Concrete provides an attractive, smooth and easily maintained surface for skatepark construction.  This makes concrete parks safer than other construction options. 

Building a skatepark is a sizable job, so it should be split into a series of smaller jobs.  This will control the amount of concrete to be placed at one time.  The formula for estimating concrete volume is provided in Basic Concepts section.  For skatepark construction use 4000 psi (pounds per square inch) concrete to a minimum depth of 4 inches.  This is poured over a minimum depth of 4 inches of  “¾ minus” (3/4 inch in diameter or less) compacted gravel (as described above).  Never use “fire water” or other concrete curing accelerators unless you are highly experienced in skatepark construction.  Using a curing accelerator makes it likely that the concrete will set-up before proper hard trowel finishing can be completed.

Structural support of the concrete comes from using number three (3/8 inch) rebar, placed and tied on a minimum of 12-inch centers.  For a skatepark this is strong stuff and will result in a slab stronger than most people’s driveways.  Obviously, through normal use there will never be anywhere near that type of stress on the slab of the skatepark.  However, this superior material will keep future cracking to a minimum.

For large construction projects like a skatepark the concrete is best placed with a pump truck.  A concrete pump truck is a specialized piece of machinery that can pump concrete through a tube attached to an overhead boom over a distance of 150 feet or more.  The last 10 feet of the tube is flexible and has handles, so that it can be moved several feet in any direction while the concrete is being pumped.  The individual placing the concrete manually controls the flexible end of the tube.  The person placing concrete must remain alert and aware of the presence of fellow workers.  The pressure necessary to pump concrete through the tube is substantial.  If there is any air in the line, the flexible end of the tube can get tossed around like a fire hose, with risk of physical injury to anyone near-by.  The pump truck operator controls the boom and the flow of concrete being placed.  The pump truck operator and the person placing the concrete communicate through a series of hand signals.  Talk with the driver well in advance so that you know what these signals are.

If and when you go to a structural engineer for advice or review of the design specifications for your skatepark, he or she will probably recommend that expansion joints be placed in the concrete at least every 8 feet (like a driveway) and offer you other recommendations that are perfectly appropriate for general concrete construction.  However, these recommendations are not appropriate for skateparks.  You will have to become an advocate for the uncommon methods used in modern skatepark construction as outlined in this book.  Take this information with you to such meetings.  The most important thing to help structural engineers and others understand about these techniques is to help them realize you are not building a parking lot or a sidewalk.  You are building a large concrete form specifically designed and engineered for the sport of skateboarding.  Form follows function.  The continuous concrete construction of a skatepark as described here results in random hairline cracking which is not felt through the wheels of a skateboard and will, therefore, not disrupt the ride (see following sections).  This construction approach is better for the building of concrete skateparks than the methods most engineers are familiar with.  Typical engineering methods result in controlled cracking through a series of expansion joints which results in the all too familiar ka-chunk, ka-chunk, ka-chunk of a standard sidewalk.  Memorize and keep repeating the following statement; “we understand that we are making a trade-off, but random hair-line cracking is better than expansion joints and will be kept to a minimum because we are using 4000 psi concrete (as strong as it gets) over compacted fill (3/4 minus) with number three (3/8 inch rebar) as reinforcement.”

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