BITUMEN:Bitumen is a hydrocarbon in compositioncontaining 85% carbon, 12%hydrogen and3% oxygen. It is a product derived during thedistillation of petroleum from the residue leftbehind. It may occur in gaseous, liquid, semi-solid or solid form. When in liquid form, it isdesignated as naphtha of petroleum. The solidform is commonly designated as Bitumen.Being a hydrocarbon it is completelydissolved by carbon disulphide.
Characteristics:Following are the main characteristics ofBitumen:(i) Its colour is black.(ii)Often it is in solid or semi-solid form.(iii)It is a sticky substance.(iv)It is a light material with specificgravity 1.10.(v)It is completely dissolves in carbondisulphide.
Uses of Bitumen:The main large-scale use of bitumen isfor the making of flexible pavements,i.e. roads and high ways. It is alsoused as water proofing agent inbuilding construction. Due to flexibleand water proof material, it is alsoused for filling joints betweenconcrete slabs.
Types of Bitumen:The main types of bitumen are given asunder:(1) Straight-Run Bitumen:This is the bitumen obtained straight from thepetroleum distillation. It is an oily substancewith comparatively lesser viscosity and canbe even sprayed.
(2) Blown Bitumen:This variety is comparatively thick andelastic. It is obtained by blowing airthrough bitumen at a high temperature.In doing so, the bitumen is partly oxidesand becomes thick and elastic. It hashigh binding power; therefore it isextensively used in the constructionalworks.
(3) Bitumen Emulsion:This type of bitumen is a liquid with aqueousmedium containing 50 to 60 % bitumen in afinely divided form. It is prepared bystirring and mixing vigorously the mixtureof hot water, molten bitumen and someresinous substances which acts as theemulsifying agent. It is used for makingand repairing roads. It is also used forcoating cast iron pipes (being water proof).
(4) Cut-back Bitumen:This is a solution of the bituminous material ina volatile solvent. Actually the volatileproducts are removed by distillation ofpetroleum. In this case the volatilecomponent called cut is added back to thesolid bitumen. It contains about 20% solventand 80% bituminous materials. The solventsused include kerosene oil, petrol. It is usedfor road making, more commonly for roadrepair work.
(5) Plastic Bitumen:It is mix consisting of bitumen, inertfiller and a thinner. It is suitable forfilling joints in the concrete slabs as ithas a good binding power and it has agood binding power and it is waterrepellent.
ASPHALT:Asphalt is a solid or semi-solid productleft behind during the distillation ofpetroleum. In composition, it is actuallya mixture of bitumen and certain inertmineral matter, like silica, alumina andlime. As such, it is only partly soluble incarbon disulphide.
Characteristics of Asphalt:Main characteristics of Asphalt are as under:(1) It has a brownish-black colour.(2) It is solid or semi solid material.(3) It is moderately elastic.(4) It is partly soluble in carbon disulphide.(5) It does not absorb water.(6) It has resistance to acids.(7) It is soft, plastic, and workable when heated.(8) It has high binding power.(9) It is good insulator for heat, electricity andsound.(10) It is never solid hard and brittle.
Uses:Main uses of Asphalt are as under:It is mainly used for the construction of flexiblepavements i.e. Roads (highways).To give ling to the swimming pools and otherwater tanks.As D.P.C in the building construction works.It is used as water - proof cover for the roofs.It is also used in the preparing of paints.
Types:There are two main types known as Natural Asphalt andResidual Asphalt.Natural Asphalt:It is the asphalt that occurs in nature. It is just collectedand used. If at all any purification is required, it is doneby simple melting and boiling. At some places it is foundin the lakes, as in South Africa, described as LakeAsphalt. It contains as much as 70% bitumen and somewater and other impurities. It is easily purified by heatingand boiling. In doing so, the water content escapes, theimpurities rise up, leaving the bituminous matter beneath.This refined asphalt is suitable for making flexiblepavements.
Another type of natural asphalt is knownas rock asphalt, found in the rocks. It is amix of rocky matter and bitumen. The%age of bitumen is about 10 to 15 %. Itcan be used as such for road making. Therock asphalt is just crushed and spreadalong the road. It is then heated andprocessed by rolling.
(2) Residual Asphalt:This is the solid or semi-solid materialleft behind after the distillation ofpetroleum. It is commonly known asartificial asphalt.In addition to the above two types on thebasis of mode of occurrence, there arefew more types which are actually thefinished products prepared from rawasphalt. These include:
TAR:Tar is a highly viscous black coloured stickysubstance derived from coal, wood or shales. Itcontains 70 % to 95% bituminous matter.However, its characteristics depend upon theraw material from which it is extracted and theamount of residual matter present in it. Themethod of distillation is used for the extractionof tar from its raw materials.This is also used for the making of roads(flexible pavements), also used as a preservativefor the timber.
Types:Depending upon the raw materialsfrom which the tar is derived, thereare three types described as:Coal Tar,Wood Tar,Mineral Tar.