Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Dudes: Skatepark Advice Requested

[Subject Prev][Subject Next][Thread Prev][Thread Next]
We're working on "skatepark" which is a pavement for cruising around on your skateboard among oddball pieces of apparatus that support your death wish.  These are half and quarter pipes up to six feet; wedges, pyramids, kink and grind rails.  The project is apparently long-awaited and so eagerly anticipated by every teenager in Virginia Beach that each of them have been moved to write a "why the heck isn't it built yet?" letter to the editor.
The site is a city park built over a landfill, Mt. Trashmore.  The geotech engineer is the prime on it, they've done 8 borings confirming the site is 5 to 8 feet of clay over 4 to 9 feet of garbage over sand.  They advised the the client that there could be up some settlement.  An adjacent asphalt parking lot shows lots of bumps and slumps but no one has any idea how that pavement was built.
Site prep for our skatepark slab includes stripping, proofrolling and an 8" compacted 21A aggregate base course.
We've detailed a six inch slab on grade with a 18" turned edge at the perimeter.
It's a rounded free form shape in plan, about 250 ft long by 150 ft wide, total area about 25,000 sf total. 
There's some angst going around regarding joints and reinforcing in this slab.
First:  I'm of the opinion no true expansion joints are required. There aren't any adjacent structures or hard pavements.  A 70 degree (F) temperature change would create a radial expansion of only about 3/4 of an inch; the only restraint is the turned-down edge.
Second:  I think there are two choices:
    a) "jointed pavement":  6x6 W2.9xW2.9 WWF with sawed joints (or keyed construction joints) at 15 feet on center each way OR
    b) "continuously reinforced pavement"  #5 @ 8" EW and no joints. (rho = .006)
Jointed seems "safe", probably controlling the crack locations. The perimeter (about 50/50 curved and tangent sections) is complicated trying to eliminate any acute angles in the joint pattern.
Continuously reinforced without joints seems slick to me, would be nice to roll on and would save a lot of joint sawing and sealing.  What sort of cracks will show up and where they would occur is a wild card though.
We're using a 4000 psi air-entrained concrete (A4 & we typically see flyash at 20% of the cement content) , moist cured 7 days under plastic.
Finish spec'd is float and then steel trowel three times
Clean and seal the saw joints with ASTM C920 Sealant ( Type M Use NT)
Three treatments of a silicoflouride solution floor hardener, more or less per COE concrete spec.
Are there any good reasons to put expansion joints in?
Is there a better choice on the pavement and reinforcing?
Is the floor hardener a mistake/waste?
Any constructive comments or suggestions greatly appreciated.
Jan Harris
Liberty Engineering, PC
Virginia Beach, VA