In the past, the use of concrete paving stones was often limited to light and medium duty applications such as driveways and sidewalks. Over the last 10 years, however, there has been a growing recognition that these versatile paving units, which are manufactured to close tolerances using high quality concrete, are ideally suited for heavy-duty applications. Many experts in the fields of engineering, city planning, and landscape architecture are recognizing the benefits of concrete pavers for municipal, commercial, and industrial applications; there are numerous examples of this in many countries.

Structural Attributes

Pavers are often selected to accommodate cost, scheduling, maintenance and aesthetic requirements. When properly installed they provide a durable and forgiving pavement structure that distributes vehicle loads to adjacent pavers, bedding sand, aggregates and subgrade. Pavers also resist moisture, surface abrasion, repeated freeze-thaw cycles, petroleum products and deicing chemicals. The excellent appearance of paving stones also plays a part in the selection process. In addition, the ability to easily remove and reinstall pavers for underground utility repairs, for example, provides an added long-term cost benefit.

Exceptional Value

According to Beau Felux, General Manager, Austin/San Antonio Division of Pavestone Company, interlocking concrete pavement, in addition to its structural and performance characteristics, is proving to have exceptional value.

"It is a rapidly growing sector of the industry,'' says Felux. "In large part this is the result of fundamental economics as demonstrated in life-cycle costing. In fact, a number of engineering studies that analyzed the life-cycle costs of concrete paving stones in heavy-duty applications have demonstrated that pavers give the best return for the amount spent while in-service. And while the use of premium materials such as interlocking concrete pavers may increase the initial capital cost of construction, the performance benefits over the lifespan of the pavement can result in significant cost savings over conventional pavement alternatives."

Advantages for Heavy-Duty Applications:

• Ability to handle very heavy and concentrated loads

• Flexible nature of the system, which allows the pavement to handle heavy loads without cracking or failing, as is the case with monolithic pavement.

• Relative ease of repair and access to underground services.

• High strength and good durability.

• Excellent resistance to abrasion and damage caused by fuel or oil spillage.

• Low maintenance requirements.

Felux claims the concrete paving stones produce excellent results in heavy-duty applications because they are mass-produced to close tolerances in factory settings where quality control can be stringently regulated.

Installation Critical for Long-term Performance

The most critical aspect of installation is ensuring full and complete interlock. Pavers should interlock vertically, rotationally and horizontally. This form of structural interlock is achieved by proper specification and installation of the base and bedding sand, and by placing the pavers close together, installing edge restraints and utilizing various lying patterns.

Studies have shown that if pavers are properly installed they actually stiffen and gain strength under heavy traffic. The paving units act as the wearing surface and contribute to the structural performance of the installation. This phenomenon, which engineers refer to as "lock up," means the pavement will perform to a much higher standard than "monolithic" asphalt pavement. This "lock up" condition requires the proper bedding sand, granular base, adequate edge restraints, and proper drainage.

These are factors that the engineer takes into account when considering such things as the strain of heavy vehicles on the subgrade and tensile strength, which is applied over the surface of the pavement under extremely heavy loads.

When designing for these kinds of conditions, the engineer must also consider such factors as impact loads, high heat and frequent concentrated loads. "Pavements used for shipping ports, for example, really take a lot of punishment. There are many cases in the past where asphalt pavements simply couldn't stand the repeated impact and loads of the gigantic forklift machinery, which is used in these facilities," explains Felux.

Glossary of Terms:

Segmental paving: A flexible surfacing in which the paving units, installed over a bedding of fine sand, and a granular base. The segmental units form the wearing surface and are part of the structure of the pavement.

Base and Bedding sand: The base is a layer of crushed granular material between the subgrade and the bedding sand. The bedding sand is a layer of fine sand placed directly on top of the prepared base and beneath the paving units.

Edge restraint: Edge restraints are products that serve to prevent movement of the pavers and loss of base material or bedding sand.

Interlock: This describes the inability of one block to move in isolation from its neighbours.

Lifecycle cost analysis: Economic analysis of the construction, maintenance and/or rehabilitation requirements of construction materials and techniques. LCM