# Payment Structure Characteristics and Behaviour Analysis with Digital Image Correlation
## 1 Introduction  
The development of technology, apart from being especially useful in improving the quality of our lives and making everyday life easier, also leads to progress in scientific processes and research. One such technology is digital image correlation (DIC), which has been used in various civil engineering research areas in the last few years. This modern and innovative research method also shows its potential in geotechnical engineering and pavement structure testing. DIC is the method for measuring in-plane displacements by using an optical system composed of digital cameras, a light source, and a computer for data acquisition [1]. This method can also be used for the observation of out-of-plane deformation by using an additional camera. The two cameras then capture the same point, giving three-dimensional data, and the method is called 3D-DIC. Within geotechnical engineering, DIC is mainly used for a very precise measurement during material characterisation. It was used for the basic size parameters of geo-material particles' measurement [2], for its microstructure characteristics [3], and for its physical and micromorphological characterisation [4]. The areas of application of this method in pavement construction are diverse, considering that most tests of road construction materials entail the failure of specimens due to load application, while the displacement is monitored. DIC serves precisely the monitoring of these displacements. The application of the DIC method in the research of asphalt and concrete pavements has increased during the last few years. [PERSON] et al. [5] pointed out the usefulness of the information obtained by the DIC technology during asphalt testing. [PERSON] et al. [6] used DIC for measuring the displacement of asphalt cylindrical specimens exposed to uniaxial compressive tests. [PERSON] et al. [7] used theDIC method for the analysis of fatigue cracks in asphalt pavement exposed to freeze-thaw cycles. Furthermore, the DIC method was used for monitoring crack development due to the indirect tensile strength of RAP asphalt specimens [8]. In their review paper, [PERSON] et al. [9] emphasised the advantages of DIC over linear variable differential transformers due to the unpredictability of the local damage location. As a result of the application of DIC during the semi-circular bending (SCB) test, [PERSON] et al. [10] were able to identify three phases of the crack development process. The reinforcement effect of different fibres on the asphalt mixture was employed by using the fracture curve of the SCB test and DIC method by [PERSON] et al. [11]. [PERSON] et al. [12] used DIC to quantify the impact of different asphalt modifiers (crumb rubber and plastic waste) on the size of the plastic zone of the material by monitoring crack development by the SCB test. The definition of the load rate at which it is possible to observe the mechanism of fracture and creep deformation for the evaluation of the low-temperature performance of an asphalt mixture was obtained by this method [13]. The DIC technology was applied in the analysis of ageing and modifiers' effect based on SCB test samples in [14]. The use of the 3D-DIC technology over the 2D-DIC technology due to SCB testing was emphasised by [PERSON] et al. [15]. Due to significant out-of-plane displacements, the 2D-DIC technology proved to be unsuitable due to only in-plane measurements being possible. The DIC method has been shown to be as appropriate for thermal expansion measurement as the grid method, but DIC requires more computational resources [16]. This method can also be used on larger samples, such as asphalt slabs, not only on standard cylindrical and semi-circular specimens, which expands its application field [17; 18; 19]. The slabs provide us with results more similar to real conditions. The usefulness of this method was highlighted in the work of [PERSON] et al. [18], where the development of cracks on the asphalt slab reinforced by various geogrids was monitored.