17.1
Initiation of cracks
Accurately
knowing causes of how cracks initiate and propagate, such problems can beforehand
be addressed toward appropriate protections and repairing. In addition to
apparent example, the concrete cylinder will be sampled for consideration of
its behaviors that will be subject to different circumstances.
To
begin with, let consider the concrete cylinder that has not reached the complete
hardening and without supports or restraints (Figure 17.1a). As its
consequence, this allows concrete itself to shrink freely towards the center
and precisely this does not induce the stress inside the concrete by any means.
Hence, under this particular condition, cracks will not be initiated.
Conversely,
if the concrete cylinder is restrained from both sides, subsequently the so
called tensile stress will be produced in the concrete itself. And according to
this behavior, it seems that concrete cylinder is left to set and freely shrink
naturally while it is being stretched to retain the original length. If this
continues, creep will then be produced along with the reduction of tensile
strength in concrete (Figure 17.1c). And whenever the tensile stress is greater
than the tensile strength in concrete, this results a beginning of cracks at
the point where concrete stress is completely vanished, which regardless whether
being fresh or hardened concrete (Figure 17.1d).
In
spite of concrete size, these 4 simple processes briefly describe the natural
behavior of cracks as mentioned.
0 ความคิดเห็น:
แสดงความคิดเห็น