Exp 10 Specific Viscosity of Liquid Asphalt

EXPERIMENT NO. 10

DETERMINATION OF SPECIFIC VISCOSITY OF LIQUID ASPHALT USING ENGLER VISCOMETER. [ASTM DESIGNATION: D 1665-98]

RELATED THEORY Specific Viscosity of liquid asphalt

ENGLER SPECIFIC VISCOSITY:

Engler specific viscosity is the ratio of time of flow for 50 ml of material in seconds using an Engler viscometer at a selected temperature to the time of flow, in second, for an equal volume of water at 20°C.
The usual temperatures for determination of specific viscosity for tar materials are 25°C, 40°C, 50°C, and 100°C, and generally the temperature is so selected that the specific viscosity is not more than 45.
Engler’s viscometer which is efflux tube was developed in Germany. The method is basically empirical but it is possible to relate efflux time to absolute viscosity using charts/tables developed by Asphalt institute for this purpose.

Note: At a temperature more than 100°C, the water will boil. So we cannot perform this test at a temperature more than 100°C.

PROPERTIES OF BITUMEN:

1-     Bitumen is both flammable and combustible.

2-     Bitumen becomes volatile at higher temperatures.

3-     The working temperature of the bitumen must be at least 100°C below the flash point.

4-     By repeated heating and cooling of bitumen, more and more volatiles will be ejected and the properties of bitumen will be altered.

LIQUID ASPHALT:

It is asphalt present in the liquid or molten state and having a flash point of about 60–70 °C. Liquid asphalt is in the liquid form due to the presence of mineral impurities.

TYPES OF LIQUID ASPHALT:

Liquid asphalt is generally found in the following two forms;

1-     Cut back

2-     Emulsion

SCOPE & SIGNIFICANCE

  • This test method is useful in characterizing the consistency of tar and tar distillates by measuring, their flow properties. It is applicable to materials that are readily liquid at temperature up to 100°C.
  • Viscosity in Engler’s degrees ≈ 1/4th of say bolt furol viscosity (seconds).
  • The degree of fluidity at application temperature greatly influences the strength characteristics of resulting paving mixes. High or low fluidity at mixing and compaction has been observed to result in lower stability values.
  • There is an optimum value of fluidity or viscosity for mixing and compaction for each aggregate grading of the mix and bitumen grade. At low Viscosity, the binder simply lubricates the aggregate particles instead of providing a uniform film thickness for binding action. Similarly high viscosity also resists the comp active effort and the resulting mix will be heterogeneous in character exhibiting low stability values.
  • Liquid asphalt is used to save large amount of energy required to melt or make the asphalt workable.Specific Viscosity of liquid asphalt

APPARATUS

  • Engler Viscometer

Cup — this is a gold-plated cylindrical brass vessel having an inner diameter of 106.0 ± 1.0 mm, closed at the top by a double walled lid. To the rounded bottom is attached a metal—encase tapered platinum efflux tube 20.0 ± 0.1 mm long with an inside diameter of 2.90 ± 0.1 mm at the top and 2.80 ± 0.02 mm at the bottom. Three metal measuring points spaced equidistantly around the circumference of the cup. They serve both for indicating when the instrument is level and for measuring the discharge of material, which is approximately 250 ml.

  • Jacket — the cup is surrounded by a jacket which holds water or other suitable liquid serving as a constant temperature bath. It is provided with a thermometer clamp and stirring device.
  • A tripod supports the apparatus and also carries a ring burner by means of which  the bath is heated. Adjustable legs on the tripod serve to level the instrument.
  • Stopper — the efflux tube in the cup is closed or opened by the insertion or withdrawal of a tapered hardwood stopper .The stopper shall be a smooth, round wooden rod 180 mm long 8 mm in diameter.
  • Receivers— Two types are required as follows:1
  • Testing Flask — 50 ml graduate calibrated at 20 °C
  • Calibration Flask — for standardization purpose there shall be available a Kohlrausch flask, with top enlarged above the graduation mark and calibrated to contain 200±0.1 ml at 20°C.
  • Thermometers — ASTM Engler Thermometers 23 °C, 24 °C and 25 °C are required, and conforming to the requirements for these thermometers.

Timer — Stop watch or other timing device graduated in divisions of 0.1  seconds or less and accurate to within 0.1 % when tested over a 60 minute period.

  • Strainer — 300 mm ASTM sieves conforming to specification.

PREPARATION OF SAMPLE

Stir the sample until it is homogeneous, using heat if necessary. Avoid inclusion of air bubbles, loss of volatile or other effects, which may influence the viscosity. Strain a representative portion of the sample through the strainer to eliminate particles. Strain the material directly into the viscometer if preferred.

PROCEDURE

Thoroughly clean and dry the cup and outlet tube of the viscometer and insert the stopper. Fill the outer bath and bring it to the required temperature of test. Maintain the temperature not more than 1 oC high for tests at 25 °C, 40 °C, or 50 °C, and not more than 2 or 3 oC for tests at 100 °C, Pour the material into the cup until it exactly reaches the top of the three measuring points when the instrument is level. Place the lid and inner thermometer into position and maintain the bath, with frequent agitation, at such a temperature that the material in the viscometer cup remains at the test temperature. Maintain these conditions for 3 minutes. Check the accuracy of the temperature reading by holding the stopper firmly in position and rotating the cover at short intervals during the first 2 minutes, but do not disturb the material during the last minute. When these conditions have been met, withdraw the stopper from the efflux tube, simultaneously start the timer.

Determine the time in seconds for 50 ml of material to flow from the viscometer. Find time of flow for the same quantity of distilled water at the same temperature.

CALCULATIONS



Calculate the Engler specific viscosity by time of flow for 50 ml. of material at the selected temperature by the lime of flow for the same quantity of distilled Water, according to the following formula:

Specific Viscosity of liquid asphalt

COMMENTS

The Experiment has been performed successfully and the Engler specific viscosity determined has been shown in the above table, the mean value of Engler specific viscosity came out to be 4.589E . The temperature was not kept constant as the apparatus was slightly damaged so we measured the specific viscosity at the room temperature.




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