Now more than ever, customers are looking for ways to prolong the results of their pavement maintenance. If you're looking for durability in pavement marking, thermoplastic can fill the need.
Thermoplastic is a plastic material made of binder, pigments, filler, and glass beads. The pigment creates the color, glass beads increase retroreflectivity, and the filler adds bulk. The binder is what makes the material tough, flexible, and creates the bond strength to adhere to the pavement surface while holding the other components together. Thermoplastic material comes in a solid block or bags of granular material, says M-B Companies Inc. Design Engineer Brian Hendrickson. The material needs to be heated to 400°F or higher before application in a molten state.
Often, the packaging material is designed to be part of the thermoplastic system and can be melted along with the thermoplastic, says Tom McSwain of Ennis Traffic Safety Solutions. This helps minimize waste when using thermoplastic for pavement markings.
The liquid thermoplastic is then applied to the asphalt or concrete surface and the resins in the thermoplastic bond or "burn in" to the pavement surface. The material dries and cools quickly, allowing roads and parking lots to be open to traffic sooner. "As you're putting it down you have to keep people from driving across the line and tracking it as you're applying it," Hendrickson says. "With thermoplastic usually that's about 100 yards behind the striper where as with other durable markings you might have to go as far as a mile."
Thermoplastic is also designed to be applied thicker than paint - usually from 30 to 120 mils - which is why it typically lasts longer, says Crown Technology LLC Sales Manager Matt Nall.
Durability is possibly thermoplastic's biggest advantage over paint. Manufacturers agree that thermoplastics will last longer than paint, depending on certain factors. Nall says the combination of mil thickness and the hot application increase thermoplastic's durability.
Thermoplastic tends to be used more in the warmer environments. In areas where snow plows work, the plows can scrap the thermoplastic material right off the pavement, decreasing the marking's longevity. The amount of traffic traveling over a thermoplastic application may also decrease its longevity, says MRL Equipment Company Equipment Sales and Specialist Cody Irons.
There are three types of resins in thermoplastic material: alkyd, hydrocarbon, and acrylic modified alkyd. Alkyd is made from natural wood-derived resins which are more resistant to oil on the pavement surface, according to Scott Shannon with Pervo Paint Co. Hydrocarbon is an oil-based resin. The third type is acrylic modified alkyd, which is a wood-derived and Methyl Methacrylate resin that is also resistant to oil.
While the specific type of resin is usually specified in the contract, Hendrickson says the contractor should handle them the same. But he cautions never to mix alkyd and hydrocarbon together, and make sure the pre-melting kettle is cleaned before switching to a different resin type. A reaction between the two resins will cause them to foam and increase the amount of material in the kettle.
Like paint, thermoplastic material also needs increased retroreflectivity properties, which is often achieved through the application of glass beads to the thermoplastic marking. Most thermoplastic also has glass beads intermixed in the material, Nall says. "As the line wears down over time the intermixed beads will become exposed to still give you bright, reflective lines," he adds.
Irons says the learning curve with thermoplastic is fairly easy, especially if a contractor is already in the pavement marking business. The material must reach the proper heat before application. But contractors also need to consider the surface temperature of the pavement.