## For Architects

### What is the maximum slope for concrete pavers?

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. For vehicular traffic, the highest slope in use is 18% (about 10 degrees) in a street in Colman, 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.

### How are crosswalks designed?

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.

### What is the AASHTO structural number of pavers?

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. For more information on structural numbers, see the AASHTO guide for design of pavement structures.

### How is base thickness determined?

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.

### How well do interlocking concrete pavements perform over the long term?

One of the best performance examples for streets and sidewalks is found in North Bay, Ontario – 20 Years Later.  Download an ICPI case study titled “North Bay”

### Are pavers effective for “Traffic Calming”?

Yes,  Pavers are very effective in calming traffic and are a solution for cities and HOA’s to calm traffic on streets or intersections that have a problem with speeding vehicles.  Please review the ICPI article titled “Traffic Calming”.  There is a picture of a “paver speed bump/plateau” under “commercial projects”.  This was install in and HOA community that had problems with speeding vehicles.  This installation greatly reduced the speed of vehicles and also adding a facelift to the intersections in terms of aesthetics and beauty.

### What are the Advantages of Pavers vs. Concrete?

In short there are many advantages.  Here are a few.  First,  Pavers are rated at a minumum of 8000 psi and the Belgard pavers are rated at 9000 psi.  This is about 4 times stronger than concrete.  A typical sidewalk is only 2500 psi.  Second,  Pavers have a very low fade rate.  This means that pavers will maintain their color.  Whereas,  concrete will fade and discolor which results in a “bleached” artificial look.  Third,  Pavers are much less of a maintenance issue.  If you have a stained paver section or a root upheaving from below, one can simply remove the pavers and fix the problem below the surface and replace the pavers.. You cannot do this with concrete.  Lastly,  pavers do not crack.  The reason is because pavers have “joints”and are installed in pieces.  On the other hand,  Concrete will always crack and dis-color.

### Is Geo-Textile Fabric needed on commercial projects?

No,  It all depends on the Soils Report and or the engineer on the project.  In many cases we add Geo-Tex as an extra assurance.  Geo-Textile fabric is designed to stop the sub-grade from mixing with the Base.  This will add extra strength and integrity to your pavement/pavers and insure “flatness” for a longer period up to 25 years.  I recommend the use of Geo-Tex on most commercial projects.  By using Geo-Tex you can also reduce the amount of base needed while still maintaining a high strength of 8000 to 9000 psi.

Yes,  Pavers are ADA compliant.  The paver style that is used is the “non-tumbled” paver or “flat top” paver.  This style of paver has a smooth surface with a non-slip surface.  All major paver manufacturers carry this style.

### Are there Paver Truncated domes that are ADA compliant?

Yes, there is a paver truncated dome that is 12″x 12″ in size and is perfectly suitable for any ADA walkway or ramp.  These pavers also come in 3 to 4 colors from Ackerstone Industries. Ackerstone also carries a “Handicap Paver Kit” that can be installed instead of using stencil paint. This adds to greater aesthetics and overall a nicer look on any project or HOA parking lot.

## For Homeowners

### How do I remove stains and fix damaged pavers?

If the stain is one or two pavers, replacing them with new pavers is the easiest way. Depending on the paver, some can be flipped over rather than replaced. Many suppliers of concrete pavers offer cleaners especially made for removing stains and for overall cleaning of the surface.

### Are there disadvantages to sealing?

Since they are a transparent paint-like coating, sealers generally need to be reapplied every three to five years. Use sealers specifically for concrete pavers. More intense use of the pavers and extrement climates often increase the need for re-applying a coat of sealer.

### Should I seal concrete pavers?

Sealing is not essential in many applications but it offers some benefits like making spills and stains easier to remove. Liquid sealers are applied after the pavers are installed and are cleaned. Paver suppliers can recommend cleaners for concrete pavers. Once applied, the sealers soak into the concrete and into the joints. The sealers in the joints help keep the joint sand in place and prevent weeds and ants, and sealers are essential for areas around swimming pools.

### What is interlock?

In short, tt’s the inability of a paver to move independently of its neighbors.  It’s the locking of the pavers that causes loads to be spread over a wider area of pavers than  where the load was applied. It’s the key to the strength of the pavement system.

### Should limestone screenings or stone dust be used under the concrete pavers? What is recommended by ICPI?

No. Most screenings and stone dust have too many fine particles that slow drainage and rut under repeated loads from tires. Sand made with crushed shells (common in Florida) shouldn’t be used either. Concrete sand is recommended. It’s the same sand mixed into concrete pavers and poured, cast-in-place concrete.

### Is it okay to use fabric designed to prevent weed growth in planting beds instead of geotextile?

No, this material is sometimes not as strong as geotextile and can tear easily.

### What is geotextile? What does it do? Is it necessary?

Sometimes called filter fabric, geotextile is made of plastic threads that allow water to pass around them, but not very small particles of soil beneath them. Geotextile separates and contains the base from the underlying soil subgrade. It allows the base to shed water, and prevents the soil around it from working its way into the base.

Without geotextile, the soil will work its way into the base and weaken it. This is a slow process that happens when the soil is saturated with water or during periods of thawing. Geotextile stops this process and extends the life of the base by many years. Geotextile is recommended for use over silt and clay soils. It is not essential in sandy soils.

### What is the base made of? What kind should be used?

The base is typically made of compacted, crushed stone that varies in size from one inch (25 mm) down to dust. Base materials used under asphalt street pavements are acceptable for use with interlocking concrete pavements. Some parts of the country use cement stabilized or concrete bases due to very weak or slow draining soils. However, most applications use a crushed stone base that’s compacted.

### What are the components of an interlocking concrete pavement?

The components include a base, bedding sand, concrete pavers with sand in their joints, and an edge restraint to contain the pavers at the perimeter.