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
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.
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.
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 =
"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.
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
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)
of a silicoflouride solution floor hardener, more or less per COE concrete
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?
comments or suggestions greatly appreciated.