**Damage Mechanism Evaluation of Large-Scale Concrete Structures Affected by Alkali-Silica Reaction Using Acoustic Emission**

**Vafa Soltangharaei 1,\*, Rafal Anay 1, Nolan W. Hayes 2, Lateef Assi 1, Yann Le Pape 3, Zhongguo John Ma <sup>2</sup> and Paul Ziehl <sup>1</sup>**


Received: 25 September 2018; Accepted: 31 October 2018; Published: 3 November 2018

**Abstract:** Alkali-silica reaction has caused damage to concrete structures, endangering structural serviceability and integrity. This is of concern in sensitive structures such as nuclear power plants. In this study, acoustic emission (AE) was employed as a structural health monitoring strategy in large-scale, reinforced concrete specimens affected by alkali-silica reaction with differing boundary conditions resembling the common conditions found in nuclear containments. An agglomerative hierarchical algorithm was utilized to classify the AE data based on energy-frequency based features. The AE signals were transferred into the frequency domain and the energies in several frequency bands were calculated and normalized to the total energy of signals. Principle component analysis was used to reduce feature redundancy. Then the selected principal components were considered as features in an input of the pattern recognition algorithm. The sensor located in the center of the confined specimen registered the largest portion of AE energy release, while in the unconfined specimen the energy is distributed more uniformly. This confirms the results of the volumetric strain, which shows that the expansion in the confined specimen is oriented along the thickness of the specimen.

**Keywords:** alkali-silica reaction; acoustic emission; pattern recognition; confinement; damage evaluation
