Site Paving
Summary
Site paving covers asphalt, concrete, and interlocking paver surfaces for vehicle and pedestrian use, each built on a prepared subgrade and aggregate base. Traffic, subgrade strength, drainage, and slope decide thickness and type, and accessible routes limit running and cross slope.
Cols
Terminology
- Subgrade: compacted native soil or fill under the pavement
- Aggregate base: compacted crushed stone or gravel layer that carries load and drains
- Hot mix asphalt (HMA): asphalt binder and aggregate placed hot in lifts
- Full-depth asphalt: asphalt placed directly on the subgrade
- Joint spacing: distance between sawed or tooled control joints in concrete
- Interlocking concrete pavers: units to ASTM C936 laid on a bedding layer
- Edge restraint: curb or restraint that holds paver units in horizontal interlock
- CBR: California bearing ratio, a measure of base or subgrade strength
- Running slope / cross slope: slope along and across the direction of travel
Standards
Guides
- ACI PRC-330-21: commercial concrete parking lots and site paving, design and construction guide
- ICPI Tech Spec 4 and ASCE 58-16: base design tables for interlocking concrete pavement
- ASTM C936: interlocking concrete paving units
Typical sections
- Residential asphalt drive: 2 to 3 in. of asphalt over a 6 to 8 in. compacted gravel base
- Light-duty asphalt lot: about 3 in. of hot mix over 6 in. of aggregate base
- Heavy-duty asphalt lot: about 6 in. of hot mix over 3 in. of aggregate base
- Illinois asphalt industry minimum design: 6 in. aggregate base, 2.5 in. asphalt base layer, and 1.5 in. surface layer, or 5 in. full-depth asphalt
- Base depth: sources differ, from 6 in. to 8 in. of dense aggregate base under commercial lots
- Concrete joint spacing example: 4 to 4-1/2 in. slabs at 10 ft; 5 to 5-1/2 in. slabs at 12-1/2 ft
- Concrete thickness: depends on truck traffic and subgrade strength; thinning beyond tolerance raises stresses and cuts pavement life
- Pavers: minimum 4 in. aggregate base (CBR 80); base options in rising stiffness are aggregate, asphalt-treated, cement-treated, and lean concrete; edge restraint is essential
Accessible routes
- Walking surfaces on accessible routes have slope, width, and surface limits; see the site elements code reference
Materials
- Hot mix asphalt: the largest use of bitumen; flexible and quick to open to traffic
- Concrete: rigid, long-lived; joints and subgrade preparation control cracking
- Interlocking concrete and clay pavers: modular, repairable, and available in permeable systems
- Natural stone and flagstone: walks and patios
- Aggregate base: crushed stone or gravel
- Fly ash and structural fill: stabilized soil and compacted fill under pavements
Detailing
- Compact subgrade and base to the specified density and proof roll before paving
- Slope surfaces to drain; ponding shortens pavement life
- Saw or tool concrete joints on the specified spacing
- Provide edge restraint for pavers and keep base thickness within tolerance; for an 8 in. base, 7-1/2 to 8-3/4 in. is acceptable in one guide
- Moisture and freeze-thaw reduce base and subgrade strength, so provide drainage
- Coordinate catch basins, trench drains, and utility covers with the paving layout
- Check accessible route slopes at curb ramps and entries
Uses
Specific uses
- Driveways and parking lots
- Roads, drive aisles, and fire lanes
- Walks, plazas, and patios
- Permeable paving for stormwater
Pros and cons
Pros
- Asphalt: lower first cost, fast to build, easy to patch
- Concrete: long service life and low maintenance
- Pavers: repairable and aesthetically flexible, with permeable options
Cons
- Asphalt needs periodic sealing and resurfacing
- Concrete cracks if joints, thickness, or subgrade are wrong
- Pavers need base and edge restraint and can settle
Manufacturing and cost
Construction
- Asphalt placed hot in lifts and rolled; concrete placed, finished, jointed, and cured; pavers set on a bedding layer over compacted base and compacted with a plate compactor
Main manufacturers and suppliers
Trade associations: ICPI, Interlocking Concrete Pavement Institute, American Concrete Pavement Association, American Concrete Institute, and National Asphalt Pavement Association.
Sources
- ICPI: construction tolerances guide for permeable interlocking concrete pavement, https://icpi.org/s/ICPI_PICPConstructionTolerancesGuideRev2021-09.pdf
- American Concrete Institute: ACI PRC-330-21 guide, https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/51732924
- Illinois Asphalt Pavement Association: parking lots, https://il-asphalt.org/asphalt-info/private-commercial/parking-lots/
- Corada: 2010 ADA Standards Section 403 walking surfaces, https://www.corada.com/documents/2010ADAStandards/403