Asphalt means complex, organically contaminated hydrocarbon compounds commonly known as ‘bitumen’, the heaviest yield from the distillation process of crude oil. Asphalt is highly viscous to semi-solid, dark brown to black in color.

Unique characteristics 

(1) For adhesion and cementation: Used as cementing materials, such as with rock fragments and scraps to pave roads and highways.

(2) For sealing: Used as sealing materials to prevent fluid penetration.

(3) Thermoplastic: Because of its physical property to become solidified at low temperatures and liquefied at high temperatures known as thermoplastic, asphalt can be easily transported and mixed with other materials at higher temperatures and at low-temperature environment, while the mixed materials can be solidified with strength. Asphalt is therefore a perfect material for road pavement.

(4) Durability: Asphalt is durable to any work environment, including low acidic or corrosive and basic environment.

Asphalt is composed of 3 constituents:

(1) Asphaltenes

Asphaltenes are brown to black powder, not melting at any high temperature but splashing as fire balls.

(2) Asphaltic resin

Asphaltic resin is the outer ring of asphaltene, dark brown in color, rigid but brittle, and can therefore be broken down into powder. The resin is melted at around 100 degrees Celsius.

(3) Oily constituents

Oily constituents are dark brown to reddish brown in color and highly viscous like lubricating oil.

Types

Asphalt used for road pavement and construction is grouped into 3 different types:

(1) Asphalt cement (AC)

Asphalt cement is semi-solid/semi-fluid at normal temperatures, black or blackish brown in color, melting at 100-140 degrees Celsius and grouped into three grades after.

• Penetration-grade asphalt cement is the basic grade derived from direct crude oil distillation.

• Blown-grade asphalt cement is derived from heating penetration-grade asphalt cement with superheated air-blow at 250-300 degrees Celsius. The output is higher durable asphalt, resistant to collision and heat.

• Hard-grade asphalt cement, derived from further distillation of penetration-grade asphalt cement under super-high temperatures and a vacuum environment, is highly durable and resistant.

(2) Asphalt emulsion

Asphalt emulsion is a mixture of asphalt cement and water, broken down into dust-like particles and fused with emulsifier chemicals. The output is emulsion-based asphalt, used as spray on road pavement. Upon evaporation of emulsion, residual asphalt remains. The asphalt emulsion is specifically used as prime coat or tack coat, a road pavement technique on existing roads without an adhesive surface.

• Rapid-Setting CRS-1 and CRS-2

• Medium-Setting CMS-2 and CMS-2h

• Slow-Setting CSS-1 and CSS-1h

(3) Cutback Asphalt

Cutback asphalt is a mixture of asphalt cement and various solvents known as ‘diluents’ or ‘cutter stocks’ such as naphtha, kerosene, and diesel. It is liquid at room temperature. When in use for road construction, it is crushed into dust-like particles and subsequently applied. The diluent evaporates slowly, leaving the cutback asphalt to solidify as asphalt cement. There are 3 main types of cutback asphalt, classified by type of solvents:

• Rapid-Curing (RC), a mixture of asphalt cement with rapidly evaporated solvents of gasoline or naphtha.

• Medium-Curing (MC), a mixture of asphalt cement with mediocre evaporated solvents of kerosene.

• Slow-Curing (SC) or Road Oil, a mixture of asphalt cement with slowly evaporated solvents of diesel. Slow-curing cutback asphalt has never been used in Thailand.