## 5 Conclusions  
Acoustic emission was utilized for monitoring the activities caused by ASR in large-scale reinforced concrete specimens. The specimens resemble common nuclear power plant containments with no shear reinforcement. An agglomerative hierarchical algorithm was used to classify the AE data based on the energy-frequency dependent features to study and identify the damage mechanisms in the specimens with different stress boundary conditions. The conclusions of this study are summarized as follows:  
* A significant portion of the AE data (in terms of cumulative signal strength) in the confined specimen was recorded by sensor 3, which was located at mid-thickness. However, the portion of cumulative signal strength for the corresponding sensor at mid-thickness of the unconfined specimen was less in comparison to the other two sensors in that specimen. This agrees with expectations, as the confined specimen exhibited increased out-of-plane expansion in comparison to the unconfined specimen, meaning that the crack distribution is expected to be more concentrated near mid-thickness of the confined specimen than near the reinforcement layers. * The frequency contents of signals in the confined and unconfined specimens evolved from low to high frequency with the age of concrete although this evolution started later in the confined specimen than the unconfined specimen. Since the high-frequency AE signals have been associated to the cracking in aggregates [17], different crack mechanisms in aggregate for the confined and unconfined specimens are expectable. However, there are different contradictory ASR cracking hypotheses that have been proposed by the researchers [33; 34; 35; 36; 37; 38; 41; 42; 43]. * There is a coincident point observed in the strain curves and the CSS of Cluster-3 in the confined specimen and Cluster-6 in the unconfined specimen. The CSS rate in terms of concrete age increases at the time (around 150 days), when the strain rate is decreasing. This point is named as inflection point of strain curve, where the curvature of strain curve changes from positive to negative. The inflection point location in terms of concrete age depends on the kinetic of ASR reaction and diffusion process. Determining the inflection point, latency and characteristic time are experimentally estimated, which are the two important modeling parameters. According to the results of AE data and clustering, the inflection point location in terms of concrete age could be estimated from the variation in CSS rate change of clustered AE data. * Monitoring of a structural system with acoustic emission can provide useful information regarding condition based maintenance and/or retrofit. For example, one potential time of action for treating affected structures is around the inflection point in the volumetric strain curve which can be approximated through acoustic emission data. This point coincided with observation of first visible surface cracking. After identifying the time of action, treatment methods may be implemented to mitigate the effects of ASR. Injection of lithium solution is a chemical alternative to mitigate ASR provided that enough solution penetration in the structure can be achieved. Another method is to remove moisture through coatings and sealers such as silane sealers and bituminous or elastomeric coatings. After conducting these methods, structures should be monitored for enough time to evaluate the efficiency of the method or methods. Conceptualization, P.Z., V.S., Y.L.P., and Z.J.M. ; Data curation, V.S., R.A., and N.W.H. ; Formal analysis, V.S. ; Funding acquisition, Z.J.M., Y.L.P and P.Z. ; Investigation, V.S., R.A., N.W.H. and L.A.; Project administration, Y.L.P., Z.J.M. and P.Z. ; Resources, Y.L.P., Z.J.M. and P.Z. ; Supervision, Y.L.P., Z.J.M. and P.Z. ; Visualization, V.S. ; Writing - original draft, V.S. ; Writing - review & editing, V.S, N.W.H., Z.J.M., Y.L.P. and P.Z.