Civil: Interlocking concrete pavers do heavy duty work

Pavements constructed using interlocking concrete pavers (ICPs) have the advantage of providing a flexible pavement structure with the ability to deform under loading. They also have the durability of a rigid pavement surface that provides high resistance to surface wear and damage due to loading. While one of the most high profile uses of interlocking concrete pavements has been in the residential driveway market, they have been used in many industrial and commercial applications including intermodal terminals, ports and airports.

The largest application to date of concrete pavers in an airport application is at Hong Kong’s new Chek Lap Kok Island airport. Over 400,000 square metres of mechanically installed concrete pavers were recently placed in service in the aircraft parking areas next to the passenger terminal, and in a cargo area that will be subjected to heavy aircraft wheel loads.

Mr. Larry Mujaj, design manager-airside, with the Airport Authority of Hong Kong, recently published a paper co-authored by David R. Smith, technical director of the Interlocking Concrete Pavement Institute of Washington, DC, that describes the state-of-the-art in precision manufacture and installation of airfield interlocking concrete pavements. The paper, presented at a recent conference at the Federal Aviation Administration, describes the details of approximately 40 commercial and military airports which have used interlocking concrete pavers over the past 15 years.

Pavers are mass-produced using machinery that applies a combination of vibration and high pressure to a zero slump, low water-cement ratio concrete mix. The resulting pavers have uniform dimensions and exhibit high compressive strength.

History

Stone sett pavements in the form of cobblestones have been used with remarkable success since Roman times when roads were constructed with tightly fitted paving units set on a compacted aggregate base. Many of these Roman roads have proven so durable they are still in service today.

The first concrete block pavements were developed in Germany prior to the end of World War I. In the 1930s further experimentation with mix designs produced high compressive strengths. Efforts to rehabilitate the transportation infrastructure after World War II led to the widespread use of concrete blocks and the rapid evolution of various block shapes which optimized their performance under traffic.

Design principles

Three aspects of interlock must be achieved when installing pavers; vertical, rotational, and horizontal. Vertical interlock is achieved by the transfer of loads to surrounding units through the sand placed in the joints between the pavers. Rotational interlock is maintained by the thickness of the pavers placed closely together, and by the edge restraints.

Horizontal interlock is primarily achieved by laying patterns that dissipate the forces from braking, turning and tire/pavement interaction during vehicle acceleration. Tests show that herringbone patterns offer greater structural capacity and resistance to lateral movement and are generally recommended for vehicular traffic. One of the most important aspects in the provision of a horizontally stable pavement is the provision of adequate edge restraints to maintain paver interlock. Primary factors in determining an adequate pavement structure include the traffic, sub-grade soil strength, pavement materials and environmental factors such as moisture in the soil and extreme temperature variations which may cause freeze/thaw cycling.

Interlocking concrete pavements for commercial and industrial applications typically consist of 80 mm thick units, manufactured with high levels of quality control, to a compressive strength generally in excess of 50 MPa. They are manufactured to close dimensional tolerances, and are typically 100 mm by 200 mm in plan. Pavers may be rectangular or one of a large number of proprietary shapes. The surfacing consists of the pavers, normally in herringbone pattern, laid on a layer of carefully selected bedding sand, approximately 30 mm thick after compaction.

Compaction forces some bedding sand up into the joints between the pavers. These joints are approximately 3 mm wide and are completely filled with jointing sand compacted by vibration. The sand-filled joints are an important feature of this form of pavement as they ensure that the pavement behaves in a flexible manner under load, and that adequate interlock is developed between individual pavers allowing the vehicle wheel load to be spread to adjacent pavers.

In general, an interlocking concrete pavement can be designed by standard methods for flexible pavements, with the pavers and sand substituting for an equal thickness of asphalt. However, the need to have segmental pavements designed by experienced pavement engineers cannot be over-emphasized.

Sealers have been developed with the specific aim of stabilizing the jointing sand between concrete pavers. Joint stabilization materials were originally formulated to prevent joint sand loss caused by jet blast from aircraft. Other benefits demonstrated by sealers have been:

Preventing sand loss caused by vacuum sweeping;

Coating the pavers, thereby making subsequent cleaning easier; and

Reducing the permeability of the joint sand thus avoiding problems associated with ingress of water and fuels into the underlying sand and pavement structure.

David Hein is principal pavements engineer at John Emery Geotechnical Engineering, Toronto. Brian Burton, of Brian Burton & Assoc., Toronto, is a member of the Standing Committee for Technical Evaluations for the Canadian Construction Materials Commission (CCMC).