Commonly asked questions about concrete and its placement.
Why is the concrete specified to be
"continuously placed" on a post-tensioned slab project?
Because the design of a post-tensioned slab
foundation is based on the entire member acting as a unit utilizing the full
allowable strength of the concrete and the steel tendons.
Are "cold joints" detrimental to the
design?
Cold joints are to be avoided for the
reason outlined above. Joints can be allowed for purposes of
controlling the placement by the engineer but must be depicted on the
plan.
What about cold weather curing additives
such as calcium carbonate?
Calcium carbonate (CC) must be limited to
a max of
1% of the design mix to prevent corrosion of the steel reinforcement.
Is continuous inspection of the concrete
placement necessary?
Fortunately, yes. Not just
because it is prescribed for structural members by the UBC but also to
help assure
the builder that placement is continuous and the mix strength is as
specified on the engineered plans.
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