PPP Notes - Pedestrian Paving

PEDESTRIAN PAVING

 (These notes are compiled from AGS)

DESIGN CONSIDERATIONS

 

• Additional design guidelines for working with unit paving systems include the following:
• Drainpipes may be omitted at well-drained areas.
• Provide positive outflow for drainpipes.
• Do not use unsatisfactory soil (expanding organic).  Satisfactory soil must be compacted to 95%.
• Hand-tight paving joints are preferred over mortar joints.  However, when mortar joints are required, and freezing and thawing are frequent, use latex-modified mortar.
• Install concrete footing edging 10 to 14 in. wide and 6 to 8 in. deep.  It is preferable to place the bottom of the footing at freezing depth.  If the freezing depth is deeper than the bottom of the footing, provide 4 in. of gravel below the footing.
• Interlocking pavers are available in concrete, hydraulically pressed concrete, asphalt, and brick in different weight classifications, compressive strengths, surface textures, finishes, and colors.  Consult local suppliers for availability.
• Subject to the manufacturer’s recommendations and local code requirements, use interlocking concrete pavers in areas subject to heavy vehicle loads at speeds of 30 to 40 mph.
• Be aware that concrete interlocking unit paver sizes may be based on metric dimensions.  When paver shape permits, use the herringbone pattern for paving that is subject to vehicular traffic.
• Continuous curb or other edge restraint is required to anchor pavers in applications subject to vehicular traffic.

 

UNIT PAVING

 

• Unit paving assemblies are used principally for applications such as shopping plazas, building entrances, walkways, patios, residential driveways, and residential parking areas. 
• But they may also be used for streets with heavy vehicular traffic and for industrial floors or other special conditions.
• There are several types of unit pavers:
• Precast Concrete Unit Pavers
• Brick Unit Pavers
• Wood Pavers
• Recycled-Rubber Pavers
• Stone Pavers
• Porous Unit Pavers

 

PEDESTRIAN AND LIGHT-TRAFFIC BRICK PAVERS

 

• Because of its more vulnerable exposure, and the constant stress or traffic, even light-traffic brick pavers must maintain higher compressive strength and lower porosity than face brick.
• ASTM C 902, “Standard Specification for Pedestrian and Light Traffic Paving Brick,” establishes the criteria for pedestrian and light-traffic brick pavers.
• Light-traffic refers to frequency or pavements that receive limited vehicular traffic at low speeds,  such as driveways and arrival courts (light does not refer to the weight of a vehicle).
• An arrival court may normally receive automobile traffic, but the occasional moving van will not damage an ASTM C 902 paver. 
• The classification of light-traffic brick pavers is dependent on its intended application and use.
• There are three weathering classes of pavers and three types of pavers, based on anticipated traffic and the required levels of resistance to abrasion by traffic.
• Classes:
• Class SX (severe exposure) should be specified where pavements may encounter freezing while saturated with water.  In contract to face brick, class SX pavers must have a minimum average compressive strength of 8000 psi.  An individual unit may not have strength below 7000 psi.
• Class MX (moderate exposure) may be called for in southern climates where freezing is not expected.
• Class NX (negligible exposure) is for interior use only.
• Types:
• Type I bricks are recommended where highly abrasive traffic is anticipated, such as in driveways or heavily concentrated pedestrian zones.
• Type II bricks are best suited for typical pedestrian environments such as public walkways.
• Type III bricks offer the least resistance to abrasion and should be used in low-traffic residential applications.

 

HEAVY VEHICULAR PAVING BRICK

 

• Where vehicular traffic is greater in speed, volume, and weight, a stronger brick is naturally required.
• Brick in heavy-traffic situations not only must tolerate the added structural load, but is also subjected to greater abrasion and the tendency for both horizontal and twisting forces.
• ASTM C 1972, “Standard Specification for Heavy Vehicular Paving Brick,” establishes the standard. 
• ASTM list two types and three application classifications for heavy vehicular paving brick.
• Types:
• Type R is intended for situations where a rigid or semirigid setting bed and base are provided (such as concrete or asphalt).  With Type R pavers, the minimum average compressive strength is set at 8,000 psi, with the rigid setting bed and base contributing to the overall compressive strength of the cross section.  Type R pavers carry a minimum thickness dimension of 2.25”.
• Type F brick is stronger and better suited for use with a flexible base (such as compacted aggregate), along with an adequately compacted subgrade.  Type F pavers are required to have a higher overall compressive strength than Type R pavers, with a minimum average of 10,000 psi.  Type F pavers must have a thickness of no less than 2-5/8”.
• Applications:
• Application PS refers to heavy paving brick for general, all-purpose use.  Where there is a greater concern for overall uniformity, including precision in dimension, degree of warping, and chipping, application PX should be specified.
• Application PA deals with paving bricks with specific visual characteristics, such as size and color.
• Consult with a landscape architect or engineer for appropriate design guidelines.

 

PAVER SELECTION

 

• Paver units are selected according to color, texture, abrasion resistance, and resistance to weathering.
• The texture of the unit affects slip resistance (the coarser the texture, the better the slip resistance).
• Abrasion resistance refers to the wear and tear an assembly is subjected to under normal use.
• According to ASTM C 902 (brick pavers) and ASTM C 936 (concrete pavers), an abrasion index classification determines the type of unit required for an intended exposure.
• A dense, hard-burned extruded brick with 8000 psi compressive strength that conforms to ASTM C 902, Class SX, Type 1 (water absorption of less than 5%, meets/exceeds ASTM C 67 freeze/thaw) resists both abrasion and weathering and is adequate for most heavy-traffic exterior applications.
• Molded brick with 4000 psi compressive strength that conforms to ASTM C 902, Class SX, Type 2, and may be adequate for most exterior pedestrian applications only.
• Some manufacturers recommend 8000 psi pavers for both vehicular and pedestrian applications.  
• Consult the manufacturer to learn which products are suitable for use as pavers in a particular application.
• For all light or heavy vehicular traffic applications, 3.125” paver thickness is recommended; 2.375” thickness is recommended for pedestrian applications. 
• Assess potential traffic loads when planning unit-paving installations.
• Heavy vehicular loads require a rigid or semi-rigid continuous base, whereas a flexible base and flexible paving are suitable for light vehicular loads (residential type).
• Use either base type for pedestrian traffic.
• Appropriate base courses for heavy traffic would include asphalt over roadbase (Class 6), concrete over Class 6 roadbase, and just Class 6 roadbase.
• When using only roadbase under heavy loads, it should be at least twice as thick as the recommended 6-in. roadbase for pedestrian traffic.
• Choose a bond pattern based on expected traffic patterns – traffic should travel perpendicular to the long dimension of the paving unit.
• For vehicular areas, use a gravel subbase (minimum 6 in. of crushed gravel) compacted to 95%, and paver sizes 8 in. square or smaller.
• Consult a civil engineer to accurately define paver sizes, shapes, gravel depth, concrete base depth, and concrete reinforcement requirements.

 

PAVER PREPARATION

 

• Proper subgrade preparation of areas to be paved is important.
• Here are relevant guidelines:
• Remove all vegetation and organic materials, and consider the location of existing or proposed underground utilities and storm drainage, as well as user convenience.
• Plan for surface and subsurface drainage.  Slope paving away from buildings, retaining walls, and so on, at .125” to .25” per foot.  Rigid paving always requires adequate surface drainage, with the long dimension of the mortar joints running parallel to the direction of runoff.  Flexible paving requires both surface and subsurface drainage.
• Prevent horizontal movement of all types of mortarless unit paver assemblies – this is imperative.  If the pavers are on an aggregate base, provide a rigid plastic edge restraint using spikes driven into the stone base designed for this purpose.  A flush concrete curb works as well.  If the paving system is over a concrete base, regardless of the setting bed (sand or bituminous), the pavers along the edge can be mortared to the base, but take care to ensure this method does not trap water which will seep into the setting bed.  Another method is to secure an angle iron to the concrete base with anchor bolts, allowing for gaps on a regular basis to permit seepage.  Cover vertical gaps with a small perforated metal sheet for bituminous setting beds, or filter fabric for sand beds, to prevent erosion.
• In addition, be aware that chamfers on both clay and concrete pavers are required for heavy driving applications (e.g., public streets and parking lots).
• Chamfered edges avoid the splintering of edges that can occur.
• There are three major types of unit paver joint material:
• Mortar
• Grout (Portland cement and sand without hydrated lime)
• Dry mixture of grout