© 2014 Elsevier Ltd.The present study is aimed at investigating the combined effects of the compressive strength and hydration development of blended cements which contain fly ash. In the first stage, chemical, physical, X-Ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FT-IR) analysis were performed in order to determine the characteristics of Portland cement and fly ash. In the second stage, the compressive strength of cement mortars and setting time, water demand and volume expansion of cement pastes were identified according to the standard cement experiments. In the last stage, XRD, FT-IR, thermal and scanning electron microscope analyses were performed in order to determine the hydration of cement pastes. Consequently, the addition of FA in Portland cement contributes to the consumption of Ca(OH)2 which is formed during the hydration of cement and leads to the formation of cementitious products, like C-S-H. Therefore, the compressive strength of fly ash blended cement mortars increased at later ages compared to the early ages.