| MasterSpec - EVALUATIONS | 08/03 (R 05/05) |
The following editing instruction relates directly to specific parts of the Section Text where it is referenced by the applicable Editing Instruction No. in the editor's notes:
This is a brief review of the characteristics of various unit paver products and setting methods. The primary considerations in selecting a unit paver system are cost, appearance, and the paver system's ability to endure expected traffic exposure and weather. All the pavers included in the Section Text are suitable for light-duty applications; for heavy-duty applications, suitable pavers are heavy vehicular paving brick, concrete pavers of suitable thickness, asphalt-block pavers, and rough-stone pavers. Concrete pavers and aggregate setting beds are the least expensive materials and methods in the Section Text; stone pavers and mortar setting beds are the most expensive. The articles in these Evaluations that describe paver types and setting-bed methods provide more information on the advantages and disadvantages of each.
The two available types of brick pavers are light-traffic paving brick and heavy vehicular paving brick. These are covered by ASTM C 902 and ASTM C 1272, respectively.
Light-traffic paving brick generally supports pedestrian and light vehicular traffic in applications such as patios, walkways, floors, plazas, and driveways. In ASTM C 902, brick is classified into three weather classes, three traffic types, and three categories related to tolerances that are referred to as applications. Weather classes and traffic types are distinguished from one another by physical requirements that relate to performance under various weather and traffic exposures. The three applications are determined by dimensional tolerances, chippage, and warpage because these qualities affect installation with different joint treatments and patterns. These classifications, which are also explained by editor's notes in the Section Text, and their applicability to various uses are summarized below.
Heavy vehicular paving brick is used in pavements subjected to a high volume of heavy vehicles, which is defined as numerous passes of daily truck traffic. Pavements subjected to a high volume of heavy vehicles include city streets, industrial pavements, and other heavily traveled roads. In ASTM C 1272, brick is classified into two types and three applications. The two types are classified according to their intended installation: sand set (Type F), or set in asphalt or mortar (Type R). The three applications are determined by dimensional tolerances, chippage, and warpage, as in ASTM C 902. Note that Type F units must meet Application PX.
Weather: For pedestrian and light-traffic paving brick, weather resistance is evaluated according to physical properties, such as compressive strength, cold-water absorption, and saturation coefficient, or according to an alternative freezing and thawing test. For heavy vehicular paving brick, there is effectively only one weather class because general requirements for this type of paving brick are at least as restrictive as requirements for Class SX pedestrian and light-traffic paving brick.
Traffic performance of pedestrian and light-traffic paving brick is evaluated by either abrasion index or volume abrasion loss. Abrasion index is calculated by dividing the brick's cold-water absorption value by its compressive strength and then multiplying that by 100. Volume abrasion loss is determined by testing according to a modified version of ASTM C 418, which measures abrasion resistance to sand blasting.
Three applications are as follows:
No slip-resistance requirement is included in ASTM C 902, but a note is provided indicating that this property should be considered when selecting brick and that any future editions of the standard may include a suitable requirement. The standard for heavy vehicular paving brick does not mention slip resistance.
Concrete pavers specified in the Section Text include small, "hand-size," solid units of high compressive strength (8000 psi [55 MPa]) that are formed to somewhat precise dimensional tolerances. They are produced by hydraulically pressing very low slump concrete into precision metal molds, are available in several thicknesses and a variety of proprietary shapes, and are designed to interlock vertically and horizontally to prevent displacement under vehicular traffic loads. ASTM C 936 limits the exposed face area of concrete pavers to not more than 101 sq. in. (0.065 sq. m) and requires that the length be not more than 4 times the thickness in order to provide an interlocking effect. Dimensional tolerances in ASTM C 936 are 1/16 inch (1.6 mm) for face dimensions and 1/8 inch (3.2 mm) for thickness. For units that are modified to produce special finishes, such as tumbled units, tolerances apply to units before applying a finish. According to National Concrete Masonry Association (NCMA) literature, concrete pavers should not be used for applications where speeds are likely to exceed 40 mph (64 km/h).
The Section Text also includes requirements suitable for larger units, lower-strength units, and custom-designed units. Pavers specified by using these alternative requirements instead of by referencing ASTM C 936 should generally be used only for pedestrian traffic. As a general rule, it is more difficult to provide uniform support for larger units, which limits their load-carrying ability. Also, custom-designed units will not generally be as strong as standard units because they cannot be economically produced using hydraulically pressed low-slump concrete. If larger units made from high-strength concrete are installed in a mortar setting bed, with full contact, over a properly designed concrete slab, they can withstand light vehicular traffic, but it is best to use smaller units complying with ASTM C 936 if they will be subject to vehicular traffic.
Most of the concrete pavers produced to comply with ASTM C 936 are made to be installed on an aggregate setting bed with tight sand-filled joints, but some are now being produced for setting in a mortar bed with grouted joints. For some shapes, the unit dimensions readily reveal the intended joint width, which indicates the intended setting method: joint widths of 1/8 inch (3 mm) or less indicate sand-filled joints; joint widths of 3/8 to 1/2 inch (10 to 13 mm) indicate grouted joints. For other shapes, the joint width can be varied to suit the setting method. Large units, lower-strength units, units that are thin in relation to their width and length, and custom-designed units are generally best installed in a mortar setting bed over a concrete slab; they are also generally best installed with grouted joints because they are not made to the tight tolerances that the hydraulically pressed units are.
Asphalt-block pavers are units made from asphalt cement, crushed-stone aggregate, and inorganic dust or filler, which are compacted under hydraulic pressure. They are available in many shapes, sizes, thicknesses, colors, and finish textures. They are generally much smoother than concrete pavers and most brick pavers and are made to precise tolerances. Asphalt blocks are also available with a ground or ground and sandblasted finish that improves their slip resistance. They are more resilient than other pavers, which makes them more suitable than other pavers for locations where they might be subject to steel-wheeled, fork-lift-truck traffic.
Rough-stone pavers, often called cobblestones, are the oldest and perhaps most durable unit pavers in general use. They are split to size from granite, in roughly rectangular shapes, and may be tumbled after splitting to give them a worn appearance. Because of their variation in size and the irregular surfaces produced by splitting them, these pavers are generally laid in mortar with medium to wide joints.
Two types of rough-stone pavers included in the Section Text are small square blocks, which are usually called durax blocks ; and larger, more elongated blocks, which are more varied in size and are often called Belgium blocks. Durax blocks can be laid in a rectilinear grid pattern or in the traditional Roman semicircular pattern, which helps minimize the formation of ruts by avoiding rows of stones running in the direction of wheel tracks. Belgium blocks are usually laid in a running bond perpendicular to traffic, but are also laid as wheel ways in running bond parallel with traffic with an infill of durax blocks. Other patterns can easily be created with the different sizes and joint widths characteristic of rough-stone pavers.
There are two methods of producing rough-stone pavers . The first method involves producing thick rough slabs from granite quarry blocks by splitting along the rift (splitting the stone along a plane where it has a natural tendency to split), using wedges and feathers (thin strips of steel) in drilled holes. The thick slabs are split into strips and then blocks using machines that have hard metal teeth that clamp down on the stone under the pressure of hydraulic cylinders and split the stone in the same fashion that tile nippers break ceramic tile. The second method begins with sawed slabs that are the thickness of the final pavers. The slabs are split into strips and then blocks using machines with hydraulically driven hard metal teeth. After splitting, the pavers made from sawed slabs are given a thermal finish to roughen the sawed face or are tumbled to roughen the face and edges. Pavers made by the first method are generally approximately 4 inches (100 mm) thick; pavers made by the second method are typically 1-1/4 to 3 inches (30 to 75 mm) thick. Pavers made by the second method have flatter faces and, therefore, provide a flatter paved surface, which is better for wheelchair access.
Pavements are described as rigid or flexible, and the substrates on which pavers are set may be similarly described, although the Brick Industry Association (BIA) calls an asphalt base semirigid. Cast-in-place concrete paving is classified as a rigid base. Asphalt courses and aggregate courses are classified as flexible bases.
A rigid base is required for pavers set with grouted joints, in order to prevent the joints from cracking; however, for other applications, the choice of base material is not governed by the rigid versus flexible classification. Pavers set in asphalt cement require either a concrete base with an asphalt leveling course or an asphalt base. Pavers set on an aggregate base generally provide the most economical installation. If the subsoil is not strong enough to support the required traffic loads for pavers set over a typical aggregate base, either the aggregate base must be thickened or an asphalt or concrete base must be used instead to spread the load over a larger area and thereby provide a stable foundation for the pavers. If the required thickness for an aggregate base becomes excessive, it may be more economical to use an asphalt base instead. The Project's geotechnical report may give recommendations for paver base materials if other conditions, such as existing construction, municipal regulations, etc., do not require a particular construction.
Besides being generally less expensive than other systems included in this Section, aggregate setting-bed applications have some other advantages. The absence of grouted joints means that deicing salts will not generally cause damage, unless the aggregate setting bed is placed over a reinforced concrete slab. Unit pavers can be replaced or reset if damaged or disturbed, and repairs to utilities or waterproofing beneath paving are simplified. The open joints also allow some air and water to penetrate to the soil under the pavers, which is desirable where tree roots extend under paving.
BIA Technical Notes, listed in the "References" Article in these Evaluations, describe several choices for leveling beds and aggregate bases. NCMA publications listed also have recommendations for these materials. To some degree, the selection of aggregate materials must depend on local availability of materials. In localities where crushed stone is readily available, it is generally the preferred material. In localities where natural aggregates are abundant, crushed stone is generally not used as a base for pavements; in areas where crushed stone must be brought in from great distances, local natural materials are often used even if they are not ideal.
Aggregate bases range from crusher-run stone to bank-run gravel to washed gravel. Crusher-run stone is the unscreened product of a stone crusher, and bank-run gravel is gravel as it is found in natural deposits, which generally contains some sand and clay. Although these products compact well, have good stability, and are less expensive than washed gravel or washed crushed stone, they do not drain as well as washed materials and could cause efflorescence if stone dust in them contains water-soluble salts. Washed gravel or stone should generally be well graded, that is it should contain a full range of sizes, so it will have good stability, and the bedding sand will not wash down into it. The requirements included in the Section Text are examples only and should be revised to suit local availability and traffic, drainage, and climatic conditions that exist at the Project.
Leveling beds, or cushion materials as they are sometimes called, are usually sand or stone screenings. Stone screenings are the residue produced when crushed stone is graded for use as concrete aggregate or other applications where the fine particles must be removed. Stone screenings made from soft rock, such as limestone, are not recommended because they generally contain too much fine material and tend to break down further over time, producing even more fine material. Stone screenings made from hard, durable rock are acceptable if they meet the gradation requirements specified. Some stone screenings are also called stone dust, and they do not meet gradation requirements because they contain excessive fine material that interferes with proper drainage. Stone dust is often recommended by contractors because it compacts well and provides a stable leveling bed as long as it is kept relatively dry. Stone screenings meeting the gradation requirements of ASTM C 448, Size No. 10, may be suitable for light-duty applications if adequate surface and subsoil drainage is provided to ensure that the leveling course cannot become saturated, or if the Project is located in an area not subject to saturating rains. Stone dust may also provide a suitable leveling base for light-duty applications in similar circumstances, but additional care must be exercised to prevent it from becoming saturated because it does not drain as well.
Geotextiles for use with brick and concrete pavers in aggregate setting-bed applications are an area not well covered in paver trade association literature. According to NCMA and certain unit paver manufacturers and installers, seek the advice of a soil engineer or other qualified person before specifying separator fabrics. Subsoil quality, gradation characteristics of base and leveling course, and traffic loading determine the need for adding this material.
The American Association of State Highway and Transportation Officials (AASHTO) has classified geotextiles by general application. AASHTO M 288 recognizes these applications as subsurface drainage, separation, stabilization, erosion control, temporary silt fencing, and paving. Properties such as permittivity, apparent opening size, and UV-light degradation are listed for each application. Manufacturers are increasingly classifying geotextiles for these uses according to AASHTO M 288.
Separation geotextiles may be used to prevent subgrade soils mixing with overlaid aggregate courses such as subbase and base courses in pavements. Separation of dissimilar materials is the primary function, with filtration a minor function.
Subsurface drainage geotextiles allow for long-term passage of water into a subsurface drain while preventing the migration of surrounding fine-soil particles. Filtration of water is the primary function; however, subsurface drainage geotextiles may also be used to prevent leveling-bed materials from washing into aggregate-base materials.
Bituminous setting-bed applications are characterized as impervious systems because they do not allow water to penetrate the setting bed. Because of this, they are considerably less vulnerable to deterioration due to freezing than are pavers set in mortar setting beds. This application method produces either a flexible pavement, when set over an asphalt base, or a rigid pavement, when set over a concrete base. With this method, ensure that the neoprene-modified asphalt adhesive is not applied too thickly because it may work its way to the surface in hot weather. When specifying portland cement concrete as a base for bituminous setting-bed applications, do not allow the use of curing compounds that prevent the asphalt from bonding to the concrete.
Setting pavers in a mortar bed with grouted joints produces a rigid pavement that is relatively impervious to water. Because this application method produces an inflexible pavement, a rigid base is required under it to prevent cracking. Usually that base is a reinforced-concrete slab placed on a compacted aggregate subbase, both of which are specified in other Sections. Latex additives are often used in the mortar mix so it will adhere better to the base slab and to the pavers. Polymer additives are also added to the grout mix to increase freeze-thaw resistance by making the grout more impervious to water.
Liquid-latex additives are recommended for thickset mortar-bed applications, although the nationally recognized standards for latex additives and latex mortar are specifically for thin-set applications. Types of additives vary among manufacturers. For a lengthier discussion of the characteristics of acrylic and styrene-butadiene-rubber (SBR) additives included in the Section Text, refer to the Evaluations in Division 09 Section "Tiling." For thickset mortar beds, it is generally not advisable to use latex additives with a separate retarder or with other materials that include a retarder. Latex additives enhance water retention, for better cement hydration, which retards curing. Using a retarder with a latex additive can result in overlong curing times. It is also not advisable to use curing compounds on concrete slabs that are to receive pavers set in mortar because the curing compound may interfere with mortar adhesion.
Polymer-modified portland cement grout consists of either a prepackaged, dry grout mix that contains the dry polymer additive ethylene vinyl acetate; or a latex additive (emulsion), which is combined with portland cement and sand or with a prepackaged dry grout mix. Colorfast pigments can be included in the prepackaged products or added separately. Products are available with the pigments blended into the liquid latex, which generally results in better mixing and discourages the Installer from watering down the liquid latex. Better color consistency is generally achieved with factory-blended products. For a discussion of pigments, refer to the Evaluations in Division 04 Section "Unit Masonry." Of the two water-emulsion types included in the Section Text, the acrylic-resin products are generally considered superior to SBR in both color retention and low water absorption.
Traffic loadings are generally the first design consideration. Heavy vehicular loadings on grade may require rigid base diaphragms or semirigid continuous bases; however, flexible bases can often be used. Light vehicular traffic, such as in residential or commercial driveways and parking lots, may be supported on flexible bases and flexible paving. Pedestrian traffic can be accommodated over any assemblies.
Subgrade preparation is also important for a successful installation. Vegetation and organic materials should be removed from the area to be paved. Soft spots containing poor subgrade material should be removed and refilled with suitable material properly compacted. Refer to the Project's geotechnical report for specific compaction requirements.
Drainage: Surface and subsurface drainage is of major importance. Generally, exterior paving should be sloped at least 1/4 inch per foot (1:50), except that smooth pavers set hand tight in a bituminous setting bed may be sloped as little as 1/8 inch per foot (1:100). Paving should be sloped away from buildings, retaining walls, and other elements capable of collecting surface water. In areas with high water tables, a porous base and cushion material of gravel may be used. Localities with impervious soils, capable of surface-water retention, may require subsurface drainage systems. Drainage grates (area drains) should be of the two-stage type that have weep holes in the sides of the drain body to drain water from the aggregate base in addition to a grate on top that provides surface drainage. It is also good to specify adjustable height drains that can be readjusted if pavers settle; drains that are adjusted by means of set screws must be dug up to be readjusted, but drains that screw together can be readjusted from above without digging them up (unless they are cast into concrete).
Edge Restraints: To prevent horizontal movement of units in bituminous and aggregate setting-bed applications, a method of containment must be provided around the entire perimeter of the paved area. This containment may be curbs or walls constructed of unit masonry, stone, or concrete, or edge restraints in the form of metal edgings or plastic or aluminum extrusions anchored to the ground with stakes. For a more detailed discussion of edge restraints, see NCMA TEK 11-1, listed in the "References" Article.
Expansion Joints: Consider the potential for thermal and moisture movement, and provide expansion joints to accommodate this movement. A single, specific spacing or expansion-joint size is not feasible for all types of installation. BIA recommends expansion joints at intervals of not more than 16 feet (5 m) for pavers set in mortar, and note that the pavers and the concrete base do not have the same expansion characteristics. General recommendations for most paver applications include providing expansion joints adjacent to curbs, walls, and edgings; at 90-degree or right-angle turns; and around penetrations.
Publication dates represent the editions on which the current Section Text is based. Standards are revised periodically, which may occur before this Section is updated again.
The following publications are useful in specifying unit pavers. Other references may be needed for design purposes.
The list of manufacturers is neither a recommendation for the companies nor an endorsement of their products. Verify manufacturers' capability to comply with indicated requirements each time the Section Text is edited.
ASPHALT-BLOCK PAVERS Hanover Architectural Products, Inc. Hanover, PA (800) 426-4242; (717) 637-0500 ROUGH-STONE PAVERS Buechel Stone Corp. Chilton, WI (800) 236-4473; (920) 849-9361 www.buechelstone.com Cold Spring Granite Inc. Cold Spring, MN (800) 328-5040; (320) 685-3621 www.coldspringgranite.com Fletcher Granite Company, Inc. North Chelmsford, MA (800) 253-8168; (978) 251-4031 www.fletchergranite.com Granicor, Inc. St. Augustin, QC CANADA (418) 878-3530 www.granicor.ca Milestone Imports, Inc. Santa Fe, NM (866) 641-1999; (505) 989-1999 www.milestoneimports.com New England Stone, LLC North Kingstown, RI (800) 232-2043; (401) 294-1200 www.nestone.com North Carolina Granite Corporation Mt. Airy, NC (800) 227-6242; (336) 786-5141 www.ncgranite.com PLASTIC EDGE RESTRAINTS BRICKSTOP Corporation Downsview, ON CANADA (800) 565-2599; (416) 739-0355 www.brickstopcorporation.com Dimex Corporation Marietta, OH (800) 334-3776; (740) 374-3100 www.dimexcorp.com PAVE TECH Inc. Prior Lake, MN (800) 728-3832; (952) 226-6400 www.pavetech.com J. T. Ryerson & Son, Inc. Chicago, IL (773) 762-2121 STEEL EDGE RESTRAINTS Border Concepts, Inc. Charlotte, NC (800) 845-3343; (704) 541-5509 www.borderconcepts.com Collier Metal Specialties, Inc. Garland, TX (800) 829-8225; (972) 494-1605 www.colmet.com J. D. Russell Company (The) Tuscon, AZ (800) 888-7425; (520) 742-6194 www.jdrussellco.com J. T. Ryerson & Son, Inc. Chicago, IL (773) 762-2121 Sure-loc Edging Corporation Holland, MI (800) 787-3562; (616) 392-3209 www.surelocedging.com ALUMINUM EDGE RESTRAINTS BRICKSTOP Corporation Downsview, ON CANADA (800) 565-2599; (416) 739-0355 www.brickstopcorporation.com Curv-Rite, Inc. Wayland, MI (800) 366-2878 www.curv-rite.com Permaloc Corporation Holland, MI (800) 356-9660; (616) 399-9600 www.permaloc.com Sure-loc Edging Corporation Holland, MI (800) 787-3562; (616) 392-3209 www.surelocedging.com PRECAST CONCRETE CURBS Hanover Architectural Products, Inc. Hanover, PA (800) 426-4242; (717) 637-0500 www.hanoverpavers.com STONE CURBS Cold Spring Granite Inc. Cold Spring, MN (800) 328-5040; (320) 685-3621 www.coldspringgranite.com Fletcher Granite Company, Inc. North Chelmsford, MA (800) 253-8168; (978) 251-4031 www.fletchergranite.com Granicor, Inc. St. Augustin, QC CANADA (418) 878-3530 www.granicor.ca New England Stone, LLC North Kingstown, RI (800) 232-2043; (401) 294-1200 www.nestone.com North Carolina Granite Corporation Mt. Airy, NC (800) 227-6242; (336) 786-5141 www.ncgranite.com Polycor Inc. Riviere a Pierre, QC CANADA (418) 323-2222 www.polycor.com Swenson Granite Co. Concord, NH (603) 225-4322 www.swensongranite.com LATEX ADDITIVES AND POLYMER-MODIFIED GROUTS Boiardi Products Corporation Little Falls, NJ (201) 256-1100 W. R. Bonsal Company Charlotte, NC (800) 738-1621; (704) 525-1621 www.bonsal.com Bostik Findley Inc. Middleton, MA (800) 523-6530 www.bostik.com C-Cure Seal Beach, CA (800) 895-2874; (281) 492-5100 www.c-cure.com Custom Building Products Seal Beach, CA (800) 272-8786; (562) 598-8808 www.custombuildingproducts.com DAP Inc. Baltimore, MD (800) 543-3840 www.dap.com Jamo Inc. Miami, FL (800) 826-6852; (305) 885-3444 www.jamoinc.com Laticrete International, Inc. Bethany, CT (800) 243-4788 ext. 235; (203) 393-0010 www.laticrete.com MAPEI Corp. West Chicago, IL (800) 992-6273; (630) 344-8000 www.mapei.com SGM Pompano Beach, FL (800) 641-9247; (954) 943-2288 www.sgm.cc Summitville Tiles, Inc. Summitville, OH (330) 223-1511 www.summitville.com TEC Incorporated H. B. Fuller Company Palatine, IL (800) 323-7407; (847) 358-9500 www.hbfuller.com