Deterioration of Retro-Reflective Sheet Under Outdoor Weathering and Weather-O-Meter

More than one million road signs are installed over thousands of kilometers of highways in India. It is a matter of great concern that there is no strategy to assess their deterioration in terms of quality of retro reflective sheets under natural outdoor weathering and artificial accelerated weathering. The work reported in this paper is focused on how fast the deterioration of reflective sheets of different colors is occurring under natural weathering conditions in India. The deterioration is simulated with artificial weathering under Xenon-Arc chamber with known parameters of weather prevailing in India. This study will help in evaluating the performance of retro-reflective sheets in hours in weather-o-meter to same level of deterioration in the field in terms of days. Data for co-efficient of retro-reflectivity was collected for White, Yellow, Red, Orange, Green, and Blue Type III reflective sheets over a period of seven years in natural weather conditions of Delhi. The best-fit curves technique was adopted to predict the life of retro reflective sheets of different colors in terms of days/months to reach its minimum allowable level. The higher values of R2 for all colors indicate that there is a strong relationship between deterioration and age of reflective sheets in terms exposure in months/days, similarly the R2 values were also found high when the exposure was made in weather-o-meter for few hours. It means that weather conditions in weather-o-meter are exactly being stimulated with prevailing weather conditions in Delhi. The study concludes that over a period of seven years the deterioration of blue color sheet is maximum and deterioration of green color sheet is minimum. This conclusion is also evident from physical parameters such as appearance of signs installed in India. The signs with blue base normally need early replacement in comparison to the signs made out of green sheet for National Highways. The parameters, which were set in weather-o-meter, need the exposure of different hours for different colors of sheets for achieving minimum allowable level of reflectivity as per ASTM standard. The tentative results indicate that reduction of retro reflectivity after 124 months outdoors could be achieved in 90 hours exposure in weather-o-meter. The deterioration varies from color to color and the exposure hours are different for different colours of sheets. This is due to difference in the properties of the pigments used in reflective sheets