A design optimization process used to determine the proportions of sand, cement, coarse aggregate, water, fly ash, water reducers, air entraining agents and fillers needed to produce a concrete mixture that has desired strength and slump properties and a minimal cost. The optimization process comprises a combination of models that accurately reflect the properties of a concrete mixture based on the properties of its individual components. The process is further capable of optimizing the durability of the cementitious mixture and of accurately calculating the expected yield of the mixture.