Exploring Bituminous Materials for Construction

Bituminous materials constitute asphalt, bitumen, and tar which are different forms of hydrocarbons. They are used for the construction of roads, roofing, waterproofing, and other applications. The bituminous materials - asphalt and bitumen are petroleum products, while tar is a dark-colored bitumen material obtained from the destructive distillation of organic substances like coal, wood, or bituminous shales. 

Among varied applications, road construction using bituminous materials is more popular as they are more durable and economical compared to concrete pavements. The features of bitumen, asphalt, and tar along with their properties and applications in the construction industry are explained briefly in this article.

What is Bitumen?

The word bitumen is derived from the Sanskrit word 'gwitumen'. Bitumen is defined by the Indian Standard Code IS 334-1951 as a non-crystalline solid or viscous material having adhesive properties that are derived from petroleum either by natural or refinery processes. 

Bitumen is manufactured by fractional distillation of crude petroleum. During the process, smaller components present in the crude petroleum like spirit, kerosene, fuel oils and lubricating oil evaporates and leaves bitumen behind.

Types of Bitumen & Uses

Bitumen is available in the following types:

1. Bitumen Emulsion
2. Blown Emulsion
3. Cutback Emulsion
4. Straight Run Emulsion
5. Plastic Bitumen
6. Modified Bitumen

Type of Bitumen	Production	Classification	Features	Applications
Bitumen Emulsion	Bitumen + Water + Emulsifying Agent	Rapid Setting (RS) Medium Setting (MS) Slow Setting (SS)	Emulsifying Agent provides stability Not heated during use. Mixed with aggregates before road works. Mixing changes color from brown to black-indication of binding	Road Repair and Soil Stabilization
Blown Bitumen/Oxidized Bitumen	Blowing semi-solid bitumen hot state by air under pressure		High softening point Solid form and do not melt even under the sun exposure for longer periods	Filler materials for concrete roads and construction joints in buildings
Cutback Bitumen	Bitumen viscosity is reduced by adding kerosene, gasoline, or light oil	Rapid Curing (RC) cutbacks [ contains gasoline] Medium Curing (MC) cutback [contains kerosene] Slow Curing (SC) cutback [Contains light Oil]	Cutbacks are a form of fluid binder. It is paved or sprayed. RC,MC and SC are subdivided into 6 categories from 0-5 in increasing order of viscosity. Eg: RC-4	Road construction and soil stabilization
Straight Run Bitumen	Distilled bitumen to a definite viscosity		Used without further heating treatment
Plastic Bitumen	Bitumen + thinner + filter in plastic form (40-45 %)			Filling cracks in masonry, stopping leakage
Modified Bitumen		Bitumen + plastics (resins/ester/synthetic resin) at low temperature	Have a greater flow for expansion	Waterproofing

What is Asphalt?

Asphalt is made by mixing bitumen with inert materials like sand, gravel, and crushed stone. At low temperatures, it remains in a solid state and takes a liquid form at 50 to 100 degrees Celsius. 

Types of Asphalt and Uses

Asphalt can be of two types based on its origin. They are:

1. Natural asphalt
2. Artificial or Mastic Asphalt

Type of Asphalt	Formation	Types	Features	Applications
Natural Asphalt	Naturally formed as fossil deposits or in certain rocks.	Lake Asphalt [ Found as fossil deposits in Trinidad at depth 3-60 m with 40 to 70 % bitumen. Rock asphalt [rocks with bonding bitumen]		Rock asphalt used for road works after slightly heating
Artificial or Mastic Asphalt	Limestone dust + sand + grit or coarse aggregate + Black Bitumen (heated to liquid form)		Tough, durable, non-flammable, non-absorbent, and noise-absorbing.	The mixture is heated for preparation and cooled to a solid form.   In site applications, it is reheated for waterproofing works.

What is Tar?

Tar is produced from the destructive distillation of coal, wood, or other bituminous materials. Tar compared to asphalt have low bitumen content.

Types of Tar and Uses

Tar can be classified based on the source of origin:

1. Coal Tar
2. Wood Tar
3. Mineral Tar

Type of Tar	Formation	Types	Features	Applications
Coal Tar	Coal is heated in closed iron vessels to form coke. The escaping gas is condensed to form coal tar.		Good Adhesive property	Road works
Wood Tar	Distillation of pine and other resinous wood		Contains creosote oil which is a preservative for wood.	Wood preservation and excellent anti-termite coat.
Mineral Tar	Distillation of  bituminous shale		Less volatile that wood tar

Difference Between Asphalt, Bitumen, and Tar

The difference between bitumen, asphalt, and tar are explained in the table below.

Test on Bituminous Materials

The grade and properties of bituminous materials are determined by two main tests called:

1. Penetration Test
2. Softening Point Test

The grade of bitumen is specified by the term penetration. Penetration-grade bitumen is semi-solid at ambient temperatures and requires to be heated to fluid for applications. For example penetration grade 80/100. The grade of bitumen is determined by a penetration test that measures the hardness of the bituminous materials. While softening point test determines the temperature at which bitumen softens.

Also Read On: EPDM Waterproofing System