Concrete paver strength with auto weight

[zdesigner]

I am specifying a 24x24x4 concrete paver with 5000psi for school site courtyard and there is a CHANCE that a car might drive over. School management is concerned pavers will chip. There will be 4" sand bed, polymeric sand finish between pavers and coutyard sides will have a poured concrete edge. How can I prove a 2" thick paver will perform well, so I do not have to go to a 4"?
Thanks for any help.

 

[concretemasonry]

If you have a 24x24 unit, it is not the type unit that will take the heavy loads that a smaller traditional paver will. With that size unit, you will be facing cracking due to the inadequate base and the flexure that accompanies it.

The 4" sand bed could be excessive and be a problem since it could become saturated due to the concrete restraint if the base is not permeable. The polymeric sand is really just a temporary excess cost item.

A heavier duty paver than can be used for car traffic is 80 mm. A normal spec for interlocking concrete pavers is 8000 psi minimum (ASTM spec) and many are in the 10,000-12,000 psi. Interlocking pavers(usually less than 8 or 9" in any direction are much smaller than what you have specified. For heavier loads like roads, airport taxiways or ship unloading facilities, 100 mm is commonly used.

Look to the Interlocking Concrete Paving Institute (icpi.org for technical information).

Dick

 

[cvg]

all good information and in addition, many pavers that are installed in public right of way are placed on a concrete slab instead of sand.

 

[hokie66]

Spaced pavers are fine for pedestrian courtyards, but there is a good chance that a vehicle will do some damage, regardless of the thickness of the paver.

 

[concretemasonry]

Placing pavers on concrete for vehicle traffic can be very expensive because of the need for drainage of the moisture, which decreases pavement capacity. Usually compacted base is superior to a concrete slab.

For heavy loads, pavers should be placed on a 1" sand setting bed over a compacted base that has the desired contours for drainage or a underground drainage system in unusual situations.

Hokie66 is correct - The spaced placement method used for larger "garden variety" concrete slabs eliminates the interlock caused by the paver shape, laying pattern and the fine sand that is vibrated into the small space/gaps formed by the spacers on the paver sides. An engineered paver installation is a system and not just a collection of materials.

Clay pavers are different animal and rarely used for higher loads.

Dick

 

[cvg]

sand base may be superior if done right, but many agencies around here still require the concrete slab in R/W. Drainage is no more difficult for a concrete slab with pavers than it is for concrete pavement. Adequate slopes must be provided to drain water to catch basins and gutters. Allowing stormwater to infiltrate into the roadway subgrade can also be problematic and will weaken it. It is generally better to drain water away rather than infiltrate unless you have very light traffic or provide sufficient subdrainage to handle it.

 

[Ron]

Your pavers are fine for pedestrians, but not for vehicles...too large. Expect cracking.

Most common method of placement is not on concrete but on compacted, stabilized base with 1" sand layer.

As ConcreteMasonry noted, you'll get failures with vehicle loads on these pavers. You can analyze ad nauseum, but pavers need to be governed by shear, not bending. If you have a 24" square paver, you introduce more bending than that small slab section will withstand.

 

[concretemasonry]

I saw a 15+ acre site that was paved with 100 mm interlocking concrete pavers that was used as a ship cargo unloading/storage facility for cargo. The vehicle traffic was 4 wheeled straddle loaders that had a gross weight of about 30,00# or more. The routed required the frequent turning.

The soil was a typical international harbor soil (silt/clay) with a high water table that had a properly compacted base. The 100mm thick pavers (about 4"x8") had a "zig-zag" configuration that were laid in a herring bone pattern for greater unidirectional strength. This is very typical of many international installations that American engineers are not familiar with. Concrete pavement would not have been practical since flexible pavement was more realistic. This was similar to other applications in K-L and other SE Asia ports.

The construction was not that different than that used on many street areas that serve the large dual steering axle buses in Europe.

Dick

 

[Ron]

Dick...I agree. Interlocking concrete pavers make an excellent pavement section. You get some good aspects of both rigid and flexible pavements...the pavers act as discrete rigid sections, but are so small that they transfer stresses more like a flexible pavement. The pavers are kept small so that bending is negligible, so they have only bearing on the prepared base and shear at the interlocks.

The Interlocking Concrete Paver Institute has some good info on pavers.

http://www.icpi.org