Pavement Design Criteria

3.1 Application

Load-Bearing Ability:

Heavy, medium, and light duty applications generally refer to the type of vehicular and pedestrian traffic which a pavement must accommodate. Heavy duty pavements are capable of accommodating vehicles, including trucks and buses typically found in city centers, institutions, large parks, and arterial highways. Medium duty pavements are capable of accommodating heavy pedestrian traffic and associated light service vehicles associated with institutions, private drives, parks, and light commercial settings. Light duty pavements are typically associated with residential and restricted public garden paths and plazas.

Table 440-2 illustrates typical loads associated with various uses and design contexts. Typical site scale developments require pavements that accommodate loads from 900 to 2 700 kg (2000 to 6000 lb). Institutional walkways that provide emergency or maintenance vehicle access, require pavements that may accommodate loads from 900 to 1 BOO kg (2000 to 4000 lb), with adequate edge reinforcement. Such loads can be supported by 40 to 75 mm (IVj to 3 in) of asphalt concrete on a 100 to 200 mm (4 to 8 in) aggregate base, or 6y 100 to 125 mm (4 to 5 in) of reinforced concrete on a 100 to 150 mm (4 to 6 m) aggregate base. Soil bearing ratings should fall within a CBfi (California Bearing Ratio) of 40-70 (Refer to Section 810: Soils and Aggregates).

Durability:

Pavement design must accommodate sustained pavement loading as well as maintenance methods and natural weathering effects. Cold climates require pavements that are able to withstand the chemical and abrasive maintenance methods used in snow removal. Hot-humid and hot-arid climates require pavements to withstand extreme daily temperature differentials and sustained wetness. Material porosity, density, hardness or flexibility, color, and finish are all characteristics which determine climatic compatibility and long-term durability Appropriate structural design and detailing may extend a pavement's effectiveness.

Safety:

Both vehicular and pedestrian pavements are required to be universally accessible according to the standards set forth by the Americans with Disabilities Act, and are therefore constrained by texture, joinery, slope, drainage, and associated site furnishings. Pavement color and finish are also constrained by reflectivity, glare, and permeability as they relate to climate setting (Refer to Section 240: Outdoor Accessibility).

Aesthetics:

Proper pavement design aims to achieve structural stability, environmental appropriateness, and cultural utility while at the same time complimenting the overall design in a way that is aesthetically pleasing Figure 440-17 illustrates several commonly used paving patterns achievable through both flexible and rigid paving systems. Care must be taken to keep patterns and textures in scale with the larger design to avoid inappropriate complexity or biand-ness. Long term maintenance should be a major factor in determining final finishes and textural treatments to insure that the design intent may be properly maintained Where limited resources are available, it is best to simplify to achieve a consistent overall appearance.

3.2 Climate

Regional climate factors of daily temperature extremes, precipitation rate and frequency, and frost/thaw cycles heavily influence pavement details and finishes.

Hot Arid: A wide variety of materials are available in this climate zone. Materials are typically light in color to avoid heat absorption, and may include glazed tiles and porous finishes due to low humidity and relatively stable temperature ranges.

Hot Humid: Drainage is critical to prevent build-up of mosses and algae, and to account for Intense periods of precipitation. Light colors are often used to avoid heat absorbtion. Stable temperatures provide for a wide variety of materials

Temperate: Darker colors are typical to absorb radiant solar energy. Frost/thaw cycles require care in aggregate base preparation and subdralnage. Heavy snow regions must account for abrasive clearing practices. Mortared unit pavers require heavy maintenance In extensive applications.

Cold: Cold climate areas require similar treatments as the temperate zone, but with more restrictions. Flexible pavements are preferred over rigid and mortared unit pavers. Reinforcing steel must be placed carefully to avoid damage through chemical assault, or extreme expansion coefficient differentials within concrete slabs and curbs.

3.3 Subgrade

Well drained or clay subsoils, rooftop gardens, or other unique site subgrade features play a significant role in determining a structural pavement design strategy.

Well drained soils: These soils are ideal for construction with regard to permeability and bearing capacity, and typically require only normal site preparation to serve as pavement subgrades.

Clay soils: These colloidal soils are subject to swelling due to moisture infiltration and have a high potential for lateral shearing. Vibration from vehicular loading may produce a pumping action resulting In upward migration of fines into aggregate bases Freeze/thaw actions create severe construction problems requiring dewater-ing, extra aggregate and fabric filtration and reinforcement.

Roof structures: Pavement design is highly restricted due to loading and drainage requirements. Special drain mats and insulation are typically required under finish pavement surfaces (Refer to Section 610: Roof and Deck Landscapes for more information).

3.4 Cost and Maintenance Cost:

Initial installation cost Is a function of material cost, labor, business overhead and profit required to install the pavement and associated support structures. Long term

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