Civil researchers continuously strive to find alternatives of environmentally friendly cements. Geopolymers are vital to the production of environmentally friendly cement. The development of geopolymer concrete is promising for change in the method of concrete production. The main purpose of this study is to evaluate mechanical properties of fly-ash based geopolymer concrete and its behavior. The key parameters include, binder (fly-ash) content, and water/binder ratio. To achieve this goal, 12 concrete mixes are prepared with different binder content (300,350, and 400 kg/m3) and water/binder ratio (35,40,45, and 50%), and use the alkaline activator consists of sodium silicate and sodium hydroxide solutions. Results exhibit that the mechanical properties improve on increasing the binder content and reducing the water/ binder ratio. Optimum mixes are identified by a binder content of 400 kg/m3 and a water/binder ratio of 35%.