Credit: Original article published here.

What Exactly Is A Crack?

A crack is simply when the concrete matrix, or the “glue” for the rocks, cannot hold bond to itself, or the aggregate in the mix, due to volume changes, over-loading, and/or repeated loading.    This creates a failure plane that extends to the exterior of the concrete that we can see in the form of a crack.  The highest tensile stress at which concrete does not crack is the modulus of rupture, which is dependent upon the concretes compressive strength.