Exp 9 Specific Gravity of Bitumen

 Specific Gravity of Bitumen

EXPERIMENT NO. 9

SPECIFIC GRAVITY TEST ON BITUMINOUS MATERIALS. ASTM DESIGNATION: D 70-76.

SPECIFIC GRAVITY Specific Gravity of Bitumen

The specific gravity of semi-solid bituminous material, asphalt cements, and soft tar pitches shall be expressed as the ratio of the mass of a given volume of the material at 25 °C to that of an equal volume of water at the same temperature.

SCOPE & SIGNIFICANCE

  1. Specific gravity of a bitumen binder is a fundamental property frequently required as an aid in classing binders for use in paving jobs.
  2. Bitumen weights sometimes have to be converted into volumes for asphalt concrete mix design calculations for which a knowledge of specific gravity is essential.
  3. Specific gravity is also used in identifying the source of bitumen binder.
  4. Bitumen binder has specific gravity in the range of 0.97 to 1.02.
  5. In case bitumen contains mineral impurities the specific gravity will be higher. Thus it is possible for a quantitative extraction of mineral impurity in bitumen.

APPARATUS

  • Pycnometer — glass, consisting of a cylindrical or conical vessel carefully ground to receive an accurately fitting glass stopper 22 to 26 mm in diameter. The stopper shall be provided with a hole 1.0 to 2.0 mm in diameter, centrally located in reference to the vertical axis. The top surface of the stopper shall be smooth and substantially plane and the lower surface shall be concave in order to allow all air to escape through the bore. The height of the concave section shall be 4.0 to 18.0 mm at the center. The stopper Pycnometer shall have a capacity of 24 to 30 ml, and shall weigh not more than 40 gram.
  • Water bath, constant-temperature, capable of maintaining the temperature within 0.1 °C of the test temperature.
  • Thermometers — calibrated liquid-in-glass, total immersion type, of  suitable range.
  • Balance — a balance conforming to the requirements of AASHTO
  • Distilled water — freshly boiled and cooled distilled water shall he used to fill the Pycnometer and the beaker

PROCEDURE

PREPARATION OF SAMPLE

1- Heat the sample with care, stirring to prevent local overheating until the sample has become sufficiently fluid to pour. While heating, keep in mind the following considerations;0201

i)-      In no case should the temperature be raised to more than 56 °C above the expected softening point for tar, or to more than 111°C above the expected softening point for asphalt.
ii)-      Do not heat for more than 30 minutes over a flame or hot plate or for more than 2 hours in an oven, and avoid incorporating air bubbles in the sample.

2- Thoroughly clean, dry, and weigh the Pycnometer to the nearest 1 mg.     Designate this mass as ‘A’.

3- Then fill the beaker with freshly boiled distilled water, placing the stopper loosely in the Pycnometer. Place the Pycnometer in the beaker and press the stopper firmly in place. Return the beaker to the water bath, and allow the Pycnometer to remaining the water bath for a period of not less than 30 minutes. Remove the Pycnometer, immediately dry the top of the stopper with one stroke of a dry towel, then quickly dry the remaining outside area of the Pycnometer and weigh to the nearest 1 mg. Designate the mass of the Pycnometer plus water as ‘B’.

4- Pour enough sample into the clean, dry, warmed Pycno

meter to fill it about three-fourths of its capacity. Take precautions to keep the material from touching the sides of the Pycnometer above the final level, and to prevent the inclusion of air bubbles. Allow the Pycnometer and its contents to cool to ambient temperature for a period of not less than 40 minutes, and weigh with, the stopper to the nearest 1 mg. Designate the mass of the Pycnometer plus sample as ‘C’.

5- Remove the beaker from the water bath. Fill the Pycnometer containing the asphalt with freshly boiled distilled water, placing the stopper loosely in the Pycnometer. Do not allow any air bubbles to remain in the Pycnometer. Place the Pycnometer in the beaker and press the stopper firmly in place. Return the beaker to the water bath. Allow the Pycnometer to remain in the water bath for a period of not less than 30 minutes. Remove the Pycnometer from the bath. Dry and weigh using the same technique and timing as that employed in # 2. Designate this mass of Pycnometer plus sample plus water as ‘D’.

CALCULATIONS



Specific Gravity of Bitumen

Calculate the specific gravity to the nearest third decimal as follows:

04

Where,
A = mass of Pycnometer (+ stopper) =  22.277 g
B = mass of Pycnometer filled with water = 74.151 g
C = mass of Pycnometer partially filled with asphalt = 55.445 g
D = mass of Pycnometer + asphalt + water = 74.628 g

OBSERVATIONS & RESULTS

Specific Gravity of Bitumen

Comments         

The experiment has been performed successfully and the specific gravity determined is 1.015 which is in the range of 0.97 to 1.02. So it is acceptable. There were no bubbles in the pycnometer so chance of error was eliminated and thus the value is correct.




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