# Glass Beads for Road Markings: Surface Damage and Retroreflection Decay Study
## 3 Methodology  
### Laboratory Testing of Road Markings  
Field evaluation of RM is quite difficult because of a plethora of factors that affect their durability; numerous researchers have struggled to find an appropriate deterioration model for R\({}_{\rm L}\) that could predict their performance [26]. Hence, fair comparison of results from various test fields is frequently impossible and burdened with high error.  
A known alternative to field evaluation is the utilisation of a turnttable, where the RM are subjected, under controlled conditions, to tyre action that can successfully imitate the wear at the road [52; 53]; this type of approach was utilised to collect some of the data reported herein. The main drawback of turntable testing is the use of idealised conditions; no literature reports were found that could directly correlate the outcome of the turntable evaluation with field performance. Nonetheless, the turntable test is an official homologation procedure for RM in Germany, Spain, South Korea, and other countries; hence, the validity of the results obtained from such idealised evaluation protocol should not be doubted. Selected basic characteristics and images of the design can be obtained from one of the test facilities running such equipment [54].  
Another type of laboratory evaluation is an in-house proprietary setup for abrasion study, a procedure developed as a quick screening test of GB adhesion to various paints. The machinery for abrasive testing comprises a slowly revolving drum, in which panels with the tested RM are exposed to an abrasive medium, to which GB are exposed uniformly and unidirectionally, as indicated in the schematic drawing shown in Figure 1. This setup is not described in any standard procedures and its accuracy has not been thoroughly assessed in a round-robin evaluation. Nonetheless, it was deemed suitable for the purpose of the presented experiment, where the extent of abrasion was sought. Because of the specificity of the protocol used and the intention of maximising GB exposure to the abrasive medium, the measured R\({}_{\rm L}\) should not be directly compared with values obtained in the field.  
For both test procedures, the base (paint) layer was a commercially procured two-component cold plastic (KP); a formula for spraying, with low viscosity and without coarse fillers. The KP comprised pigments and fillers suspended in acrylic monomers and oligomers that would, upon intermixing with an initiator immediately prior to the application, polymerise on the road surface. Because of the low viscosity during application of the formula designed for spraying, such KP can easily penetrate road surface cracks to furnish good adhesion; such formula is also suitable for the renewal of structured RM that lost their R\({}_{\rm L}\) but have retained the intact structure. Because KP is considered a solvent-less  
Figure 1: Schematic drawing of the abrasive test setup.  
RM system, the loss of film build due to evaporation of volatile organic compounds is minimised [55]. Hence, it could be assumed that the applied film was equal to the dried film, within a reasonable error margin.