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Interlocking concrete pavements are a special dry mix pre-cast piece of concrete commonly used in exterior hardscaping pavement applications. Unit Pavements or block paving, nicknamed concrete pavements 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 60 mm (for light traffic) and 80 mm (heavy traffic). 50 mm 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.
Paving has been around for almost 5,000 years. One of the oldest paved roads was discovered in the summer of 1994, in Giza, Egypt. This road was built over 4,600 years ago as a route to connect an ancient basalt quarry to Lake Moeris and used to transport large stones for the construction of the temples of Giza. This ancient road measures 7 1⁄2 miles (12.1 km) in length and 6 1⁄2 feet (2.0 m) in width. The road was paved with thousands of slabs of sandstone and limestone and some logs of petrified wood. The still standing road was used to carry massive stones using sleds and proved to be reliable.
In 500 B.C., during the Roman Republic, Rome introduced the segmental pavers in their road system. The Romans needed their armies to travel quickly within the empire and the current kinds of roads posed many problems. The roads were often muddy, created too much drag, and also created lots of dust in heavily transited areas. To solve that problem the Romans created roads with deep roadbeds of crushed stone and a top layer that included six sided capstones. The Roman roads provided the troops with much faster transportation and proved to be reliable as they still stand to this day.
Over time many roads were built and paved based on the Roman road design and natural stones and clay were used to pave the roads up until the 18th century. At that point, British builders realized the importance of selecting clean stones for surfacing to make better roads. The selection of clean stones made road paving a bit costly until later on when concrete pavers could be manufactured. Most of these roads provided a means of fast transportation with the use of horse-drawn carriages.
In the 1940s Holland faced a problem with its roads because Holland is situated below sea level, therefore the ground constantly shifts, moves and sinks. Poured concrete was not an option because it is not flexible and would strain and crack. Therefore, Holland turned to the use of individual stones placed in sand, which provided a flexible yet durable road that would not be affected by shifts and movements of the ground.
After World War II, most of Europe was in ruin and reconstruction began. The roads where rebuilt using paving stones as they have historically proved to be able to withstand certain demands that concrete and asphalt could not meet. German engineer, Fritz Von Langsdorff developed a choice of shapes and introduced the use of colors in concrete pavers. Historically pavers where often made of natural stone or clay, but the introduction of concrete paving stones turned out to be more economical to produce and had tremendous pressure resistance. The first concrete paving stones where installed in Stuttgart, Germany.
Interlocking concrete pavers are now an efficient and economical choice as mass production started in the 1960s in Germany. In the 1970s production technology spread through Europe and other parts of the world including the United States. Since then America has seen a significant growth of concrete interlocking pavers and has been growing steadily. Still to this day Europe has approximately 8 square feet per person installed, compared to less than 1 square foot per person in the United States.
Interlocking pavers are manufactured by machinery in factories. They consist of both fine and coarsely grained aggregate, along with cement compounds. The ingredients are put through pressure and vibration courses, which produce a strong, durable concrete that can then be molded into various shapes and designs.
Manufacturing of pavers is done on two types of machines in general. The first being more popular, more productive, cost effective, yielding high strength product is through block making machines. The movements are controlled through hydraulics and the compaction is done through eccentric weight vibrators. An aggregate mix of sand, rock, and cement. The mixture is then poured into a mold called "the shoes". The mixture is then hammered into the mold using several thousand pounds of pressure from the eccentric weight vibrators. They are typically then tested to make sure that the water to mixture ration is correct. Following this, the pavers go through a curing process that can last eighteen to twenty hours. The curing process and additional processes can vary based on the style of paver. The other choice is of hydraulic press machines that deny each of the above mentioned advantages still common in few countries because of their low capital demand. There is no vibration to move the material in the mold; thus voids may remain present.
|Wikimedia Commons has media related to Pavers (Pavements).|
- Interlocking Concrete Pavement Institute
- National Precast Concrete Association
- PaveShare - ICP Education
- Concrete Paving