Theoretical thickness = (C/S Area of the section ) / (Semi perimeter in contact with the atmosphere.)
Where, semi perimeter = perimeter /2
For example, Consider a 150 mm side cube, and assume these three sides are exposed to the atmosphere
Thus the theoretical thickness for the given cube and given exposure conditions is 100 mm.
Where is it used?
Theoretical thickness is generally used in the study of creep or drying shrinkage of a structure. During dry shrinkage, the water is expelled outside of the concrete. As a result, the water travels a path. This path is expressed in terms of theoretical thickness.