Aggregate – “The rock that carries the load.” A broad category of coarse particulate material used in construction, including sand, gravel, slag and crushed stone. Aggregates are a component of composite materials such as concrete and asphalt concrete; the aggregate serves as reinforcement to add strength to the overall composite material. Aggregates are also used as base material under foundations, roads, and railroads.
Air Voids – Internal spaces in a compacted pavement mix, expressed as a percentage by volume of the total compacted mix. The ideal pavement mix has between 3% - 7% air voids. Too little air voids does not allow the pavement to be flexible under varying temperatures. Too many air voids can lead to premature failure of the pavement.
Alligator Cracking – A series of interconnecting cracks caused by fatigue failure of the asphalt surface under repeated traffic loading. The cracks propagate to the surface initially as a series of parallel longitudinal cracks. After repeated traffic loading, the cracks connect, forming many-sided, sharp-angled pieces that develop a pattern resembling chicken wire or the skin of an alligator. Alligator cracking is considered a major structural distress and is often accompanied by rutting.
Asphalt Cement (AC) – A complex hydrocarbon found as a natural deposit or as a residue from distilling crude oil to remove petroleum, motor oils, naphtha and kerosene. Asphalt cement is dark brown or black in color and at normal temperature is a solid but as the temperature is increased it becomes sticky and then oily. Asphalt cement makes up about 5% of the volume of the mix and is used to hold together the aggregate particles in the Hot-Mix Asphalt.
Backfilling – The process of placing topsoil or stone along the edges of new pavement to help support the edge and to create a safe and suitable transition to the surrounding elevations. When done correctly, it provides a medium to allow the water to flow off of, and away from the paved surface.
Backhoe – A power-driven excavating vehicle with a hinged bucket at the end of a long, jointed arm. It digs by drawing the bucket toward the power unit.
Base Course – The layer in the pavement system immediately below the wearing course (or the binder course, if used). It usually consists of a larger maximum aggregate size (25 mm or 1”), creating a strong foundation for the wearing course.
Batch Plant – A manufacturing facility that produces asphalt paving mixtures by creating batches rather than continuously. Batch plants are more suited for small manufacturing runs and frequent changes in mixture types.
Binder Course – The layer in the pavement system between the wearing course and the base course. It usually consists of a maximum aggregate size of 19mm (3/4”), providing additional strength to the overall pavement system. This layer is often only used in roadway construction.
Bitumen – A class of black or dark-colored (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons, of which asphalts and tars are typical.
Bituminous Concrete Base Course (BCBC) – The name given to the base course pavement designed using the Marshall mix design method.
Cold Planer – A self-propelled construction machine, or an attachment for a construction machine, specifically designed to mill the surface of existing pavement. It consists of a rotating drum with cutting teeth to mill the surface of the existing pavement to the desired depth.
Compaction – The process of densifying the Hot-Mix Asphalt while it is in a hot, pliable state, to pack the aggregate particles together and to remove as much of the air voids as possible. Compaction gives the mix strength, resistance to rutting, seals the surface from the ingress of water, and gives a smooth riding surface.
Coverage – The roller moving the entire width of the mat one time.
Crown – The center of a cambered road. Most roads are created with a raised center creating a minimum of 1.5% - 2% slope to the edge of the pavement. The crown is essential for proper drainage of precipitation off the road surface. Not recommended for a single width road as it will not permit proper snow removal with a plow.
Dump Truck – A heavy-duty truck with a bed that tilts backward to dump loose material (i.e. aggregate or asphalt pavement).
ESAL (Equivalent Single Axle Loads) – The effect on pavement performance of any combination of axle loads of varying magnitude equated to the number of 18,000 lb. single-axle loads that are required to produce an equivalent effect.
Excavation - The act of digging, or of making hollow, by cutting or scooping out a part of the ground.
Gradation – The distribution of aggregate particle sizes. Aggregate gradation is a way of describing the proportions of the various sizes of crushed stone, sand and filler, by passing the aggregate through a set of sieves and measuring the weight retained on each sieve.
Grade (or Gradient) – The pitch of a slope , often expressed as a percent tangent, or "rise over run". It is used to express the steepness of slope on a hill , roof , or road , where zero indicates level (with respect to gravity ) and increasing numbers correlate to more vertical inclinations.
Grader – A piece of heavy equipment used to level or smooth road or other surfaces to the desired gradient.
Hand Tamper – A hand tool, consisting of a long handle with a steel plate on the end measuring approximately 8” square. It is typically used to compact the edges of the new pavement or other small areas that motorized compaction equipment is unable to access.
Hot-Mix Asphalt (HMA) – The many different types of mixtures of aggregate and asphalt cement that are produced at an elevated temperature in an asphalt plant. Pavement designers specify different mixture types to satisfy different pavement performance demands and to accommodate variability in the nature and cost of available aggregates and asphalt cement supplies. It is sometimes referred to as macadam, blacktop or asphalt pavement.
Job Mix Formula (JMF) – The end result of a successful mix design is a recommended mixture of aggregate and asphalt binder. This recommended mixture, which also includes aggregate gradation and asphalt binder type is often referred to as the job mix formula (JMF) or recipe.
Leveling Course – Used to provide a relatively uniform level working platform for placing binder or wearing course.
Lift – A layer of asphalt pavement.
Longitudinal Joint – Formed when a new mat is placed alongside an existing mat.
Lute – A hand tool, consisting of a long handle with an aluminum screed on the end. It is typically used for spreading and leveling asphalt.
Macadam – Another name for Hot-Mix Asphalt (HMA).
Marshall - A method of mix design developed by the U.S. Army Corps of Engineers (USACE) and adapted by the Asphalt Institute, for the design of mixes for highway pavements in the United States and abroad, using impact compaction.
Mat – The term used to refer to the pavement layer when it is still hot during placement and compaction operations.
Milling – A process by which the surface of existing pavement is grinded down to the desired depth utilizing a cold planer. This is typically done for one of the following reasons: to create a smooth transition between the new and existing paving, to remove inconsistencies in the existing pavement prior to an overlay, or to remove a layer of pavement to prevent elevation problems prior to an overlay.
National Asphalt Pavement Association (NAPA) – The National Asphalt Pavement Association is the only trade association that exclusively represents the interests of the Hot-Mix Asphalt producer and paving contractor on the national level with Congress, government agencies, and other national trade and business organizations. NAPA supports an active research program designed to answer questions about environmental issues and to improve the quality of HMA pavements and paving techniques used in the construction of roads, streets, highways, parking lots, airports, and environmental and recreational facilities.
Northeast Center of Excellence for Pavement Technology (NECEPT) – The Northeast Regional Superpave Center. It is located at the Pennsylvania Transportation Institute (PTI) at the Pennsylvania State University. NECEPT's primary mission is to facilitate implementation and validation of the results of the Strategic Highway Research Program (SHRP) by promoting partnering between governmental agencies, industry (including materials, suppliers, contractors and consultants) and universities throughout the Northeast.
Overlay – A method of adding another layer of Hot-Mix Asphalt (HMA) wearing course to an existing pavement to provide additional strength and a smoother surface. This is a common method for restoring older pavement on a road, parking lot or driveway. Also referred to as a resurface or cap.
Pass – The entire roller moving over one point in the mat one time.
Paver – A piece of heavy equipment, usually consisting of a tractor unit and a screed that is used to spread and level Hot-Mix Asphalt (HMA) pavement.
Pennsylvania Department of Transportation (PennDOT) – Through the active involvement of customers, employees and partners, PennDOT provides services and a safe intermodal transportation system that attracts businesses and residents and stimulates Pennsylvania’s economy. Additionally, PennDOT publishes Publication 408, which contains current construction specifications for PennDOT projects.
PennDOT Certified Bituminous Field Technician – This certification is for technicians directly involved with bituminous pavement construction, testing and inspection. A written examination must be passed before receiving the five year certification.
PennDOT Certified Bituminous Plant Technician – This certification is for technicians directly involved with bituminous pavement mixture design, Hot-Mix Asphalt (HMA) production, process control and/or quality assurance testing. A written examination must be passed before receiving the five year certification.
PennDOT Publication 408 – A publication created by the Pennsylvania Department of Transportation containing specifications for all construction projects to be completed under the direction of PennDOT. In the state of Pennsylvania, this is also often considered the industry standard guideline to be used on most private jobs.
Pennsylvania Asphalt Pavement Association (PAPA) – PAPA is an organization uniting individuals, partnerships, firms and corporations having common interests related to the hot mix industry. Founded in 1932, PAPA is the oldest and first such organization in the U.S. PAPA represents over 80% of the asphalt businesses and at least 90% of the plants in Pennsylvania.
Proof-Rolling – A technique used in the construction industry to test the suitability of the subgrade. It is typically performed by driving a fully loaded tandem-axle dump truck over the area to be tested. The engineer will look for deflection or rutting by the truck to determine if the subgrade is adequate to support the pavement structure.
Reclaimed Asphalt Pavement (RAP) – Excavated asphalt pavement that has been pulverized, usually by milling, and is used like an aggregate in the recycling of asphalt pavements.
Resurfacing – A method of adding another layer of Hot Mix Asphalt (HMA) wearing course to an existing pavement to provide additional strength and a smoother surface. This is a common method for restoring older pavement on a road, parking lot or driveway. Also referred to as an overlay or cap.
Rut – A sunken track or groove made by the passage of vehicles. Rutting is usually caused by poor subgrade or subbase material that is insufficient to support the traffic load.
Sawcut – The action of using a power saw with a specialty blade (usually a diamond blade) to cut through asphalt pavement or concrete.
Segregation – The separation of the course and fine aggregate in the mix, collecting and distributing these fractions so that the Hot-Mix Asphalt is no longer uniformly textured. When segregation occurs in a pavement it will lead to premature failure.
Scratch Course – A paving course used to fill wheel ruts and other local, small depressions to the level of the surrounding pavement.
Screed – The rearmost portion of an asphalt paver that levels off the Hot-Mix Asphalt (HMA) pavement creating a smooth finish.
Scuffing – A surface blemish on newer pavement that is always caused by a fairly concentrated maneuver or rotation of a tire in a stationary or braking mode. The problem is generally of a temporary and superficial nature.
Skid Steer – A self-propelled land vehicle propelled by an internal combustion engine with hydraulically-powered mechanical arms capable of utilizing various connecting attachments to aid in construction or demolition in many construction-related fields. The name 'skidsteer' originates from the method used to steer the vehicle. Instead of wheels articulating on steering linkages, they are held firmly in place and steering is accomplished through certain wheels stopping or reversing direction during travel to execute a turn. This wheel stoppage causes a forced skid. This type of machine is sometimes called a skid loader.
Subbase – The course in the asphalt pavement structure immediately below the base course, typically consisting of a course aggregate such as 2A or 2RC stone. This course is critical to the overall strength of the structure.
Subgrade – The underlying soil prepared to support a pavement structure of pavement system. It is the foundation of the pavement structure.
SUPERPAVE® – Superior Performing Asphalt Pavement. A method of mix design, developed under the Strategic Highway Research Program (SHRP), whereby samples are compacted with a SUPERPAVE gyratory compactor and tested for volumetric properties. The SUPERPAVE system was developed to give highway engineers and contractors the tools they need to design asphalt pavements that will perform better under extremes of temperature and heavy traffic loads.
Swale – A shallow, trough-like depression that carries water mainly during rainstorms or snow melts.
Tack Coat – A diluted slow set asphalt emulsion that ensures a bond between existing pavement and an overlay.
Time Available for Compaction (TAC) – The time (in minutes) that a particular mix is at the right temperature range for efficient compaction. Compaction must be accomplished before the mat cools to a temperature below 175 degrees.
Transverse Joint – Constructed across the pavement whenever paving is being suspended (i.e. for the day).
Vibratory Plate – A gas-powered compaction tool used to compact areas that cannot be reached by a larger vibratory roller. The force is produced by a rotating eccentric weight that causes the large plate bottom to pulsate.
Vibratory Roller – A double steel drum roller that has two types of compactive forces that are applied to the hot mix asphalt; static weight, caused by the weight of the machine and dynamic (impact), produced by a rotating eccentric weight inside the drums which rotates about the shaft inside the drum.
Wearing Course – The upper (surface) layer in the pavement system. It usually consists of a smaller maximum aggregate size (9.5 mm or 3/8”). It is designed to provide a smooth riding surface and to seal the surface from water penetration.
Sources:
Asphalt Institute, Website Glossary of Terms
Northeast Center of Excellence for Pavement Technology (NECEPT). PENNDOT Bituminous Pavement Field Technician Program Handout, 2006.
U.S. Army Corps of Engineers(USACE). Hot-Mix Asphalt Paving Handbook, 2000.
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