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The Perfect way To Pave
Over two thousand years ago , the mighty Romans developed a simple system for building reads which helped them control much of their world a marvel of its time, some of these reads are still in use today.
The system consisted of a well compacted base of limestone (or lime and gravel), covered with a tight fitting cut stone, which produced and excellent and economical roadway that remained virtually maintenance free in all types of weather.
The Romans used natural cut stone for their surface; today's modern paving stone is manufactured o high-strength "no-slump" concrete in a modern precast concrete plant, under controlled conditions which produce units in many shapes and colors.
There are two types of concrete paving stones: solid interlocking units used in paving roads, sidewalks, parking areas and other public spaces; and "Turfstone" which allows the growing of grass or other plant material in the voids and provides soil stabilization for projects in recreational areas, along highways, parking areas and storage areas.
THE ADVANTAGES OF INTERLOCKING PAVERS
Interlocking pavers have the unique ability of transferring loads and stresses over large areas of paving, by means of a "bridging" action between the individual units. Such spreading of the load allows heavier weights and traffic over sub bases which normally would require concrete that is heavily reinforced whit steel.
Because interlocking pavers are manufactured in a variety of shapes and colors, they allow the designer infinite possibilities to comply with specific criteria of projects as well as the latitude of interesting designs.
Other advantages:
- Permanently mark parking bays, cross walks, traffic lanes and other identified areas.
- Street repair is simplified, as streets can be opened for such activity as utility line repair, and the pavers replaced to their original configuration without the need for additional materials.
- Use of the open type stones in ecologically sensitive areas provides one solution to the increasing concern for the environment. Voids in the stones allow the return of rainfall back into the ground, rather than enabling it to run off as waste.
- Properly installed, pavers resist shifting, sinking or buckling providing an excellent surface for walking, bicycling, driving cars, trucks, and even fork lifts.
LAYING COURSE AND SUB-BASE
The Laying course consists of clean, sharp sand placed to a thickness such that when the blocks are vibrated into place the resulting thickness of the laying course is about ¾" to 1 ¼" thick. Many opinions exist concerning the maximum size, gradation, and moisture content of the sand used for the laying course. This suggests that the performance of the block pavement is not sensitive to these variables over a fairly wide range. To achieve uniformity, however, the sand should be obtained from one source and before use protected so as to maintain uniform moisture content.
As with any pavement, the sub-base for paving block is of primary importance. Inasmuch as the block pavement can be considered as flexible pavement, the sub-base should be that required for conventional asphalt pavements; it could consists of old pavements, unjointed concrete slabs or most any old road. They are all suitable sub-base for concrete block paving. The required thickness of a sub-base will depend upon both the expected service loads and the soil conditions; the need for a substantial sub-base materials and standards must comply with the requirements of the local road authority.
For light duty usage in residential construction, a sub-base from 3" to 5" is recommended. I.e. patios, pool decks, walkways. For driveway use, one would be well advised to place a compacted sub-base of from 4" to 8", depending upon how well the driveway area drains after a rain. The material used for the sub-base should be a well graded gravel (Class 11) having a maximum topside of about 1 ½ inches and containing about 10 percent sand sizes. A thick sub-base should be compacted or vibrated, prior to placing the next layer. Having the sub-base well compacted is important to the durability of the finished construction.
CONSTRUCTION
After the sub-base is in place at the correct surface level and is free of debris and mud, the sand laying course is spread evenly between curbs. This is followed by screeding wide the sand to the desired level. For roads up to about 16 feet wide the sand course is usually screeding, it is important that care is taken during the screeding operation. A cambered screed board is used for pavements with a cambered cross-section. To avoid unevenness caused by pre-compaction, the sand must not be walked on or disturbed once it has been screeded.
Figure 2 shows a typical cross-section of a concrete block pavement consisting of the sub-base, the laying course of sand and the blocks themselves. To help keep the blocks from being displaced horizontally, precast or cast-in-place curbs are used for medium and heavy duty installations.
Rectangular units should be layed in a herringbone pattern to prevent "creep" under traffic, permitted by the opening of joints. Interlocking units may be laid in running or stretcher bond as their interlocking design resists the forces that cause "creep." Each block is place against the adjacent units without disturbing the sand or other units, (Developments are taking place at this time relative to mechanized placement of individual units or clusters of block that are tied together with break-away webs.) The order of laying should be such that it is never necessary to force a block between those already laid.
Where whole units do not fit at the edges of a pavement, cut block are used to fill the spaces. Spaces left around manholes and drainage inlets are treated in the same manner. This is readily accomplished with a small hydraulic block splitter. Spaces less than about 1-5/8" (40mm) can be filled with sand.
After enough area is laid to make vibration worthwhile, the block are vibrated to their final level with a plate vibrator, . The vibrating action compacts the sand and also forces some sand up between the joints. After the initial vibration, sand is brushed over the surface and is vibrated into the joints by an additional two passes of the vibrator. This locks the block together so that they no longer act as individual units but as a group in distributing loads. Vibration also evens out any minor variations in level between units. The vibrator should not be passed closer than about one yard from and unrestrained edge. After surplus sand is removed the pavement is completed and ready for traffic. If heavy trucks are used to deliver materials close to the work, the sanding and vibrations should be done before the trucks are permitted to enter that section of the pavement.
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