BITUMEN /ASPHALT

DEFINITION

A black or dark brown non-crystalline solid or viscous material, composed principally of high molecular weight hydrocarbons, having adhesive properties, derived from petroleum either by natural or refinery processes and substantially soluble in carbon disulphide.

Bitumen that have been used in paving, includes……

NATIVE ASPHALT : A mixture occurring in nature in which bitumen is associated with inert mineral matter.

  ROCK ASPHALT : A naturally occurring

rock formation, usually calcareous, a sandstone in the pores and veins, of which is found impregnated. 

PETROLEUM ASPHALT : These are products of the distillation of crude oil.

ORIGIN

Asphalt materials have been utilized since 3500 B.C. In building and road construction. Their main uses have been as adhesives, waterproofing agents, and as mortars for brick walls.

These early asphalt materials were native asphalt. These native asphalts were found in pools and asphalt lakes. For example Trinidad and Bermudez lake deposits (asphalt lake).

Trinidad Lake Asphalt

First US hot mix asphalt (HMA) constructed in 1870.

Demand for paved roads exceeded the supply of lake asphalts in late 1800, lead to use of petroleum asphalts

Basic Refining Process Asphalt is simply the residue left over from

petroleum refining. Crude oil is heated in a large furnace to about

340° C (650° F) and partially vaporized.  It is then fed into a distillation tower where the lighter components vaporize and are drawn off for further processing.

The residue from this process (the asphalt) is usually fed into a vacuum distillation unit where heavier gas oils are drawn off.  Asphalt cement grade is controlled by the amount of heavy gas oil remaining.  Other techniques can then extract additional oils from the asphalt. 

Depending upon the exact process and the crude oil source, different asphalt cements of different properties can be produced.  Additional desirable properties can be obtained by blending crude oils before distillation or asphalt cements after distillation.

REFINERY OPERATION

RAW MATERIAL

It is a hydrocarbon product of Petroleum crude which is semi solid material. Bitumen by definition is soluble in carbon disulphide.

The hydrocarbons that make up bitumen can

generally be made up of the following : Asphaltenes Resins Oils

Asphaltenes are large, high molecular weight hydrocarbon fractions precipitated from asphalt by a designated paraffinic naphtha solvent. Asphaltenes have a carbon to hydrogen ratio of 0.8. It is insoluble in n-heptanes/n-pentane, etc. Asphaltenes constitute the body of the asphalt.

Resins are hydrocarbon molecules with a carbon to hydrogen ratio of more than 0.6 but less than 0.8. It provides ductility and adhesiveness to asphalt.

Oils are hydrocarbon molecules with a carbon to hydrogen ratio of less than 0.6. Oils influence the viscosity and flow of the asphalt.

Constitutes of Bitumen : Complex chemical mixture of molecules

that are predominantly hydrocarbons with a small amount structurally analogous species (sulphur, nitrogen, oxygen atoms). Some trace quantities of metal such as vanadium, nickel, iron, mg, calcium.

Carbon : 82-88 % Hydrogen : 8-11 % Sulphur : 0-6 % Oxygen : 0-1.5 % Nitrogen : 0-1 %

CLASSIFICATION

 Native Bitumen Cutback Bitumen Bitumen Emulsions Modified Binder

ASPHALT CEMENT/NATIVE BITUMEN :

  The primary asphalt product produced by the distillation of crude oil. They are produced in various viscosity grades, the most common being AC 2.5, AC 5, AC 10, AC20 and AC40.

The viscosity grades indicate the viscosity in hundreds of poises ±20% measured at 60°C. For example, AC 2.5 has a viscosity of 250 poises ±50.

 

CUTBACK BITUMEN/LIQUID ASPHALT Bitumen, the viscosity of which is

reduced with a suitable volative diluent usually a petroleum distillate.

It is a fluid binder that can be handled at air temperatures.

It can be mixed with aggregates in cold condition.

Types and grades are based on the type of solvent, which governs viscosity and the rates of evaporation and curing.

1. RC (Rapid Curing) : use naphtha or gasoline as a solvent. high volatility of solvent tack coats, surface treatments

2. MC (Medium Curing) : use kerosene as a solvent moderate volatility stockpile patching mix  3. SC (Slow Curing) : use diesel fuel as a solvent low volatility prime coat, dust control

 

BITUMEN EMULSIONS : A liquid product in which a substantial amount

of bitumen is dispersed in a finely divided droplets in an aqueous medium containing an emulsifier and a stabilizer.

The emulsifying unit breaks up the asphalt cement and disperses it, in the form of very fine droplets, in the water carrier. When used, the emulsion sets as the water evaporates. The emulsion usually contains 55-75% asphalt cement and upto 3% emulsifying agent.

Emulsifier gives surface charge to asphalt droplets suspended in water medium

Cationic Emulsions : asphalt particles have positive charge adhere better with negative particles

(e.g. , silica) acid in nature also work better with wet aggregates

and in cold weather

Anionic Emulsions : asphalt particles have negative charge

adhere better with positive surface

charges (e.g.,limestone) alkaline in nature

  There are three grades of the two types of

asphalt depending on amount and type of agent used (C indicates cationic type and its absence indicates anionic type) :

Rapid Setting (RS or CRS) — A quick setting emulsion used for surface

treatment, penetration macadam and tack coat.

 

Medium Setting (MS or CMS) — A medium breaking emulsion used for plant or

road mixes with fine aggregates between 5 percent and 20 percent retained on 2.36 mm sieve.

- Used for open graded premix work and bituminous macadam.

Slow Setting (SS or CSS) — A slow breaking emulsion used for plant or

road mixes with graded fine aggregates greater than 20 percent, passes a 2.36 mm sieve and a portion of which may pass a 75 µm sieve.

- Used in slurry seal, seal coat, soil/sand stabilization, etc.

TYPES AND GRADES OF BITUMEN EMULSION (CATIONIC)

Specification for Cationic Bitumen Emulsion for use in pavement Applications (First Revision)

The use asphalt emulsions is growing due to various problems with asphalt cutback including

The solvents in the cutbacks, such as gasoline, which are lost due to evaporation becoming more expensive. With emulsions, water is the main material that evaporates.

Evaporation of the solvents in the cutbacks releases hydrocarbons into the atmosphere which are damaging to the environment.

Emulsions can be used at lower temperatures and are not as likely to ignite as cutbacks.

Petroleum asphalt flow chart

MODIFIED BINDERS

More stable under heavy loads, braking and accelerating forces and shows increased resistance to permanent deformation in hot weather.

It resists fatigue loads and having better adhesion between aggregates and binders.

 

Types of Modifiers : Sulphur Natural Rubber Crumb Rubber from discarded tyres Styrene-butadiene-Styrene (SBS) Ethylene vinyl acetate (EVA), polypropylene,etc

General requirements of modifier :

Be compatible with bitumen Be able to resist degradation of bitumen at

mixing temperature Be capable of being processed by conventional

mixing lying machinery Produce coating viscosity at application

temperature Maintain premium properties during storage,

application and in service Be cost-effective

Polymer Modified Binder (PMB) A straight run bitumen, the

characteristics of which have been improved by addition of polymers, namely, styrene-butadiene-styrene (SBS), ethyl vinyl acetate (EVA) or polyethylene (PE).

Crumb Rubber Modified Binder (CRMB)

A straight run bitumen whose characteristics have been modified by addition of crumb or natural rubber.

Advantages of modified bitumen:

Lower susceptibility to daily seasonal temperature variations

Higher resistance to deformation at elevated pavement temperature

Better ageing resistance properties Higher fatigue life of mixes Better adhesion between aggregates and

binder, especially under exposure to water Preventing cracking and reflective cracking Overall improved performance in extreme

climatic conditions and under heavy traffic conditions.

Some other bitumen :

 Blown Bitumen (Oxidised Bitumen) —

Bitumen, the properties of which are modified by blowing air through it at a comparatively high temperature and pressure.

- used in wide variety of industrial application including roofing, flooring, pipe coating, etc.

Warm Asphalt – It is produced using a synthetic zeolite (aluminum silicate) during mixing at the plant to create a foaming effect in the binder.

- use in Europe - To apply bitumen at reduced temperatures 

Foamed Bitumen – created by the computer controller injection of a predetermined amount of cold water (usually around 2.5%) into hot bitumen in the mixing chamber of a pavement recycling unit.