Pavement markings are installed to keep pilots, motorists, and pedestrians safe. The need for safety increases even more at night. One way contractors can increase the visibility of pavement markings is with glass beads. "High index of refraction glass bead products afford drivers to have continuous delineation, increased preview distance, and amplified roadway contour vision," says Kevin Hall, technical service representative for Potters Industries Inc.
Glass beads have been used in pavement markings for years and have become mainstream and often mandatory in some places. The beads - embedded in the liquid binder - bend light, and that combination creates retroreflectivity of the pavement markings. This retroreflective light is reflected back to the viewer, making the markings easier to see. Another benefit: the glass beads can be made out of recycled glass.
These beads are most often used on crosswalk intersections, highway, and airport markings, says Abe Martinez, manager for Mar-Don LLC. Although they are not required for parking lot or private commercial markings, Martinez says it's an option all contractors should offer their customers.
The Application Process
Contractors adding glass beads to their marking application can choose from several kinds and sizes of glass beads. Aside from the standard glass beads, contractors can also purchase direct melt glass beads which are crystal clear or high index glass beads which have a higher index of refraction than standard glass beads, Hall says.
Generally, for reflection, the bigger the bead the more reflection you'll get, Martinez says. Often, the size of the glass beads is specified by a governing agency.
Years ago, glass beads needed to be applied by hand. A crew member would use a striping or thermoplastic unit to apply the pavement marking. A second crew member would follow behind broadcasting the beads over the just applied marking.
With this method it's possible for the beads to be spread over parts of the pavement where there is no liquid binder. With nothing to embed in, the beads are left loose, increasing the possibility of an unsafe slip hazard in that area.
Manufactures have introduced new units to replace this manual method. The units offer directional application of glass beads and an improved concentration of the beads on the marking, Hall says. "It's generally preferred to have equipment that balances operator ease of use with material flow control and versatility to accommodate all various glass bead products," he adds.
Mar-Don, for example, offers a bead hopper that is attached behind the paint spray guns of a walk-behind striper. According to Martinez, the hopper features total precision glass beading and no tubes to clog or malfunction. The operator uses settings to apply or stop the application of the glass beads. This allows the bead to be applied almost simultaneously after the paint is applied, Martinez says. "The beads have to be applied when the paint is wet so they will stick," he adds. Martinez reminds contractors to make sure the unit is not applying the beads at a larger width than the marking, which again could result in loose beads not embedded in the liquid binder.
For long-line truck applications glass beads can be applied using air-assist tanks that spray the beads out of the guns right behind the paint guns, Martinez says.
Glass beads can be added to paints, thermoplastics, and epoxies - the liquid binder in this process. The amount, type, and coating of glass beads will vary depending on the type of binder a contractor is using, Hall says. Be sure to ask your bead supplier or manufacturer for proper application practices and considerations when choosing beads and binder material.
If applying glass beads to public roadways or airports, the amount and size of glass beads may already be specified. For example, Martinez says he has often seen DOTs and the FAA requiring 6 to 10 lbs. of beads per gallon of paint. That much may not be necessary for parking lot applications but may be desired because it will offer more reflection.