Development of a Pavement Marking Management System: Measurement of Glass Sphere Loading in Retroreflective Pavement Paints

Of critical economic importance to roadway management agencies is the retroreflectivity of edge lines and centerlines and the retention of retroreflectivity with exposure to weather, snowplowing, road salt and sand, and traffic density. This study evaluated factors affecting the performance and durability of painted edge lines and centerlines on specific Michigan roadway sections as part of a project to develop a practical pavement marking management system. An ill-defined aspect of retro-reflectivity is the relationship of glass sphere content and the decay of retroreflectivity over time and from seasonal maintenance. Two techniques were developed to quantify the glass sphere content of retroreflective pavement paints. In the first method, aluminum plates are fastened to the roadway and painted in the field as the painting crew applies the striping. The plates are retrieved and pyrolyzed at elevated temperature, with observations made on weight changes of the painted plate. A mass fraction of glass spheres can then be calculated. In the second method, the painted plates are photographed at low magnifications. The macrographs are converted to a binary image that is evaluated using image analysis software to determine the number of spheres per area, average size, and aerial percent. The glass sphere content, as determined by pyrolysis and image analysis, is correlated with retroreflectivity measurements collected on the same samples. These new methods will lead to a better understanding of factors related to the retroreflectivity loss of pavement paints and ultimately to improved products and maintenance practices.