In this study, surface interaction mechanisms of the reference (OPC) and fly ash blended cements (FAC) were investigated. The physical, chemical, mineralogical and mechanical properties of OPC, fly ash (FA) and FAC, as well as the electrokinetic potentials (zeta potential) of FA-OPC particles were examined. After cement pastes were prepared with OPC and FA, they were water-cured for 2, 7 and 28 days. The pastes were made using X-ray diffraction (XRD), differential thermal analysis (DTA) and Fourier transform infrared spectroscopy (FT-IR) in order to determine their mineralogical composition and the determination of the phases developed during the hydration. Furthermore by scanning electron microscope (SEM) 28 days microstructures of pastes were determined and mortars were examined following strength tests. While the addition of FA has increased the setting time and the amount of water demand, amount of portlandit (Ca (OH)(2)) decreased during the hydration. Moreover FA has shown different electrokinetic behaviors and surface features compared to OPC. These variations effected on compressive strength of mortar samples.