Pedestrian areas and residential driveways can achieve interlock with 2 3/8-inch thick pavers. Vehicular pavements require 3 1/8-inch thick pavers.
Thicker pavers are needed to resist greater force from braking and accelerating tires. Paver dimensions require special consideration in selection. Interlock decreases as the unit size increases and this suggest that larger paving units should be kept out of vehicular traffic. A useful rule is a length divided by width, sometimes called aspect ratio.
When it exceeds 4, the units generally aren’t suited for constant vehicular traffic. When the aspect ratio is between three and four, pavers can be used in areas with limited vehicular use such as residential driveways. A 4 x 8 x 2 3/8-inch or a 6 x 12 x 3 1/8-inch paver falls into this range and is suited for residential driveways.
Pavers with an aspect ratio of thre or less can be used in any vehicular application.
For residential driveways, one consideration that contributes to long-term support is the laying pattern. There should be a discontinuity in the bond line pattern. This is the reason why the industry recommends herringbone patterns because no joint is longer than one and a half pavers.
Popular random patterns have entered the market with similar bond line breaks. These patterns can be used in residential driveways because they can help resist repeated forces from wheel loads.
Larger units (often 12×12 inch and larger) are called paving slabs. ICPI recommends using units at least 3 1/8-inches thick for driveways. It is a good idea to limit the amount to well under half of the- area. Keeping the larger slab units out of expected driveway wheel tracks will also help maintain a stable surface.
If running bond patterns are used in a residential driveway, bond lines should run perpendicular to the wheel travel direction (see Figure 1).
Figure 2 shows a herringbone pattern used in a residential driveway and it illustrates the discontinuity of joint lines. With units having a length to thickness ratio of less than 4, herringbone offers the strongest interlocking patterns compared to others.
With well-compacted crushed stone road base material placed under an inch of bedding sand, and of course jointing sand between the pavers, herringbone patterns offer the highest load-spreading capability compared to other patterns.
For more construction best practices, please see Technical Resources at www.icpi.org.