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Particle Analysis of Road Materials

Glass Beads for Pavement Markings

Glass beads can enhance the nighttime visibility of various objects including paint used to mark lanes on roads and highways. The size and shape of the beads is critical to the reflective characteristics. The more perfectly round the bead, the more the light reflects back to its source, providing visibility of the marking in low-light conditions.

Measurement of bead size and roundness has been traditionally performed using sieves following ASTM method D1214, the Round-o-Meter following ASTM D1155-89, and manual microscopy. Automated digital image analysis provides higher quality data and faster results because it can do both size classification and a roundness measurement at the same time. Advantages of this approach include quicker analysis time, more reproducible results, complete shape characterization of each bead, and digital images of the sample.

The CAMSIZER P4 analyzer has been used successfully in many laboratories to characterize the size and shape of glass beads used for pavement markings. Customers currently using this instrument include both glass bead manufacturers and end users such as departments of transportation.

Asphalt Emulsions

Asphalt emulsions are droplets of asphalt dispersed in water with the aid of an emulsifying agent. Particle size of the asphalt droplets is critical to stability and application performance. Asphalt emulsions are manufactured by a high-speed, high shear mechanical device (usually a colloid mill) that divides the asphalt into tiny droplets and disperses it in the water. Typical products have a size range from sub-micron up to ten microns, with an average particle size in the one to five micron range. Variation in settings, raw materials, and requirements of the final product will vary both the average size and distribution width.

HORIBA laser diffraction particle size analyzers are a proven technology for measuring asphalt emulsions. Systems from the full-featured LA-960 Particle Size Analyzer to the portable LA-350 have been successfully used for these measurements.