Interlocking Pavers

A special type of paver

Paver (flooring)

An interlocking concrete paver is a pre-cast piece of concrete or brick commonly used in exterior hardscaping applications. Pavers were developed in Europe and introduced into the United States in the early 1970s....

 referred to as an “interlocking concrete paver” or also a segmental paver has emerged over the last couple of decades in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 as a very popular alternative to brick

Brick

A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

, clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

 or concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

.

Segmental pavers have been used for thousands of years. The Romans

Ancient Rome

Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 built roads with them that are still there. But it wasn’t until the mid 1940’s that pavers began to be produced out of concrete. It started in Holland where all the roads are made to be flexible because Holland 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

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

 perform far better than concrete. Before the paver was made from concrete either real stone

STONe

is a Japanese manga written and illustrated by Sin-Ichi Hiromoto. Kodansha released the two bound volumes of the manga on April 23, 2002 and August 23, 2002, respectively.The manga is licensed for an English-languague released in North America be Tokyopop...

 or a clay product had to be employed.

The first concrete pavers were shaped just like a brick, 4” by 8” 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.

How Are Interlocking Pavers Made?

Pavers are made from a very dry mix of gravel

Gravel

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

, sand, cement

Cement

In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

 and color. Since there is very little water, the mixture is moved on conveyor belt

Conveyor belt

A conveyor belt consists of two or more pulleys, with a continuous loop of material - the conveyor belt - that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the drive pulley while the unpowered pulley...

s 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

Construction Aggregate

Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...

.
When the mold is moved away, the pavers are in their finished state.

Pavers are said to have zero slump

Concrete slump test

The concrete slump test is used for the measurement of a property of fresh concrete.The test is an emprical test that measures the workability of fresh concrete. More specifically, it measures the consistency of the concrete in that specific batch. It is also used to determine consistency between...

. The more the slump, the weaker the concrete. A slump test is done in a laboratory

Laboratory

A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...

 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

Truck

A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

 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 2000 pound per square inches (13,789.5 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 8000 pound per square inches (55,158.1 kPa) to meet industry standards. Usually when tested they far exceed this minimum. That means a paving stone driveway

Driveway

A driveway is a type of private road for local access to one or a small group of structures, and is owned and maintained by an individual or group....

 is at least four times stronger than a regular concrete driveway.

How Interlocking Pavers Interlock

When one thinks of interlocking paving stones one often gets the idea of dog bone shape stones that fit together like a jigsaw puzzle

Jigsaw puzzle

A jigsaw puzzle is a tiling puzzle that requires the assembly of numerous small, often oddly shaped, interlocking and tessellating pieces.Each piece usually has a small part of a picture on it; when complete, a jigsaw puzzle produces a complete picture...

. That is not the case at all. The interlocking comes from the fact that each stone can NOT move independently from its neighbor. In fact there are two important aspects of an interlocking paving stone job that keeps the pavers interlocked.

The first is the sand. As simple as this might seem the sand creates the interlock. Not any sand though, it must be a sharp angular sand (also called Joint Sand and Polymeric Sand) that will lock together. If you filled the joints between the pavers with silica sand, each particle is perfectly round, it’s like putting ball bearing

Ball bearing

A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit...

 between the pavers and they WILL then be able to move independent of the stone next to them. Pavers are made with a small ridge on the side of each one so there is space for the sand.

The picture below shows pavers being lifted. Notice the whole surface lifts, not just one paver. The fact that the whole surface moves together demonstrates the sand holding the pavers together.

The second important aspect is the edge restraints (the border that is holding the pavers together). Since they are sitting in sand not mortar

Mortar (masonry)

Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...

 if the edge is not held firmly in place they could start to spread apart. This would create larger and larger opening between the pavers that would eventually be so wide that there would no longer be friction

Friction

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

 between the stones.

With the second condition in place you have now created interlock.

Installation of Interlocking Concrete Pavers

The correct installation of interlocking concrete pavers

Step 1: Demolition

Demolition

Demolition is the tearing-down of buildings and other structures, the opposite of construction. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for re-use....

 – remove old driveway or patio

Patio

A patio is an outdoor space generally used for dining or recreation that adjoins a residence and is typically paved. It may refer to a roofless inner courtyard of the sort found in Spanish-style dwellings or a paved area between a residence and a garden....

. Go down a minimum of 7”.

Step 2: Compact the sub base – the dirt that will be directly under the base material.

Step 3: Install the base – Class II Road Base is used. This is composed of various sizes of gravel. See the picture of the sieve.
A sieve

Sieve

A sieve, or sifter, separates wanted elements from unwanted material using a woven screen such as a mesh or net. However, in cooking, especially with flour, a sifter is used to aerate the substance, among other things. A strainer is a type of sieve typically used to separate a solid from a liquid...

 is used to test soil and base material. There is a wire mesh at the bottom of each pan. At the top the mesh will allow ¾” rock through, the next one down will be ½”, then ¼” all the way to the last pan that will allow only “fines”. A fine is described as a particle that can pass through a #200 mesh. A #200 mesh has 350 openings per square inch. This is actually like a fine cloth. Water will not pass through a #200 mesh but fines will. So these particles are very small!

Certified base has correct quantities of all the above sizes so that it will compact to at least 95%. Imagine stepping on a field of marbles – they would move. Or even stepping in sand at the beach - not very firm. That’s because they are all the same size.
Since certified base comes with the right proportions, the end result will be a very firm sturdy base.

The base should be compacted and at least twice as shown below.


To achieve the desired level of compaction, 98% base should be compacted in “lifts”. A lift is a layer of material, base, or dirt to be compacted. For base, the lifts should be no more than 4” thick. The compactor should be a very heavy duty machine that produces a minimum of 5000 pound per square inches (34,473.8 kPa). Smaller machines will never achieve the desired 98% compaction.

Step 4: The next step is the sand bedding. (this is angular sand as mentioned above) –a one inch sand bed is screeded in place, the pavers are laid on top.

Step 5: Cutting the pavers – the edges are cut with a dry saw and each fit precisely in place.

Step 6: Install restraints – Since pavers are set in sand, they need to be held together by something. What holds them together is the borders or the outside perimeter. This outside edge is referred to as a restraint. Once they are finally held in place, they can not move yet the entire surface is flexible. As compared to a poured in place concrete surface which is rigid. As a word, flexible, best describes the interlocking concrete surface whereas rigid would describe a concrete surface.

There are several types of restraints as shown below.
Step 7: Compacting the pavers – Once the restraints are in place, the next step is to compact the pavers in doing so, the pavers are pushed into the bedding sand and the sand is forced up between the pavers.

Step 8: Sand between the pavers – Once this is done more sand, either the same bedding sand or joint sand that comes in bags, is swept between the pavers and the pavers are compacted again. In using a vibrating plate compactor, all the joints between the pavers are filled.

See also

Video: How to Install Paving Stones

Video: Paving stone machine

Video: Paving stone machine animation

Pics: Installed Paving Stones