Commonwealth of Pennsylvania
Department of Transportation
PA Test Method No. 742
October 2013
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
2.1
Balance- A balance conforming to the requirements of AASHTO M-231, Class
G2.
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
C (77 ± 0.9ºF).
o
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.
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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 (Gb) at 25ºC (77 ºF) (AASHTO T-228).
4.2
Effective Specific Gravity of the combined aggregate (Ga)- 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
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October 2013
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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 (Gm) is determined as follows:
Maximum Specific Gravity (G m ) =
A
(1)
A+D+E
Where:
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
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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 (Ga) shall be determined as
explained in AASHTO T-228. Given Ga, F, Gb, and Gm, 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:
P=
100 G b  G a 
- 1 (2)

Ga - Gb  Gm 
7.3
Knowing the values Ga, Gb, and Gm, 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 (Gm) is connected using a straight line to (Ga). 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 (Ga)
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 (Gm) in accordance with Section 7.1 of this PTM. Knowing the
bitumen content (P) and the specific gravity of the bitumen (Gb), the effective
specific gravity of the aggregate (Ga) can be determined by using Equation (2)
which has been rearranged algebraically as Equation (3) below:
Ga =
G m (100 - P)
(3)
G
m x P
100 Gb
This equation can be conveniently solved by operations on lines 1 through 9 on
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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 (Ga) 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 (Ga) 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 (Gm)
± 1.0 g
± 0.5 g
± 0.003 units
Sp. Gr. of the Bitumen (Gb)
± 0.010 units
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Effective Sp. Gr. of the Aggregate (Ga)
± 0.010 units
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Table 1
CONVERSION FACTORS
Factors
Test Temp.-ºC(ºF)
F1
Factors
F2
Test Temp.-ºC(ºF) F1
F2
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
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Table 2
DETAILS OF THE PENNSYLVANIA PYCNOMETER
A.
Pennsylvania Pycnometer composed of:
(a)
(b)
(c)
B.
A Heavy Wall Flask- 4000 mL, with a T
s 55/50 outer joint
A Vacuum Adapter with a T
s 55/50 inner joint
Special Overflow Cap- The main part is a T
s 65/50 inner joint with a small cap
s 7/15 on top
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)
Scientific Glass Company
735 Broad Street
Bloomfield New Jersey 07003
(b)
Kontes Glass Company
Vineland, New Jersey 08360
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WORK SHEET NO. 1 (PTM No. 742)
Project No.
Line
Mix Type
Producer & Location
Type Aggregate
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 F1 = Mass of Water in the Pyc. at Test Temperature [
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 = Gm of Displaced Water
11
Line 10 x Factor F2 = cc of Displaced Water
12
Line 3 ÷ Line 11 = Max. Sp. Gr. Of the Mix (Gm)
13
(Ga ÷ Line 12) - 1
14
(J x Line 13) = % Bitumen
Ga
Effective Sp.Gr.of the Agg. (Line 9, Sheet 2)
Gb
Sp.Gr.of the Asphalt
Operator:
K
Ga - Gb
Date:
J
(100 x Gb) ÷ K
Laboratory:
ºC(
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WORK SHEET No. 2
EFFECTIVE SPECIFIC GRAVITY OF AGGREGATE (Ga)
Type Aggregate
Mix Type
Producer
Plant
Sample Identification
LINE
1
Line 12(Gm) of Sheet No. 1
Gm
2
Known % Bitumen
P
3
Sp.Gr. Of Bitumen
Gb
4
Line 2 ÷ Line 3
P/Gb
5
100.0 - Percent Bitumen
100 - P
6
Line 1 x Line 4
(GmxP)Gb
7
Line 1 x Line 5
Gm(100-P)
8
100.0 - Line 6
100-GmP/Gb
9
Line 7 ÷ Line 8 = Eff. Sp. Gr.
Ga
Operator
Date
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