Asphalt 1a6a

Asphalt

• Asphalt is one of the oldest materials used in construction. • Asphalt binders were used in 3000 B.C., preceding the use of the wheel by 1000years. • Asphalt came from various locations around the world.

Trinidad lake asphalt

• Today, practically all asphalt cement is from refined petroleum.

Types of asphalt products • Asphalt used in pavements is produced in 3 forms: – Asphalt cement – Asphalt cutback – Asphalt emulsion

• At room temperatures, asphalt cement is a semisolid material that cannot be applied readily as a binder without being heated. • Liquid asphalt products, cutbacks and emulsions, have been developed and can be used without heating. • Although liquid asphalt products are convenient, they cannot produce a quality of asphalt concrete comparable to what can be produced by heating neat asphalt.

Asphalt cement

Asphalt cutback • A cutback is produced by dissolving asphalt cement in a lighter molecular weight hydrocarbon solvent. • When the cutback is sprayed on a pavement or mixed with aggregates, the solvent evaporates, leaving the asphalt residue as binder. • Disadvantages: – Petroleum cost have escalated and the use of solvent is not anymore cost effective. – Cutbacks are hazardous materials due to volatility of solvents. – Application of cutbacks releases environmentally unacceptable hydrocarbons into the atmosphere.

Asphalt emulsion • An alternative to dissolving the asphalt in a solvent is dispersing the asphalt in water as emulsion as. • In this process the asphalt cement is physically broken down into micron-sized globules that are mixed into water containing an emulsifying agent. • Emulsified asphalt typically consist of about 60% to 70% asphalt cement, 30% to 40% water and a fraction of a percent of emulsifying agent.

Uses of asphalt • The main use of asphalt is in pavement construction and maintenance. In addition, asphalt is used in sealing and waterproofing various structural components, such as roofs and underground foundations. • The selection of the type and grade of asphalt depends on the type of construction and climate of the area.

Asphalt cement • Also called asphalt binders, are used typically to make hot-mix asphalt concrete for the surface layer of asphalt pavements. • It is also used in patching and repairing both asphalt and portland cement concrete pavements.

Liquid asphalts (emulsion and cutbacks) • Are used for pavement maintenance applications, such as

Fog seals • A fog seal is a light application of a diluted slow-setting asphalt emulsion to the surface of an aged pavement surface. Fog seals are low-cost and are used to restore flexibility to an existing HMA pavement 

Chip seals • Chipseal (also chip seal) is a pavement surface treatment that combines one or more layer(s) of asphalt with one or more layer(s) of fine aggregate.

slurry seals • A slurry seal is the application of a mixture of water, asphalt emulsion, aggregate (very small crushed rock), and additives to an existing asphalt pavement surface. A slurry seal is similar to a fog seal except the slurry sealhas aggregates as part of the mixture.

Microsurfacing • A cold-mix expansion of slurry seal with a higher polymer and asphalt residual content, better quality aggregate and fast-setting chemicals.

Term

Paving applications of asphalt Description

Application

Hot mix asphalt

Carefully designed mixture of asphalt cement and aggregates

Pavement surface, patching

Cold mix

Mixture of aggregates and liquid asphalt

Patching, low volume road surface, asphalt stabilized base

Fog seal

Spray of diluted asphalt emulsion on existing pavement surface

Seal existing pavement surface

Prime coat

Spray coat asphalt emulsion to bond aggregate base and asphalt concrete surface

Construction of flexible pavement

Tack coat

Spray coat asphalt emulsion between lift of asphalt concrete

Construction of new pavements or between an existing pavement and an overlay

Chip seal

Spray coat asphalt emulsion (or asphalt cement or cutback) followed with aggregate layer

Maintenance of existing pavement or low volume road surfaces

Slurry seal

Mixture of emulsion, well-graded fine aggregate and water

Resurface low volume roads

Microsurfaci Mixture of polymer modified ng emulsion, well-graded crushed

texturing., sealing, crack filling, rut filling, and minor

Performance grade binder characterization • Several test are used in the performance grade method to characterize the asphalt binder.

Pressure aging vessel • It is designed to simulate the oxidative aging that occurs in asphalt binders during pavement service.

Flash point

• At high temperature, asphalt can flash or ignite in the presence of open flame or spark. The flash point test is a safety test that measures the temperature at which flashes.

Rotational Viscometer test • This test is to determine the viscosity of bitumen.

Bending beam rheometer test • The bending beam rheometer measures the midpoint deflection of a simply ed prismatic asphalt binder subjected to a constant load applied to its midpoint • The Bending Beam Rheometer (BBR) test provides a measure of low temperature stiffness and relaxation properties of asphalt binders. These parameters give an indication of an asphalt binder’s ability to resist low temperature cracking.