# Glass Beads for Road Markings: Surface Damage and Retroreflection Decay Study
## 5 Sustainability Calculations  
Because two independently prepared cradle-to-grave Life Cycle Assessments (LCA) done according to the standard ISO 14044 established that the key parameter for sustainability of RM was their service life [62; 64], it was possible to simplify the calculation of environmental friendliness for the analysed RM and concentrate only on the usage of raw materials, according to a previously employed methodology [41]. The use of such a methodology was possible and appropriate because **at the end of their service life RM are not replaced, but renewed with another layer of paint and glass beads**[3]. Particular attention should be paid to the consumption of TiO\({}_{2}\), a major environmental impactor, because of the energy consumption and generation of waste that occur during the process of its manufacture [65; 66]. It was assumed that the impact of GB preparation from recycled versus virgin materials would be similar; this assumption is valid because the key parameter in the LCA of GB was the energy consumption [67]: heating the raw materials to circa 1200 \({}^{\circ}\)C and heating the recycled crushed float glass to circa 1200 \({}^{\circ}\)C would demand similar energy. It can also be assumed that the environmental cost of mining and refining the raw materials might be somewhat higher than using glass from recycling. It may be worth adding that recycled glass with higher RI is not readily available. Effects associated with the energy sources were disregarded. Errors in such analyses could originate from using the estimates of service life; with exponential line fits of R\({}^{2}\) between 0.73 and 0.85, there are definitely uncertainties. An additional source of variation is the material composition. Nonetheless, such doubts do not affect the overall picture. Hence, based on the results from the laboratory assessment (see Table 4) and the composition of GB (see Table 1) supplemented by the typical composition of sprayed cold plastic (Table 6), it was possible to estimate the sustainability of the analysed RM, defined as long-term resource usage needed to maintain appropriate R\({}_{\rm L}\). For this purpose, the analysed period was arbitrarily assumed to be 100,000 drum rotations for the abrasive testing and 1 \(\times\) 10\({}^{8}\) tyre passes for the turntable testing. To set appropriate boundaries for this analysis, factors associated with the events of RM application (including energy usage for the machine, labour costs, and environmental expenses associated with the obstruction of vehicular traffic during each event of marking) were excluded. The results from the analysis based on the outcomes of the abrasive testing, given in Table 6, demonstrate that the long-term consumption of raw materials was lowest when _premium_ GB (sample _SP_) were used, and highest with the _high index_ GB (sample _HI_). The outcome, relative to the sample _SP_ assumed to have a value of 1.0, is visualised in Figure 10; the high consumption of TiO\({}_{2}\) in the case of sample _HI_ must be noted. The outcome of identical assessment based on the data from the turntable study, with the assumed very high failure level (drop of R\({}_{\rm L}\) to 500 mcd/m\({}^{2}\)/lx), is shown in Table 7. The spreading rates that were utilised by the test facility were used. While being aware of inadequacy and possible error of this type of calculation that excludes subsequent performance, it can be seen that the sample _SH\({}^{t}\)_ (a 7:3 mixture of _premium_ GB and _high index_ GB) furnished RM system that demanded the least resources. The outcome, relative to the sample _SH\({}^{t}\)_ assumed as 1.0, is visualised in Figure 11; again, large consumption of TiO\({}_{2}\) in case of using _high index_ GB (sample _HI_) is obvious. Figure 10: Relative long-term material consumption to maintain \(R_{\rm L}\) > 150 \(\rm{mcd/m^{2}/lx}\) for 100,000 drum rotations (abrasive testing). The _premium_ GB (sample _SP_) was assumed as 1.0 (arbitrary unitless scale).