AASHTO M 247 Glass Beads for Road Marking

The standard "AASHTO M 247 Glass Beads for Road Marking," published by the American Association of Highway and Transportation Officials (AASHTO), covers glass beads to be deposited or sprayed onto road markings to create a reflective road marking. According to this standard, there are three types of glass beads used in road marking:

• Type I: Known as the standard rating. This type is typically used for general-purpose road markings with a specific rating for standard reflectivity.
• Type II and Type III: Known as modified gradations. Type III is designed for high-performance applications and offers a wider size range (180-1180 µm) and improved retroreflection with a refractive index of at least 1,5.

Any of these grading types can be obtained with flotation characteristics upon buyer's request.

Any of the above rating types can be achieved with a moisture resistant coating if specified by the purchaser.

These beads have excellent nighttime retro-reflective properties, helping drivers see road lines more realistically at night.

In general, beads should be made of transparent, clean, colorless glass, smooth and spherical in shape, free from milkiness, pits or excessive air bubbles, and should meet the following specific requirements:

• Grading: Beads must meet the grading requirements for the type given in the table titled “Grading of glass beads.”
• Roundness: Glass beads must have at least 70 percent true sphericity.
• Crushing strength: The retained 0,425 mm (No 40) sieve should be minimum 133 N.
• Refractive index: Glass beads must have a minimum refractive index of 1,5.
• Moisture resistance (flow properties): Beads should not absorb moisture during storage. They should remain free of lumps and agglomerates and should flow freely through dispensing equipment.
• Flotation: When tested in accordance with this standard, a minimum of 90 percent of the beads should float in xylene.

Sampling should be done randomly at the following rates: 45 kg sample (in full bags) per 4535 kg shipment. On arrival, the material should be reduced to approximately 1 kg in a sample separator.

The following requirements must be tested using the specified test methods:

• Rating: According to ASTM D1214 standard
• Roundness: According to ASTM D1155 standard
• Crushing: According to ATSM D1213 standard

The refractive index shall be tested by the liquid immersion method (Becke line method or equivalent) at a temperature of 25 degrees plus/minus 5 degrees.

Optional coatings can be applied for flotation, moisture resistance, or adhesion to paint or thermoplastic materials. These coatings enhance durability and performance in wear and tear or adverse weather conditions.

With regard to flow properties, beads shall flow smoothly when tested in accordance with the first procedure described in this standard, but if they are not specified as moisture resistant they shall be tested in accordance with the second procedure.

When performing a flotation test, beads weighing approximately 1 g are determined to the nearest 0,005 g. The beads are distributed evenly into a clean, standard 100 mm glass Petri dish, previously weighed to 0,0005 g. The dish is gently vibrated to obtain as uniform a layer of beads as possible. Xylene is added from one side of the dish at a rate of 10 to 15 mL per minute from a burette until 30 mL have been added. The floating beads are then carefully withdrawn by suction through a suitably narrowed distribution tube connected to a receiving vessel. Excess beads are withdrawn to ensure no remaining beads are lost, and the dish is dried in an oven at 110°C (plus or minus 5°C). The dish is weighed, and the percentage of floating beads is calculated.

In short, the AASHTO M 247 standard covers the specifications of glass beads used in road markings to improve visibility and safety on roads. These glass beads are critical for creating retroreflective road markings, which increase visibility for drivers at night and in adverse weather conditions. Retroreflection allows light from vehicle headlights to be reflected back at the driver, making road markings highly visible in low light or wet conditions. This standard ensures consistency and quality in glass beads used in a variety of transportation projects.

According to the AASHTO M 247 standard, glass beads are primarily used in:

• Hot melt thermoplastic paint: Beads are embedded or sprayed onto thermoplastic signs for durability and high reflectivity.
• Water-based or solvent-based paints: Beads are dropped onto wet paint to create reflective road markings.
• High-performance markings: Type III beads are used in high-traffic or smart infrastructure environments and increase visibility for both drivers and autonomous vehicle systems.

These beads make road markings visible in low light, rain or fog, significantly improving road safety and reducing the risk of accidents.

The retroreflective properties of AASHTO M 247 compliant glass beads are crucial for:

• Night visibility: The beads reflect headlight light, making road markings stand out. For example, Type III beads can increase retroreflection by up to 60 percent compared to conventional solutions.
• Adverse weather conditions: Coated beads maintain performance in rain or moisture, ensuring consistent visibility.
• Smart infrastructure: High-performance beads support systems in autonomous vehicles, adapting to modern transportation needs.
• Durability: Coated beads extend the life of road markings by resisting wear caused by traffic and environmental factors.

This standard emphasizes safety in use and handling by stating that glass beads may contain hazardous substances or processes. Because this standard does not address all safety concerns, users should establish appropriate safety and health practices and adhere to legal limits.

As a result, the AASHTO M 247 standard ensures that glass beads used in road markings meet stringent quality and performance criteria, improving road safety and visibility. By specifying material properties, test methods, and application guidelines, it supports the creation of durable, reflective road markings suitable for a variety of conditions and modern infrastructure needs. Whether for traditional highways or smart roads, glass beads compliant with this standard play a vital role in transportation safety and efficiency.

Our organization, which has been serving for many years and meticulously following global developments in science and technology, conducts testing, measurement, and analysis in a wide range of areas for businesses in every sector with a skilled team and extensive infrastructure. In this context, we also provide testing services in accordance with the "AASHTO M 247 Glass Beads for Road Marking" standard.