ASPHALT PAVING LIBRARY And Definitions

1. Terms Used in Paving Projects

Asphalt Terms

 

   Asphalt Concrete

Asphalt concrete is a material made of several ingredients that is used as a surface on roads, parking lots, driveways, and similar areas. Often shortened to just “asphalt”, it is also known as bitumen (actually a component of the mix that sticks the parts together), bituminous asphalt concrete, flexible pavement, or occasionally tarmac.

 

   Asphalt Cement

Asphalt concrete is made of a collection of ingredients that are bound together by asphalt cement, a byproduct of the petroleum production process. As part of the mix, asphalt cement is usually less than 10% of the whole.

 

    Bitumen/Bituminous Asphalt Concrete

See “Asphalt Concrete”.

 

    Blacktop

This is a term used colloquially to mean “asphalt”, but actually has no technical meaning. Blacktop should never be used in any technical specifications or work orders.

 

    Flexible Pavement

    See “Asphalt Concrete”.

 

   H.M.A.C.

“Hot Mix Asphalt Concrete” is the full name of asphalt. Other terms exist, such as “blacktop”, but it is important to use the correct term on any job specification as use of an incorrect material would seriously impact the strength and usefulness of the surface.

 

   Tarmac

See “Asphalt Concrete”.    

 

   Density (thickness or compactness)

Density is a measurement of how atomically solid a particular material is at a set volume. In terms relating to asphalt, the density of a layer is determined by the amount of rolling and compaction applied. The more compaction, the denser the asphalt.

 

    Nuclear Density

A method of measuring the density of a material by monitoring the penetration of radiation.

 

    Joints (aka Seams)

Also known as seams, joints are the areas where two separate sections of asphalt meet on the surface. An entire parking lot or roadway will not be laid in a single run or “pull”, and so joints occur where one run starts and another ends. This is often clearly visible after the whole area has been completed.

 

    Transverse Joint

A joint in the asphalt surface that is perpendicular to the direction in which the asphalt was initially laid down or the direction of the road.

 

    Tracking

Surface materials being moved from one place to another by shoes, car tires, etc. An undesirable effect that can often be avoided by using the right surface coatings.

 

2. Terms Relevant to Creating a Road

    Drainage Systems

Surface water is a problem waiting to happen for an asphalt surface, so proper drainage must be maintained through a system of drains and pipes. The water can be assisted in its journey by implementing a camber or slope in the surface so it is not entirely flat.

 

     Fall

The angle at which a surface slopes.

   

     Grade

This is a term describing the angle or slope at which a surface is situated in order to assist with drainage. Used as a verb (i.e., to grade, grading, etc.), it describes the process of implementing this angle.

 

Slope

The angle at which a surface is laid to assist with drainage.

 

3. Materials Used in Paving Projects

    Aggregates

The largest component of an asphalt mixture, sometimes over 95% of the whole. Aggregates, or more properly “construction aggregates” are materials made of particles that can be of various sizes. Examples include sand, gravel, and small rocks.

 

Concrete

Concrete is a hard material used for building made of a mixture of cement, sand, gravel and water. Different ratios will provide different strengths and properties, so it is important to mix correctly.

 

      Portland Cement Concrete Pavement (PCCP)

The full name for concrete.

 

 Emulsions

An emulsion is the end product of combining two materials through mechanical means that do not ordinarily mix, such as oil and water. When combined in a specific way where one substance is finely dispersed throughout the other, an emulsion is created.  

 

       Fog Seal Emulsion

An asphalt emulsion that is used to help maintain the surface of an asphalt pavement. A fog seal is a fine, diluted asphalt emulsion that can be sprayed on the surface. This will seal small cracks, restore the coloration of the surface, and may slow the aging process.

 

       Geotextiles

Geotextiles are additive materials used to give particular performance advantages to asphalt layers. They are fabric-like and can help with stabilization and the prevention of certain types of cracking.

Reclaimed Asphalt Pavement (RAP)

 

“Reclaimed Asphalt Pavement” is the term given to ground up particles of previously laid asphalt pavement that are recycled and reused with a new asphalt mixture. This is a more environmentally-friendly product than new materials extracted from the earth to produce asphalt mixes, but some applications will still prefer non-recycled asphalt.

 

       Superpave or Super Performing Asphalt Pavement

“Superior Performing Asphalt Pavement” is a particular type of pavement. A method is used that designs asphalt surfaces with mixes and additives taking into account the specific features of the local environment and the intended use. This will include the potential for particular types of weather, the amount and weight of traffic, and so on.

 

4. Equipment Used in Paving Projects

    Drag Box Spreaders

These are devices that are used to spread asphalt whilst being pulled (or dragged) along by a truck. As they rely on the speed of motion of the vehicle and on gravity, the layer of asphalt they provide will most likely not be even.

 

     Heat Lance

A heat lance is a tool that produces a high-velocity, high-temperature stream of air. It works with a combination of propane and compressed air, and is used to remove debris from pavement cracks. By preheating cracks, sealant adheres more strongly, so it serves a double purpose.

 

     Tow-behind Pavers

These pavers may look similar to Drag Box Spreaders. However, they are designed in an entirely different way to spread asphalt such that it produces a much higher quality surface.

 

     Screed

This is a part of a paving machine. It spreads the asphalt on the ground, smooths it out, and provides a small amount of compaction. Screeds are adjustable and can be used to help set the thickness of the layer and the angle at which it is laid.

 

5. Layers Used in Paving Process

    Subgrade

Below the base of any pavement, there will be a layer of soil. The soil must be properly prepared before a foundation is installed. This prepared soil is known as subgrade.

 

     Base

The base is the bottom layer of material used in asphalt paving, and could be considered a foundation layer. A solid base is required as it bears the weight of the asphalt and traffic above. In essence, the asphalt paving is a protective layer for the base. The thickness of the base will vary depending on the expected load above, and can be made from a variety of products, including stone, rock, or even an asphalt variant. An incorrectly specified base will lead to problems later on as it will shift and move if made of the wrong materials or laid too thinly.

    

      Limestone

Also known as limerock, this is a sedimentary rock that is often used as a base (or foundation) layer in paving.

 

     Stone Base

A bottom or foundation layer made of an assortment of differently sized crushed stones.

 

     Asphalt Binder

This is a layer of asphalt between the rock foundation and the driving surface. While the surface layer is fine and smooth, the binder layer often utilizes aggregates that are more coarse. Whilst it is usable for driving on, especially for construction traffic, it is not suitable as a permanent road surface.

 

    Asphalt Base

This is the foundation layer of an asphalt application made of aggregate and asphalt. The aggregate tends to be smaller in this mix, and it is often laid over a stone base.

 

    Asphalt Surface

The surface is the top layer, the driving surface. It is also known as the wearing course (or layer) and sometimes as “blacktop” colloquially. The top layer of a pavement is generally made from an asphalt mix that only uses smaller stone aggregate to provide smoothness and durability.

 

    Full-Depth Asphalt Pavement

A full-depth asphalt pavement requires a foundation/base layer, an asphalt base, and a surface layer. When all these layers (or courses) are made from materials that are asphalt-based, it is known as a full-depth asphalt pavement.

 

    Mat Asphalt

This is a new asphalt surface as laid down by a paving machine or as it is being compacted.

 

    Tack Coat

This is a coating for existing asphalt pavement that is used to help adherence between old and new asphalt when a new top layer is being laid or when cracks are being repaired. Often it is an asphalt emulsion.

 

Wedging

A layer of asphalt applied prior to the final top layer that is intended to eliminate any imperfections in the lower surface and make it straightforward to obtain a perfect top layer.

 

6. Processes Used in Paving

Cold In-Place Recycling or C.I.P.R.

“Cold In-Place Recycling” is a process that involves removing existing pavement, grinding it, and reusing it as a component of new paving.

 

Chip Seal

This is a process for protecting and potentially improving the surface of the top layer of asphalt. Hot oil and small pieces of crushed aggregate – chips – are placed over the surface and compressed with a pneumatic roller.

 

Compaction

The process of compressing a material to make it tighter and smaller. This reduction of volume is essential in base layers to help prevent settling, as any underground movement will affect the surface layer.

 

Infrared

An existing asphalt surface can be softened to aid repair by applying heat to the surface. Infrared uses radiated heat to facilitate this. The process allows repairs to be completed in cooler weather, and can also be used as a preparation for decorative processes where the surface needs to be partially malleable.

 

Laydown

The action of putting the asphalt in place. The paving machine will “lay it down”.

 

Overlay (aka Resurfacing)

Also known as resurfacing, this is the process of adding an additional layer of asphalt over an existing old or worn surface. The original surface must be made solid and have no loose particles first, otherwise, the overlay will soon crack and offer no improvement over the older surface.

 

Routing

The process of increasing the size of an existing crack. This allows a standard size defect in the pavement, making it easier to apply sealant. With the crack made to the appropriate size, the durability of the repair will be improved.

 

7. Problems that may Occur

Base Failure

A base failure is caused by too much weight bearing down on the surface of the road. The base will fail if it has been made too thin, poorly laid or designed, or damaged by ingress of water. It will be unable to support the appropriate amount of weight, leading to shifting and cracking that will be visible all the way through to the top layer.

 

Subgrade Failure

Should the soil of the subgrade be unable to support the weight of the road and traffic above, subgrade failure can occur. This is not always a design or preparation fault, but may be caused by excess water. A repair can be made by digging out the material and replacing it with a compacted variant or a further sub-base of stone.

 

Cracking

When the asphalt layer splits or separates, cracks will form. This can be caused by many factors including weather conditions, the age of the installation, too much weight, and so on.

 

      Reflective Cracking

The appearance of cracks in an asphalt surface that match cracks in a lower surface. Processes can be employed to prevent cracks from reflecting, but the ultimate solution is to fix the lowest crack and resurface above.

 

Transverse Cracking

A crack in the asphalt surface that is perpendicular to the direction in which the asphalt was initially laid down or the direction of the road.

 

Deflection

This occurs when the pavement does not stay in the desired shape when subjected to weight.

 

8. Sealcoating and Sealer Components

Sealcoating

A covering applied to an asphalt surface to protect against the weather, oil damage, etc. Preservation and restoration of color can also be achieved.

 

Components of Sealers

Coal-Tar

Coal-tar is a major component of sealers and is traditionally a by-product of the steel industry. It is a thick dark liquid, which is the residue left behind after burning coal.

 

      Gilsonite (aka North American Asphaltum)

Gilsonite is a shiny brittle black material found in Utah, also known as North American Asphaltum. Sealers can be produced by using crushed Gilsonite, but their use is limited by the need to apply solvents to obtain the desired liquidity. An excess of solvent may damage asphalt surfaces.

 

Slurry Seal

This is a type of sealcoating used in areas where high-speed vehicular traffic may be found. The machine used to apply the sealcoat manufactures the material as it moves along. The components include an asphalt emulsion, aggregate, and a combination of additives. Differently sized aggregates are used for different applications.

 

Microsurfacing

A slurry seal made with large aggregate.

 

9. Information Assisting the Public and Employees

Americans with Disabilities Act or A.D.A.

The Americans with Disabilities Act is a federal act that specifies how standards must be applied in relation to people who suffer from disabilities. Many different types of disability are covered under the Act, including assistance for those with mobility issues, impaired vision, and so on, to facilitate accessibility in an equal manner to able-bodied people. Further regulations and laws are in place to expand on the scope of the ADA, and these vary by state.

 

        International Symbol of Accessibility or I.S.A.

I.S.A. is the abbreviation for International Symbol of Accessibility, a well-known symbol representing accessibility for those who are handicapped. Colloquially called the “handicap symbol”.

 

        Strategic Highway Research Program or S.H.R.P.

“Strategic Highway Research Program” is a federal research program set up to find the most effective and durable pavement designs and materials, as well as the methods for laying and maintaining pavements.