This module will provide a general overview of the types and uses of asphalt materials.
Hot Mix Asphalt (HMA) is made up of graded aggregates and asphalt binder. They are generally mixed in a hot mix plant (either batch type or continuous mix type) to meet the specifications of the using agency for the end-result whether it be for a parking lot, an airfield runway or an interstate highway.
Asphalt binders and tar are both considered bitumen materials. Quite often these two terms are used interchangeable due to misconceptions resulting from their similarity in appearance and in the parallel applications. However, asphalt binders and tar are two distinctly different materials with different origins and different physical and chemical characteristics. Asphalt binders is a dark brown to black cementitious material that is either naturally occurring or is produced by petroleum distillation. Tar, on the other hand, is primarily manufactured from the destructive distillation of coal and has a very distinctive odor.
An asphalt binders at room temperature is a solid. To be able to mix it with an aggregate it must be made into a liquid. This can be done by heating the asphalt binders , adding a petroleum solvent to it to make it a cutback asphalt or by adding water to it to make it an emulsion. Each of these will be discussed in further detail in this module and in the course.
Asphalt binders plus aggregates will produce hot mix asphalt. Over the years, a number of terms have been used to describe the material. This slide shows the many names you will find either in state and federal specifications or the technical literature. The AASHTO Subcommittee on Materials is establishing HMA as the industry standard.
Almost all of the asphalt binders produced in the United States today is obtained by the processing of crude oil. Many refineries in the US are located need water transport or are supplied by pipelines from the crude field or marine terminals. This slide shows a listing many of the sources of asphalt-bearing crude oils.
This is a photo of a typical refinery.
The first step in the processing of all crude petroleum is the straight reduction by distillation. The distillation principle is based on the concept that various crude fractions which have different boiling ranges. Because asphalt binders is made up of the highest boiling fractions, it becomes the residuum from the refinery tower. The crude oil is introduced into a distillation tower where the lightest components vaporize, rise to the top, cool, condense, and are drawn off for further processing. The bottom fraction from this unit is called vacuum processed, steam refined asphalt binders . The grade of asphalt binders is controlled by the amount of heavy gas oil removed.
Vacuum residuum is subjected to solvent deasphalting to extract additional amounts of high boiling point fractions for applications as lube manufacture. A high softening point, hard asphalt binder is obtained by this process. This hard asphalt binder can be used as a blending component for producing paving grade asphalt binders.
In the Rose process, the residuum is mixed with a low-boiling hydrocarbon solvent (such as, normal pentane) under supercritical conditions. The mixture is then fed into a separator to separate the components in an asphalt. These materials can then be blended to provide speciation grade asphalt binders.
Asphalt binder is generally used to produce Hot Mix Asphalt (HMA) through a batch plant such as this. Batch plants are sized for the tonnage in the batch. While facilities have been produced over the years with capacities from 3/4 ton (1/2 tone) to 20 ton (18 tone), typical sizes found in the field range from 2 ton (1-3/4 tone) to 6 ton (5 tone).
Or they are manufactured through a unitized dryer/mixer, which are a marriage of a drying drum and a continuous pugmill. This is the most popular type of plant.
Asphalt binders are generally used to produce hot mix asphalt
Hot mix asphalt is used to construct highways. The specifications for these roads are generally prepared by the various state DOTs.
It is used by both civil and military aviation to construct airfield pavements. The specifications for these facilities are usually written by the FAA or the military service that owns the airfield.
A major use of HMA is for parking lots for residential buildings as shown in this photo or for industrial facilities. In some areas this represents 30 to 40 % of the market for hot mix asphalt (HMA).
Most of the automobile race tracks use HMA for the surface. The construction of these tracks presents some unique construction problems. This slide shows the problem associated with trying to pave on the steep slope associated with the curve on one of those tracks.
In recent years the railroads have tried to develop longer life road beds. HMA is being used below the ballast rock to provide a strong, impermeable base for the track system.
Hot Mix Asphalt pavements do require maintenance and one of the uses of asphalt binders is as a crack filler for HMA pavements. These materials generally are a combination of asphalt binders and reclaimed tire rubber.
To be able to use an asphalt binder, it must be made into a liquid. One of the ways to do that is to dissolve it in a light petroleum to make different grades of material. The different curing rates, rapid, medium, slow are the result of using different solvents. These materials are used less now than they were 20 to 30 years ago because of environmental concerns. The asphalt binder hardens around the rock by the evaporation of the distillate. This distillate puts hydrocarbons into the air stream which add to the air pollution problem. In many urban areas they have been totally outlawed.
This slide shows the relative percentages of distillate in each of the different cutback asphalts. Cutback asphalts are graded by viscosity. A viscosity of 30 is more fluid than a viscosity of 3000. The viscosity is controlled by varying the amount of solvent included in the product.
This slide outlines the different uses for cutback asphalts.
The third way asphalt binders are made into a liquid is by emulsification with water. The heated asphalt cement is feed into a colloid mill with water and an emulsifying agent (generally a soap-like material). It is then feed into storage tanks. The resultant product is similar to the cutback asphalts but without the distillate and the resulting air pollution problems.
As with cutback asphalts there are different grades of asphalt emulsions. The different grades are determined by the different emulsifiers used.
Asphalt emulsions can be manufactured with different particle charges. Aggregates also have different surface charges that are dependent on their geological nature. The concept is that unlike charges attract and thus the bond between the asphalt binders and the aggregate will be better.
Emulsions can be used as a fog seal for maintenance purposes. In this picture the asphalt emulsion is sprayed and followed immediately with a sand to improve the skid resistance.
Another use for asphalt emulsions is in the construction of a aggregate surface treatment where about 0.25 gypsy of asphalt emulsion is spray applied to the surface and (continued next slide)
Another use is in a maintenance treatment - slurry seal - where the asphalt emulsion is mixed with a fine sand and then resultant product is squeegeed onto the asphalt pavement.
Hot Mix Asphalt is used in over 90% of the highways used in the United States.
Block 1 SP 14
Types & Uses of Asphalt
Types and Uses
Basics of Refining Crude Oil
Types and Uses
Asphalt Binders are broken down into 2
• Asphaltenes and resins
Blended to produce asphalt binders of
Types and Uses
Residuum Oil Supercritical
Asphalt binder is broken down into 3
Blended to produce asphalt binder of
Types and Uses