A
AASHTO: The American Association of State Highway and Transportation Officials is an association comprising highway engineers from U.S. states and Canadian provinces. It develops structural design methods for pavements, material standards, testing procedures, and other guidance documents related to roads, highways, and transportation.
Abrasion: The process of mechanical wear, grinding, scraping, or rubbing away of a surface due to friction, impact, or a combination of both.
Absorption: The weight of water soaked or drawn into a material during immersion under specified conditions, typically expressed as a percentage of the material’s dry weight.
ADA Design Guidelines: Design standards under the Americans with Disabilities Act, outlining requirements for pavement transitions, openings, curb ramps, and detectable warnings, overseen by the U.S. Access Board.
Admixture: Chemical additives incorporated into concrete during mixing to enhance production efficiency and improve hardened properties such as density, absorption, appearance, durability, and strength.
Aggregate: Materials such as sand, gravel, crushed stone, shell, or slag used in road construction, as base material, mixed with cement to create concrete or mixed with bitumen to produce asphalt.
Albedo: The proportion of outbound solar radiation reflected by a pavement surface relative to the incoming solar radiation.
Angularity: The sharpness of edges and corners of particles, commonly used to describe sand and aggregates.
Aquifer: A porous geological formation capable of storing and yielding water for consumption.
ASCE: The American Society of Civil Engineers.
ASCE 58-16: A technical manual published by ASCE that provides guidelines for the structural design of interlocking concrete pavement for municipal streets and roadways.
ASCE 68-18: A technical manual from ASCE focused on the design of permeable interlocking concrete pavement systems.
Aspect Ratio: The ratio of a paving unit’s length to its thickness. For example, a paver measuring 6 inches wide by 12 inches long by 3 1/8 inches thick has an aspect ratio of 3.8:1. Compare to Plan Ratio.
Asphalt-treated Base: A road base material consisting of crushed stone combined with bitumen to enhance stiffness and resist rutting caused by wheel loads.
ASTM: The American Society for Testing and Materials International, a global organization that develops and publishes technical standards for materials, products, and systems.
ASTM C936: A standard specification defining the requirements for solid concrete interlocking paving units, including dimensions, tolerances, maximum absorption, minimum compressive strength, abrasion resistance, and freeze-thaw durability through various test methods.
ASTM C1319: A product standard specifying requirements for concrete grid paving units.
ASTM C1491: A standard outlining specifications for roof pavers.
ASTM C1782: A product standard for utility or common concrete paving slabs.
ASTM E2840: A standard practice for conducting pavement condition index surveys on interlocking concrete roads and parking lots.
B
Ballast Block: A specialized unit designed for rooftop equipment ballast and/or protecting roof membranes. When used for membrane protection, it is typically installed over an aggregate bedding layer to prevent direct contact with the membrane. Compare to pedestal set. Formerly known as Roof Pavers. Refer to ASTM C1884.
Band Cutter: A tool resembling pliers, designed for safely cutting metal or plastic bands used to secure cubes or bundles of units.
Base or Base Course: A material of designed thickness placed between the bedding layer and the subgrade (or subbase, if used). It supports paving units and bedding materials and may consist of open-graded or dense-graded aggregate, with or without Portland cement or asphalt treatment, asphalt, or concrete.
Base Rake: A rake with both flat and toothed sides, used for moving and leveling aggregate base material. It may also be used to evenly spread joint sand across unit surfaces for quicker drying.
Basket Weave Pattern: A paving pattern in which two or more rectangular units are laid side by side, with adjacent pairs rotated 90° to create an alternating layout. Also referred to as “parquet pattern.”
Bedding Layer: The aggregate material directly beneath segmental concrete units. In non-permeable applications, it is typically a 1-inch (25 mm) thick layer of sand conforming to ASTM C33 or CSA A23.1 standards. For permeable applications, it is a 2-inch (50 mm) thick layer of open-graded angular aggregate, such as ASTM No. 8 stone. This layer facilitates bedding of the pavement surface during installation and is sometimes called the “bedding course.”
Bedding Sand Degradation Tests: The evaluation of sand attrition measures how much the sand breaks down when subjected to wear and abrasion. This process involves conducting tests where sand samples are placed in a container along with steel balls or other abrasive materials. The container is then agitated to simulate mechanical stress. To assess the extent of sand degradation, sieve analyses are performed both before and after the test to determine the amount of fine particles produced. These tests help evaluate the durability of bedding sand, especially when exposed to heavy loads or repeated traffic. A common method used for this purpose is known as the Micro Deval test.
Bentonite Clay: A clay rich in montmorillonite minerals, characterized by significant swelling when wet, often used for sealing openings.
Best Management Practice (BMP): A structural or nonstructural approach designed to manage stormwater runoff and reduce water pollution effectively.
Bishop’s Hat: A five-sided concrete paver with a flat top and beveled edges. It is a versatile paving unit that can be arranged to create various patterns. Often with a 45° herringbone pattern.
Bitumen Setting Bed: A bedding layer comprised of a bitumen/sand mix, to which neoprene-asphalt mastic adheres the paving units. Typically, it is less than 1 inch (25 mm) thick and is most often placed over a concrete base.
Blending: The practice of mixing paving units from multiple bundles or cubes during installation to achieve an even distribution of color.
Blind Spacer: A spacer that stops short of the paver top surface. This variation of spacer is not visible after paver installation and the joints are filled with sand. See Spacer.
Bound Base: An aggregate base or subbase mixed with Portland cement, bitumen, or another material to increase structural capacity and stiffness, though permeability is typically reduced. Also called a “treated base.”
Bulge or Belly: A convex distortion on a paving unit’s side, caused by excessive water in the concrete mix during production.
Bundle: Multiple layers of paving units stacked vertically or lined up horizontally (for larger slabs), bound together with plastic wrap and/or straps for transport. Bundles may be palletized or strapped and moved using specialized clamps or wheeled equipment on-site. They are then tagged with order and shipment details. Also referred to as a “cube.”
Bundle Buggy: A wheeled device, motorized or manual, designed to transport portions of bundled paving units of a cube around a job site.
C
California Bearing Ratio (CBR): A standardized test to measure soil that calculates the ratio of (1) the force per unit area required to penetrate a soil mass with a 3 in. sq. (19 cm sq.) circular piston (approximately 2 in. (51 mm) diameter) at the rate of 0.05 in. (1.3 mm)/min, to (2) that required for corresponding penetration of a standard material. The test is usually performed at 0.1-inch (2.5 mm) penetration, as per ASTM D1883.
Cation: A positively charged ion or group of ions that can interact with soil particles, facilitating the attachment of metals from stormwater runoff to the soil.
Cement: A binding material, such as Portland cement or asphalt, used to create stronger composite materials. Commonly refers to Portland cement.
Cement-Aggregate Ratio: The weight ratio of cement to fine and coarse aggregates in concrete.
Cement-Treated Base: A road base made of crushed stone mixed with cement to enhance stiffness and resistance to rutting under wheel loads.
Chamfer: A 45° beveled edge, typically 1/16 to 1/4 inch (2-6 mm) wide, around the top of a paving unit. It enables water drainage, aids snow removal, prevents edge chipping, and defines individual units.
Choke Course: A layer of smaller aggregate particles compacted into another layer of larger particles to provide stability and smoothness. The smaller particles fill voids and blend together, but do not pass through the larger material.
Clay: A fine-grained soil, or the fine-grained portion of soil, that exhibits plasticity (putty-like behavior) within a range of water content and demonstrates significant strength when air-dried. The term refers to soil particles finer than 0.002 mm in diameter.
Cluster: A group of paving units arranged in a single layer, designed to be picked up, held, and placed by machinery onto a bedding layer during installation.
Coarse Aggregate: Aggregate that primarily retained on the U.S. Standard No. 4 (4.75 mm) sieve, or the portion of a mixture retained by the No. 4 sieve.
Cohesion: The property of soil that holds its particles together.
Combined Sewer Overflows (CSOs): Instances where stormwater and sanitary sewage overflow from the combination in the same conveyance system. These overflows bypass treatment facilities and discharge raw sewage into a body of water.
Compaction: The process of consolidating solid particles, such as soil, sand, or aggregate, by removing air pockets through particle compression. Water is not effectively removed during compaction.
Compressibility: Property of soil that causes it to deform under stress of a weight bearing load.
Compressive Strength: The maximum load resistance of a concrete unit under pressure, measured and expressed as force per unit area (e.g., pounds per square inch or newtons per square millimeter).
Concrete Grid Paver: A type of segmental concrete paving unit with surface openings ranging from 20–70% in a lattice or castellated style. These pavers are used for erosion control or soil stabilization and can create vegetated, drivable surfaces. Typically sand-set, the openings may be filled with topsoil and seeded, or with aggregate to reduce surface runoff.
Concrete Sand: Washed sand meeting ASTM C33 or CSA A23.1 grading requirements, with limits on the percentage passing the No. 200 (0.075 mm) sieve. It is commonly used in the production of ready-mix concrete and as bedding sand.
Course: A single row of installed paving units or a row within a bundle or cube.
Creep: Gradual lateral movement of paving units caused by horizontal forces, such as those generated by braking vehicles.
Crown: The slightly convex shape of a roadway cross-section, designed to facilitate surface drainage and interlocking of pavers.
Crushed Stone: A construction material produced at a quarry by mechanically crushing rocks, boulders, or large cobblestones. Each resulting aggregate features well-defined edges on all surfaces.
Crusher Run: The unscreened byproduct of a stone crusher, comprising a mixture of various aggregate sizes.
CSA: Canadian Standards Association.
CSA-A231.1: A product standard for precast concrete paving slabs, defining standards for dimensions, minimum flexural strength, and freeze-thaw durability with deicing salts.
CSA-A231.2: A product standard for precast concrete pavers (interlocking units), specifying requirements for dimensions, minimum compressive strength, and freeze-thaw durability with deicing salts.
Cube(s): Refer to Bundle.
Curve Number (CN): A numerical value representing a given area’s hydrological soil group, plant cover, impervious cover, interception, and surface storage. Curve numbers are used to calculate runoff volumes from rainfall depth. Permeable Interlocking Concrete Pavements (PICP) typically have CN values between 45 and 80, often reducing the post-development CN of a site, compared to the pre-development CN.
D
DCOF (Dynamic Coefficient of Friction): A measurement that classifies the interaction between a wet surface and a passing shoe, used to evaluate the slip resistance of wet surfaces. The AcuTest device is commonly used for this purpose. It simulates and measures the resistance that is required to keep one object which is already in motion, moving over another object. Refer to ANSI A137.1-2012.
Deflection: A temporary downward movement of a pavement structure caused by traffic loads.
Degradation Testing: Assessments of sand or aggregate to determine their resistance to changes in particle size or gradation under applied loads.
Dense-Graded Aggregate: A compacted crushed stone material with a gradation that produces tiny voids between particles although the spaces are not visible. It is commonly used in base layers and includes particles ranging from 1/2 inch (38 mm) or 3/4 inch (19 mm) down to fines passing the No. 200 (0.075 mm) sieve. Such aggregates should meet ASTM D2940 gradation requirements. Often, the local department of transportation specified aggregate for road base should suffice as a segmental pavement base.
Density: The mass per unit volume of a substance. Typically expressed in pounds per cubic foot (kg/m).
Dentated Unit: A paving unit with indentations along its sides to increase the area, thereby enhancing interlock with adjacent units when installed.
Detention Pond or Structure: The temporary storage of stormwater runoff in an area to reduce peak discharge rates and allow for pollutant settling.
Dimensional Tolerance Testing: The process of verifying that the dimensions of manufactured units (length, width, thickness) conform to the specified +/- tolerances. For slabs (ASTM C1782), the warpage across the full length, width, and diagonal dimensions are also confirmed to be within an acceptable range.
Drainage Coefficient: A factor used to adjust the layer coefficient of pavement materials, reflecting the extent of their ability to resist weakening when wet or saturated. Refer to Layer Coefficient.
Dry Mix Joint Sand Stabilizer: Joint sand treated with chemical agents that activate upon contact with water, activates them to bind sand particles together. This process stabilizes the joint sand, reduces permeability and sand loss, and helps prevent weed growth.
E
Edge Unit: A paving unit designed with a straight, flush side or a precisely cut edge for placement against an edge restraint.
Edge Restraint: A structural element, such as a curb, edging, or building, that borders the edge of segmental concrete pavement and prevents horizontal movement of the units. Restraints can be visible or concealed.
Efflorescence: A white crystalline deposit of calcium carbonate that appears on concrete surfaces as a result of chemical reactions involving calcium hydroxide, a byproduct of cement hydration, and carbon dioxide from the atmosphere. This phenomenon occurs when water-soluble calcium hydroxide is transported to the surface through capillary action, where it reacts with carbon dioxide to form calcium carbonate and water. Calcium carbonate is the most common type of efflorescence. Over time, this deposit often diminishes naturally, influenced by environmental conditions. Its occurrence is purely cosmetic, posing no risk to the structural integrity or quality of the concrete.
Elasticity: Property in soil that allows soil to return to its original configuration when the compression force is removed.
Elastic Deformation: A temporary change in the shape or position of pavement caused by applied loads, where the pavement returns to its original form once the load is removed. Compare to permanent deformation under Rutting.
Elephant’s Foot: A solid extension at the base of a unit, typically caused by excessive mold wear that results in rounding at the mold’s bottom. Also referred to as Legs.
Embodied Energy: The total energy used throughout a pavement material or product’s lifecycle, encompassing extraction, refining, processing, fabrication, transportation, installation, usage, maintenance, removal, and eventual recycling or disposal.
Engraved Units: Paving units inscribed with letters or images, either during or after manufacture, using molding, shot blasting, or wet cutting techniques. Engraved units may also refer to units that feature cast metal plates embedded in their surfaces.
Environmental Product Declaration (EPD): A manufacturer-issued declaration outlining the environmental impacts associated with the production of a specific material. EPDs may contribute to points for LEED-certified projects.
Equivalent Single Axle Loads (ESALs): Summation of equivalent 18,000 pound-force (80 kN) single axle loads used to combine mixed traffic to a design traffic load for the design period; also expressed as Equivalent Axle Loads or EALs.
Erosion: The process by which soil is worn away, displaced, or moved by water, wind, ice, or gravity.
Expansion: Increase in a material’s volume due to an increase in the moisture content.
F
Face Mix (or Hard Facing): A thin top layer of fine aggregate and cement, often colored, which is applied to a unit’s surface to enhance appearance, abrasion resistance, or provide a base for a textured finish.
Failure: The point at which a pavement does not perform its intended function. For flexible pavements, failure is often defined by exceeding a specified rut depth. See ASTM E2840.
False Joints: Surface grooves on units that mimic full joints. This contributes to the visual enhancement of the joint pattern and expedites installation by eliminating the need for separate sub-units. Also called Dummy Grooves.
Fineness Modulus: A numerical factor that is calculated by summing the cumulative percentages by weight of the sample retained on a specified series of sieves and dividing the total by 100. In the United States, standard sieve sizes are No. 100 (0.150 mm), No. 50 (0.300 mm), No. 30 (0.600 mm), No. 16 (1.18 mm), No. 8 (2.36 mm), No. 4 (4.75 mm), 3/8 in. (9.5 mm), 1 1/2 in. (37.5 mm), 3 in. (75 mm), and 6 in. (150 mm).
Fines: Silt and clay particles in soil or aggregate, typically smaller than the No. 200 or 0.075 mm sieves.
Finished Grade: The final elevation of soil, subgrade, subbase, base, or pavement surface, often specified in construction plans. Also referred to as Finish Elevation.
Flag: See Paving Slab.
Flash: A thin, brittle layer of cement on the bottom or top edges of a cement segmental paver, caused by minor liquid cement leakage during molding. Also called Flange or Burrs.
Flexible Pavement: A pavement structure that conforms to and distributes loads to the subgrade. Stability is achieved through aggregate interlock, friction, and cohesion in the base and subbase layers.
Flexible Segmental Paving System: A paving system with four main components; Granular base that is compacted to uniform thickness, Sand Bedding layer, Edge Restraints to prevent paver shifting, and Pavers.
Flexural Strength: A measure of a unit’s resistance to bending failure, expressed in pounds per square inch (psi) or megapascals (MPa).
Flowable Fill: A low-strength concrete mixture, also known as Unshrinkable Fill or Controlled Low Strength Material (CLSM), used to fill utility trenches or other excavated pavement openings. See ASTM D6103, D6023, D6024, and D4832 for specifications.
Freeze-Thaw Durability Testing: Tests exposing units to controlled cycles of freezing and thawing, either partially or fully submerged in water, with or without deicing salts. Results are expressed as mass loss after a specified number of cycles.
Frost Action: The effects of freezing and thawing of moisture within pavement materials.
Frost Heave: The raising of a pavement surface caused by the accumulation and expansion of ice within the base, subbase, or underlying soil or rock layers.
G
Geogrid: A two-dimensional or three-dimensional lattice made from various plastics, used for soil stabilization. Two-dimensional geogrids are flat with square, rectangular, or triangular openings, while three-dimensional geogrids, ranging from 4 to 8 inches (100 to 200 mm) high and help stabilize cohesionless soils and open-graded bases under loads.
Geotextiles: Woven or non-woven plastic fiber fabrics used for separation, reinforcement, or drainage between subgrade and aggregate layers.
Gradation: A measure of the particle size distribution in soil or aggregate, represented by the percentage of the total sample mass that passes through specified sieve sizes. This classification helps describe the range and proportion of different particle sizes within the material. Refer to ASTM C136.
Grade:
(noun) The slope of a finished surface of an excavated area, such as subbase, base, or pavement, typically expressed as a percentage.
(verb) The process of leveling a surface using manual or mechanized equipment.
Gravel: Rounded or semi-rounded rock particles that pass through a 3-inch (75 mm) sieve and are retained on a No. 4 (4.75 mm) sieve. Typically found in streambeds or riverbanks, as they have been naturally smoothed by the flow of water. Gravel is classified by the Unified Soil Classification System as soil with particles sizes of No. 4 sieve size and larger.
H
H-20 and HS-20 Loading: A vehicular load classification used in AASHTO bridge design and other suspended structures, such as utility covers for vehicular traffic. This term is sometimes incorrectly applied to pavement design.
Half Stone: A manufactured half-unit used to fill voids on a cube of units. Used for mechanically installed “stitching.”
Hard Facing: Dense top layer of hard fine aggregates.
Herringbone Pattern: A paving pattern where the joints do not exceed the combined length and width of the paving units. The pattern can be oriented at 45° or 90° angles relative to the main direction of traffic flow.
Hotspot: A land area that generates stormwater runoff with contaminant concentrations significantly higher than typical stormwater.
Human Scale: The design principle of utilizing unit sizes, patterns, colors, and textures in large spaces or next to large buildings to create a more comfortable, less overwhelming, and more relatable user experience.
Hydrological Soil Group: A classification system developed by the U.S. Natural Resources Conservation Service (formerly U.S. Soil Conservation Service) that categorizes soils (A through D) based on runoff potential. Group A soils have high permeability and low runoff, while Group D soils exhibit low permeability and high runoff.
I
Impervious: Resistant to water penetration.
Impervious Cover: Surfaces such as pavements, roofs, sidewalks, or driveways that prevent rainwater from infiltrating the underlying soil.
Infiltration: The process by which water moves downward through a permeable pavement system and into the subgrade soil.
Infiltration Rate: The rate at which water enters and moves through voids in unsaturated aggregate or soil, typically expressed in inches per hour or meters per second. Refer to ASTM C1781, D3385, and D5093. Also, the rate at which water enters a permeable pavement. Not to be confused with Permeability or Saturated Hydraulic Conductivity.
Interlock: The compressive and frictional forces between paving units that prevent rotation or shifting horizontally or vertically. These forces enable the transfer of loads across the pavement. Also refers to the inability of individual units to move in relation to adjacent units.
Interlocking Concrete Pavement: A pavement system of small, hand-sized concrete units designed for high surface interlock due to their shape, size, and pattern. Units are laid in patterns, compacted into bedding sand, and joined with joint material to create structural interlock for load support and distribution.
Interlocking Concrete Pavement Institute (ICPI): An organization that merged with the National Concrete Masonry Association (NCMA) to form the Concrete Masonry and Hardscape Association (CMHA).
J
Joint: The space between paving units filled with jointing sand (for non-permeable pavements) or small open-graded aggregate (for permeable pavements) to prevent unit contact after installation.
Joint Filling Sand: Sand used to fill spaces between paving units. Also called Jointing Sand.
Joint Material: Material, such as sand (for non-permeable pavements) or small aggregates (for permeable pavements), used to fill joints between units and facilitate interlock.
Joint Sand: Sand swept into unit openings for non-permeable applications to fill joints.
Joint Sand or Material Gap: The vertical distance from the bottom of a unit’s chamfer to the top of the sand in the joint.
Joint Sand Stabilizer: A liquid-penetrating or dry-mix material applied to joint sand to provide early stabilization, reduce permeability and sand loss, and helps prevent weed growth. See Dry Mix Joint Sand Stabilizer, Liquid Penetrating Joint Sand Stabilizer.
Joint Spacing: The distance between the sides of two adjacent units, excluding spacers, typically filled with joint material or permeable aggregate. This measurement does not include the chamfer.
Jointing Material Gap: The vertical distance from the bottom of a unit’s chamfer to the top of the jointing material within the joint.
K
Karst Geology: Geological regions underlain by carbonate rock, often including sinkholes and/or limestone caverns.
K-pattern: A paving pattern consisting of one square unit surrounded by rectangular units, also known as an I-pattern or Muster K pattern.
L
Layer Coefficient: A dimensionless value in the AASHTO flexible pavement design procedure that represents the material strength per inch (25 mm) of thickness of a pavement layer, including the surface, base, or subbase. For example, a 4 in. (100 mm) thick concrete paver and 1 1/2 in. (38 mm) of bedding sand have a layer coefficient of 0.50 per inch (25 mm), resulting in a Structural Number (SN) of (4 + 1.5) × 0.50 = 2.75
Laying Face: The exposed vertical surface of a row of units on the bedding sand layer; the working edge where paving units are laid.
Laying Pattern: The sequence of unit placement that creates a repetitive geometry, often chosen for visual or structural benefits.
Lean Concrete: Concrete with a low cement content, used as a structural base material or as flowable fill in utility trenches.
Leadership in Energy and Environmental Design (LEED): A certification program developed by the U.S. Green Building Council (USGBC) to assess and promote the sustainability of building materials, systems, and construction practices. The USGBC also provides a separate evaluation framework for site sustainability, known as Sustainable Sites.
Life Cycle Analysis (LCA): A comprehensive assessment of the environmental impacts associated with all stages of a product’s life cycle, including raw material extraction, material processing, manufacturing, distribution, construction, use, maintenance, repair, and end-of-life disposal or recycling.
Life-Cycle Cost Analysis (LCCA): A calculation method evaluating all anticipated costs over a pavement’s life span. Factors influencing results include initial construction, maintenance, periodic rehabilitation, salvage value, inflation, discount rate, and analysis period. Discounted cash-flow methods, such as present worth or annualized cost, are used. Sensitivity analysis identifies variables with the most significant impact on cost.
Lift: A compacted layer of soil or aggregate achieved through the use of compaction equipment.
Lippage: The vertical misalignment between the surface of one unit and its adjacent unit. Excessive lippage is sometimes referred to as “fish scale.”
Liquid Penetrating Joint Sand Stabilizer: A polymer liquid applied over paving units, penetrating the joint sand. Once cured, it stabilizes the sand, reduces permeability and sand loss, and helps prevent weed growth.
Lock Up: The initial settling phase of concrete paver installation gradually becomes more rigid under traffic, reaching a stage where no further settling takes place unless there is a failure in the base or subgrade. Also referred to as Progressive Stiffening.
Low Impact Development (LID): A stormwater management strategy that mimics natural processes by managing rainfall at its source through decentralized, small-scale controls distributed across a site.
M
Macro Texture: Surface irregularities on pavement with dimensions typically 0.5 mm or larger. These deviations do not directly influence tire-pavement interaction.
Markers: Units with distinct colors, textures, or shapes used to denote underground utilities, traffic directions, parking stalls, lanes, or pedestrian/vehicular zones.
Mechanical Installation: The use of machinery to lift and place pre-assembled layers (clusters) of units directly onto the bedding layer in the desired pattern. This method increases paving efficiency compared to manual placement.
Mechanistic-Empirical Design: A method for analyzing the structural responses of pavement to applied loads by modeling stresses and strains, with the results validated through full-scale load testing.
Micro Texture: Irregularities on a pavement surface, considered deviations from a perfectly flat plane, where the dimensions of these variations are typically less than 0.5 millimeters.
Modified Proctor Compaction Test: A modified version of the Standard Proctor Compaction Test measuring the relationship between density and moisture content under higher compaction forces. Refer to ASTM D1557.
Modulus of Elasticity (Elastic Modulus): The ratio of stress to strain for a material under specific loading conditions.
Moisture Content: The water weight percentage found in the pore space of soil, aggregate, sand, or base relative to the solid material weight.
Mortar: A mixture of cement paste and fine aggregate (sand).
Mortar Sand: Sand used in mortar, typically conforming to ASTM C144 or CSA A179 standards.
Mortar-set Pavement: A paving method where units are adhered to a concrete base with mortar, with joints filled using mortar or stabilized joint material.
Mosaics: Paving units arranged into pictorial maps, murals, or geometric patterns. They are used to represent locations, highlight specific areas, or convey movement.
MS4: Municipal separate storm sewer system. Public agency owned stormwater conveyance systems, including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, and storm drains.
Multi-Colored Units (Color Blend): A unit with two or more colors, typically resulting in a variegated appearance.
N
National Concrete Masonry Association (NCMA): An organization that merged with the Interlocking Concrete Pavement Institute (ICPI) to form the Concrete Masonry and Hardscape Association (CMHA).
National Pollutant Discharge Elimination System (NPDES): A regulatory program aimed at controlling water pollution by regulating point sources (e.g., sewage discharge) and non-point sources (e.g., runoff) into U.S. water bodies, such as streams, lakes, and bays. Implemented via permits and pollution control plans at state and local levels for sewage discharge and runoff from construction sites, urban areas, and farmland.
Nuclear Density Testing: A method using a nuclear density gauge to measure the density, moisture content, and level of compaction of soils and dense-graded aggregates quickly and accurately in the field. This process involves inserting a probe into the compacted soil or aggregate base that emits low-intensity radiation. See ASTM D2922.
O
Observation Well: A perforated pipe installed vertically into an open-graded base to monitor water infiltration rates into the underlying soil.
One/One Hundred Year Storm: Statistical term indicating the probability of recurrence of a rainfall event, where there is a 100% chance of occurring within a given year/an event with a 1% chance of occurring within a given year.
Open-Graded Aggregate: Washed, crushed stone with a gradation yielding large voids between the particles to allow water infiltration and storage. Used in joints, bedding, base, and subbase of permeable pavements or as drainage course below non-permeable pavements.
Optimum Moisture Content: The water content at which a soil achieves its maximum dry density under a given amount of compaction effort.
Organic Impurities: Decomposing materials such as peat, roots, or topsoil found in soil, sand, or aggregate.
Organic Soil: Soft, compressible soil composed of materials like peat humus or vegetation, characterized by poor suitability for construction purposes.
Outlet: The discharge point of water from a pavement system, typically into a storm sewer or natural watercourse.
P
Partial Infiltration: A permeable pavement design where some water is detained to promote infiltration into the soil while excess water is discharged via drain pipes.
Parquet Pattern: A laying pattern with two or more rectangular units placed side-by-side, with adjacent pairs rotated 90° in an alternating sequence. Also known as a Basketweave Pattern.
Paver: A segmental concrete paving unit, typically rectangular, square, or dentated, designed to fit into various laying patterns. These units are generally no larger than 12 inches (300 mm) in length or width, with an aspect ratio of 4 or less. For pedestrian applications, an aspect ratio of less than or equal to 4:1 is recommended. Vehicular applications require an aspect ratio of less than or equal to 3:1. Pavers rely on interlock as the primary method of load distribution and are tested for compressive strength. Refer to ASTM C936 and CSA A231.2 for local criteria. Compared to Plank or Slab.
Pavement Performance: The serviceability trend of pavement under repetitive loads.
Pavement Rehabilitation: Maintenance to extend a pavement’s service life of an existing pavement, including adding surfacing material or addressing structural and functional deficiencies. May involve partial or complete replacement.
Pavement Structure: A combination of subbase, base, and surface courses placed on a subgrade to support and distribute traffic loads to the roadbed.
Paver Extractor: A tool designed to grab and remove individual units from a laying pattern.
Paver Splitter: A manually operated machine, sometimes with hydraulic assistance, used for cutting paver units. Also known as a “guillotine splitter.”
Paving Slab: A paving unit larger than an interlocking concrete paver. Generally do not exceed the dimensions of 36×36 in. Unlike concrete pavers, paving slabs do not rely on interlock as the primary means of load distribution. Also referred to as Flag.
Peak Discharge Rate: The maximum instantaneous flow rate from a detention or retention pond, open-graded base, pavement surface, storm sewer, stream, or river, typically associated with a specific storm event.
Pedestal Set: An installation method for units supported at minimum on four corners using polystyrene blocks or plastic pedestals. Commonly used on rooftops to protect roofing materials and allow for maintenance access.
Performance: The cumulative traffic or Equivalent Single Axle Loads (ESAL) a pavement withstands before reaching failure, requiring rehabilitation or reduced serviceability.
Performance Period: The expected serviceable lifespan of a pavement before requiring major maintenance or rehabilitation, often expressed as the design period or life. Typically, in North America, 20 to 40 years is used.
Permeability: The rate of water movement through a soil column under saturated conditions. Measured in the laboratory per ASTM or AASHTO tests, and is expressed in inches per hour or meters per second. Refer to ASTM D2434. Compare to Infiltration.
Permeable Interlocking Concrete Pavement: A segmental concrete pavement with 33/16 to 1/2 in. (5 to 13 mm) wide joints between units, and the use of open-graded aggregates for the joint, bedding, base and subbase materials. This system allows for stormwater infiltration, storage, subgrade infiltration, and discharge through an outlet. Also known as permeable pavement.
Pervious or Permeable Surfaces/Cover: Surfaces that permit rainfall infiltration, including vegetated areas, grid pavers, or permeable pavers/slabs.
Plan Ratio: The length-to-width comparison of a unit expressed as a ratio. Example: A 4 in/100 mm wide by 8 in/200 mm long paver has a plan ratio of 2:1. Compare to Aspect Ratio.
Plank: A segmental concrete paving unit characterized by a long and narrow shape with both an aspect ratio and plan ratio of at least 4:1. Compare to Paver and Slab.
Plastic Limit:
The water content at which soil transitions from a plastic to a semisolid state of consistency.
The water content at which soil begins to crumble when rolled into a thread approximately 1/8 inch (3.2 mm) in diameter.
Plate Compactor: Also known as a plate vibrator. Used to compact subgrade, base, and subbase materials; set units into the bedding layer; and vibrate joint material into unit joints.
Porosity: The volume of voids in a soil or aggregate divided by the total volume of the material.
Portland Cement: A type of hydraulic cement which is a grey to white powder made from pulverized clinker containing hydraulic calcium silicates, often with added calcium sulfate in one or more forms.
Pozzolanic Materials: Substances like fly ash, pozzolan, silica fume, or blast furnace slag, used to replace cement in concrete mixtures to improve density and durability of the concrete.
Prepared Roadbed: In-place roadbed soils compacted or stabilized according to provisions of applicable specifications.
Present Serviceability Index (PSI): A numerical rating, typically ranging from 0 (completely non-functional) to 5 (new/perfect), that summarizes various measurements of pavement condition. It provides a convenient method for evaluating the overall condition and performance of pavement over time, as defined by AASHTO pavement design methods.
Pre-treatment: BMPs designed to filter and store pollutants before further filtering, settling, and processing in other BMPs for stormwater pollutant reduction.
Proctor Compaction Test: A test measuring the relationship between soil density and moisture content under standard compaction effort to identify the maximum achievable density. See ASTM D698.
Progressive Stiffening: The tendency of pavement to stiffen over time under repeated traffic loads, enhancing structural performance. Also called “lock-up.”
Pumping: The ejection of saturated bedding or joint sand through joints, cracks, or edges of units under load application.
R
Reflecting: Using units to replicate geometric patterns, shapes, colors, or textures in the surrounding site.
Retention Pond: A water body or structure designed to collect and store runoff, allowing it to infiltrate into the subgrade. When the runoff volume exceeds the pond’s storage capacity, the excess water is discharged through an overflow device connected to a storm sewer or watercourse.
Roof Pavers: See Ballast Block.
Roughness Index: The total measured vertical changes over a pavement surface divided by the pavement’s length.
Running Bond Course: A course of units where the long sides (lengths) abut edge restraints. Also known as a “sailor course.”
Running or Stretcher Bond: A laying pattern with continuous joint lines in one direction and units are laterally offset from row to row.
Runoff: Water flowing off a site during or after rainfall.
Runoff Coefficient: The ratio of runoff depth to rainfall depth.
Run-on: Water, other than direct precipitation, entering a site during or after rainfall.
Rutting: Permanent deformation caused by repeated traffic loads that exceed the pavement’s structural capacity to maintain its original profile.
S
Sailor Course: A row of pavers laid with the longer side abutting edge restraints. See Running Bond Course.
Sand: Granular material derived from natural erosion or manufactured by crushing aggregates, composed of subangular or round particles. Defined as material passing a 4.75 mm sieve and retained on a 0.075 mm sieve. Different from manufactured sands, which are made by crushing course aggregates.
Sand Spreaders: Broom attachments used with motorized equipment to distribute joint sand efficiently across pavement surfaces.
Saturated Hydraulic Conductivity: A measurement of a soil’s ability to transmit water under saturated conditions when subjected to a hydraulic gradient. It differs from (unsaturated) hydraulic conductivity in the vadose zone or the infiltration rate, which refers to the movement of water into and through the openings of unsaturated soil.
Screed Board or Strike Board: A straight, rigid tool (wood or metal) used to level bedding material to grade by pulling it across guides or rails set on the base course or edge restraints.
Screed Guides or Bars: Grade strips, such as pipes, that guide the screed to produce the desired elevation for the bedding layer.
Screenings: A residual product unsuitable for bedding sand, produced as a by-product from crushing rock, boulders, cobble, gravel, blast furnace slag, or concrete. Most particles pass a No. 4 (4.75 mm) sieve; typically, limestone or granite.
Sealer: A liquid material applied to reduce absorption, enhance color, and sometimes reduce abrasion of paving units. Sealed pavers are often easier to clean.
Sediment: Soils transported and deposited by water, wind, ice, or gravity.
Segmental Concrete Pavement: A pavement system comprising modular units placed over a bedding layer, base, and subbase in scenarios where it is required. Can be further classified as interlocking concrete pavement, permeable interlocking concrete pavement, concrete grid pavement, or concrete slab pavement depending on the type of paving unit and aggregates used.
Segmental Pavement: A pavement made up of individual, discrete units. The surface is typically constructed from materials such as concrete, clay, or natural stone.
Slab: A segmental concrete paving unit characterized by a large surface area and a high aspect ratio (greater than 4:1). Because of their size, slabs are typically used in pedestrian applications and do not rely on interlock as the primary method of load distribution. They are tested for flexural strength. Refer to ASTM C1782 and CSA A231.1 for local criteria. Compare to Paver and Plank.
Serviceability: The pavement’s ability to serve its intended traffic (pedestrians, cars, trucks, buses). Measured primarily by the Present Serviceability Index (PSI), which ranges from 0 (very poor) to 5 (perfect).
Shrinkage: The volume reduction of soil due to moisture loss.
Sieve Analysis: Practice that determines particle size distribution within a particular sample of soil using a series of sieves.
Silt: Soil particles finer than 0.02 mm but coarser than 0.002 mm.
Skid Resistance: A measure of a surface’s frictional properties related to tires.
Slip Resistance: The Americans with Disability Act (ADA)’s Accessibility Guidelines Section 302 states that “Floor and ground surfaces shall be … slip resistant.” The ADA guidelines provides no specific method of assessment or numerical values that must be achieved. However, an ADA Advisory Statement states: “A slip resistant surface provides sufficient frictional counterforce to the forces exerted in walking to permit safe ambulation.” One potential reference is ANSI A326.3 American National Standard Test Method for Measuring Dynamic Coefficient of Friction of Hard Surface Materials, which covers all hard flooring surfaces. The test method includes a wet Dynamic Coefficient of Friction (DCOF) acceptance criteria of ≥0.42. It should be noted however that for exterior applications a wet DCOF value of 0.42 may not necessarily be suitable and specifiers may require higher value to reduce the risk of slips and falls.
Slump: A measure of the consistency and water content of freshly mixed concrete, determined by the subsidence of a specimen after immediately removing a cone-shaped mold. See ASTM C143. Note: Most concrete units are made using zero-slump concrete due to low water content and are not tested for slump.
Soil Separation Fabric: A permeable geotextile or fabric placed between subgrade and the lowest level of aggregate base or subbase to reduce rutting.
Soil Stabilization: Chemical or mechanical treatments to improve and maintain soil stability and engineering properties. Common chemical stabilizers include lime, fly ash, cement. Geotextiles and geogrids are typically used as mechanical stabilizers.
Solar Reflectance (SR): A measure of a material’s ability to reflect solar energy, determined using ASTM C1549, Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer. This method measures the solar reflectance of flat, opaque materials in both laboratory and field settings. A commercial portable solar reflectometer, calibrated with specimens of known solar reflectance, calculates reflectance by taking measurements at wavelengths of 380 nm, 500 nm, 650 nm, and 1220 nm.
Solar Reflective Index (SRI): A measure of a surface’s ability to remain cool in sunlight by reflecting solar radiation and emitting thermal radiation. Determining Solar Reflective Index takes Solar Reflectance (SR) and Thermal Emittance into consideration.
Soldier Course: One or two courses of pavers with the short side (width) abutting edge restraints.
Solid Color Unit: A paver unit with one color, achieved by adding pigments like iron oxide, metal oxide, or other mixed metal oxide to the concrete mix.
Spacer Bars or Nibs: Small protrusions on the sides of a paving unit, typically 1.5 to 2 mm for non-permeable pavers and up to 12 mm for permeable pavers, designed to maintain a minimum joint space for jointing material. Spacer bars help prevent edge chipping and spalling. Some cannot be seen after installation. See Blind Spacer.
Spall: A flake-shaped fragment detached from a unit’s edge or surface due to impact, weathering, or pressure from adjacent units.
Stabilized Base: An aggregate base mixed with cement, asphalt, or other materials added to enhance structural capacity.
Stabilized Subgrade: Soil subgrade stabilized with materials like cement, lime, or fly ash to increase load-bearing capacity.
Stack Bond: A laying pattern where the joints are continuous in both directions.
Standing Screed: An aluminum screed with handles, allowing one person to pull it across bedding material while standing, rather than kneeling.
Storm Water Pollution Prevention Plans (SWPPP): A key requirement of stormwater permits issued under the National Pollutant Discharge Elimination System (NPDES), which identifies potential sources of pollution that could impact the quality of stormwater discharges from a construction site. A SWPPP outlines the practices to be implemented to reduce pollutants in stormwater discharges and ensures compliance with the construction permit’s terms and conditions. SWPPP requirements may vary by state. (Source: Construction Industry Compliance Assistance Center)
Strain: The change in length per unit of length in a given direction.
Stress: The force applied per unit area.
Structural Number (SN): A key component of the flexible pavement design method developed by AASHTO. It is a dimensionless value that represents the relative strength of a pavement structure. The SN is determined through an analysis of factors such as traffic, roadbed soil conditions, and environmental factors. It is the sum of layer coefficients, where each coefficient reflects the material strength and thickness of the individual pavement layers.
Subbase: A designed layer of material placed on a subgrade to support a base course, typically consisting of aggregate particles larger than those in the base. The layer or layers are placed on the subgrade.
Subgrade: The underlying soil layer upon which the pavement structure is constructed.
Sustainable Development: Development that meets present needs without compromising the ability of future generations to meet theirs, including sustainable pavement design.
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Tactile Units: Units detectable by visually impaired individuals due to differences in color or texture from surrounding surfaces, often achieved with detectable warnings like truncated domes.
Tensile Strength: The maximum stress a unit can withstand under axial tensile loading, measured based on the specimen’s cross-sectional area before loading.
Textured or Architectural Finish: Altered unit surfaces using mechanical methods such as shot blasting, bush hammering, tumbling, grinding, polishing, flame treating, or washing to create visual effects or simulate stone appearance. The finish of a unit can also be accomplished by the manufacturing mold.
Treated Base: An aggregate base or subbase combined with Portland cement, bitumen, or other stiffening materials to enhance structural capacity, but reduce permeability. Also called a bound base.
Time of Concentration: The time required for water to travel from the most remote point of a watershed to its outlet.
Topsoil: Surface soil that typically contains organic matter.
U
Unbounded Base: An aggregate base or subbase made solely of aggregate material, commonly used with segmental concrete pavements. Unlike bound or treated bases, an unbounded base allows liquids and gases to pass through the voids between aggregate particles. It is used in applications where drainage is desired, added stiffness is unnecessary, or the cost of a bound base is not justified.
Unified Soil Classification System (USCS): A standardized laboratory system for classifying soils, as outlined in ASTM D2487.
Urban Heat Island: An urban area hotter than surrounding rural areas due to factors like impermeable surfaces, denuded landscapes, low-albedo surfaces, pollutants, large buildings, and heat generation from vehicles and machinery.
V
Void Ratio: The ratio of the volume of voids to the volume of solids in a soil or aggregate.
W
Warpage: The maximum allowable vertical deviation from a straight edge placed across the full length, width, or diagonal dimension of a slab (as defined in ASTM C1782).
Water-Cement Ratio: The ratio of water weight to cement weight in a concrete mixture. Units typically have lower water-cement ratios (0.27–0.33) than standard concrete, improving strength and durability.
Wearing Course: The surface layer of pavement, consisting of units with specified joint material on a bedding layer.
Wearing Surface: The topmost surface of a pavement that contacts traffic.
Wind Uplift: The lifting effect on roof-installed units caused by a pressure gradient between the top and bottom surfaces due to wind. Minimum unit weights required to resist uplift are site-specific and need to be calculated individually and expressed in pounds per square foot (or kg/m3).
Z
Zoning: Using variations in unit color, texture, shape, laying pattern, or elevation to differentiate between pedestrian and vehicular areas or distinct districts.
