PENETRATION TEST OF BITUMINOUS MATERIAL

The consistency of bituminous material depends upon several factors such as constituents, temperature, etc. at temperature ranges between 25⁰ and 50⁰ C most of the paving bitumen grades remain in semi solid or in plastic states and their viscosity is so high that they do not flow as liquid. The consistency of the bitumen is determined by penetration test, which is very simple test and indirect method also.

PROCEDURE FOR BITUMINOUS MIX PROPORTIONING

The proportioning of bituminous concrete includes the following steps:

1. Determine the nature and characteristics of the aggregate available.
2. To fix an aggregate grading which meets all the requirements and which is possible to develop practically.
3. Determine the blending percentages of aggregates which will result in the desired gradation aggregate.
4. To determine the gradation limits for the individual aggregates.
5. Preparation of test specimens using the aggregate and a range of bitumen contents.
6. Analyze the test specimen for specific gravity, voids and stability.
7. Selection of the optimum bitumen content from the test data.
8. Consistency and quality of bitumen content.

CONSISTENCY OF BITUMINOUS MATERIAL

Consistency carries a great importance in the selection and use of bituminous materials. Role of consistency is two fold.

1. Effect of temperature on consistency and  
2. Consideration of consistency at some specified temperatures. This helps in grading various materials. 

To understand the concept of consistency and temperature: relationship, consider two semi-solid bitumen. One of them is said blown bitumen and the other regular paving grade straight run bitumen. Both bitumen at 25°C have the same penetration. If each of these bitumen are heated to 46°C arid tested for penetration it will be found that the consistency of straight run bitumen is much less than that of blown bitumen. When both are further heated the difference in consistency becomes even more pronounced. Straight run bitumen will become a liquid where as the-other is still in semi plastic state. At about 121°C, bitumen will become thin liquid where as blown bitumen will not acquire the same fluidity. At nearly 177°C both become equally thin fluids. Now if both the bitumen is allowed to cool to 0°C, paving bitumen will become much harder than blown bitumen. Thus it can be said that the consistency of the paving bitumen is affected more by temperature changes than that in blown bitumen. This property of bitumen is called temperature susceptibility. This property of bitumen differs for the bitumen obtained from different crude oils, but this change is minor, com­pared with that exist between blown and paving bitumen

PROPERTIES OF BITUMINOUS MATERIAL

According Mr. F.N. Hveem properties of paving bituminous materials can be grouped under following four heading:

1. Consistency
2. Durability or Resistance to weathering
3. Rate of curing
4. Resistance to water action.

 Quality of bitumen and its suitability for any given use are completely defined by these four properties.