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76 Aggregate: Crushed stone or gravel used in concrete and hot-mix asphalt mixes and for base and subbase, jointing, and bedding materials. Airside: Area of airport with aircraft operations, typically within secured areas. Asphalt-treated permeable base (ATPB): Open-graded base material with liquid asphalt added for stability. Base/base course: A material of a designed thickness placed under the surface wearing course of paving and bedding courses. It is placed over a subbase or a subgrade to support the surface course and bedding materials. A base course can be compacted aggregate or asphalt stabilized aggregate, asphalt, or concrete. For permeable pavements, the base may also serve as a reservoir course or layer. Bedding course: A layer of coarse, crushed, and washed aggregate screeded smooth as bedding for the pavers. This material generally conforms to the grading requirements of ASTM No. 8. This layer is generally around 2 in. thick. Best management practice (BMP): A practice designed to infiltrate, temporarily store, or treat stormwater runoff in order to reduce pollution and flooding. California Bearing Ratio (CBR): A test method and result that renders an approximation of the bearing strength (expressed as a percent) of soil compared to that of a high-quality, compacted aggregate base. Testing follows ASTM D1883 or AASHTO T 193. Cement-treated permeable base (CTPB): Open-graded base material with cement added for stability. Choke course: A layer of aggregate placed or compacted into the surface of another layer to provide stability and a smoother surface. The particle sizes of the choke course are generally smaller than those of the surface into which the choke course is being pressed. Clay soil: For this document, a fine-grained soil with more than 50% passing the No. 200 sieve with a high plasticity index in relation to its liquid limit (according to the Unified Soil Clas- sification System). Cleanout: A drainage structure providing access to the underdrain system to allow cleaning of the underdrain pipe. Coarse aggregate: Typically that portion of an aggregate retained on the No. 4 sieve. Compaction: The process of inducing close packing of solid particles such as soil, sand, aggre- gate, or a combination thereof. Glossary
Glossary 77 Compressive strength: The measured maximum loading resistance expressed as force per unit area, such as pounds per square inch. Concrete pavement: For the purposes of this document, concrete pavement is pavement made with cement as the binder, plus water, aggregate, and air. Concrete pavers: Precast concrete units meeting the requirements of ASTM C936 or CSA A231.2. Consolidation: For this document, the process of removing entrapped air from freshly placed concrete. Conventional pavement: A pavement structure with low permeability and supporting pedes- trians and vehicles. Typical examples are PCC, HMA, and interlocking concrete pavement placed on dense-graded bases. Drainage is accomplished by surface flow over the pavement. Crushed stone: An aggregate produced from mechanical crushing of rocks, boulders, or large cobblestones at a quarry. Faces of each aggregate particle have well-defined edges because of the crushing operation. Dense-graded aggregate base: A compacted aggregate base whose gradation yields very small voids between the particles with no visible spaces between them. Density: Measure of mass per unit volume. Design storm: A rainfall event that has a given percent chance of it or a larger storm occurring in a given number of years. Detention pond or structure: Pond or drainage structure designed to temporarily store stormwater runoff. Equivalent single-axle loads (ESALs): 18,000-lb single-axle loads used to combine mixed traffic to a design traffic load for the design period. Filter course: A layer in a permeable pavement system for water quality or hydrological pur- poses. It is usually made of sand, with its location varying in the pavement cross-section depend- ing on the system design. Fine aggregate: Generally considered aggregate material passing the No. 4 sieve, such as sand. Flexible pavement: Hot-mix asphalt is an example of a flexible pavement. Flexural strength: Also known as modulus of rupture, or bending strength, flexural strength is a material property, defined as the stress in a material just before it yields in a flexure test. Geomembrane: Material used for separation or to prevent drainage between pavement layers or neighboring soils. Geotextiles or geotextile fabrics: Woven or non-woven fabrics used for separation, reinforce- ment, or drainage between pavement layers or neighboring soils. Gradation: Soil, sand, or aggregate distributed by mass in specified particle-size ranges. Gradation is typically expressed in percent of mass of sample passing a range of sieve sizes in accordance with the ASTM C136 test method. Grade: (noun) The slope of finished surface of an excavated area, base, or pavement, usually expressed in percent; (verb) To finish the surface of same by hand or with mechanized equipment. Gravel: Rounded or semi-rounded particles of stone that will pass a 3-in. sieve and be retained on a No. 4 sieve, which naturally occurs in streambeds or riverbanks that have been smoothed by the action of water.
78 Guidance for Usage of Permeable Pavement at Airports Hot-mix asphalt pavement: For the purposes of this document, pavement made with asphalt as the binder. See also concrete pavement. Impermeable pavement: For the purpose of this document, a pavement with a dense surface that does not allow water to pass through. See also conventional pavement. Infiltration rate: The rate at which stormwater moves into the top surface of the pavement or ground, measured in inches or centimeters per hour. Interlocking concrete pavement: A system of paving consisting of discrete, hand-sized paving units with either rectangular or dentated shapes and manufactured from concrete. Either type of unit is placed in an interlocking pattern and compacted into coarse bedding sand, the joints are filled with sand, and the units are compacted again to start interlock. The paving units and bedding sand are placed over an unbound or bound aggregate layer. Joint: The space between concrete paving units typically filled with small-sized, open-graded aggregate, or the separation of a concrete pavement slab from the neighboring slab. Jointing aggregate: Small-sized aggregates used to fill the openings between pavers. The aggregate size typically varies the joint width. Layer coefficient: From the 1993 AASHTO pavement design procedure. A dimensionless number that expresses the material strength per 1 in. of thickness of a pavement layer (surface, base, or subbase). Life-cycle cost analysis: A method of calculating all costs anticipated over the life of the pave- ment, including construction costs. Factors that influence the results include the initial costs, assumptions about maintenance and periodic rehabilitation, pavement user and delay costs, salvage value, inflation, discount rate, and the analysis period. Lift: During placement of a pavement system, a layer or portion of a layer that is placed and worked on separately from another layer. Low-impact development (LID): Developmental design that tries to mimic the natural hydrologic cycle. Mechanistic design: Analysis of structural response of applied loads through modeling of stresses and strains in a pavement structure. Modulus of elasticity (or elastic modulus): The ratio of stress to strain for a material under given loading conditions. Observation well: A perforated pipe inserted vertically into an open-graded base and used to monitor water levels within the pavement system. Open-graded base: Generally a crushed stone aggregate material used as a pavement base that has no fine particles in it. The void spaces between aggregate can store water and allow free drainage from the base. Outlet: The point at which water is discharged from an open-graded base through pipes into a stream, lake, river, or storm sewer. Pavement structure: A combination of subbase, base course, and surface course placed on a subgrade to support traffic loads and distribute them to the subgrade. Peak discharge rate: The maximum short-term flow from a detention or retention pond, open-graded base, pavement surface, storm sewer, stream, or river, usually related to a specific storm-size event.
Glossary 79 Perforated underdrain: A perforated piping system to carry water flow from the pavement system, typically the reservoir layer for a permeable pavement system. Its vertical location varies depending on design and conditions such as retention or detention, water quality issues, and frost depths. See also underdrain. Performance period: Refers to the period of time that an initial pavement structure will last before requiring rehabilitation. Permeability: The rate of water movement through a soil column, most commonly under saturated conditions (saturated hydraulic conductivity). Permeable grid pavers: A cellular grid system filled with dirt, sand, or gravel. This system provides grass reinforcement, ground stabilization, and gravel retention. Permeable interlocking concrete pavement: A type of permeable pavement made of discrete, hand-sized paving units with rectangular or dentated shapes that are manufactured from con- crete. These paving units are placed on a highly permeable bedding layer, and the joints are filled with a highly permeable aggregate. Permeable pavement: A surface with penetrations capable of passing water and supporting pedestrians and vehicles. Typical examples are pervious concrete, porous asphalt, permeable interlocking concrete pavement, and permeable or grid pavers. Permeable pavement system: A permeable pavement and the underlying layers/courses and features for support, storage, and so forth. Pervious concrete: A type of permeable pavement made of Portland cement concrete. Porous asphalt: A type of permeable pavement made of hot-mix asphalt. Porous friction course: A top layer of pavement that has large enough voids for water to infiltrate and typically placed over an impermeable pavement layer. The flow then moves horizontally to the sides of the pavement. The phrase may also be used to indicate the material itself. Prime coat: Typically an application of an asphalt cutback or emulsified asphalt to a prepared base prior to placement of hot-mix asphalt. Proctor density: The Proctor compaction test is a laboratory method of experimentally deter- mining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density. Reservoir bed, course, or layer: The layer in a permeable pavement system for detention or retention of water. Retention pond or structure: Collects runoff and allows for infiltration into the soils below for long-term storage instead of detained discharge. See also detention pond or structure. Rigid pavement: Concrete is an example of a rigid pavement. Sand: For this document, soil larger than the No. 200 sieve and passing the No. 4 (according to the Unified Soil Classification System). Serviceability: The ability of the pavement to serve the type of traffic (vehicular) that uses the facility. The primary measure of serviceability is the present serviceability index (PSI), which ranges from 0 (very poor road) to 5 (perfect road). Silt: For the purpose of this document, soil with no more than 50% passing the No. 200 that has a low plasticity index in relation to the liquid limit (according to the Unified Soil Classification System).
80 Guidance for Usage of Permeable Pavement at Airports Structural number (SN): A calculation used by AASHTO to assess the structural capacity of a pavement to handle loads based on ESALs and soil subgrade strength. Subbase: The layer or layers of specified or selected material of designed thickness placed on a subgrade to support a base course. Subgrade: The soil upon which the pavement structure is constructed. Tack coat: Typically an application of an asphalt cutback or emulsified asphalt applied between layers of hot-mix asphalt to promote bonding between the layers. Time of concentration: The time runoff takes to flow to a drainage areaâs most distant point to the point of drainage. Treated base: An aggregate base with cement, asphalt, or other material added to increase its structural capacity. Underdrain: A piping system to carry flow from the reservoir layer of a permeable pavement system. Its vertical location varies depending on design and conditions such as retention or detention, water quality issues, and frost depths. See also perforated underdrain.
Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACIâNA Airports Council InternationalâNorth America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing Americaâs Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation
TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED N O N -PR O FIT O R G . U .S. PO STA G E PA ID C O LU M B IA , M D PER M IT N O . 88 ISBN 978-0-309-44649-5 9 7 8 0 3 0 9 4 4 6 4 9 5 9 0 0 0 0