SPECIFIC GRAVITY TEST ON BITUMEN

Introduction

Specific gravity is defined as the ratio of the mass of a given volume of the bituminous material to the mass of an equal volume of water, the temperature of both being specified as 27⁰C.

Apparatus

• Specific gravity bottle of 50 ml capacity, ordinary capillary type with 6 mm diameter neck or wide mouthed capillary type bottle with 25 mm diameter neck
• Balance having least count of 1g

Procedure

1. The specific gravity bottle is cleaned, dried and weighed along with the stopper.
2. It is filled with fresh distilled water, stopper placed and the same is kept in water container for at least half an hour at temperature 27⁰C.
3. The bottle is then removed and cleaned from outside. The specific gravity bottle containing distilled water is now weighed.
4. The bituminous material is heated to a pouring temperature and is poured in the above empty bottle taking all the precautions that it is clean and dry before filling sample materials. The material is filled up to the half taking care to prevent entry of air bubbles.
5. To permit an escape of air bubbles, the sample bottle is allowed to stand for half an hour at suitable temperature cooled to 27⁰C and then weighed.
6. The remaining space in the specific gravity bottle is filled with distilled water at 27⁰C , stopper placed and is placed in water container at 27⁰C.
7. The bottle containing bituminous material and containing water is removed, cleaned from outside and is again weighed.

Calculation

The specific gravity of the material is calculated as follows:

Specific gravity = weight of bituminous material/weight of equal volume of water

= (c-a)/[(b-a)-(d-c)]

Where,

a = weight of specific gravity bottle, g

b = weight of specific gravity bottle filled with distilled water, g

c = weight of the specific gravity bottle about half filled with bituminous material, g

d = weight of the specific gravity bottle about half filled with material and the rest with distilled water, g

Results

At least three measurements should be made for determining value of the specific gravity

Precautions

• It is necessary that all precautions are taken in making the specific gravity bottles thoroughly cleaned and dried in the first weighting.
• The surface of the specific gravity bottle should be cleaned dry after filling with water, before weighing.
• The test temperature should be firmly adhered to.
• Inaccurate balance would never give reproducible results.

Reference

IS 1202-1978-Determination of specific gravity