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• Best Practice Manual
• Case Studies
• Glossary

• Operational Safety
  • Safety Responsibility
  • Safety Considerations
  • Safety Areas
  • Construction Marking and Lighting
  • Foreign Object Damage (FOD)
  • Disorientation
• Security
  • Terminology
  • Responsibilities and Actions
• Handwork
  • Placement by Shovel
  • Lute and Rake Use
• Work around Fillets, Light Fixtures, and Utilities
  • Fillets
  • Light Fixtures
  • Utilities
• Markings
  • Paint Type
    • Waterbourne
    • Epoxy
    • Methyl Methacrylate (MMA)
    • Solvent-Based
  • Retroreflectivity
  • Marking Application
  • Temporary Markings
  • Marking Removal
• Off Peak Construction
  • Project Planning
    • Cost Considerations and Staging
    • Work Hours and Liquidated Damages
    • Roughtness Considerations
  • Construction Practices
    • Weather
    • Lighting
    • Surface Preparation
    • Production and Transport
    • Placement and Compaction
    • Transitions and Cleanup
• Acknowledgements

Retroreflectivity

Type III glass beads in the arrowhead, with a higher index of refraction (1.9), provide better visibility than Type I glass beads in the tail with a lower index of refraction (1.5) (photo credit: D. Spiedel)

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Reflectivity

An airless paint truck applies 3-ft. wide markings with the nozzles on the left and then applies glass beads with the trailing nozzles on the right (photo credit: D. Spiedel)

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Paint Spayer

Glass beads (see Image) are often added to improved night visibility because they are retroreflective (they send light back where it came from regardless of the original angle of the light). These beads have requirements for gradation, roundness, specific gravity, crushing strength and index of refraction. Some markings are required to have glass beads while other markings are only recommended to have glass beads.

Glass beads for airfield markings are typically either Type I or Type III. Type III is about 10 times more expensive per pound but has a higher index of refraction, which is supposed to provide better reflectance (see Image). However, the Air Force studied Type I and III beads and found that the Type III beads lost more reflectivity over time (70% loss in 9 months versus only 11% for Type I).

Glass beads should be applied as soon as possible to fresh paint (see Image). If the paint begins to cure and form a thin surface skin, the beads may not embed properly. Proper embedment is usually taken to be about 50% of the bead in the paint. Glass beads are generally added at between 7 and 15 lbs/gallon depending upon paint type and glass bead type. Glass beads also provide friction for airfield markings. If glass beads are not used, silica sand can be used to improve friction.