Types of bitumen - properties and uses .

Bitumen :-

A material of either natural or pyrogeneous origin. 

It is a soluble in carbon disulphide .It may be in solid , semi -solid ,liquid , or gaseous .

It consist of 85 part of carbon , 12 part of hydrogen ,and three parts of oxygen .

Properties of bitumen :

1. It is mostly available in solid or semi solid state.
2. It is black or brownish black in color.
3. It posses adhesive properties when soften by heat .
4. When heated it melts and give distinctive odour when heated.
5. It is completely soluble in carbon disulphide (CS2)

Forms of bitumen and its uses :-

• Following are the usual forms of bitumen

1 )Bitumen emulsions :
It can be used as stabilizing agents 

2) Blow bitumens :

It can be used as roofing or damp proofing felts , in the manufactur of pipe asphalts and joints filler.

3) straight run bitumen :

In the manufacture of pipe asphalts and joint filler.

4) plastic bitumen :-

 It is used for the cracks in the masonary structure for sopping the leakage .

5) Cut -back bitumen :

It can be applied coat as bitumen paints .

Types of bitumen :-

Following are the types of bitumen.

1. Asphalt
2. Tar
3. Cut -back
4. Emulsion

A)  Asphalt  :- 

 A material or mechanical mixture in which bitumen is associated with inert mineral matter is known as asphalt.

 Asphalt may be found as a natural deposit or prepared by distillation of crude petroleum in a refinary process.

  It is a natural byproduct of distillation of crude petroleum .In fact , it is substance containing high percentage of bitumen and some inert mineral substance .

  Actually the main difference between bitumen bitumen and asphalt is as follows:-

When crude petroleum is fractionally distilled in refineries the product is called bitumen , while the natural distilled productive is known as asphalt .

 It is blackish brown in colour , non -inflammable , but burns with a smokey flame at 250°c temperature .

 According to source , asphalt can be classified as :

1) Natural or lake ashphalt :

 This is natural asphalt found in lake .it consists about 40 to 70% bitumen and about 39% water ,lime , clay and sand etc .

  Lake asphalt is refined by boiling it in tanks.In this process the water evaporate , and the impurities float to the surface and removed .

 It is one of the best material for road construction .

2) Rock Asphalt :-

  This asphalt is occurred from the porous rock structure such as sand rock or limestone .

The rock asphalt contains about 20% bitumen and rest stone .

Forms of Asphalt :-

• Asphaltic emulsion 
• Asphaltic cement 
• Mastic asphalt
• Cut -back asphalt .

Properties of asphalt :-

    Following are the properties of asphalt:-

1. It is black brownish black in colour .
2. It is reasonably elastic .
3. It is good insulator of electricity , heat and sound.
4. It is a water -proof and can be cleaned properly .
5. It is non - inflammable and non - absorber.

B) Tar :-

  It is a viscous liquid  obtained when natural organic material such as wood, coal ,oil are carbonized or distractively distilled in the absense of air .

It contain about 70 to 95 % of bituminous content . The properties of tar depend upon the type of raw material used for manufacture , method of distillation and proportion of the residual matter contained.

Types of tar :-

1) Coal tar : 

  It is a black in colour , has heavy and strong odour and is in liquid state .

 The coal tar is used for making macadam roads and for preserving timber.

2) Wood tar :

  It can be obtained by the process of distillation of pines and other resinuos wood. 

It has high preservative property .

3) Mineral tar :- 

  It can be obtained by distilling bitumenous shale .

C) Cut - back bitumen:-

 To modify the properties of residual product or to dispose it off economically a fraction of the distillate is mixed to it. The new product obtained is known as cut - back .

 Cut -backs contain about 80% asphalts and 20 % solvent.

They are only used when the surface of the road and aggregate are dry.

D) Emulsion bitumen :-

A mixture of two unmixable liquids , the one dispersed in the other in the form of droplets is known as emulsion .

 Bitumen emulsion consists of asphalt or particles of size about 3x10^-3 dispersed in water in the presence of some emulsifying agent added at the rate of 1%.

 Bitumen emulsion can be applied at normal temprature without heating .

It is useful for damp surface .

When bitumen emulsion spread over the road surface and the bitumen particle reunite again .at this stage its occur color changes from brown to black .

 A bitumineous emulsion contains 58%to 65% by weight of bitumineous material.

Following are the advantage and disadvantage of using cut -back and emulsion for bituminous road construction work :

Advantages:-

1. The progress of work is more , since the time otherwise required for heating bituminous material can be saved .
2. They eliminate costly plant which otherwise required for heating the bituminous material and also save heavy expenditure on fuel and labour.
3. They can be quickly applied and are extremely useful for patchwork of bituminous surface.

Disadvantage :-

1. They involve extra cost in their production and transportation .
2. They have less percentage of bitumen content and do not give as good result as hot asphalt or tar.
3. They are not suitable for large - scale construction work of bituminous roads .
4. They require bitumen of high penetration.