||A quantitative understanding of the efficiency of fly ash as a mineral admixture in concrete is essential for its effective utilization. To overcome the disadvantages of traditional decomposition approaches, we proposed a novel unification approach. In this approach, using nonlinear regression and optimization technique, the compressive strength model and the efficiency factor model are generated at the same time. That is, the efficiency factor model is a part of the compressive strength model. The efficiency factor model reported could be helpful in the design of fly ash concretes at different age, at different replacement percentage, and different water-binder ratio with greater confidence.