An interlocking concrete paver is a type of paver. This special type of paver, also known as a segmental paver, has emerged over the last couple of decades in the United States as a very popular alternative to brick, clay or concrete.

Segmental pavers have been used for thousands of years. The Romans built roads with them that are still there. But it was not until the mid-1940s that pavers began to be produced out of concrete. It started in the Netherlands where all the roads are made to be flexible because the country is below sea level and the ground shifts, moves and sinks. Poured concrete is not an option because it will crack. Individual units not set in concrete placed in sand perform far better than concrete. Before the paver was made from concrete either real stone or a clay product had to be employed.

The first concrete pavers were shaped just like a brick, 4” by 8” (10cm x 20cm) and they were called Holland Stones and still are today. These units turned out to be far more economical to produce and were exceedingly strong.

Pavers are made from a very dry mix of gravel, sand, cement and color. Since there is very little water, the mixture is moved on conveyor belts and then funneled into the paver mold. A press is inserted into the mold and vibrated at the same time. The high pressure and the vibration causes the water to set the cement and creates a bind between the aggregate. When the mold is moved away, the pavers are in their finished state.

Pavers are said to have zero slump. The more the slump, the weaker the concrete. A slump test is done in a laboratory to test the strength of concrete. It is done by placing concrete in an 8” tall cone, which is then turned upside down and removed. The amount the concrete slumps from the original 8” is measured. For instance, if it now measures 6”, it is said to have a 2” slump. If one has a very wet mix, it would not hold up at all and would run all over the table.

The strength of concrete is achieved in three main ways.

  1. The amount of water (the less water, the stronger).
  2. The amount of cement in the mix (the more cement, the stronger).
  3. The amount and size of aggregate (the bigger, the stronger).

Concrete delivered in a truck needs to be fairly wet to get it out of the truck. Typical concrete from a concrete truck will produce a surface with a load strength of about 2,000 pounds per square inch (14,000 kPa).

A surface is tested for strength by placing a point load onto it and exerting a direct force until it fails. The pressure is calculated, and that is the failing point. Pavers need to withstand a minimum of 8,000 pounds per square inch (55,000 kPa) to meet industry standards. Usually when tested they far exceed this minimum. That means a paving stone driveway is at least four times stronger than a regular concrete driveway.