Understanding the Basics of Hard-Court Construction is Easy
Across the country - from neighborhood developments and apartment complexes to public parks and private clubs - hard courts prevail because, in general, they are easy to care for. And while they may all look alike from above, it's the differences below the surface that can determine what's right for your facility.
Learning the nuts and bolts of hard-court construction is my - in fact, it's information you'll need for your next upgrade or expansion when you are speaking with contractors or design professionals. More important, knowing some of the fundamentals will help you make better decisions about which pavements are appropriate for your site, how much the court might cost and its expected durability.
Start with a Good Foundation
Underneath the acrylic finish found on most hard courts today either is asphalt, reinforced concrete or post-tensioned concrete - each with its own advantages and disadvantages. Choosing one of these three hard courts for your facility could mean either years of trouble-free maintenance or costly repairs down the road.
Hard courts, whether asphalt or concrete, have the same basic composition below the pavement. Each begins with a "subgrade" of compacted ground. Topsoil and organic matter, such as tree roots, stumps, peat or muck, must be removed, otherwise it will decompose over time and lead to settling and cracking of the pavement above. Then a heavy roller levels out the stable ground.
Next, for all types of hard courts, comes a "base course," consisting of densely compacted crushed stone. The crushed stone remains porous, which keeps the pavement from heaving during heavy rains or winter freezing. Depending on your climate and soil conditions, the base course is usually between 6 and 8 inches thick. Now you're ready for the pavement.
Asphalt Pavement Courts
Asphalt, which was introduced to the construction industry in the middle of the last century, technically is not the pavement itself but a gooey liquid petroleum byproduct. This liquid is heated and mixed with crushed stones to form the pavement. For court construction, the heated mixture is trucked to the site, dumped into a paving machine and laid over the gravel base course.
Asphalt pavement is usually installed in two layers. The first layer, called the "binder" or "intermediate" layer, forms the basic structure and strength of an asphalt pavement. The second layer, called the "topping" or "leveling" course, is formed with smaller sized stones, giving the surface a smooth, fine-textured appearance. The smaller stones also allow the pavement to be graded much more accurately, giving the court its proper, though extremely flat, slope. As the pavement layers cool, they harden or "cure," forming what is technically called asphaltic or bituminous concrete - in layman's terms - "blacktop." In total, an asphalt court pavement is 3 to 5 inches thick.
Even though the asphalt pavement becomes hard during the curing process, it nevertheless remains a "flexible" pavement. As the court warms and cools due to seasonal temperature changes, the asphalt actually swells and shrinks. This movement is not detectable to the court user, but, as we'll explain further on, it is an important part of the structure of the pavement.
Reinforced Concrete Pavement Courts
Though less common than asphalt, concrete, due to its makeup (portland cement, crushed stone and water) is significantly harder than asphalt and therefore is described as a "rigid" pavement. When used for pavements, concrete is reinforced with wire mesh or steel bars to give it greater strength and resistance to cracking.
The perimeter of a concrete court is laid out over the crushed stone base course with wood or steel forms. The reinforcement is placed above the base course and a 4- to 6-inch-thick liquid concrete mixture is poured into the form. Quickly, the surface of the concrete is then smoothed out with screeds, trowels and brooms. Concrete is hard enough to walk on- within a day or so after pouring, but it takes a full month for it to thoroughly cure before it can be surfaced.
As concrete warms and cools due to seasonal or even daily temperature changes, it noticeably expands and contracts. For this reason, a concrete court must have joints that allow for this. Unfortunately, a reinforced concrete court requires these expansion joints within the playing area of the court, and under extremes of cold or with improper construction, expansion joints can widen, becoming a tripping hazard. This, and the fact that concrete tends to develop hairline cracks, has led most designers and contractors to abandon the use of standard reinforced concrete courts.
Post-Tensioned Concrete Courts
Post-tensioned concrete, first developed in the 1950's for building foundations, has been widely used for tennis courts for more than 20 years. Today, it is the preferred concrete-court construction technique.
Post-tensioned concrete is, in fact, a reinforced concrete pavement, but it differs in the way it is reinforced. Instead of using wire mesh or steel bars, post-tensioned courts are reinforced with wire cables. After concrete is poured then cured for a few days, wire cables are tightened under thousands of pounds of pressure.
The pulling or "tensioning" of the cables compresses the concrete, giving it greater strength and resistance to cracking than standard reinforced concrete. "Post-tensioning" also gives concrete so much more strength that post-tensioned courts usually only have an expansion joint at the net line. Multiple courts can be constructed side to side up to 180 feet in length (three full-sized courts) before an expansion joint is required lengthwise.
The downside is that post-tensioned courts, like standard reinforced concrete courts, still can develop hairline cracks. However, cracking is less frequent and movement of these cracks is less pronounced.
Cost, Ease of Construction and Durability
Before deciding which court type would best suit your needs, here are a few things to consider. A completed tennis court (whether asphalt or concrete) will probably cost between $24,000 and $50,000, depending on the surface type, style of fencing, the number of courts being constructed and the court's location.
A post-tensioned court pavement generally costs between $24,000 and $30,000. It is extremely durable, lasting 40 years or more.
Construction requires highly specialized workers, but post-tensioned concrete can be dropped by bucket or pumped into place with long hoses, reaching hard-to-get areas like wooded sites or rooftops.
Post-tensioned concrete is able to bridge over poor, expansive soils. Expansive soils occur throughout the U.S., but they are most prevalent in areas such as Louisiana, Texas, Colorado, California, Idaho, Nevada and Arizona.
It is an excellent choice if you are building a hard court over an existing clay or fast-dry court since soft courts act like expansive soils.
It is a good choice for the reconstruction of a cracked or deteriorated asphalt court. If you were to repave the asphalt court, you would have to first remove or pulverize the existing pavement to prevent cracks from radiating through. Post-tensioned concrete can be installed right over a cracked court, saving time and money.
Concrete is not compatible with acrylic surfacing systems and therefore needs to be properly primed before a surface is installed, an extra step that adds slightly to the cost of the surfacing.
Remember, issues of cost, durability, site engineering, ease of construction and type of surface all go into making informed decisions about what type of hard court is right for you. If you keep in mind these basic concepts about pavements and their design and construction requirements, hard courts aren't really so hard after all.
by Andrew R. Lavallee, ASLA and Sheldon Westervelt, P.E.