FAQ for Designers
- What is the maximum slope for concrete pavers?
- How are crosswalks designed?
- What is the AASHTO structural number of pavers?
- How is base thickness determined?
- How well do interlocking concrete pavements perform over the long term?
For non-vehicular uses such as embankment stabilization, the maximum slope is determined by the angle of repose of the bedding sand, typically around 35 to 38 degrees, assuming the subgrade is stable at that angle. For vehicular traffic, the highest slope in use is 18% (about 10 degrees) in a street in Colma, California. Special consideration is given to the drainage of the bedding sand at the bottom of the slope. Contact ICPI for details and guidance. Intermittent concrete header beams are generally not required.
Concrete headers typically used in paver crosswalks perform like bridge abutments. The pavement on aggregate base located on both sides of the header (in and outside the crosswalk) will deform at the junction of flexible pavement and rigid concrete. Why? Because there's no interlock between the aggregate base and the adjacent concrete. For that reason, most crosswalks should be placed on a concrete base with concrete headers separating the pavers from the adjacent pavement (typically asphalt). The base on the immediate sides of the concrete base should be stabilized with cement to provide additional stiffness and reduce the likelihood of deformation at its junction with the concrete headers. The concrete base under the pavers should have drain holes, typically 25 to 50 mm diameter. They should be at the lowest elevations and covered with geotextile to prevent loss of bedding sand. For more information, read ICPI Tech Spec 20 on crosswalks.
Paver and bedding sand are considered as a single layer whose structural number is 0.44 per inch or 1.82 for 80 mm thick pavers and 25 mm of bedding sand. This structural contribution is equivalent to the same thickness of asphalt but is not weakened by hot temperatures. For more information on structural numbers, see ICPI Tech Spec 4 on Structural Design of Interlocking Concrete Pavements.
ICPI follows the design methods for flexible pavement in AASHTO Guide for Design of Pavement Structures. There is a structural equivalency between asphalt and concrete paver/sand layer. ICPI Tech Spec 4 offers design guidance that follows this design procedure.
One of the best performance examples for streets and sidewalks is found in North Bay, Ontario - 20 Years Later. Actually, the pavement has been in service for over 30 years while surviving cold winters with deicing salts and large snow plows.