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Concrete Paver

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Asphalt/Aggregate/Concrete Equipment
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Miller M7500 Formless Crawler Curb and Gutter Concrete Paver
Concrete pavers
are a type of construction equipment used to pave roads, curbs, sidewalks, airports, parking lots, driveways, recreational areas, and more with concrete.

Concrete is used because of its high resistance to abrasion, skidding, and indentations that occur due to extreme temperatures. Additionally, it is less likely to crack under stress and can support heavy loads and vehicle traffic.

The modern type of paver is known as slip form and is capable of spreading the concrete, striking excess off the slab, reinforcing it with an oscillating vibratory apparatus, shaping it with an extrusion finisher and refining the surface with a float finisher component.

Contents

[edit] History

Concrete pavers serve a very specific purpose of paving concrete for roadways, curbs, and walkways, but the method of doing so started off much more differently than is practiced today. The concept of interlocking stones has been in existence for some 5,000 years. Originally, roads were made from rock segments in Crete at 3,000 B.C. Similarly, the Romans used crushed aggregate that was fused together to create interlocking paving stones.[1]

Projects such as the Bavian Canal were paved with concrete that was made of part lime, two parts sand, and four parts limestone by the Assyrians in 609 B.C.[2]

It was the tragedy of World War II left nations in need of rebuilding and a new method of paving concrete emerged in the Netherlands. This method meant concrete would replace the formerly used clay bricks for the main source of roadway building materials.[3]

The first patent for the kind of concrete that is used today, Portland concrete, was taken out by an Englishmen known as Joseph Aspdin in 1824. Portland cement consisted of a concoction of limestone and clay burned in extreme temperatures of 2,700 degrees Fahrenheit.[4]

This new form of interlocking pavement stones made its way to Germany in the 1960s and became widespread throughout most parts of the world in the 1970s.

Using concrete as opposed to other materials proved to be stable, steady, and reliable, features that were all in want when rebuilding passageways for increasingly mechanized nations. The growing population in cities and the demand of automobiles meant that concrete would be responsible for supporting and creating a means of access to travel that was never before seen nor needed. Concrete was able to withstand vehicles and traffic that would inevitably grow with each progressing year and would face the demands of severe weather and other environmental or man-made factors that would occur.

The result of using concrete to build the roadways in North America has resulted in approximately 12 million square yards (60 million m2) of concrete pavers produced.

2006 Gomaco GT3600 Curb and Gutter Machine

[edit] Slipform Paver

Traditional pavers used metal forms to spread freshly poured concrete, but the time required to prepare these metal forms became very time-consuming. The more complex building applications such as modern highways and airports have demanded special paving equipment that could complete projects rapidly and efficiently. Roadways were no longer able to undergo weeks or months of construction. Slipform pavers have provided many of the paving jobs that are completed in present day.

The name slipform comes from operational function of the concrete paver. The side form of the paver slides across the concrete slab edges to provide smooth surfaces that consolidate and harden. It does this with the help of an auger accessory .[5]

Concrete is poured onto form plates in front of the paver. These form plates are usually metal and are typically 10 feet (3 m) long and eight to 12 inches (20 to 30 cm) in height. They are kept in position by metal pins that are locked in the sockets of locking plates. The locking plates and the receiving key, which are located on opposite ends, enable the concrete to harden and solidify while the paver smoothens the surface. The form plates allow the concrete to be paved in particular patterns, such as vertical interlocking, horizontal interlocking, and the most common form, the herringbone form.[6]

Slipform pavers are form-riding units that vibrate and distribute concrete. Screeds strike off excess concrete by using tamping bars to manipulate the lower level of concrete, all the while the concrete is being vibrated for reinforcement.[7]

Slipform pavers also use a conveyor belt to allow them to prepare the concrete for paving, as well as dowel inserters that vibrate dowels into the poured concrete and are equipped with final float-finishers.[8]

Slipform pavers are efficient because they can tackle the task of spreading, compacting and completing the finishing touches to poured concrete. The concrete that is used with the slipform paver is required to have a consistency of one to four inches (2.5 to 10 cm). Slipform pavers can pour concrete up to 10 inches (25 cm) thick at rivaling speeds of 20 feet (6.1 m) per minute.

Attachments, accessories, and other equipment are also used in conjunction with the slipform paver. These include grade trimming machines, concrete saws, and finishing equipment: tube finisher, burlap drag, and curing machines.[9]

Concrete saws cut the completed concrete slabs into longitudinal and transverse shapes. They can be adjusted to cut slabs at particular lengths, typically between 1/3 to ¼ of the slab thickness.

Concrete finishers are used to manipulate the consolidated concrete surface so that it is strengthened and can endure the stresses placed upon it. Water can be added to produce a more uniform surface.

The modern types of slipform pavers can perform most of the tasks associated with the concrete process. Pavers, working at a speed as high as 30 feet (9.1 m) per minute, can also consist of oscillating extrusion finishers and a float finisher that strengthens the final product.[10]

[edit] Features/How it Works

Concrete consists of Portland cement, water, and aggregate that has been mixed together, consolidated and hardened to produce a uniform surface. Concrete is mixed either by transit mixing, where concrete is batched at a plant and transported via truck; or central mixing, where it is mixed in a stationary mixer and transported by truck operating at agitating speeds, also known as a truck agitator.[11]

A bedding sand is placed over the top of the existing roadway and the concrete is prepared and poured. The paver inserts dowels into the correct position to continuously vibrate the concrete without disturbing it. Screeds, operating at speeds of zero to 80 revolutions per minute, strike away excess concrete from the slab and the shape is smoothened with an extrusion finisher and a float finisher.

Gomaco GP35004TRK Concrete Paver
The paving of concrete is similar to that of asphalt. They differ in the way that the aggregate is mixed and consolidated.

The thickness of the base is calculated upon the amount of traffic and vehicle usage that occurs. Regions with colder climates and poor soil quality sometimes require a thick base as well.

Concrete that is distributed and interlocked will be able to resist horizontal, vertical, and rotational movements. To achieve the vertical interlock, joint sand is transferred throughout surrounding concrete pavements. Rotational interlock provides support against settlement varieties, while horizontal interlock protects the concrete against breaking, turning, and the acceleration of vehicles on roadways. The herringbone pattern is said to be the most effective pattern by some researchers. This pattern contains a series of zig-zag stones.[12]

Different processes are used for different applications. For curbs, gutters, sidewalks and other median-type paving, slipform and extrusion-type pavers are used. The subgrade and position of the curb or gutter is determined and the type of machine used for these applications have become so specialized that they are used for curb and gutters in particular.[13]

The surfaces are calculated to be uniform at a certain level and a subgrade is deemed appropriate for the circumstances. When the concrete is spread, a finisher rides the surface to add the finishing touches to the poured concrete. Form-riding curing occurs once the finishing is complete. The curing machine provides a self-powered pump that sprays the surface and is a feature for further smoothening the uniform concrete slab.

[edit] Common Manufacturers

[edit] References

  1. Abstract. TAC. 2008-09-09.
  2. Peurifoy, Robert L. Construction Planning, Equipment, and Methods. McGraw Hill: Boston, 2002.
  3. Paving Stone. Pacific Paving Stone. 2008-09-09.
  4. Peurifoy, Robert L. Construction Planning, Equipment, and Methods. McGraw Hill: Boston, 2002.
  5. Peurifoy, Robert L. Construction Planning, Equipment, and Methods. McGraw Hill: Boston, 2002.
  6. Nunnally, S.W. Managing Construction Equipment. Prentice-Hall: New Jersey, 1977.
  7. Day, David A. and Benjamin, Neal B.H. Construction Equipment Guide. John Wiley Sons: New York. 421-27.
  8. Peurifoy, Robert L. Construction Planning, Equipment, and Methods. McGraw Hill: Boston, 2002.
  9. Nunnally, S.W. Managing Construction Equipment. Prentice-Hall: New Jersey, 1977.
  10. Day, David A. and Benjamin, Neal B.H. Construction Equipment Guide. John Wiley Sons: New York. 421-27.
  11. Peurifoy, Robert L. Construction Planning, Equipment, and Methods. McGraw Hill: Boston, 2002.
  12. Abstract. TAC. 2008-09-09.
  13. Nunnally, S.W. Managing Construction Equipment. Prentice-Hall: New Jersey, 1977.