Interlocking concrete pavements or pavers are a special dry mix pre-cast piece of concrete commonly used in exterior hardscaping pavement applications. Unit Pavements or block paving, nicknamed pavers in the United States were developed before the Second World War by the Dutch and introduced into the United States in the early 1970s.
Interlocking paving stones are installed over a compacted stone sub-base and a leveling bed of sand. Concrete paving stones can be used for walkways, patios, pool decks and driveways and airport or loading docks.
Instead of connecting the pavers by pouring grout between the joints as one would with tiles, sand particles are spread over the pavers and tamped down. The sand stabilizes the interlocking pavers, yet allows for some flexibility. This type of pavement will absorb stress such as small earthquakes, freezes and thaws, and slight ground erosion by flexing. Therefore, they do not easily crack, break or buckle like poured asphalt or poured concrete.
Some of the special tools needed for installing interlocking pavers are vibrating compaction machine or "Vibra Plate" and Shear Cutter. The former is used to compact the base material to 90% density minimum and also to set and interlock the pavers into the sand bed. The latter is used to cut the pieces to fit at corners and edges. The sand does not easily wash out with rain or garden hose water. Polymeric Sand or a sealant can be used to further lock or coagulate the sand. There are many other tools involved in preparing sub-grade, base materials, sand bed and installing unit pavements correctly.
Standard thicknesses are 60mm (for light traffic) and 80mm (heavy traffic). 50mm too is common in some countries like Pakistan (used for footpaths etc.).
Benefits of paver over asphalt and poured concrete include high compressive strengths (7000+psi as per BS and 8000+psi with no more than 5% absorption as per ASTM codes and as high as 19,000+psi depending on manufacturer and type of unit pavement), pleasant look, time saving, easy removal and relaying.