The Relationship Between the Embedment Depth of Glass Beads and the Retroreflectivity of Road Markings

Bead Embedment Depth: The depth to the embedment of glass beads can be assessed by close-up visual inspection. Beads should be embedded into the pavement marking material at 60 percent of the bead diameter for maximum retroreflective performance. For the material that is "behind" the bead is the actual image that is reflected back to the driver, it is crucial that proper embedment depth should be achieved. The figure below shows the effect of bead embedment depth on retroreflectivity.

Figure: Effect of bead embedment depth on retroreflectivity.

As is clearly showed in the figure that beads not embedded deeply enough will cause the light to be reflected in many directions instead of back to the driver, greatly reducing the retroreflectivity. In addition, after very little traffic wear, insufficiently embedded beads will be easily worn away. Beads that are embedded too deep will still reflect light, but to a lesser extent. Therefore, if errors in embedment are made, it is better for the beads to be too deep than too shallow, as can be observed in Figure above.

During the striping operation, if the beads appear to be too high or too low, notify the operator to make adjustments. In the case of hot-applied materials, such as thermoplastic，the material temperature has a major effect on bead embedment. The pressure of the bead applicator also effects bead embedment.