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| FUAQ |
| Why concrete fails at considerably lower stress than the strength of bulk paste or aggregate? |
Concrete is generally considered as two
phase material i.e paste phase & aggregate phase. There is also a third
phase called the transition phase which represents the interfacial region between
the particles of coarse aggregate & hardened cement paste. The interfacial zone is 10 to 50 mm in
thickness.
 Transition zone is a plane of weakness due
to poorer bond between paste & aggregate , in general.
Transition zone develops microcracks due
to drying shrinkage or temperature
variation even before the structure is loaded. When structure is loaded &
at high stress levels, these micro cracks propagate and bigger cracks are
formed resulting in failure of bond. It
is because of this presence of Transition zone that concrete fails at considerably lower stress
than the strength of bulk paste or aggregate. |
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