by the use of the statistical t-test. Dense-Graded Field Mixtures Gmm values were measured for two dense-graded field mixtures using three devices at the settings found to provide the highest Gmm values. The resulting air voids were computed using these measured Gmm val- ues and assumed Gmb values of 2.404 for the 9.5-mm mixture and 2.422 for the 19.0-mm mixture. It was found that placing the water prior to adding the mix- ture consistently produced higher Gmm values. The dif- ference in air voids that resulted from the difference in Gmm was as high as 0.23%, as found for the 19.0-mm mixture tested using the HMA or the Humboldt device, or as low as 0.11%, as found for the 9.5-mm mixture tested using the Orbital or Humboldt device. A paired t-test was conducted to evaluate if the mean Gmm from the Water First and Sample First pro- cedures were the same. For the 9.5-mm and 19.0-mm dense-graded field mixtures, the computed t values from the comparison of the Gmm values of the Water First and Sample First methods were 8.07 and 4.786, respectively. Comparing these computed t values with the critical t value of 2.571 (for a 5% level of significance and 5 degrees of freedom, given 6 mea- surements) indicates that the Water First method pro- duces significantly higher Gmm values than the Sample First method. Gap-Graded (SMA) Field Mixtures The Gmm of the three SMA field mixtures were measured using three devices at the settings found to provide the highest Gmm values. The resulting air voids were computed using these measured Gmm val- ues and assumed Gmb values of 2.532, 2.357, and 2.339 for the 9.5-mm, 12.5-mm, and 19.0-mm mix- tures, respectively. It was found that placing the water prior to adding the mixture consistently pro- duced higher Gmm values. On average, the difference in air voids that resulted from the difference in Gmm was about 0.2%; however, the difference could be as high as 0.35%, as found for the 19.0-mm SMA field mixture tested using the Syntron device. A paired t-test was conducted to evaluate whether the mean Gmm values from the Water First and Sample First procedures were the same. For the 9.5-mm, 12.5-mm, and 19.0-mm SMA mixtures, the com- puted t values of the Gmm from the Water First and Sample First methods were 3.636, 4.782, and 4.880, respectively. Comparing these computed t values with the critical t value of 2.571 (for a 5% level of signif- icance and 5 degrees of freedom, given 6 measure- ments) indicates that the Water First method produces significantly higher Gmm values than the Sample First method. Dense-Graded Laboratory Mixtures The Gmm of the 4.75-mm and 12.5-mm dense- graded laboratory mixtures were measured using three devices at the settings found to provide the highest Gmm values. The resulting air voids were computed using the measured Gmm values and assumed Gmb values of 2.444 for the 4.75-mm mixture and 2.466 for the 12.5-mm mixture. It was found that placing the water prior to adding the mixture consistently produced higher Gmm values. On average, the differ- ence in air voids that resulted from the difference in Gmm was about 0.1%; however, the difference was as high as 0.2% for the 12.5-mm mixture tested using the Syntron device. A paired t-test was conducted to evaluate whether the mean Gmm from the Water First and Sample First procedures were the same. For the 4.75-mm and 12.5-mm dense-graded laboratory mixtures, the com- puted t values from the Water First and Sample First methods were 7.073 and 3.037, respectively. Com- paring these computed t values with the critical t value of 2.571 (for a 5% level of significance and 5 degrees of freedom, given 6 measurements) indicates that the Water First method produces significantly higher Gmm values than the Sample First method. In summary, this experiment established that the change in Gmm as a result of the change in the order of placement of the mixture and water in the vacuum container of the various devices was statistically and practically significant. Therefore, to facilitate the re- lease of air from the mixture and achieve the highest Gmm, adding water to the vacuum container before placing the mixture is suggested. 22

Effect of Vacuum Duration on Gmm Measurement For the purpose of improving accuracy and preci- sion of Gmm measurements, the effect of vacuum du- ration on Gmm and its variability was investigated. The three SMA field mixtures were used for this evalua- tion. Two replicates of each mixture were tested at Setting 6 of the Gilson device for vacuum/agitation durations of 5, 10, 15, 20, and 25 minutes. It was found that Gmm increased with the increase in the vacuum/agitation time until a maximum was reached at or about 20 minutes. Increasing the vacuum/ agitation time to 25 minutes resulted in a decrease in Gmm. Visual observation indicated that the water was slightly cloudy after 20 minutes of vacuum/ agitation and became substantially cloudy after 25 minutes. Analysis of the variability of the Gmm mea- surements for the five agitation durations indicates that higher variability is usually observed at higher vacuum/agitation durations, but that there was no specific trend of increase or decrease in variability with increasing time. The significance of the difference between the Gmm obtained at various durations of vacuum/agitation should indicate if a higher duration is necessary to pro- duce a more accurate measurement of Gmm. From a practical point of view, the significance of the differ- ence between the Gmm is derived from an evaluation of the difference in air voids. Air voids were calculated using assumed Gmb values of 2.532, 2.357, and 2.339 for the 9.5-mm, 12.5-mm, and 19.0-mm SMA mix- tures, respectively. The difference between the air voids from 15 minutes of agitation, which is specified in AASHTO T 209, and the air voids from 20 minutes of agitation, which produced the highest Gmm, was less than 0.1%. This difference is not considered practi- cally significant. The statistical comparison of Gmm values for various vacuum/agitation durations was conducted using a Scheffé test. F values were computed for comparisons of Gmm of all combinations of vacuum/ agitation durations. Of the computed F values, none was greater than the critical F value of 5.192 (for a 5% level of significance). Therefore, the vacuum/ agitation duration does not significantly affect Gmm. Based on the above findings, a vacuum/agitation period of 15 minutes appears appropriate for Gmm measurement. Although a higher Gmm value was mea- sured at 20 minutes of agitation, there was no prac- tical or statistical difference in Gmm between 15- and 20-minute durations of vacuum/agitation. FINDINGS AND CONCLUSIONS This report presents the results of research to evaluate the effects of key equipment and method- ological variables on the measurement of the theo- retical maximum specific gravity (Gmm) of asphalt mixtures for possible refinement of the AASHTO T 209 test method. The variables examined include agitation and device type, vibration intensity of me- chanical shaking tables, order of placing water and mixture in vacuum container, and duration of the vacuum/agitation process. This section summarizes the findings and conclusions of the research. The Gmm measurements at various settings of the devices evaluated in the research indicated that for each vibratory device, Gmm of the mixture increases with the increase in intensity of vibration until the highest Gmm of the mixture is reached. From that point on, a further increase in vibration intensity re- sulted in a decrease in Gmm. This phenomenon may be related to stripping of the asphalt. Gmm values from manual agitation were always smaller than the highest Gmm values from mechani- cal agitation devices. In most cases, manual agita- tion produced Gmm values that were equivalent to Gmm produced by the mid-range intensity settings of the mechanical devices. The results of the statistical analysis indicated that for four out of nine mixtures tested in the research, measurements from manual agitation were significantly different from those of at least one mechanical device. In addition, the dif- ference between air voids from manual agitation and from mechanical devices ranged from 0.2% to 0.4%, which could be practically significant. Therefore, use of manual agitation for the measurement of Gmm is not suggested. Investigation of the change in Gmm resulting from change in the device type indicated that, statistically, the differences between the Gmm of the nine mixtures measured using various devices were not significant. Therefore, based on statistical results, it could be concluded that if vibrating devices are operated at their optimum settings, they should produce Gmm val- ues that are statistically the same. Even devices with a single, constant setting (HMA Vibrating Table, Ag- gregate Drum Washer, and Corelok) would produce Gmm values that are statistically the same as the Gmm values produced by the optimum settings of vibrat- ing devices with variable settings. Evaluation of the air voids from various devices indicated that for three out of nine mixtures, the 23

differences between the air voids from at least two devices were greater than 0.2%, which could be prac- tically significant. Differences between the air voids measured by a state DOT and by a contractor using a different vibrating device could impact the accep- tance of a project. Therefore, it is proposed that the same method and apparatus used for measuring Gmm for a mix design be used for quality assurance testing of that mix during production. The relationship between the energy of vibration and the highest Gmm produced by a device indicated that, although the highest Gmm values from various vibrating devices were very similar, the vibration properties of the mechanical devices were very dif- ferent. For example, the Gmm values measured using Syntron and Humboldt devices are comparable, but the kinetic energy of the Syntron table is two orders of magnitude greater than that of the Humboldt device. It is speculated that the amount of energy produced by a device is not necessarily the same as the amount of energy transferred to the mixture. In selecting the optimum setting for each device, it was found that the variability of Gmm was not a defining factor as there was no correlation between measured Gmm and the vibration settings. For all Gmm measurements, the difference between replicate measurements at any setting was smaller than 0.007, which is much less than the acceptable difference between two replicate measurements as specified in AASHTO T 209. The change in Gmm values arising from changing the order of placement of water and mixture in the vac- uum container indicated that adding the mixture to water produced higher Gmm values. Statistical analysis of Gmm values and evaluation of the computed air voids confirmed the significance of the increase in Gmm as a result of placing the water first. It is speculated that the release of air is facilitated by adding the mixture to water as opposed to adding water to the mixture. Therefore, it is proposed that AASHTO T 209 be re- vised to specify placing the water in the vacuum con- tainer prior to adding the mixture. The effect on Gmm of duration of vacuum/agitation of the three SMA mixtures indicated that Gmm in- creased with increasing the vacuum/agitation time until the highest Gmm was achieved, after a 20-minute vacuum/agitation period. Further increase of the vacuum/agitation duration resulted in a decrease of Gmm. Although the highest Gmm was obtained after the 20-minute vacuum/agitation period, statistical analy- sis of Gmm values and evaluation of the air voids indi- cated that the difference in Gmm and air voids between the 15-minute and 20-minute agitation periods was not significant. In addition, the variability of mea- surements was slightly greater after 20 minutes than after 15 minutes of vacuum/agitation. Therefore, it is suggested that the 15-minute vacuum/agitation time specified in T 209 be maintained. Based on the data gathered in the study, several proposals are made related to the optimum settings of four vibration devices. Table 5 provides the proposed settings and their corresponding vibration properties. For the Humboldt device, the highest Gmm of the nine mixtures were produced over the range of Set- tings 7 to 10. Based on the concern with water clar- ity at Settings 8 through 10, however, and given the lack of significant difference between the Gmm from those settings and Setting 7, Setting 7 was selected as the optimum setting of Humboldt device. For the Gilson device, the majority of the highest Gmm measurements occurred at Settings 6 and 7; however, the occurrence of substantial cloudiness at Settings 6 and above resulted in selecting Setting 5 as the optimum setting. For the Syntron device, a few optimum readings occurred at Setting 8; however, based on issues with water cloudiness at higher settings and given a lack of significant differences in Gmm between Setting 7 and Setting 8, Setting 7 was selected as optimum. For the Orbital device, the highest Gmm were ob- tained at vibration levels in the range from 210 rpm to 300 rpm. Based on increasing water cloudiness at higher settings, however, a vibration level of 240 rpm was selected as optimum for the Orbital device. Laboratories are advised to adjust their vibration devices to the settings recommended in Table 5 to en- sure accurate measurement of the Gmm of their asphalt mixtures. Finally, agencies should note that any pro- posed changes to the current test procedures resulting from this research may result in increased Gmm values that can or will affect air voids of laboratory- and field- compacted specimens. Agencies should consider the effect of such changes on acceptance criteria and pay factors in their specifications. 24

Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP). Persons wanting to pursue the project subject matter in greater depth should contact the CRP Staff, Transportation Research Board of the National Academies, 500 Fifth Street, NW, Washington, DC 20001. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. Subscriber Categories: Highways • Materials ISBN 978-0-309-21382-0 9 780309 213820 9 0 0 0 0

AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values Get This Book
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TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 369: AASHTO T 209: Effect of Agitation Equipment Type on Theoretical Maximum Specific Gravity Values evaluates the effect of using various devices and methods on measured values of theoretical maximum specific gravity (Gmm) used to determine the air void content and the in-place density of hot-mix asphalt (HMA) as described by the American Association of State Highway and Transportation Officials (AASHTO) T 209, Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures.

According to the report, AASHTO T 209 describes a test method for determination of the theoretical maximum specific gravity (Gmm) and density of uncompacted HMA. The Gmm and the density of HMA are fundamental properties whose values are influenced by the composition of the HMA mixtures in terms of types and amounts of aggregates and asphalt materials.

Gmm is used to calculate percent air voids in compacted HMA and to provide target values for the compaction of HMA. Gmm also is essential when calculating the amount of asphalt binder absorbed by the internal porosity of the individual aggregate particles in HMA.

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