In this study, the potential usage of fly ashes obtained from thermal power plants in construction sector is investigated. After oil crisis in 1970's, the researches are done increasingly to find alternative energy source, to decrease using energy and to produce cheap materials. The studies concerning by-products in construction sector are continued in the present time. Fly ashes caused very important environmental pollution. For this reason using and evaluation in various areas of fly ash is very important. The properties of fly ash showed that this material is a pozzolanic material and can be widely used in construction sector.