# Durability and Safety Performance of Pavements with Added Photocatalysts
## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Freeze-Thaw Resistance**} & \multicolumn{2}{c}{**Ultrasounds**} & \multicolumn{2}{c}{**Intake of Water**} & \multicolumn{2}{c}{**Slip Resistance**} \\  & & \(\Delta\)f (\%) & & \(\Delta\epsilon_{e}\) (\%) \& \(\Delta\epsilon_{\text{e}}\) (\%) \& \(\Delta\epsilon_{\text{S}}\) (\%) \& \(\Delta\epsilon_{\text{R}}\) (\%) \& \(\Delta\epsilon_{\text{R}}\) (\%) \\ \hline S1-A & **Intermediate** & 26.3 & 11.7 & \(\mathbf{-825}\) & \(\mathbf{-1020}\) & \(\mathbf{-0.39}\) & \(\mathbf{50.16}\) \\ S2-A & Good & 66.0 & \(\mathbf{42.5}\) & \(\mathbf{-494}\) & \(\mathbf{-619}\) & \(\mathbf{33.73}\) & \(\mathbf{80.26}\) \\ E1-A & Good & \(\mathbf{-231}\) & \(\mathbf{-6.1}\) & \(\mathbf{-267}\) & \(\mathbf{-295}\) & \(\mathbf{6.51}\) & \(\mathbf{1.52}\) \\ E2-A & Good & \(\mathbf{-8.2}\) & \(\mathbf{14.3}\) & \(\mathbf{-85}\) & \(\mathbf{-14}\) & \(\mathbf{5.33}\) & \(\mathbf{-1.90}\) \\ E3-A & Intermediate/Good & \(\mathbf{-50.6}\) & \(\mathbf{-72.7}\) & \(\mathbf{-156}\) & \(\mathbf{-104}\) & \(\mathbf{5.13}\) & \(\mathbf{27.88}\) \\ \hline E1-T & **Peor/Very poor** & 32.4 & \(\mathbf{-45.9}\) & \(\mathbf{4}\) & \(\mathbf{-9}\) & \(\mathbf{-3.44}\) & \(\mathbf{25.98}\) \\ E2-T & **Foor** & 21.8 & \(\mathbf{-40.0}\) & \(\mathbf{41}\) & \(\mathbf{64}\) & \(\mathbf{-10.97}\) & \(\mathbf{-0.62}\) \\ E3-T & **Foor** & 25.0 & \(\mathbf{-30.9}\) & \(\mathbf{14}\) & \(\mathbf{10}\) & \(\mathbf{-9.68}\) & \(\mathbf{12.63}\) \\ \hline T1 & **Intermediate/Foor** & 18.3 & \(\mathbf{38.2}\) & \(\mathbf{-7.2}\) & \(\mathbf{-10.8}\) & \(\mathbf{-5.74}\) \\ \hline T2 & Good & \(\mathbf{-9.9}\) & \(\mathbf{-51.2}\) & \(\mathbf{-227}\) & \(\mathbf{-28}\) & \(\mathbf{-1.78}\) & \(\mathbf{34.52}\) \\ \hline \hline \end{tabular} Note: green shaded cells, values underlined: better performance than the respective reference; red shaded cells, values in bold typeface: poorer performance than the respective reference; unshaded cells: approximately the same performance as the reference (\(\pm\)10% difference).  
\end{table} 
Table 6: Summary of findings for photocatalysts treated material. the transducers spaced at 4 cm (initial data for freeze-thaw tests), the time was shorter than in the reference, inferring that the former material was more compact and homogeneous. Conversely, UPTT was longer in the photocatalytic than in the reference slabs. This discrepancy has been attributed to the difference in transducer spacing. When the sensors were very close, the signal travelled across the continuous, compact layers of the emulsion, whereas when they were spaced farther apart, the likelihood of finding discontinuities in the photocatalytic layer is higher. In the latter setup the ultrasonic waves would penetrate the concrete, crossing the photocatalytic layer-substrate interface twice. A schema explaining this difference is given in Figure 15. Further to that premise, the decline in freeze-thaw resistance observed in all the E-T materials could be attributed to deterioration in the photocatalytic layer only whilst tile integrity would remain unaffected, a postulate consistent with the optical microscope findings. Capillary porosity accessible to water would also decline, raising the resistance to water penetration, especially in E2-T and E3-T, as borne out by the MIP values. Although the pendulum tester showed a pattern of higher slip resistance, no general trend could be determined for surface roughness in the emulsion-coated paving tiles. The differences between the intrinsic characteristics of built-in photocatalyst paving tiles T1 and T2 determined visible differences in their behaviour. Dense, compact T1 had no air voids and scantly any capillary porosity. With the inclusion of a photocatalyst its durability-related properties remained unaltered or varied slightly and for the better with one exception. Its freeze-thaw resistance declined, a finding consistent with the delamination of the photocatalytic surface observed in the freeze-thaw test.