2.3.3.2
Placing and Casting
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NOTE: Select chamfer required. Consult with local
producers. Where project requires a large quantity
of piling, a specific value may be specified,
otherwise, use a minimum or a range of values.
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Perform concrete casting within 3 days after pretensioning steel; however,
do not deposit concrete in forms until placement of reinforcement and
anchorages have been inspected and approved by pile manufacturer's quality
control representative. Produce each pile of dense concrete straight with
smooth surfaces with reinforcement retained in its proper position during
fabrication. Use vibrator with heads smaller than the minimum distance
between steel for pretensioning. Make surface of pile ends perpendicular
to axis of pile. Chamfer, [a minimum of 19 mm 3/4 inch,] [[_____] mm inch,]
[between 19 and 28 mm 3/4 and 1 1/8 inch,] ends of piles and corners of
square piles.
2.3.4
Curing of Piles
Cure piles using moist or accelerated curing.
2.3.4.1
Moist Curing
a.
Impervious sheeting: ASTM C 171; waterproof paper, clear or white
polyethylene sheeting, or polyethylene-coated burlap.
b.
Pervious sheeting:
AASHTO M 182.
c.
Liquid membrane-forming compound:
ASTM C 309, white pigmented,
Type 2, Class B.
2.3.4.2
Accelerated Curing
After placement of concrete, moist cure for a period of 4 hours.
Accelerate curing until concrete has reached specified release strength.
Enclose casting bed for accelerated curing with a suitable enclosure.
During application of steam or heat, increase the air temperature at a rate
not to exceed 15.6 degrees C 60 degrees F per hour. Cure at a maximum
temperature of 15.6 degrees C 160 degrees F until concrete has reached
specified release strength. Reduce temperature at a rate not to exceed
15.6 degrees C 60 degrees F per hour until a temperature of -7 degrees C 20
degrees F above ambient air temperature is reached. After accelerated
curing, moist cure using either water or membrane curing until a total
accelerated and moist curing time of 72 hours is achieved.
2.3.5
Detensioning
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NOTE: Specify "release strength." Release strength
of 30 MPa 4000 psi (design strength of 35 MPa 5000
psi) or 0.8 of the 28 day design strength is
desirable; however, some regions use 0.7 of the
design strength (25 MPa3500 psi for design strength
of 35 MPa 5000 psi). A minimum release strength of
0.6 of the design strength is required. Check with
local pile manufacturers.
SECTION 02395
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