SOFTENING POINT TEST OF BITUMINOUS MATERIAL

Bitumen does not suddenly change from solid to liquid state, but as the temperature increases, it gradually becomes softer until it flows readily. All semi-solid state bitumen grades need sufficient fluidity before they are used for application with the aggregate mix. For this purpose bitumen is sometimes cut back with a solvent like kerosene. The common procedure however is to liquefy the bitumen by heating. The softening point is the temperature at which the substance attains particular degree of softening under specified condition of test. In case of bitumen, it is usually determined by ring and ball test.

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