Concrete and Tensile Strength
It is a fact that tensile strength of concrete is about
10% of its compressive strength!! Why do concrete members have such
a weak tensile strength?
The requirements for tensile strength is that the molecules or atoms hold
together when being pulled apart. If the material has many grain boundaries
or cracks, then the material pulls apart easily.
The requirements for compression resistance is for the atoms and molecules
not to slip past each other. As long as the grains remain in place, then the
material can resist compression without necessarily having tensile strength.
Greg (Roberto Gregorius)
Concrete is a brittle substance. You can push on it hard and it is strong.
But if you try to "stretch" it, it fractures. That is one of the reasons that
steel reinforcing bars are used in concrete construction and also why concrete
used in road paving has "expansion" grooves. It is hard but does not withstand
"stretching" forces, such as the freezing of water.
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Update: June 2012