## 1 Introduction  
Structure health monitoring is an important part of the optimal operation period maintenance of the civil concrete facilities. During the service period, structures are subjected to various loading and environmental conditions leading to the deterioration processes within the material. The primary danger to structure durability is posed by internal defects which can lead to structural unsurveleability regarding safety and stability. Moreover, in the case of an earthquake or flood, the caused sudden loads can severely damage in-service structures and can lead to their final collapse. Concrete structures are popular worldwide structure types owing to their material versatility and relatively low cost: only since the 1950s, a large number of concrete structures have been made in Japan [1]. Concrete is a complex heterogeneous construction material with multiple discontinuities in the internal structure that accumulate under external forces and strongly affect the performance of the engineering structure. There are preliminary microcracks even prior to the loading caused by the differences in mechanical properties of coarse aggregate and cement paste and randomly distributed within the concrete matrix on the interface of both these phases [2]. Pre-existing defects developed in a structure during external factors' actions are the predominant origin of destruction initiation processes in concrete and define their general deformational behavior. New defects may develop and coalesce with primary flaws leading to material deterioration and future structure failure [3]. The analysis of these processes is complicated, and the resulting damage degree cannot be evaluated by only mechanical properties' degradation. Therefore, there is a necessity to obtain more comprehensive information about the internal structure changes caused by defects such as cracks and voids developed during continuous loading to evaluate the damage degree precisely and establish efficient maintenance of concrete structures subsequently. In this research, the analysis of the fracture behavior of concrete is conducted by such advanced non-destructive testing (NDT) techniques as Acoustic Emission (AE) and Digital Image Correlation Method (DICM) which allow recording micro-crack events and strain evolution in concrete. AE is a widely used elastic wave-based NDT method in structure monitoring to identify and characterize the damage process of concrete material [4]. By analyzing the AE signal descriptors recorded during fracture, the characterization of the nucleation and growth of the cracking pattern [5,6] and measurement of the deterioration of concrete structure [7,8] can be conducted. [PERSON] et al. also used a combination of AE and CT techniques to study the fatigue fracturing evolution of granite with pre-existing flaws caused by repeated freezing-thawing cycles [9]. DICM is a full-field technique that can be applied to any type of material to investigate fracture evolution processes. In the work of [10], pre-peak and post-peak strain characteristics were described for rock specimens under uniaxial compression, and the observation that a major failure plane, due to strain localization, becomes noticeable only long after the peak stress occurs was made. [PERSON] et al. investigated the limits of accuracy of the DICM strain measurement system on polymeric materials under different environmental conditions and concluded the proper strain determination in terms of longitudinal and transverse strains as well as in terms of global average and local strains [11]. The DICM technique is also used to investigate the strain distribution fields and cracking phenomena in asphalt materials [12]. The study of fracture evolution in concrete has also been investigated in numerous research. [PERSON] and [PERSON] analyzed the fracture behavior of three different types of concrete under compression [13].