Masonry Magazine December 1992 Page. 26
brick paving surface.
However, the brick paving surface does, in fact, contribute to the load-carrying capabilities of the pavement and may be considered in design if it is of sufficient thickness and constructed properly. In order for the brick pavers to be considered when calculating thickness, they must be compacted into place as described in Technical Notes 14A and the Flexible Brick Pavements design guide. If brick pavers are not compacted into place, they should be neglected in the pavement thickness design but still must meet certain minimum thicknesses to act as a wearing surface. These suggested minimum thicknesses for mortarless brick paving are: light traffic, 1½ in. (38 mm); medium traffic, 2¼ in. (57 mm); and heavy traffic, 2-5/8 in. (67 mm). In order for the brick pavers to be considered in resisting load they must have a 2-5/8 in. (67 mm) minimum thickness, excluding chamfers, to achieve interlock. Interlock is the effect of frictional forces, induced by sand beneath and between the brick pavers, which restricts movement of the paver and transfers loads between adjacent pavers. In the case of heavy traffic, the brick pavers and sand setting bed are compacted into place and contribute to the load-carrying capabilities of the system.
A mortared brick paving surface should always be supported by a rigid base or suspended diaphragm. Without a rigid support, the paving system will deflect and cause cracking in the brick paving surface. The primary resistance to vertical loading is developed by the flexural strength of the concrete slab on grade or the roof or floor diaphragm. There is no minimum thickness for the paving unit to adequately transfer vertical loads. The required thickness to perform adequately as a result of horizontal loads and pavement deflection is in the range of 1/2 in. (13 mm) to 2¼ in. (57 mm) depending on traffic conditions and slab support. Thicker pavers are more likely to stay in place in the event of cracking.
Horizontal Loads.
In addition to vertical loads, vehicular traffic imparts horizontal forces to the paving assembly from braking, acceleration and turning actions of the wheels. Resistance to horizontal forces is provided by the bond pattern of the brick paving assembly, the pavement edging and the bond of the brick units to the base.
Mortarless brick paving resists horizontal forces by transferring these forces through brick units and sand filled joints to rigid edging by means of an interlocking bond pattern. The greatest resistance to horizontal forces is obtained when the direction of vehicular traffic flow is perpendicular to the long joints in the bond pattern. Therefore, continuous joints in running bond and other bond patterns should be laid perpendicular to the traffic flow. The herringbone bond pattern resists loads in all directions and should be used in heavy vehicular areas.
Mortared brick paving resists horizontal forces imparted by vehicles due to the bonding of the units to the base by the mortar setting bed and full head joints. Thus, bond pattern and unit orientation are not critical for load transfer in mortared paving.
Drainage
Adequate drainage of flexible and rigid paving systems is an extremely important design consideration for successful performance and durability. Ponding water can cause deterioration of the paving in areas of repeated freeze/thaw and cause slippery conditions. Continued saturation of the base, subbase and subgrade can reduce load capacity due to weakening of the soil and cause deformations or rutting of the pavement.
The best way to obtain drainage of the pavement is to slope the paving surface to provide as much surface drainage as possible. A slope of 1/8 in. to 1/4 in. per ft (1 to 2 mm per 100 mm) is suggested. Large paved areas and vehicular traffic areas may require a slope greater than 1/4 in. per ft (2 mm per 100 mm). The paving system should be sloped away from buildings, retaining walls and other elements capable of collecting or restricting surface runoff. To improve surface drainage, the direction of continuous mortar joints should run parallel to the desired direction of surface runoff.
Mortarless paving requires both surface and subsurface drainage. The majority of drainage should occur on the surface. However, some water will penetrate downward until it reaches an impervious layer. This layer may be a concrete or asphalt base, a flexible base compacted to high density, an impervious soil such as clay or an impervious membrane used to separate pavement layers. Water not drained off the pavement surface will percolate to the top of this impervious layer, possibly causing ponding of the water. Due to these conditions, subsurface drainage is required.
Mortarless brick paving constructed over a porous base such as gravel may permit drainage through the entire system to the subgrade. The use of a geotextile between the sand setting bed and the base will permit drainage without allowing migration of the sand setting bed into the base.
Drainage in mortared brick paving systems is restricted to the surface by full mortar joints and good bond between the brick paving units and the mortar. A drainage system should be designed so standing water is kept to a minimum. Surface runoff is removed by pavement edge drainage or by drains within the paving. Drains and drainage systems must be designed to remove the anticipated amount of water. The amount of drainage required varies with the size and location of the pavement and the amount of annual rainfall. Most commercial paving applications require gutters, scuppers or surface grates for surface drainage. In subsurface drainage applications, drains should have slotted openings on all sides below the paving surface. Setting bed material should be protected from washout into the drains by the use of screens or geotextiles.
To prevent water from ponding against curbs, weepholes should be installed through the curb at a maximum spacing of 24 in. (600 mm) o.c. along the entire edge. The weepholes should be formed by tubes or pipes with sufficient size to allow water drainage. Curb gutters can also be used when the gutter is sloped toward a drain. Figures 7 and 8 are examples of drainage in flexible and rigid base paving systems.