Full Issue (17 MB) - Pile Driving Contractors Association

VI-RO spinning machine. This process involves placing zero
slump concrete in layers in a steel form barrel while spinning
the form barrel at a low revolution speed. Revolution speed is
high enough that concrete being charged into the form moves
to the sides of the form by centrifugual force but slow enough
to allow the safe placement of concrete in the form. After filling
the form with the required volume of concrete, the revolution
speed is increased to allow compaction of the concrete.
Strict quality control standards were followed with four
test cylinders made for every 10 pile sections produced. Two
cylinders are immediately transported to the lab to cure in
accordance to AASHTO T-23 standards. These two cylinders
are broken at age 28 day. The two remaining cylinders are
match cured with the pile sections. One is broken at the end
of the steam curing cycle and one cylinder is broken at the age
of 7 days to verify that the section has achieved tensioning
strength.
Upon completion of the spinning cycle each pile section
is steam cured in a kiln at a minimum of three hours at temperatures
from 130° minimum and 180° maximum. They are
stored for the final curing period and reach a 28-day strength
of not less than 7,000 psi.
The full length cylinder piles are then assembled from
the pile sections. Pile sections are placed on “lay down” racks
where they are inspected. The post tensioning
tendon core holes are aligned
and two ½” diameter, 270 ksi low relaxation
strands are installed in each core
hole. Ends of the pile sections are “buttered”
with polyester resin. Sections are
butted together and become a single
unit by stressing with hydraulic jacks.
The strands are stressed to a predetermined
202,500 ksi.
Once the stressing is finished and
after the joint compound has set, the
tendon holes are grouted with a mixture
of cement and water. The grout is
64 • Q4 • 2009