The thermoplastic material that your local asphalt companies use for pavement markings contains pigments for color, glass beads for reflectivity, a filler to add bulk, and a binder to hold everything together and create a flexible, tough material that will form a strong bond with the pavement.
The contractor would begin by ensuring that the pavement is dry and clean. If other markings exist, he will remove them. Depending on the condition of the pavement, it may be necessary to apply a primer. The thermoplastic striping material will be heated in a special kettle to a temperature of at least degrees Fahrenheit.
The contractor can then use one of three methods to apply the material. The extrusion method places the equipment directly in contact with the pavement during the application. A ribbon application uses a gun that remains an inch or two above the surface to lay down a stripe of material. The spray method uses a gun positioned four or five inches above the surface; atomized air applies the material.
Because the thermoplastic material will solidify in less time than it takes paint to cure, pavements can be reopened much faster. Chemistry matters. Join us to get the news you need. Don't miss out. Renew your membership, and continue to enjoy these benefits. Not Now. Grab your lab coat. Let's get started Welcome! It seems this is your first time logging in online. Please enter the following information to continue. As an ACS member you automatically get access to this site.
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Thank you! Road Markings Pigments, polymers, and reflective spheres help keep you safe on the road by Jyllian N. Kemsley September 6, A version of this story appeared in Volume 88, Issue Why glass recycling in the US is broken Scientists synthesize large borophene crystals Glowing dyes could store digital data for the long term.
Credit: Shutterstock. Of all the standard driving safety devices—seat belts, air bags, antilock brakes—one thing that many of us likely take for granted is the road markings that help keep cars away from other vehicles on the straight and narrow as well as the curvy and treacherous.
You might also like What's that stuff? Self-Darkening Eyeglasses. Share X. To send an e-mail to multiple recipients, separate e-mail addresses with a comma, semicolon, or both. Submit Sending Daniel May 29, AM. Very helpful article, pls can i get more info on how to prepare a low cost road marking paint that can be applied on roads in Africa.
GG August 25, PM. Hi, I live in Bend, Oregon and the thermo they put down for crosswalks is a complete hazard.
Ribbon application uses a pressurized gun to apply thermoplastic in the same manner as the gravity extrusion method. Hot-sprayed thermoplastic is the most common application method used for striping on TxDOT roadways and provides many advantages over other application types.
The main difference between sprayed thermoplastic and the other application methods is that the hot thermoplastic is combined with pressurized air in spray applications. The primary advantage to sprayed application is that striping can occur at higher speeds 2—8 mph and markings are ready for traffic in one minute.
Sprayed applications often produce a better surface bond than extrusion and ribbon applications. However, sprayed thermoplastic markings are not as well suited for applying markings thicker than mils when compared to extrusion and ribbon applications.
Figure shows a typical sprayed thermoplastic application. Anchor: igrtop Figure Typical sprayed thermoplastic operation. The temperature of the thermoplastic material is a very important factor in the performance of the thermoplastic-roadway surface bond. For proper bonding, the following conditions must exist:.
It must be emphasized that a clean and dry pavement surface is critical for thermoplastic materials to achieve proper bonding with the pavement surface. If primers are used, they must be given proper cure time until tacky prior to applying the marking material. Special pavement heating devices are now available that are effective for removing pavement surface moisture and elevating the pavement surface temperature, allowing for better thermoplastic bonding.
Table describes problems and solutions associated with the application of thermoplastic markings. Flowing Line i. Because of the thermal bonding characteristics between thermoplastic and asphalt, nearly all thermoplastic materials are well suited for application on new HMAC surfaces.
This includes both hydrocarbon and alkyd thermoplastics. As HMAC surfaces wear and become more brittle through traffic exposure and oxidization, the use of a primer is suggested when applying thermoplastic directly to the pavement surface.
Suitable minimum thickness of thermoplastic on new HMAC surfaces is 90 mils. Suitable restripe thickness on HMAC surfaces is 60 mils. Not all thermoplastic materials have been shown to provide suitable durability on concrete surfaces.
In other words, thermoplastics that are suitable on asphalt surfaces may not be suitable for concrete surfaces. Because the thermal bond is not available between thermoplastic materials and concrete surfaces, mechanical bonding is relied upon. For mechanical bonding to occur, the concrete surface must be porous enough to allow the liquid thermoplastic to seep into the pores and create a tight mechanical bond after cooling.
This is often not the case with new concrete pavements, suggesting the use of primers. A major thermoplastic bonding failure on concrete is shown in Figure Major thermoplastic failure on concrete.
Certain thermoplastic products have been identified that provide suitable bonding with concrete either with or without a primer. Suitable minimum thickness of thermoplastic on new HCC surfaces is 90 mils.
Suitable restripe thickness on HCC surfaces is 60 mils. When thermoplastic markings are applied to coarse surfaces such as surface treatments, thickness plays a major role in the durability and retroreflective performance over time. As with all asphalt surfaces, suitable thermal bonding is achieved. However, much of the thermoplastic material seeps into the voids between the aggregates, leaving very little material on the top of the aggregates.
This lack of material at the top of the aggregate leads to accelerated wear of the thermoplastic and premature bead loss. Research has shown that thermoplastic thicknesses of mils or greater provide better performance than thinner applications on surface treatments. In most cases, a restripe thickness of 60 mils is suitable on surface treatments, although a greater thickness may sometimes be necessary.
Durable pavement markings, such as thermoplastic, are desirable on high-traffic-volume roadways because they require fewer restripe cycles, reducing the amount of worker exposure and delay to traffic. However, on very low-volume roads, paint may provide comparable performance to durable materials at a much lower cost. Thermoplastic materials provide suitable performance for a broad range of traffic volumes. Because thermoplastic dries very quickly, it is well suited for higher traffic volume roadways.
However, thermoplastics may not be the most durable marking in areas where very high-traffic volumes or heavy weaving result in increased tire wear. Other two-component materials or permanent tapes may provide better durability under extreme traffic conditions. One drawback to thermoplastic materials is that they are sensitive to environmental changes — especially the alkyd materials used extensively throughout Texas.
Many sources state that surface moisture and air temperature are the two most important factors that influence the long-term durability of thermoplastic markings. Thermoplastics are especially susceptible to moisture-associated bonding failures. Therefore, thermoplastic materials may not be the best material for pavement markings in locations that are very humid or susceptible to dew formation during times that would affect striping operations, such as striping at night. Thermoplastics perform better than standard traffic paints in areas where snowplowing is common but still suffer some loss in durability depending on the number of snowplow passes.
Table summarizes the recommended uses of thermoplastic pavement markings. Estimated cost per year of service life per lf. Traffic paints are the oldest and most widely used pavement marking materials in existence. Paint is a common pavement marking material used by TxDOT, although its use has recently declined as thermoplastic has become more popular. Paint still remains the most inexpensive of all pavement marking materials, although its cost has increased slightly as new formulations have been introduced.
Paint is almost exclusively used for longline applications, often in maintenance projects, and is currently the only longline material applied by state forces. Check with TxDOT materials laboratory for approved formulations, as they are subject to change. Conventional traffic paint consists of three interwoven elements: pigment, binder, and glass beads. Each element is important because different paints react differently to different pavement surfaces, traffic wear, and environmental wear.
Binder materials or resins are usually latex or acrylic materials that provide the adhesive and cohesive properties of the material. A myriad of traffic paint formulations exists, including solvent-based and water-based. Increased environmental awareness in the late s and early s led to a decline in use of volatile organic compounds VOCs in the United States. This awareness also led to a decline in the use of solvent-based paints and an increase in the use of water-based paints, which contain far fewer VOCs.
TxDOT has not allowed solvent-based paint for many years, relying exclusively on water-based formulations. In addition, most state DOTs have disallowed solvent-based paints. Water-based paints are environmentally friendly, are much easier to handle than solvent-based paints, and greatly decrease the safety hazards to workers. Water-based paints also become track-free much quicker than solvent-based paints.
Humidity has very little effect on the track-free times of water-based paints because these paints begin to set as a result of the drop in pH due to evaporation of the ammonia. Most of the water-based paint placed for longline applications is applied by spraying the paint onto the surface using a striping truck. Paint adheres to the pavement surface through mechanical bonding within the pores of the pavement surface.
Although paints are less sensitive to changes in temperature, moisture, or other environmental characteristics than thermoplastic materials, surface preparation is still important. To achieve proper bonding, the following conditions must exist:. Paints are often applied at a thickness ranging from 15—25 mils.
As a rule of thumb, the optimal speed of a striping truck applying mil markings is 10—12 mph. Paint thickness can influence drying time and therefore should be specified with discretion depending on the drying time needed.
Application of a primer material is not necessary on any roadway surface, although a double application of paint is sometimes specified. Table summarizes problems that have been encountered with the use of paint as a striping material and suggests solutions for these problems.
Decrease atomizing air pressure or clean paint screens. Marking is thick on one side and thin on the other. A number of external factors — including traffic volume, pavement surface roughness, and environmental wear — greatly affect paint performance. Research has shown that paints often have lower initial retroreflectivity values and degrade at a much faster rate than other marking materials, which is why they are usually not classified as a durable marking material.
Paints also experience decreased performance on coarse roadway surfaces such as surface treatments because the paint is applied thinly. On low-volume roadways, paints have been known to provide service lives of up to 2 years. Three months is often the paint service life on roads that have a very high ADT. Because of their relatively short service lives, most paints are only used on low-volume highways, although the new acrylic resin formulations have shown promise as a durable marking on high-volume roadways within TxDOT.
The thinner applications and lack of opacity of the pigments often cause paints to have a tendency to appear dull or faded in color when compared to other materials. Some organic pigments used in yellow paint or two-component materials have a tendency to appear white at night under headlamp illumination. Lead-chromate-based yellow markings usually do not experience this phenomenon.
Table summarizes the recommended uses of paint pavement markings. On new surface treatments, paint should only be used as a temporary marking for up to 6 months. Preformed tapes are cold-applied, preformed pavement marking materials that are supplied in continuous rolls of various lengths and widths. Preformed tapes have the advantage over sprayed or extruded materials because they do not require expensive application equipment or experienced operators to place, and they require no drying or curing times.
While tapes have a significantly higher initial cost than most other materials, the service lives are usually superior to most other materials, including thermoplastics, often making them a cost-effective choice in locations with high traffic volumes.
A myriad of preformed tapes exist, although only a small number are described here. Preformed tapes are frequently used for transverse markings, but are often used for longitudinal lines in high-traffic areas. Tapes are highly durable and abrasion resistant in most applications. Because of their high installation costs and slow application procedure, they are often used only in locations with the most severe traffic conditions that require frequent replacement of standard pavement markings.
Preformed tapes can be classified by the expected service life and by material composition. There are only two classifications for service life: permanent and temporary. A permanent preformed tape is any material that bonds with the pavement surface so that it cannot be removed by hand and has a service life of at least 1 year. This includes any inlayed installations and thick overlaid installations that have achieved good bond with the surface.
Permanent preformed tapes are usually made of a plastic binder material with glass beads embedded onto the surface. Two of the common types of plastics binders used for permanent tapes are urethane and pliant polymer, contrasted as follows:. Temporary tapes are typically used for short-term applications such as work zones.
These tapes are much thinner than permanent tapes, have foiled backs, and are pre-coated with a self-bonding adhesive. The preformed tape material consists of a single layer pigmented binder and glass beads that are applied to a metal foil backing. Two forms of temporary marking tapes are available and vary based on their adhesive strengths. The first is intended for use in projects where marking removal will not be required.
The use may be short- or long-term, but the markings cannot be easily removed. The other type is intended for easy removability and can be removed by hand leaving no trace of a marking. This type is most often used in construction zones and is preferred when markings must be removed. Removable preformed tapes must conform to DMS A clean pavement surface is very important for tapes to achieve a good bond. Preformed tapes may be inlaid or overlaid. Inlaid markings will outperform overlaid markings if a good bond is achieved.
Tire traffic over the tape installation will help achieve a good bond. Tapes should not be installed on tine-textured concrete pavement, as the materials will be easily removed by tire wear. Installation of the tape on a deteriorated asphalt pavement surface will accelerate abrasion and adhesion failures. Inlay Method. The inlay method is preferred on newly constructed or resurfaced asphalt pavement. Application usually follows the pavement breakdown roller.
The tape is then rolled into the pavement surface with a steel drum roller during the final rolling of the pavement. The roller fuses the plastic into the hot asphalt surface creating an excellent bond and sealing out moisture. Overlay Method. On existing pavement and concrete pavement, the overlay method is used. The overlay method is also often used on new pavement surfaces, although the inlay method is preferred due to superior performance.
The tape is applied directly on and bonded to the surface with an adhesive. Pressure-sensitive adhesives work best when overlaying permanent tapes on new asphalt pavement surfaces. The use of contact cement is recommended when installing the tape on concrete or over older markings. Manufacturers suggest 2 coats on the pavement surface and 1 coat on the tape. This is also true for all surfaces with heavy turning or weaving movements over the markings.
Markings are initially bonded with a light hand roller or vehicle tire and permanently bonded by traffic wear. If properly installed, all permanent and some temporary marking tapes achieve and maintain bonding to the pavement surface that will last for the life of the pavement. Tapes should always be removed prior to placement of new markings. Therefore, removal of these markings becomes a challenge and is the major drawback to their use.
Removal of permanent tapes can only be achieved by a small number of methods, which are often destructive to the pavement surface. Burning and scraping of the marking materials with an oxygen torch is one method.
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