The first segmental roadways were built by the Minoans about 5,000 years ago. The Romans built the first segmental interstate system, which was longer than the current U.S. interstate highway system. Most would agree that paving stones offer an “Old World” beauty and charm, but the strength and longevity of interlocking pavers is often overlooked in North America. This article will explain the basics of interlocking pavers, and it will address common misconceptions about pavers.
It is important to understand that a paving stone installation is an engineered system; pavers are simply a part of this system. The components of a paving stone installation, from the bottom up, are: compacted sub-grade (or soil layer), Geotextile fabric, compacted aggregate base, bedding sand, edge restraint, pavers, and joint sand. Unlike cast in place concrete, interlocking pavers are a flexible pavement. It is this flexibility that allows point load from a truck or car tire to be transferred and distributed through the base layer to the sub-grade. By the time the load has reached the sub-grade, the load has been spread over a large area, and the sub-grade does not deform.
Concrete, on the other hand, is a rigid pavement. Its function is simply to bridge soft spots in the soil. Poured concrete will crack and break due to loads, shrinkage, soil expansion, and frost heaving of the sub-grade. Concrete is one of the most vital materials in construction, but poured in place concrete makes a poor paving surface. This is due to its relative inability to flex and its low tensile strength. Fiber reinforcement and rebar can enhance the tensile strength of concrete, but cracking and breaking are inevitable.
Modular paving stones are typically made of hardened precast concrete or kiln-fired clay. Properly installed pavers are interlocked, so a load on one paver is spread among several pavers and eventually transferred through the base layer. Factors that affect interlock are paver thickness, paver shape, paver size, joint widths, laying pattern, and edge restraint. Most paver manufacturers offer a lifetime warranty when their products are professionally installed. Natural stone such as Flagstone and Bluestone is not suitable for flexible paving, and they are typically mortar-set on a concrete slab. Because interlocking pavers are joined with sand (instead of mortar), they can be uplifted and replaced inexpensively. For example pavers can be uplifted to access underground utilities and reinstated when work is complete.
Paving system designs are based on variables that include soil make-up, anticipated load stress, climate, water table, and rainfall. The materials used for aggregate base and bedding sand vary geographically. Soils that are high in clay and loam are unsuitable for compaction and cannot be used as base material; in these cases a graded crushed stone is substituted. Proper compaction of the sub-grade and base material is crucial to the long-term performance of a paving system, and in vehicular applications the compacted base depth can be over 12 inches. The edges of a paver installation must be restrained to ensure interlock and prevent lateral creep. The most common types of edge restraint are staked-in plastic edge restraint, precast concrete curb, and cast-in-place concrete. Bedding sand materials include angular sand, manufactured sand, and polymeric sand.
The beauty and longevity of a paving stone system is determined by its designer and installer. Properly installed pavers offer a lifetime paving solution. Improperly installed pavers may fail in a matter of years. When choosing an installer look for training, experience, and references.
Q: Are pavers permeable (or pervious)?
A: The majority of paver installations are impermeable (impervious). However, most manufacturers offer permeable pavers, which are installed on an open graded base. A permeable system is designed to store water in the base material so it can be released back into the soil. These systems reduce runoff, recharge groundwater, and eliminate the need for detention ponds.
Q: Can pavers be installed on a steep slope?
A: Yes, pavers perform very well on steep grades, but joint erosion can occur under heavy rainfall. In these cases polymers are added to the joint sand to prevent sand wash.
Q: Do pavers settle over time?
A: Settlement is almost never an issue with properly installed pavers. However, soft areas in the sub-grade must be addressed before base placement. Trash pits and decaying organic material should be removed and replaced with compacted base material.
Q: Can pavers be used for highways?
A: Paving systems can handle tremendous loads, and they are often used in airports and seaports for this reason. However, pavers are not suited to high speed vehicular traffic and braking forces.
Q: Will pavers help with my drainage issues?
A: Water management is addressed during the design phase. When very little slope or a negative slope exists, surface drains; channel drains; and drain lines are used to move water away from structures.
Q: Will weeds grow in the joints?
A: Airborne weeds can take root in bedding sand, but they are easily controlled with weed killers. Polymeric joint sand can be used to prevent weed growth and stabilize joints.
Q: Where do I find a good installer?
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