Concrete is a heterogeneous material with a highly non linear behavior, which is mainly caused by the
initiation and propagation of micro cracks within the several components of the material. The damage behavior of
concrete is usually simulated on the macro scale using complex constitutive models. The direct determination of the
homogenized material parameters is often difficult and sometimes impossible. Furthermore these materials models do
not explicitly represent effects and bond behaviors of interfaces between the several components. So in order to predict
of concrete behaviors and characteristics, it should be modeled as a three phase composite material consisting of
aggregate, interfacial transition zone (ITZ) and cement paste. The size and distribution of aggregate affects concrete
characteristics. Because of the random distribution and size variation of aggregate in concrete, the modeling of
concrete behavior based on component in meso structure is difficult and so we must use simple assumption. In this
paper with mixing design and grading curve we developed a simple method to replace real aggregate with equivalent
sphere aggregate with effective diameter. So we can use simple methods instead of complex numeral and randomness
or x ray methods to find effective diameter and use it to determine two arrangements with maximum and minimum
aggregate volume as a repeatable basical element .As a result we can use this element to modeling the behavior of
sample concrete in meso scale and three phases.
