Bitumen penetration test

OBJECTIVES

 

        i.            To determine the consistency of bituminous material.

      ii.            To assess the suitability of bitumen for use under different climatic conditions and various types of construction.

APPARATUS REQUIRED

        i.         A penetrometer consisting of a needle assembly with total weight of 100 gm and device for releasing and locking needle in any position.

      ii.         A graduated dial gauge to read the penetration value.

    iii.         Penetration values can be read with this dial up to 0.1mm.

    iv.         Thermometer – Range 0.44 degree Celsius readable up to 0.2 degree Celsius.

      v.         Time measuring device with an accuracy ±0.1 sec.

THEORY

Bitumen is a viscous liquid or solid black or dark brown in color, having adhesive properties consisting essentially of hydrocarbons, derived from crude oil during fractional distillation or from asphalt occurring in natural form and soluble in carbon disulphide.

Penetration is a measurement of hardness or consistency of bituminous material. It is the vertical distance traversed or penetrated by the point of a standard needle to the bituminous material under specific condition of load, time and temperature. This distance is measured in one tenth of a millimeter. This test is used for evaluating consistency of bituminous materials.

Penetration test is the most commonly adopted test on bitumen to grade the material in terms of its hardness. An 80/100 grade bitumen indicates that its penetration value lies between 80 and 100. The grading of bitumen helps to assess its suitability for use in different climatic conditions and types of construction. For bituminous macadam and penetration macadam IRC suggests bitumen grades 30/40, 60/70 and 80/100. In warmer regions, lower penetration grades are preferred to avoid softening whereas higher penetration grade like 180/200 are used in colder regions, so that excessive brittleness does not occur. Highest penetration grade is used in spray application works.

PROCEDURE

        i.            Firstly, the sample of bitumen was heated and made fluid. It was poured into the container to a depth at least 10mm more than the expected penetration. The sample was protected from dust and allowed it to cool in an atmosphere at a temperature between 15° to 30° C for one hour. Then was placed it along with the transfer dish in the water bath at 25° ± 0.1 °C, unless otherwise stated.

      ii.            The transfer dish was filled with water from the water bath to depth sufficient to cover the container completely, the sample was placed on it and put it upon the stand of the penetration apparatus.

    iii.            The needle was cleaned with benzene, dried it and loaded with the weight. The total moving load required was 100 ± 0.25 gms including the weight of the needle, carrier and super-imposed weights.

    iv.            The needle was adjusted to just contact the surface of the sample.

      v.            The pointer of the dial was made to read zero and needle was released for exactly five minutes and machine was adjusted to measure penetration.

    vi.            Three readings were recorded for each sample. The points on the surface of the sample was not less than 10 mm apart and not less than l0mm from the side of the dish. After each test needle was cleaned.

OBSERVATION

Lab temperature: 25°C

Sample No.	Penetration value readings			Average value	Penetration value(mm)
Sample 1	92	86	100	92.667=93	9.3

RESULT

Thus, the penetration grade value of the sample=80/100

CONCLUSION AND DISCUSSION

Penetration test is done to determine the grade of bitumen with respect to its hardness. Grading of bitumen helps to assess its suitability in different climatic conditions and types of construction. For bituminous macadam and penetration macadam, IRC suggests bitumen grades 30/40, 60/70, 80/100. In warmer regions, lower penetration grades are preferred to avoid softening whereas higher penetration grades like 180/200 are used in colder regions to prevent the occurrence of excessive brittleness. High penetration grade is used in spray application works. The 80/100 sample means its penetration value lies between 80 to 100. The sample has low penetration as compared to 180/200 which means it is hard and it is used in hot climate.

PRECAUTIONS

        i.            There should be no movement of the container while needle penetrates sample.

      ii.            The sample should not be disturbed by external matters.

    iii.            The needle should be cleaned with benzene and dried before penetration.