# Payment Structure Characteristics and Behaviour Analysis with Digital Image Correlation
## 2 Materials and Methods  
### Materials and Samples  
For CBGM characterisation, natural river gravel (Figure 1) was used with cement CEM II/B-M (P-S) 32.5R as a binder in 3%, 5%, and 7% of aggregate dry mass. Optimal water content (OWC) and maximum dry density (MDD) were defined by EN 13286-4 [37]. For 3%, 5%, and 7% cement content, OWC was 4.91%, 5.35%, and 5.53%, respectively, while MDD was 2.08 g/cm\({}^{3}\), 2.12 g/cm\({}^{3}\), and 2.15 g/cm\({}^{3}\), respectively. For compressive strength and the elastic modulus of elasticity, cylindrical samples (diameter of 10 cm and height of 12 cm) were made according to the standard EN 13286-51 [38]. Three samples of each kind were made and cured for 28 days in a temperature- and humidity-controlled chamber (20 \({}^{\circ}\)C and 90% relative humidity) for a compressive strength test conducted according to EN 13286-41 [39]. During the compressive strength test, 3D-DIC was used for displacement measurement and the modulus of elasticity calculation following the guidelines from EN 13286-43 [40].  
For the testing behaviour of a three-layer pavement structure, 3D-DIC was applied for pavement system monitoring. For this test, the pavement structure setup was comprised of unbound granular material (UGM), CBGM, and an asphalt-wearing course (Figure 2). The UGM course was made of a natural river gravel with the grain size distribution presented in Figure 1. The optimal moisture content and maximum dry density determined according to EN 13286-4 [37] were 4.79% and 2.01 g/cm\({}^{3}\). The UGM was inbuilt by a vibrating hammer in mould with dimensions of 50 \(\times\) 50 \(\times\) 10 cm covered with geotextile, controlling the mass and geometry of the inbuilt material and calculating the water content and density of the unbound base layer after compaction. The UBM courses were made in such a way that their humidity deviated up to 1% from the optimum and with a degree of compaction up to a minimum of 98%. For each mixture, one sample of the UGM was made to reduce the influence of variations in the quality of this layer on the test results, but also to rationalise the amount of material and the time required for making the samples. As for the mechanical characteristics' test presented earlier in the text, the CBGM course was made with the same materials. The CBGM was inbuilt in mould dimensions of 45 \(\times\) 35 \(\times\) 10 cm, in one layer by vibrating hammer compaction for 10 min. After compaction, the samples were left in the mould for 24 h and, then, unmoulded and cured for 27 days by covering them with wet cloth at room temperature. The wearing course was simulated by AC 11 surf slab dimensions of 40 \(\times\) 35 \(\times\) 4 cm, and it was made according to EN 12697-33 [41]. As an aggregate for the asphalt mixture, eruptive stone was used according to standard EN 13043 [42]. Before the test, the surface of the asphalt slab samples was painted white to increase the contrast between the points on the surface that were monitored by the 3D-DIC system, so as to make it easier to recognise the stochastic pattern. For each cement content, three pavement structure setups were made.  
Figure 1: Grain size distribution of used natural aggregates.  
Figure 2: Pavement structure test setup.