How/when
it forms?
Cold
joints are formed primarily between two batches of concrete where the
delivery and
placement of the second batch has been delayed and the initial placed
and
compacted concrete has started to set.
The
basic rule is to try to avoid cold joints by pouring straight through
until the
job is finished.(or plan for a proper construction joint)
Implications:
The
full knitting together of the two batches of concrete under vibration
to form a
homogeneous mass is therefore not possible, unlike the compaction of
two fresh
workable batches of concrete. This could be a potential plane of weakness.
Cold
joints, unlike cracks that form in hardened concrete through tensile
restraint,
are not gaps in the concrete but merely seams containing no appreciable
void
structure. They are usually linear, closely joined and bonded. However,
there
is a danger of small voids in areas where the concrete is not fully
compacted,
as with any concrete pour.
Generally,
cold joints are not a problem
structurally if the joint is in compression.
However,
the location of the joint within the structure, the structural function
of the
element and aesthetics need to be considered when assessing a cold
joint.
