Turkey is located on such a seismically active region that many high-magnitude earthquakes have attacked the areas. Large number of reinforced concrete structures are collapsed or heavily damaged due to these earthquakes. It is crucial to evaluate the condition of the concrete structures in seismically active zones before and after the earthquake to decide whether the structure could continue its service for habitation or not. Consequently, quantitative damage estimation of concrete material is conducted by applying acoustic emission (AE) testing under unconfined uniaxial compression test of core samples taken from the concrete structures. Damaged concrete samples are examined based on fracturing behavior under unconfined compression. AE behavior of concrete under compression is dependent on the degree of damage and could be analyzed by the rate-process analysis. Core samples were collected from two reinforced concrete buildings damaged by Simav Earthquake that hit Kutahya City on May 19, 2011. In compression tests, compressive strengths and Young's moduli of these samples were determined. After estimating Young's modulus of the intact state from the correlation between AE rate and a damage parameter in each core, the damage levels of structures are quantitatively estimated.