Chp-4 Bituminous materials.pdf

BITUMINOUS MATERIALS: Bituminous materials are widely used in road construction and maintenance. After gaining experience from their use in obtaining smooth riding surface, bituminous mixtures are being used as structural layers. These materials are...

BITUMINOUS MATERIALS: Bituminous materials are widely used in road construction and maintenance. After gaining experience from their use in obtaining smooth riding surface, bituminous mixtures are being used as structural layers. These materials are considered to be flexible from structural point of view. SOURCES OF BITUMEN: The most common source of bitumen is through petroleum crude. It is also found as rock asphalt is some parts of Europe and as lake Asphalt in Trinidad. 3 Indian crude does not yield good bitumen suitable for roadwork, except Digboi bitumen 2 (in Assam). 1 Thus, India gets its entire bitumen through imported crude. PHYSICAL PROPERTIES OF BITUMEN: 2 It is a viscous liquid, black or brown in colour. It consists predominantly of hydrocarbons derived from petroleum crude. It is soluble in carbon disulphide. It is insoluble in water. 1 Its specific gravity is around 1. It has water proofing properties. It is thermoplastic i.e. it becomes soft on heating and in the reverse process becomes hard on cooling. It oxides slowly. It is chemically inert. Types of Bitumen. Straight-Run Bitumen: This is the bitumen obtained straight from the petroleum distillation. It is an oily substance with comparatively lesser viscosity and can be even sprayed.. Cutback Bitumen The viscosity of bitumen is reduced by a volatile diluents Cut back bitumens are available in three type-. Rapid Curing (RC). Medium Curing (MC). Slow Curing (SC) The cutbacks are designated by numerals representing progressively thicker or viscous cutback For example RC-2 is more thick than RC-1 but RC-2, MC-2 and SC-2 have same viscosity RC-0 and SC-0 may have 45% solvent and 55% bitumen where as RC-5 and MC-5 may contain 15% solvent and 85% bitumen  RC-Cutback They have penetration value of 80 to 120 eg., petroleum such as naptha or gasoline MC-Cutback They have good wetting properties. eg., kerosene and light diesel oil SC-Cutback These can be obtained by blending bitumen with high boiling point gas oil or by controlling the rate of flow and temperature of crude during the first of refining. Bituminous Emulsion Emulsion is a two phase system consisting of two immiscible The bitumen/tar content in emulsion range from 40 to 60% and the remaining portion is water The average diameter of globules of bitumen portion is about 2 mm Emulsion are used especially in maintenance and patch repair works The main advantage of emulsion is that is can be used in wet weather even when it is raining Emulsions can be used for soil stabilization in deserts. 4. Bituminous primers In bituminous primer the distillate is absorbed by the road surface on which it is spread. The absorption therefore depends on the porosity of the surface. Bitumen primers are useful on the stabilised surfaces and water bound macadam base courses. Bituminous primers are generally prepared on road sites by mixing penetration bitumen with petroleum distillate. Tar Tar can be produced in 3 stages 1. Carbonization of coal to produce crude tar ii. Refining or distillation of crude tar iii. Blending of distillation residue with distillate oil fraction to give desired road tar RT-1 is lowest viscosity used for surface painting where as RT-4 may be used for premix in macadam RT-5 is used for grouting which has highest viscosity Tar and Bitumen (Comparison) Bitumen is a petroleum product whereas tar is produced by the destructive distillation of coal or wood Bitumen is soluble in 'carbon disulphide' and 'carbon tetrachloride' but tar is soluble in only toluene Bitumen is more resistant to water than tar Tar is more temperature susceptible resulting in great variation in viscosity with temperature The free carbon content is more in tar as seen from the solubility test.