# A Methodological Approach to the Study of Retroreflective Pavements
## 3 Results and Discussions
### Stage 2: Approximation to the Retroreflectance Measurement  
Figure 14 shows the variation in reflectance when varying the entrance angle between the direction of the incident light source and the measurement direction of the reflectance. These angles are 45\({}^{\circ}\) (typically used) and 0\({}^{\circ}\) (as shown in Figure 11). The reflectance values are given in Table 6. Firstly, it is observed that for both types of aggregate, reducing the entrance angle leads to an increase in the retroreflectance. This increase is nearly constant throughout the visible range for both white and black mixtures. However, for the mixtures with warm colours, the increase is more pronounced at wavelengths near the infrared range, while for the colder-shaded mixtures, it is more pronounced at wavelengths nearer the ultraviolet range, regardless of the type of aggregate used to manufacture the mixtures. This demonstrates the retroreflective capacity of the designed bituminous mixtures, suggesting that the adverse effects on the health of users could be reduced if the radiation reflected towards them is minimised.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Bituminous Mixture**} & \multicolumn{4}{c}{**Reflectance (\%)**} \\ \cline{2-5}  & \multicolumn{2}{c}{**45\({}^{\circ}\)**} & \multicolumn{2}{c}{**0\({}^{\circ}\)**} \\ \cline{2-5}  & **Mean** & **Std. Dev.** & **Mean** & **Std. Dev.** \\ \hline AUTL-LW & 52.4 & 2.3 & 78.0 & 9.7 \\ \hline AUTL-GW & 49.1 & 2.6 & 82.7 & 11.6 \\ \hline AUTL-PW & 59.5 & 10.2 & 78.2 & 10.9 \\ \hline AUTL-LO & 20.5 & 1.5 & 32.4 & 5.8 \\ \hline AUTL-GO & 16.0 & 2.5 & 26.4 & 4.3 \\ \hline AUTL-PO & 23.3 & 2.4 & 28.7 & 9.1 \\ \hline AUTL-BR & 25.2 & 2.2 & 35.9 & 2.1 \\ \hline AUTL-GBR & 21.9 & 2.3 & 36.1 & 1.6 \\ \hline AUTL-PBR & 27.9 & 2.0 & 36.5 & 4.2 \\ \hline AUTL-LR & 12.4 & 1.6 & 19.1 & 1.9 \\ \hline AUTL-GR & 12.6 & 2.0 & 19.4 & 2.4 \\ \hline AUTL-PR & 15.5 & 2.3 & 21.9 & 3.1 \\ \hline AUTL-LBL & 23.4 & 1.6 & 38.4 & 2.1 \\ \hline AUTL-GBL & 27.0 & 2.4 & 38.9 & 2.1 \\ \hline AUTL-PBL & 26.4 & 1.3 & 36.9 & 8.5 \\ \hline AUTL-LB & 8.9 & 0.6 & 14.3 & 2.7 \\ \hline AUTL-GB & 9.5 & 1.4 & 11.0 & 3.1 \\ \hline AUTL-PB & 7.6 & 2.7 & 10.4 & 2.2 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Reflectance values in the visible spectrum for different measurement angles.  
Figure 14: Reflectance for the observation angles between the direction of the incident light and the measurement directions of 45 and 0\({}^{\circ}\). Results for the mixtures made with (**a**) limestone aggregates, (**b**) granitic aggregates, and (**c**) porphyry aggregates.  
The samples used in this stage, where the entrance angle is 45\({}^{\circ}\), differ from those used for the same angle in the previous stage. In this case, the samples have been exposed to solar radiation for a long period of time. This has caused the lighter samples to be slightly darker than the original ones, while the darker ones appear slightly lighter. Therefore, the reflectance values are only directly comparable within each stage of the study. Nevertheless, as seen in the previous stage, the aggregate type influences only the lightest mixtures (white and ochre), among which the limestone aggregate exhibited slightly higher values in general.  
It must be remembered that all the measurements with the spectroradiometer were conducted with the same light entrance angle with the surface (45\({}^{\circ}\)). Therefore, it is proposed to analyse the effect that the variation in this angle would have on the retroreflectance values. A priori, it could be thought that the texture of the mixture will also influence the measurements obtained; therefore, in addition to the AUTL-type mixtures, two further types of mixtures have been considered, a BBTM 8A and an AC 16S, both with different textures.