As a detailed inspection of a concrete structure in service, core samples are usually drilled out and then mechanical properties are measured. In this study, damage estimation of concrete structures from core samples is developed, applying acoustic emission (AE) and X-ray computed tomography method. Concrete-core samples were taken from reinforced concrete of an existing canal. These samples are strongly damaged by freezing and thawing process. Crack distributions of concrete-core samples were inspected with helical Computerized Tomography (CT) scans, which were undertaken at 1-mm intervals. After helical CT scan, damage of testing samples was evaluated, based on fracturing behavior under compression and AE activity. AE behavior is dependent on the degree of damage, and could be approximated by applying the AE rate-process analysis and damage mechanics. AE generation behavior is associated with crack volume due to damage accumulation in concrete. The damage is quantitatively defined by a scalar damage parameter in damage mechanics. Applying the scalar damage parameter, quantitative estimation of damage is proposed in terms of relative modulus of elasticity which is named "durability index". By calculating the durability index, the initial damage of samples is estimated from AE database. The decrease in mechanical properties could be evaluated by comparing the average CT number with the durability index, both of which are affected by internal cracks generated. Thus, the damage of concrete structures is quantitatively evaluated by AE and X-ray computed tomography method. (C) 2010 Elsevier Ltd. All rights reserved.