# Payment Structure Characteristics and Behaviour Analysis with Digital Image Correlation
## 3 Results and Discussion
### The 3D-DIC for Pavement Structure Analyses
As the load cycles progressed, from first to fourth, and stresses increased, the trends of deformation for each mixture type were amplified, meaning that the end of the last cycle can offer much information regarding broader behaviour, such as non-localised behaviour. Figure 8 enables such an insight with an overlay of the vertical displacement fields on the asphalt's surface. Firstly, it is visible that the mixture with 3% cement content was the most flexible, in terms of the range of vertical deformation being around 9 mm. Additionally, there was visible localised behaviour without the possibility of a proper stress distribution in an area wider than the input load. This suggests a failure of the lower layers beneath the load and a lack of stiffness to enable a wider distribution of stresses. With an increase of cement content to 5% and 7%, the behaviour significantly changed, showing clear signs of greater stiffness, which was most visible for the lower range of deformation within the entire surface. It should be noted that the differences in behaviour between 5% and 7% cement content on the system level were evidently smaller than on the material level. Namely, the total range of deformation was within 0.5 mm (around 10%), and there was a gradual decrease in deformation away from the load introduction area. The 7% cement content system showed greater stiffness as there was a smaller area within the 2.4 to 3.6 mm range, which was to be expected due to the higher modulus value of the supporting layer. Nevertheless, the use of 7% did not seem to offer large enough benefits in comparison to the 5% cement content structure. Figure 7: Vertical displacement at the end of each loading cycle. Figure 8: Displacement fields at the end of the 4 th loading cycle for samples with various levels of cement. Furthermore, it can be concluded that increasing the percentage of cement resulted in a stiffer system with fewer total vertical displacements. The moduli of elasticity, as well as the compressive strength, as shown in Table 1, varied significantly depending on the amount of cement. With an increase in cement content from 3% to 5%, there was an increase in the compressive strength and modulus of elasticity by 140% and 190%, respectively. With an increase in cement content from 5% to 7%, there was an increase in the strength and modulus of elasticity by 38% and 19%, respectively. On the other hand, the 3D-DIC pavement system analyses showed an increase in vertical displacement for the last three loading cycles with an average of 26% and 44% for increasing cement content from 3% to 5% and from 5% to 7%, respectively. The increased strength that came with the increased cement content from 5% to 7% is not fully expressed because it was not fully utilised within the pavement system. This means that increasing the cement content did not provide obvious benefits to the pavement system such as those recorded during the \"pure\" material testing. Part of the differences in the stiffness and the strength of the CBGM itself were \"lost\" within the pavement system. Namely, the pavement structure is a system made of materials differing in strengths, stiffness, and ductility, which assume non-linear weights in defining the system's response. It is shown that certain trends of the material behaviour defined at the simple material level of each independent pavement layer will significantly differ when it is placed in the system, depending on the ratios of different properties. Therefore, it can be concluded that this approach of observing the pavement structure is more suitable and provides more realistic data for predicting the behaviour of the pavement structure in real conditions instead of analysing the pavement layers individually. In the future, the potential of defining coefficients that should take this effect into account should be explored when defining the characteristics of each pavement layer that is used to calculate the stresses and strain state and to predict the behaviour and service life of the pavement structure itself.