# Glass Beads for Road Markings: Surface Damage and Retroreflection Decay Study
## 6 Discussion  
The relative results from the abrasion experiment were independently confirmed through the turntable testing. Nonetheless, direct comparison of R\({}_{\rm L}\) values obtained with  
\begin{table} \begin{tabular}{c c c c} \hline \hline
**GB Type** & **Standard** & **70\% Premium + 30\% High Index** & **High Index** \\ \hline
**Sample Code** & \(\text{SF}^{t}\) & \(\text{SH}^{t}\) & \(\text{HI}^{t}\) \\ \hline Approximate composition of GB: [1] & & & \\ Titanium dioxide in GB [2] & 0\% & 20\% & 30\% \\ Amorphous silica and other ingredients in GB [2] & 100\% & 80\% & 70\% \\ \hline Material consumption (kg/m\({}^{2}\)) per one & & & \\ application event [1] & & & \\ Glass beads [3] & 0.90 & 0.90 & 0.90 \\ Titanium dioxide & 0.06 & 0.24 & 0.33 \\ Polymeric binders & 0.24 & 0.24 & 0.24 \\ Fillers, additives, amorphous silica & 1.20 & 1.02 & 0.93 \\ DBPO & 0.012 & 0.012 & 0.012 \\ Calculated service life (tyre passes \(\times\) 10\({}^{6}\)) until & 3.9 & 9.7 & 4.1 \\ R\({}_{\rm L}\) \(<\) 500 mcd/m\({}^{2}\)/lx & 25.5 & 10.4 & 24.3 \\ Renewals needed per 1 \(\times\) 10\({}^{8}\) tyre passes [4] & 25.5 & 10.4 & 24.3 \\ \hline Material consumption (kg/m\({}^{2}\)) per 1 \(\times\) 10\({}^{8}\) tyre passes & & & \\ Sprayed cold plastic [1] & 15.3 & 6.2 & 14.6 \\ Glass beads & 23.0 & 9.3 & 21.8 \\ Titanium dioxide & 1.5 & 2.4 & 8.0 \\ Polymeric binders & 6.1 & 2.5 & 5.8 \\ Fillers, additives, amorphous silica & 30.6 & 10.6 & 22.6 \\ DBPO & 0.306 & 0.124 & 0.291 \\ \hline \hline \end{tabular}   
* Assumed sprayed cold plastic  
these tests was not possible and was never intended; only relative assessment was sought. While this can indicate the robustness of the utilised in-house abrasion testing procedure, field outcomes for particular roads and conditions will always be the ultimate test that cannot be replaced. The sustainability analyses confirmed for the nth time that the lowest overall resource consumption was correlated with the longest service life. Any argumentation that the furnished values were only estimates and might correlate weakly with the outcome from the field can be dismissed upon examination of our previous work, where the data were collected in the field and the same patterns were observed [32; 33; 38; 40; 41; 68]; indeed, it was those data which prompted us to undertake this effort. It should be noted that similar relative performance of _standard_ and _premium_ GB was also measured in the field in the United States [63]. Thus, uncertainties associated with the service life from this laboratory study would be minimised due to the same relative materials performance, within a reasonable range of variation, that were measured in the field. Separately, one ought to ponder upon the report of 'diminishing returns' from higher \(\mathrm{R_{L}}\)[69], which was confirmed in the case of sample _HI_ and disproved in the case of sample _SP_. Visual analysis of the differences in physical damage to GB showed that those with RI 1.9 (_high index_, sample _HI_) were less resistant to abrasion than other GB types--this can serve as an explanation for the quicker loss of \(\mathrm{R_{L}}\) that ultimately led to a service life similar to measured for GB characterised by RI 1.5 (_large_, sample _ML_), in spite of the much higher initial \(\mathrm{R_{L}}\). This was also reflected in the calculated coefficients of \(\mathrm{R_{L}}\) decay \(\mathcal{C}\) and \(D\): the absolute value of \(\mathcal{C}\) for sample _HI_ was almost twice higher than for sample _SF_ (in the case of the turntable test, the corresponding \(D\) was 3.2 times larger). The outcome of previously reported research [39; 40] indicating that initial \(\mathrm{R_{L}}\) cannot be used to determine long-term performance was confirmed. The optical microscope and SEM images of damage evolution explained the phenomenon. It may be stipulated that the differences between the resistance of evaluated GB types to damage were caused by their different chemical compositions.