Commonwealth of Pennsylvania PA Test Method No. 742 Department of Transportation 14 Pages LABORATORY TESTING SECTION Method of Test for BITUMEN CONTENT OF BITUMINOUS CONCRETE MIXTURES (Pennsylvania Pycnometer Method) 1. SCOPE 1.1 This method of test covers a procedure for determining the bitumen content of bituminous concrete mixtures. 2. APPARATUS G2. 2.1 Balance- A balance conforming to the requirements of AASHTO M-231, Class 2.2 Pennsylvania Pycnometer- A 4000 ml heavy wall glass pycnometer, fitted with a vacuum adapter, capillary stopper, and overflow cap. (Table 2 and Figure 1). The pycnometer shall be sufficiently strong to withstand a partial vacuum (air pressure less than 30 mm of mercury). 2.3 A vacuum pump or water aspirator for evacuating air from the pycnometer 2.4 Dial type vacuum gauge- 0 to 760 (0 to 30 inches) of mercury vacuum OR Mercury filled absolute pressure manometer calibrated to at least 1 mm divisions 2.5 Vacuum Trap- Consisting of a 600 ml filter flask fitted with a rubber stopper 2.6 Tubing and connectors assembly as shown in Figure 2 2.7 Water Bath- The bath temperature shall be maintained at a temperature of 25 ± 0.5 o C (77 ± 0.9ºF). 2.8 Thermometers- Temperature range 19 to 27ºC (66 to 80ºF) and 20 to 47ºC (69 to 116ºF) as prescribed in ASTM Specification E-1.
Page 2 3. CALIBRATION OF PYCNOMETER 3.1 Calibrate the pycnometer by accurately determining the mass of water at 25 ± 0.5 ºC (77 ± 0 9ºF) required to fill the pycnometer with the capillary stopper and overflow cap in place. Allow some water to overflow through the capillary tube while inserting the capillary stopper. Make sure the capillary tube is filled to the top and that no air bubbles are present after the pycnometer is kept immersed in the constant-temperature water bath for one hour. A vacuum shall be applied to remove the air bubbles, if necessary. Dry the outside of the pycnometer with an absorbent paper or cloth towel prior to weighing. 4. TEST DATA- The following data must be obtained to calculate the bitumen content. 4.1 Specific Gravity of bitumen (G b ) at 25ºC (77 ºF) (AASHTO T-228). 4.2 Effective Specific Gravity of the combined aggregate (G a )- This value is determined by testing samples having a known bitumen content. The procedure is explained in Section 8 of this PTM. 5. TEST SAMPLES 5.1 The sample shall be obtained in accordance with PENNDOT Methods of Sampling Bituminous Mixtures. Inspect the sample for coating deficiencies and note any problems found. 5.2 The size of the sample of bituminous concrete shall be 1000 to 2000 g. In no case shall the selection of a sample of a pre-determined mass be attempted. 6. PROCEDURE 6.1 Separate the particles of the sample, using care not to fracture the mineral particles, so that the particles of the fine aggregate portion are not larger than 6.3 mm (1/4 inch). If the mixture is not sufficiently soft to be separated manually, place it in a large flat pan and warm it in an oven until it can be handled. 6.2 Place approximately 1000 ml of room temperature water in the pycnometer to prevent asphalt stains. Determine the mass of the pycnometer plus the added water. Record the mass on Line 2 of Work Sheet No. 1. 6.3 Place the warm bituminous concrete sample (Note 2) in the pycnometer and
Page 3 obtain the mass of the pycnometer, water, and sample. Record the mass on Line 1 of Work Sheet No. 1. 6.4 Remove the entrapped air from the pycnometer by subjecting the contents of the pycnometer to a partial vacuum, more than 635 mm (25 inches) mercury vacuum or less than 125 mm mercury absolute pressure, for 10 ± 2 minutes. Agitate the container and contents either continuously by using a mechanical device or manually by vigorously shaking at intervals of about 2 minutes. NOTE 1- The release of entrapped air may be facilitated by the addition of a suitable wetting agent such as Aerosol OT at a concentration of 0.01 percent, or 1 ml of 10 percent solution in 1000 ml of water. 6.5 Fill the flask with water. If filling the flask causes air bubbles, these air bubbles shall be removed by using a stirring rod or an additional vacuum, if necessary. Bring the contents of the flask to a temperature of between 20 ºC (68 ºF) and 37.8 ºC (100ºF) (Note 2). Determine the mass of the pycnometer and contents (completely filled) and record on Line 9 of Work Sheet No. 1. Ensure that the capillary tube is filled to the top and that the capillary cap is in place. Dry the outside of the pycnometer prior to weighing. Immediately after weighing, measure the temperature of the water in the pycnometer and record on Line 5 within the parentheses. NOTE 2- For rapid determinations of maximum specific gravity at the bituminous concrete plant, the sample from the truck shall be spread in a shallow pan and allowed to cool so that the temperature of the contents in the pycnometer (mix & water) does not exceed 37.8ºC (100 ºF). For hot mixes, chilled water may be used to cool the mix to a temperature below 37.8ºC (100 ºF). 7. CALCULATIONS 7.1 The maximum specific gravity of the voidless mix (G m ) is determined as follows: Where: Maximum Specific Gravity (Gm) = A A + D + E (1) A = mass of the mix in air D = mass of the pycnometer filled with water E = mass of the pycnometer filled with water and mix The equation above can be solved by operations in lines 1 through 12 of Work Sheet
Page 4 No.1. Factors F1 and F2 for the corresponding test temperatures are given in Table 1. If the mixture contains porous aggregate not completely coated, follow the supplemental procedure given in Section 11 of AASHTO T-209. 7.2 The effective specific gravity of the aggregate (G a ) shall be determined as explained in AASHTO T-228. Given G a, F, G b, and G m, the percent bitumen content can be determined over the range of temperatures from 20.0 to 37. 8 ºC (68 to 100ºF) by operations in lines 13 and 14 of Work Sheet No. 1, or by solving the following equation: 100 Gb Ga P = G - a Gb Gm -1 (2) 7.3 Knowing the values G a, G b, and G m, the bitumen content can also be determined by use of the attached nomograph which has been prepared to solve Equation (2) at 25ºC (77ºF). This nomograph is not applicable at other temperatures. The maximum specific gravity of the mix (G m ) is connected using a straight line to (G a ). At the point where this line crosses the 1.02 Sp. Gr. of AC line, proceed horizontally to the line that is applicable to the specific gravity of the asphalt being used and read the percentage by weight of asphalt in the total mix. 8. EFFECTIVE SPECIFIC GRAVITY OF AGGREGATE (G a ) 8.1 The effective specific gravity of the aggregate is determined by testing a sample of the mix that has been prepared in the laboratory with a known asphalt content (P). In order to obtain accurate results, the gradation and asphalt content of the sample must match, as closely as possible, the gradation and asphalt content of the mix being produced at the plant. The sample shall be about the same size as the samples that are tested for bitumen content. 8.2 Transfer the prepared mix to the pycnometer and determine the maximum specific gravity of the mix (G m ) in accordance with Section 7.1 of this PTM. Knowing the bitumen content (P) and the specific gravity of the bitumen (G b ), the effective specific gravity of the aggregate (G a ) can be determined by using Equation (2) which has been rearranged algebraically as Equation (3) below: Gm (100 - P) Ga = Gm x P 100 - Gb (3) This equation can be conveniently solved by operations on lines 1 through 9 on
Page 5 Worksheet No. 2. 8.3 At least 10 bituminous samples of known asphalt content shall be tested to establish the effective specific gravity of the aggregate (G a ) for an asphalt plant. Calculate the average of the 10 determinations and then determine the maximum (+) and minimum(-) variations from this average. If the values vary more than ± 0.010, discard these values and recalculate the average and re-determine the variation. A minimum of 6 values shall be used to establish the final average. 8.4 Testing Frequency- The specific gravity of the aggregate may change during production. The effective specific gravity (G a ) should be re-determined if the type or source of any of the aggregates being used in the mix is changed, or if the gradation of the aggregate changes enough to require a change in the job-mix formula. NOTE 3-While transferring the mix from the mixing bowl to the pycnometer, some fine material and asphalt will stick to the bowl and spatula. This weight loss must be accounted for to determine the actual asphalt content (P) of the mix added to the pycnometer. To determine the mass of this material, determine the initial mass of the mixing bowl and the spatula, including the adhering fine material and asphalt. Wash the mixing bowl and the spatula with successive portions of solvent to dissolve the asphalt. Decant the supernatant liquid after each washing operation. When the supernatant liquid is a straw color, decant the last portion. Place the spatula and bowl in an oven to evaporate the remaining solvent. Determine the final mass of the dry bowl, spatula, and aggregate fines. The difference between the initial mass and final mass is the mass of asphalt lost during transfer to the pycnometer. Remove the spatula, weigh the bowl and aggregate. Wipe dry the aggregate in the bowl, and weigh the clean, empty bowl. The difference between these masses is the mass of the aggregate fines remaining in the bowl. The masses of asphalt and aggregate fines lost during transfer are subtracted from the original mix masses to determine the percent of asphalt in the mix added to the pycnometer. 9. ACCURACY OF METHOD 9.1 The bitumen content of the bituminous mixture will vary by ±0.10 percent for the following variations in the measurements: Mass of the specimen Mass of displaced water Maximum Sp. Gr. of the Mix (G m ) Sp. Gr. of the Bitumen (G b ) ± 1.0 g ± 0.5 g ± 0.003 units ± 0.010 units
Page 6 Effective Sp. Gr. of the Aggregate (G a ) ± 0.010 units
Page 7 Table 1 CONVERSION FACTORS Factors Factors Test Temp.-ºC(ºF) F 1 F 2 Test Temp.-ºC(ºF) F 1 F 2 20.0(68) 1.0012 1.0018 29.4(85) 0.9988 1.0042 20.6(69) 1.0010 1.0019 30.0(86) 0.9986 1.0044 30.5(87) 0.9984 1.0045 21.1(70) 1.0009 1.0020 31.1(88) 0.9982 1.0047 21.7(71) 1.0008 1.0021 31.6(89) 0.9981 1.0049 22.2(72) 1.0007 1.0023 22.8(73) 1.0005 1.0024 32.2(90) 0.9979 1.0050 23.3(74) 1.0004 1.0025 32.8(91) 0.9977 1.0052 33.3(92) 0.9975 1.0054 23.9(75) 1.0003 1.0026 33.9(93) 0.9974 1.0056 24.4(76) 1.0001 1.0028 34.4(94) 0.9972 1.0058 25.0(77) 1.0000 1.0029 25.6(78) 0.9999 1.0031 35.0(95) 0.9970 1.0060 26.1(79) 0.9997 1.0032 35.6(96) 0.9968 1.0062 36.1(97) 0.9996 1.0064 26.7(80) 0.9996 1.0034 36.7(98) 0.9964 1.0066 27.8(81) 0.9994 1.0035 37.2(99) 0.9882 1.0068 27.8(82) 0.9992 1.0037 28.3(83) 0.9991 1.0039 37.8(100) 0.9960 1.0070 28.9(84) 0.9989 1.0040
Page 8 Table 2 DETAILS OF THE PENNSYLVANIA PYCNOMETER A. Pennsylvania Pycnometer composed of: (a) (b) (c) A Heavy Wall Flask- 4000 ml, with a Ts 55/50 outer joint A Vacuum Adapter with a Ts 55/50 inner joint Special Overflow Cap- The main part is a Ts 65/50 inner joint with a small cap s 7/15 on top B. Accessories for the Pycnometer: (a) (b) (c) (d) (e) (f) (g) (h) Vacuum Gauge- 0 to 762 mm (0 to 30 inches), 6.4 mm (1/4 inch) ips male T-connectors- 6.4 mm (1/4 inch) Kimble or Nalgene polypropylene (2 Nos.) Valve to tubing connector- Female, 6.4 mm (1/4 inch) ips threaded brass with a fiber washer Rubber tubing- Neoprene vacuum 6.4 mm (1/4 inch) ID., 4.8 mm (3/16 inch) wall 3 m (10 ft) Filter Flask- Vacuum trap, 500 ml, heavy wall with side tabulation Rubber stopper- One hole, Neoprene (fusiform safety bore) Filter pump- Aspirator, 96.5 mm (3.8 inch) ips thread Alternate for item g above: Welch Dist-o-pump, Model 1399 B or equivalent, Vacuum obtainable 2 Pa (15 micron), 35 liters/min, 248.6 W (1/3 HP), 750 RPM, 115 Volts AC, 60 cycles. C. Known Suppliers of Pennsylvania Pycnometer complete with accessories: (a) (b) Scientific Glass Company 735 Broad Street Bloomfield New Jersey 07003 Kontes Glass Company Vineland, New Jersey 08360
Page 9 WORK SHEET NO. 1 (PTM No. 742) Project No. Mix Type Producer & Location Type Aggregate Line Sample Identification 1 Mass of Mix + Pyc. + Initial Water 2 Mass of Pyc. + Initial Water 3 Line 1 - Line 2 = Mass of the Mix (A) 4 Mass of Water in the Pyc. at 25 ºC (Calibration) 5 Line 4 x Factor F 1 = Mass of Water in the Pyc. at Test Temperature [ ºC( ºF)] 6 Mass of the Dry Pycnometer 7 Line 5+Line 6=Mass Pyc.+ Water at the Test Temperature 8 Line 3 + Line 7 9 Mass of Pyc. + Water + Mix (E) 10 Line 8 - Line 9 = G m of Displaced Water 11 Line 10 x Factor F 2 = cc of Displaced Water 12 Line 3 Line 11 = Max. Sp. Gr. Of the Mix (G m ) 13 (G a Line 12) - 1 14 (J x Line 13) = % Bitumen G a Effective Sp.Gr.of the Agg. (Line 9, Sheet 2) G b Sp.Gr.of the Asphalt Operator: K G a - G b Date: J (100 x G b ) K Laboratory:
Page 10 WORK SHEET No. 2 EFFECTIVE SPECIFIC GRAVITY OF AGGREGATE (G a ) Type Aggregate Mix Type Producer Plant Sample Identification LINE 1 Line 12(G m ) of Sheet No. 1 G m 2 Known % Bitumen P 3 Sp.Gr. Of Bitumen G b 4 Line 2 Line 3 P/G b 5 100.0 - Percent Bitumen 100 - P 6 Line 1 x Line 4 (G m xp)g b 7 Line 1 x Line 5 G m (100-P) 8 100.0 - Line 6 100-G m P/G b 9 Line 7 Line 8 = Eff. Sp. Gr. G a Operator Date
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