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

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

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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 19.0-mm NMAS mixtures were obtained from con- first heated in their boxes at 135 5C (275 9F) struction sites at the National Institute of Standards for about 2 hours. The materials were then worked and Technology, Gaithersburg, Maryland, and gap- until a loose mixture condition was obtained. Me- graded stone matrix asphalt (SMA) 9.5-mm, 19.0-mm, chanical splitter and quartering methods were used and 25.0-mm NMAS mixtures were obtained at to split the mixtures to the appropriate size for test- construction sites in Richmond, Virginia. The mix- ing in accordance with AASHTO R 47.3 Mixtures ture designs of the dense-graded laboratory-prepared were then dried in the oven at 105 5C (221 9F) and plant-produced mixtures are provided in Table 2; to constant mass. HMA particles were further sepa- however, the mixture designs for the SMA mixtures rated by hand so that the particles of the fine aggre- were not available from the contractor. gate portion were no larger than 6.3 mm (1/4 in.). The Plant-produced samples were obtained in con- mixtures were then cooled to room temperature before formance to the requirements of AASHTO T 168 weighing and testing. and stored in sealed boxes until the time of testing.2 The laboratory mixtures were designed accord- To prepare the plant mixtures for testing, they were ing to the Superpave mix design procedure. Non- 2 3 AASHTO T 168-03, Sampling Bituminous Paving Mixtures. AASHTO R 47-08, Reducing Samples of Hot Mix Asphalt In Standard Specifications for Transportation Materials and (HMA) to Testing Size. In Standard Specifications for Trans- Methods of Sampling and Testing, 30th Ed. (CD-ROM), Amer- portation Materials and Methods of Sampling and Testing, ican Association of State Highway and Transportation Offi- 30th ed. American Association of State Highway and Trans- cials, Washington, D.C., 2010. portation Officials, Washington, D.C., 2010. 4

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

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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