Pavement Marking Handbook: Pavement Marking Material Descriptions

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Section 4: Pavement Marking Material Descriptions

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Introduction

A majority of the pavement markings placed on TxDOT roadways over the past five years fall into one of three categories: thermoplastic, water-based paint, and preformed tape. However, other materials exist that have shown positive performance either in Texas or elsewhere, which warrants their discussion in this handbook.

Each material contains three primary components: binder (glue), surface glass beads (reflectors), and pigment (color). For thermoplastic markings, glass beads are also intermixed into the material and often become exposed as the binder material is worn down by traffic. The various pavement marking materials are often categorized by the type of binder material used.

Table 2-4 shows materials and their uses described in this section.

Anchor: #i1013841Table 2-4. Pavement Marking Materials Described in this Section
Material	Brief Usage Note	Special Approval Required*
thermoplastic	See DMS-8220	-
water-based paint	See DMS-8200	-
preformed tapes	See DMS-8240	-
epoxy	experimental use in Texas	Yes
polyurea	experimental use in Texas	Yes
modified urethane	experimental use in other states	Yes
methyl methacrylate (MMA)	extensive use in other states	Yes
profiled thermoplastic	experimental use in Texas	-
contrast markings	experimental use in Texas	-
heated-in-place thermoplastic	transverse lines, words, and symbols only	-
ceramic buttons	previously used extensively in Texas	-
* Materials designated here as experimental require special approval from TRF or CST-MAT for use.

This section includes in-depth descriptions of commercially available materials and typical uses. Information on pavement marking material selection based on characteristics of a given roadway can be found in Section 7 of this chapter. Although every attempt was made to include descriptions of all commercially available materials, new materials and formulations frequently become available. Therefore, materials that are not described herein may be used with approval from TRF or CST-MAT on an experimental basis until substantial performance data is obtained. Use of experimental materials may be considered for problem areas where other typical materials may not have provided the desired performance.

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Summary of Material Use

Each of the materials, with the exception of heated-in-place thermoplastic, may be used as either a transverse (shortline) or longitudinal (longline) application, although performance in either case may vary. Further details on the performance of these materials are provided later in this chapter. Ceramic buttons are currently not an approved marking material due to the fact that they are not a retroreflective material and therefore provide poor nighttime visibility. Table 2-5 provides a summary comparison of the characteristics of each material described in this section.

Anchor: #i1013897Table 2-5. Summary of Material Use
-	Use Based on Pavement Surface			-	-	-
Material	Conc.	Asp.	Seal.	Lane Closure Required	TxDOT Specifications	See Table #
Thermoplastic	L	Y	Y	No	Yes	2-6, 2-7, 2-8
Water-Based Paint	Y*	Y*	Y*	No	Yes	2-9, 2-10
Preformed Tape	Y	Y	N	Yes	Yes	2-11
Epoxy	Y	Y	L	Yes	Yes**	2-12, 2-13
Polyurea	Y	Y	L	Yes	Yes**	2-14
Modified Urethane	L	L	L	Yes	Yes**	2-15
Methyl Methacrylate	L	L	L	Yes	No	2-17
Profiled Thermoplastic	Y	Y	N	No	Yes	-
Contrast Markings	Y	Y	L	No	No	-
Heated-in-Place Thermoplastic (not for use in longlines)	Y	Y	Y	Yes	Yes	-
Ceramic Buttons	L	N	N	Yes	No	2-15
Y = Suitable for use. N = Not recommended. L = Limited use. * = Refer to Table 2-10 for traffic volume conditions. ** = Refer to Multipolymer Specification SS 1513.

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Supplemental Material Performance Information

The National Transportation Product Evaluation Program (NTPEP) performs performance evaluations on a number of different pavement marking materials on various pavement surface types and under various traffic volume levels and environmental conditions. Reports documenting these evaluations are available through NTPEP or the American Association of State Highway and Transportation Officials (AASHTO). TxDOT also maintains similar field test decks used for performance comparison of various marking materials.

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Thermoplastic Markings

Thermoplastics have been used as a pavement marking material in the United States since the late 1950s and have been the most common pavement marking material used on roadways in Texas for years. Thermoplastic is so named because the mixture of plasticizer and resins that serves to hold all of the other ingredients together exists as a solid at room temperature, but becomes liquid when heated. The popularity of thermoplastic markings can be attributed to several factors including:

readiness for immediate use
high durability
good retroreflectivity
relatively low cost.

When properly formulated for a given roadway surface and correctly applied, thermoplastic pavement markings have been known to last from 5 to 8 years depending on traffic volumes, but research has shown that usual service lives range from 2 to 3 years depending on traffic volumes.

Thermoplastic materials are very sensitive to the variables governing application, warranting strict quality control during application. The following are the key variables that influence the durability and retroreflectivity performance of thermoplastic markings:

material composition
application procedure
roadway surface
traffic
environment.

If applied properly, thermoplastic materials provide durability and retroreflective performance that far surpass that of standard traffic paints. However, because thermoplastic materials are very sensitive to the variables involved with application, they may not be the most suitable material for certain situations. The following segments describe the types, application, performance, and suggested uses of thermoplastic materials.

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Thermoplastic Marking Material Characteristics

Thermoplastic materials are classified by TxDOT as a Type I pavement marking material, with material specifications falling under DMS-8220 and tested using Test Method Tex-863-B. Thermoplastic materials consist of four general components: binder, pigment, glass beads, and filler material (usually calcium carbonate, sand, or both). Thermoplastic materials are classified into two basic categories based on the type of binder: hydrocarbon and alkyd. Hydrocarbon thermoplastic is made from petroleum-derived resins, while alkyd thermoplastics are made from wood-derived resins. Alkyd thermoplastics are currently the standard thermoplastic allowed for use by TxDOT as a pavement marking material under DMS 8220. Hydrocarbon thermoplastics are currently only allowed for use by TxDOT through a special provision to DMS 8220. A side-by-side comparison of the two types of thermoplastic materials is shown in Table 2-6.

Anchor: #i1014013Table 2-6. Comparison of Thermoplastic Material Types
-	Type of Thermoplastic
Characteristic	Hydrocarbon	Alkyd
Binder Source	Petroleum	Wood
Application Temperature	Approximately 420°	Approximately 420°
Oil Soluble?	Yes	No
Heat Stability	More	Less
Sensitivity to Changes in Application Properties	Better Suited	Not As Well Suited
Durability	Less	More
Expected Life Under Normal Conditions	Up to 5 years	Up to 5 years

The ability for thermoplastic materials to bond to the roadway surface is based on the thermal properties of the thermoplastic binder and the roadway surface along with the porosity of the surface. Thermoplastic is well suited for use on asphalt surfaces because the thermoplastic develops a thermal bond with the asphalt via heat fusion. When applied to hydraulic cement concrete surfaces, bond formation occurs by the liquid thermoplastic seeping into the pores of the concrete and forming a mechanical lock to the concrete surface. Primers are recommended prior to thermoplastic application on all hydraulic cement concrete surfaces and asphalt surfaces that are more than two years old, heavily oxidized, or have exposed aggregates.

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Thermoplastic Marking Application Methods

Most of the thermoplastic longlines placed on TxDOT roadways are applied by spraying the hot thermoplastic onto the surface. Therefore, sprayed applications are the major focus of the information in this segment. However, it is worth noting that there are other methods of applying thermoplastic markings to the roadway surface, such as gravity extrusion and ribbon application.

Gravity Extrusion. Gravity extrusion was the application method of choice for many years, and is well suited for application of thicker markings. Extrusion occurs by pouring hot thermoplastic into a trough or shoe, which has a gate set to produce a desired thickness. However, extrusion is a relatively slow process (3 mph).

Ribbon Application. Ribbon application uses a pressurized gun to apply thermoplastic in the same manner as the gravity extrusion method.

Hot-Sprayed. 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 100 mils when compared to extrusion and ribbon applications. Figure 2-10 shows a typical sprayed thermoplastic application.

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Figure 2-10. Typical sprayed thermoplastic operation.

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Thermoplastic Marking — Surface Preparation

The temperature of the thermoplastic material is a very important factor in the performance of the thermoplastic-roadway surface bond. Suitable application temperatures range from 400–450°F, with 420°F as the recommended temperature for most applications. For proper bonding, the following conditions must exist:

The pavement surface must be free of dirt, dust, and other contaminants.
The pavement surface must be free of poorly adhered existing markings, glass beads, and curing compound.
The pavement surface must be free of moisture.
Pavement and air temperatures must be at least 50°F and 55°F, respectively, to ensure proper rate of cooling.

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 2-7 describes problems and solutions associated with the application of thermoplastic markings.

Anchor: #i1014053Table 2-7. Tips and Trips for Thermoplastic Application
Trips	Tips
Debonding	Unclean road surface Low temperatures Moisture in pavement Defective material Marking speed too fast
Bubbles in line	Moisture in pavement Overheated material
Flowing Line (i.e., no defined edge), line with excessive rounded edges	Material too hot
Cracks in line	Temperature stress from overheating Low temperatures Material applied too thin
Rough line surface or crumbly edges	Material temperature too low Material has been scorched Moisture in pavement
Smooth, shiny, glossy line	No or insufficient glass beads or beads too deeply embedded
Smooth line with slight dimples	Glass beads too low Bead gun too close to application shoe
Cratered line	Glass beads have popped out Material is too cool or bead gun located too far back
Greenish yellow appearance	Material has been scorched Material reheated too many times or inadequate cleaning of application pots
Splattering	Material too hot or too cold
Dingy or dull white color	Material has been scorched Material reheated too many times or inadequate cleaning of application pots Yellow thermoplastic not completely removed before white was added to the application pots
Lumps in line	Material is either overheated or underheated Charred material has been overheated where unblended pigments and fillers have been underheated

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Thermoplastic Marking — Effect of Pavement Surface on Performance

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 2-11.

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Figure 2-11. 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 100 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.

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Thermoplastic Marking — Effect of Traffic on Performance

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.

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Thermoplastic Marking — Environmental Effects on Performance

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 should also not be used unless the pavement temperature is 50°F and the air temperature is 55°F. 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.

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Thermoplastic Marking Use Summary

Table 2-8 summarizes the recommended uses of thermoplastic pavement markings.

Anchor: #i1014096Table 2-8. Use of Thermoplastic1 Pavement Markings
-	Asphalt			Concrete			Surface treatments
-	AADT <1,000	AADT 1,000 –10,000	AADT >10,000	AADT <10,000	AADT 10,000 –50,000	AADT >50,000	AADT <1,000	AADT 1,000 –10,000	AADT >10,000
Use²	Y	Y	Y	L	L	N	Y	Y	Y
Material suggestions	TxDOT standard			specific concrete formulation		-	TxDOT standard
Typical minimum thickness (new)	90 mils			90 mils	90 mils	-	100 mils
Typical minimum thickness (restripe)	60 mils			60 mils	60 mils	-	60 mils
Surface prep.	Clean & dry.			Clean, dry, & primer-sealer (refer to Item 678 or manufacturer recommendations).		-	Clean, dry, & remove loose stones.
Expected Service Life	up to 4 years	up to 4 years	up to 3 years	up to 4 years	up to 4 years	-	up to 4 years	up to 4 years	up to 3 years
Approx. bid price for new surface in 2002 (per lf)	$0.20			$0.35		-	$0.20
Estimated cost per year of service life (per lf)	$0.05	$0.05	$0.07	$0.07	$0.09	-	$0.05	$0.05	$0.07
Footnotes: 1. TxDOT Specification Thermoplastic unless noted otherwise. 2. Y = suitable for use; N = not recommended; L = limited use.

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Water-Based Paint

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.

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Water-Based Paint — Material Characteristics

Paints are classified by TxDOT as Type II pavement markings, with material specifications falling under DMS-8200, WPT-12, and YPT-12 for white and yellow, respectively. The current DMS-8200 specification specifically calls for Rohm-Haas Fast Track HD-21A or Dow DT-400 acrylic emulsion resins. 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 1980s and early 1990s 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.

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Water-Based Paint Application

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:

The pavement surface must be free of dirt, dust, and other contaminants.
The pavement surface must be free of poorly adhered existing markings, glass beads, and curing compound.
The pavement surface must be free of moisture.
Pavement and air temperatures (including wind chill) must be at least 40°F.

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 15-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. TxDOT Specification Item 666.4.4 contains more information on paint application rates. Application of a primer material is not necessary on any roadway surface, although a double application of paint is sometimes specified. Table 2-9 summarizes problems that have been encountered with the use of paint as a striping material and suggests solutions for these problems.

Anchor: #i1014221Table 2-9. Trips and Tips for Paint Applications
Trips	Tips
Thick centers	Decrease paint tank pressure. Close control screw slightly. Increase atomizing air pressure. Reduce pump pressure. Increase temperature of material.
Thin centers	Decrease atomizing air pressure or clean paint screens. Increase paint tank pressure. Decrease temperature of material.
Marking is thick on one side and thin on the other	Replace tips or clean them out.
Marking is too wide	Lower application gun. Select proper tip size. Adjust tip angle.
Marking is too narrow	Raise application gun. Select proper tip size. Adjust tip angle. Clean spray nozzle.
Marking is too thin	Open the control screw slightly. Increase the pump pressure. Increase the air pressure. Decrease the application vehicle speed.
Marking is too thick	Close the control screw slightly. Decrease the pump pressure. Decrease the air pressure. Increase the application vehicle speed.
Discoloration of paint on new asphalt roadway	Apply a second coat of paint.

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Water-Based Paint Performance

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. However, a reasonable target value for service life, under “normal” conditions is approximately 6 to 12 months. 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.

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Water-Based Paint Use Summary

Table 2-10 summarizes the recommended uses of paint pavement markings.

Anchor: #i1014252Table 2-10. Use of Paint Pavement Markings
-	Concrete			Asphalt			Surface Treatments
-	AADT <1,000	AADT 1,000 –10,000	AADT >10,000	AADT <10,000	AADT 10,000 –50,000	AADT >50,000	AADT <1,000	AADT 1,000 –10,000	AADT >10,000
Use¹	Y	Y	L	Y	L	N	Y	L	N
Thickness	15–25 mils			15–25 mils			15–25 mils
Surface prep.	Clean & dry.			Clean & dry.			Clean, dry, & remove loose stones.
Expected service life	Up to 1 year			Up to 1 year			Up to 1 year²
Approx. bid price (per lf)	$0.08			$0.08			$0.08
Estimated cost per year of service life (per lf)	$0.08			$0.08			$0.08
Footnotes: 1. Y = suitable for use; N = not recommended; L = limited use. 2. On new surface treatments, paint should only be used as a temporary marking for up to 6 months.

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Preformed Tapes

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 should be installed according to TxDOT Specification Item 668.

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.

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Preformed Tapes — Material Characteristics

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.

Permanent. 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 must conform to DMS-8240 and are classified by TxDOT in this specification as Types A and B based on application procedures and expected service life. 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:


Urethane:	Pliant Polymer:
Typically 60 or 90 mils thick. Cold-extruded plastic with intermixed and surface glass beads. Often pre-coated with pressure-sensitive adhesive.	Typically 30 or 60 mils thick. More flexible than urethane tapes. Intermixed and surface glass beads. Often pre-coated with pressure-sensitive adhesive.

Temporary. 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-8241.

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Preformed Tapes — Application

The manufacturer’s application procedures for preformed tape must be strictly followed. 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. The asphalt should still be warm, approximately 130°F. 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.

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Preformed Tapes — Removal

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. Often, however, the permanent tapes have achieved such a tight bond to the surface that they must be ground off, which scars the pavement. This is especially true of permanent markings that have been inlayed into the pavement surface.

Most of the temporary tapes that are in use are easily removed by hand or by a mechanical roller with no special equipment required.

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Preformed Tapes — Performance

Preformed plastic tapes generally have good durability and abrasion resistance. Preformed tape typically exhibits better performance on bituminous asphalt pavement than on hydraulic cement concrete because of the adhesive characteristics. Inlaid tapes almost always outperform overlaid tapes. Tapes are known to distort in areas that have a high amount of turning movements or weaving over the markings. A clean surface is more important for tapes than for any other material. Therefore, tapes must be applied in areas where good bonding can be ensured. If applied properly, tapes can provide durability and visibility for many years. In most cases these materials are so durable that the tape material will typically outlast its retroreflective properties.

Preformed plastic tapes are most commonly used for shortline markings, including: crosswalks, stop bars, and words and symbols. However, their use as a longline application is increasing nationwide. Permanent tapes are well suited for severe conditions where frequent replacement is required due to their ease of application. Temporary preformed tapes can be used in construction or maintenance jobs requiring temporary delineation or altered travel lanes. Preformed tapes require little or no equipment to apply and the roadway is open almost immediately after installation.

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Preformed Tapes — Use Summary

Table 2-11 summarizes the recommended uses of permanent preformed tape pavement markings. Temporary preformed tapes should only be used for short-term applications such as in work zones.

Anchor: #i1014367Table 2-11. Use of Permanent Preformed Tape Pavement Markings
-	Asphalt			Concrete			Surface Treatments
-	AADT <1,000	AADT 1,000 –10,000	AADT >10,000	AADT <10,000	AADT 10,000 –50,000	AADT >50,000	AADT <1,000	AADT 1,000 –10,000	AADT >10,000
Use¹	N	Y	Y	N	Y	Y	N	N	N
Surface prep.	-	Remove existing markings, clean, dry, & apply adhesive		-	Remove existing markings, clean, dry, & apply adhesive		-	-	-
Expected service life	-	Up to 4 years		-	Up to 4 years		-	-	-
Approx. bid price (per lf)²	-	$2.57		-	$2.57		-	-	-
Estimated cost per year of service life (per lf)	-	$0.43		-	$0.43		-	-	-
Footnotes: 1. Y = suitable for use; N = not recommended. 2. Price includes required removal of existing markings.

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Epoxy

Researchers first introduced two-component epoxy-resin paints as a pavement marking material in the 1970s and have since developed it into a common pavement marking material used by many agencies. Epoxy materials are durable, sprayable materials that provide exceptional adhesion to both bituminous surfaces and hydraulic cement concrete surfaces with good abrasion resistance. Epoxies are more expensive than standard paints and are about the same cost or slightly more expensive than most thermoplastics. A variety of formulations are available on the market from many vendors.

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Epoxy Performance

Epoxy pavement markings are durable markings recognized for exceptional durability on asphalt and concrete surfaces alike. This exceptional durability is a result of tight bonding to the pavement surface that results from the chemical reaction that occurs when the two components are mixed. Research has shown that epoxy paints are generally less sensitive to application factors than thermoplastic materials, allowing epoxy to have exceptional durability under many different roadway conditions. Epoxies can be applied at surface temperatures as low as 35°F and when pavement surfaces are slightly wet. On low-mid-volume roadways, epoxies have been known to provide service lives in excess of four years. Epoxies require proper cleaning of the pavement surface to achieve the best bond. Application of a primer material is not necessary on any roadway surface. Epoxies are often applied at thicknesses of 15 mils.

One drawback associated with epoxies is that they often take much longer to dry than other materials. Some formulations take over 40 minutes to dry. If a two-component marking material, like epoxy, does not dry within the manufacturer’s recommended drying time, the components likely did not react properly and will not cure. In this case, the two component products must be removed and the road must be restriped. Newer formulations exist that provide no-track drying times as low as 30 seconds depending on weather conditions, but are often slightly more expensive than slow cure epoxies. Fading due to color instability under ultraviolet lighting is also an issue with some epoxy paints. Epoxies also cannot be placed over markings made from other materials, limiting their use as a restripe material. Table 2-12 summarizes some problems that have been encountered using epoxy striping materials and potential remedies of those problems.

Anchor: #i1014459Table 2-12. Trips and Tips for Epoxy Application
Trips	Tips
Thick centers	Replace tip. Decrease tip size. Increase pressure.
Thin centers	Replace tip. Increase tip size.
Surging pattern	Leaks or restrictions in supply hose may be causing pulsating application. Check hydraulics.
Marking is thick on one side and thin on the other	Replace tips or clean them out.
Marking is too wide	Lower application gun. Select proper tip size. Adjust tip angle.
Marking is too narrow	Raise application gun. Select proper tip size. Adjust tip angle.
Marking is too thin	Increase tip size. Slow down application vehicle. Increase pressure.
Marking is too thick	Decrease tip size. Speed up application vehicle. Decrease pressure.
Dark marking	Decrease hardener amount. Rebuild high pressure pumps.
Marking takes too long to cure	Increase hardener amount. Rebuild high pressure pumps.
Some spots didn’t cure properly	Clean or change check valves. Check accumulator pressures.
Railroad tracking	Increase temperature of material. Replace tips. Adjust material pressure.

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Epoxy Use Summary

Table 2-13 summarizes the recommended uses of epoxy pavement markings.

Anchor: #i1014502Table 2-13. Use of Epoxy Pavement Markings1
-	Asphalt			Concrete			Surface Treatments
-	AADT <1,000	AADT 1,000 –10,000	AADT >10,000	AADT <10,000	AADT 10,000 –50,000	AADT >50,000	AADT <1,000	AADT 1,000 –10,000	AADT >10,000
Use²	Y	Y	Y	Y	Y	Y	Y	Y	Y
Thickness	15–25 mils			15–25 mils			15–25 mils
Surface prep.	Remove old mkgs, clean, & dry			Remove old mkgs, clean, & dry			Remove old mkgs, clean, & dry
Expected service life	Up to 4 years	Up to 4 years	Up to 3 years	Up to 4 years	Up to 4 years	Up to 3 years	Up to 4 years	Up to 4 years	Up to 3 years
Approx. bid price (per lf)	$0.40			$0.40			$0.40
Estimated cost per year of service life (per lf)	$0.10	$0.10	$0.13	$0.10	$0.10	$0.13	$0.10	$0.10	$0.13
Footnotes: 1. A wide variety of epoxy materials are currently available, possessing varying degrees of quality. The information in this table is based on the cost and performance of special formulations of epoxy that are designed for high-quality and high-durability pavement markings commonly used by state DOTs nationwide. 2. Y = suitable for use.

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Other Materials

Other materials that have been used by TxDOT on an experimental basis or have seen substantial use by other transportation agencies warrant discussion here. These other materials include epoxy paints, polyurea, modified urethane, methyl methacrylate, and heated-in-place thermoplastic. Each material is available from multiple vendors. Discussions of these materials follow.

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Polyurea

Polyurea markings are a sprayed, two-component durable pavement marking material that is relatively new to the pavement marking market. Various formulations of polyurea markings exist on the market and are available from a number of vendors. Polyurea pavement markings have been used on an experimental basis by TxDOT.

Polyurea materials are marketed as durable pavement markings that provide exceptional color stability, resistance to abrasion, and adhesion to all pavement surfaces. Polyurea markings appear to be less sensitive to pavement surface moisture than thermoplastics and can be applied at temperatures as low as freezing. Most of these materials are marketed as fast curing materials, achieving proper bonding and no-track conditions in 2 minutes or less. Polyurea markings have been reported to have service lives of up to 5 years, although limited data exist to support this statement.

One of the drawbacks associated with polyurea materials is that some must be applied by a special striping apparatus, which limits the number of contractors available to apply the material. Other polyurea materials, however, can be applied by a standard epoxy truck. The type of truck required is based on the resin-catalyst mix ratio. Polyurea mixes with a 2:1 mix ratio can be applied with a standard epoxy truck. Table 2-14 summarizes the recommended uses of polyurea pavement markings.

Anchor: #i1014605Table 2-14. Use of Polyurea Pavement Markings1
-	Asphalt			Concrete			Surface Treatments
-	AADT <1,000	AADT 1,000 –10,000	AADT >10,000	AADT <10,000	AADT 10,000 –50,000	AADT >50,000	AADT <1,000	AADT 1,000 –10,000	AADT >10,000
Use²	Y	Y	Y	Y	Y	Y	Y	Y	Y
Thickness	15–25 mils			15–25 mils			15–25 mils
Surface prep.	Remove existing markings, clean, & dry			Remove existing markings, clean, & dry			Remove existing markings, clean, & dry
Expected service life	Up to 4 years	Up to 4 years	Up to 3 years	Up to 4 years	Up to 4 years	Up to 3 years	Up to 4 years	Up to 4 years	Up to 3 years
Approx. bid price (per lf)	$1.00			$1.00			$1.00
Estimated cost per year of service life (per lf)³	$0.25	$0.25	$0.33	$0.25	$0.25	$0.33	$0.25	$0.25	$0.33
Footnotes: 1. The cost and performance of polyurea is based on limited experimentation both in Texas and nationwide. 2. Y = suitable for use. 3. Prices include a proprietary retroreflectivity-enhancing ceramic element embedded into the marking surface. Polyurea materials applied without the proprietary ceramic element may be less expensive.

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Modified Urethane

Modified urethanes are a two-component, durable marking material with similar performance characteristics to those of polyurea and epoxy. Material costs are reported to be slightly more expensive than epoxy but less than polyurea. This product is marketed as being slightly more durable than epoxy but with much quicker cure times (2 minutes) and better ultraviolet color stability. This material can be sprayed from any standard epoxy truck.

Because so little experience exists with modified urethane pavement marking materials, they should be used only on an experimental basis within Texas, although this material seems to have promise on concrete roadways. More data are needed before conclusive recommendations can be made. Table 2-15 summarizes the recommended uses of modified urethane pavement markings.

Anchor: #i1014708Table 2-15. Use of Modified Urethane Pavement Markings1
-	Asphalt			Concrete			Surface Treatments
-	AADT <1,000	AADT 1,000 –10,000	AADT >10,000	AADT <10,000	AADT 10,000 –50,000	AADT >50,000	AADT <1,000	AADT 1,000 –10,000	AADT >10,000
Use²	L	L	L	L	L	L	L	L	L
Thickness	Manuf. Recommendations			Manuf. Recommendations			Manuf. Recommendations
Surface prep.	Remove Existing Markings, Clean & Dry			Remove Existing Markings, Clean & Dry			Remove Existing Markings, Clean & Dry
Expected service life	Up to 4 years	Up to 4 years	Up to 3 years	Up to 4 years	Up to 4 years	Up to 3 years	Up to 4 years	Up to 4 years	Up to 3 years
Approx. bid price (per lf)	$0.63			$0.63			$0.63
Estimated cost per year of service life (per lf)	$0.16	$0.16	$0.21	$0.13	$0.16	$0.21	$0.16	$0.16	$0.21
Footnotes: 1. Based on use in other states. 2. L = limited use.

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Ceramic Buttons

TxDOT has used ceramic buttons extensively over the years. Until the recent change to TxDOT’s Signs and Markings Manual, which strongly discouraged the use of buttons, they were the third most often used pavement marking material in Texas behind thermoplastic and paint. While buttons often last for at least 2 years under the heaviest traffic conditions on concrete, the major complaint against their use is the lack of retroreflectivity provided by the materials rendering them nearly invisible under headlamp conditions on unlit roadways. While retroreflective raised pavement markings (RRPMs) are always used with buttons to supplement the lack of retroreflectivity, RRPMs generally have short service lives making for poor nighttime visibility conditions when the RRPMs fail. Buttons do provide a tactile and audible sensation when driven over, similar to that of rumble strips, which may be considered a safety benefit.

Ceramic buttons are very different in appearance and application from all other marking materials. If used, they must be supplemented by RRPMs to provide nighttime visibility. Due to the fact that they are a non-retroreflective material, they are somewhat unpopular as a pavement marking material. The availability of application equipment and labor, especially in Texas, makes them an attractive material choice, although they are comparatively expensive. Table 2-16 shows recommendations pertaining to the use of ceramic button pavement markings on concrete.

Anchor: #i1014811Table 2-16. Use of Ceramic Button Pavement Markings on Concrete
-	Traffic Condition
-	AADT <10,000	ADDT 10,000–50,000	AADT > 50,000
Use	Limited use	Limited use	Limited use
Service prep.	Clean, dry, & apply epoxy adhesive	Clean, dry, & apply epoxy adhesive	Clean, dry, & apply epoxy adhesive
Expected service life	Up to 5 years	Up to 4 years	Up to 3 years
Approx. bid price (per button)¹	$1.40	$1.40	$1.40
Estimated cost per year of service life (per lf)	$0.28	$0.35	$0.47
Footnotes: 1. Price includes required removal of existing markings or buttons.

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Methyl Methacrylate (MMA)

Methyl Methacrylate is a nonhazardous, two-component, durable pavement marking material. The material exists as a solid that is mixed in a static mixer immediately prior to application. MMA can be sprayed or extruded onto the pavement. The material forms a strong bond to the pavement surface by exothermic reaction (release of heat) that occurs during the mixing process.

Methyl methacrylate was originally marketed as an environmentally friendly alternative to solvent-borne paints. However, MMA has been shown to provide much longer service life than standard traffic paint. A service life of greater than three years is common. In addition, the material is designed to be resistant to oils, antifreeze, and other common chemicals found on the roadway surface. MMA reportedly bonds well to concrete pavements. MMA materials are usually applied at thicknesses of 40 mils. Because MMA does not rely on the addition of heat to cure, it is an attractive material in cold-weather climates. Research in cold-weather climates has shown very good performance for MMA. Costs for methyl methacrylate have been reported to be comparable to those of epoxy materials. As with all other two-component marking materials, a drawback to the use of MMA is that it requires special equipment for application. Table 2-17 summarizes recommended use of methyl methacrylate pavement markings on concrete.

Anchor: #i1014855Table 2-17. Use of Methyl Methacrylate (MMA) Pavement Markings
-	Asphalt			Concrete			Surface Treatments
-	AADT <1,000	AADT 1,000 –10,000	AADT >10,000	AADT <10,000	AADT 10,000 –50,000	AADT >50,000	AADT <1,000	AADT 1,000 –10,000	AADT >10,000
Use	Limited use			Limited use			Limited use
Thickness	40 mils			40 mils			40 mils
Surface prep.	Remove existing markings, clean, & dry			Remove existing markings, clean, & dry			Remove existing markings, clean, & dry
Expected service life	Up to 5 years			Up to 5 years			Up to 5 years
Approx. bid price (per lf)	$2.50			$2.50			$2.50
Estimated cost per year of service life (per lf)	$0.50			$0.50			$0.50

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Profiled Thermoplastic

Profiled thermoplastic markings are sprayed or extruded thermoplastic markings that are constructed with an alternating elevated and recessed profile. The purpose of the profiled pattern is to provide nighttime retroreflectivity under wet conditions, and in cases where the profiles are large enough, a rumble effect can be felt when driving over the markings. The elevation-recession pattern may be placed using one of many methods. The two most popular methods are inverted-profile markings and raised-profile markings. Descriptions of each follow.

Inverted-Profile Markings. Inverted-profile markings are created by a cog rolling over wet thermoplastic giving the line a corrugated appearance. Figure 2-12 shows a typical inverted-profile pavement marking.

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Figure 2-12. Typical inverted-profile thermoplastic marking (profile view).

Raised-Profile Markings. Raised-profile markings are created by extruding a thermoplastic marking of normal thickness with a raised thermoplastic “bump” (approximately 300 mil) at uniform spacing (often 3 ft). Figure 2-13 shows a typical raised profile pavement marking.

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Figure 2-13. Typical raised-profile thermoplastic marking (overhead view).

Performance and Use. Profiled thermoplastic generally performs well on all types of pavement surfaces. These markings often cost significantly more than standard thermoplastic (up to six times as much), but are often warranted by the contractor. The good performance may be attributed to the stringent contractor-supplied on-site inspection provided during most applications.

It should be noted that profiled markings are not necessarily limited to thermoplastic materials. Profiled markings may be constructed from materials other than thermoplastic as long as the same visual-tactile benefit is provided.

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Contrast Markings

Human vision is tuned to detect edges of contrasting color or brightness. Many concrete and heavily oxidized asphalt pavements are so light in color that during the day, white pavement markings appear to blend in with the pavement surface. To improve the visibility of pavement markings on light-colored pavements, markings are often applied over the top of a compatible black marking material. The underlying black material is usually applied at a greater width than the actual marking (minimum 1 inch) so that it provides a contrasting border around the marking. Contrast markings on white lane lines can also be applied with longitudinal leading or tailing sections of black material at least 12 inches in length. While many materials may be used as contrast markings, compatibility between the top and bottom materials must be ensured. Figure 2-14 shows a typical contrast pavement marking for a lane-line application, and Figure 2-15 shows a lead-lag type of contrast marking application.

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Figure 2-14. Typical bordered-contrast pavement marking for lane line.

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Figure 2-15. Typical contrast pavement marking for lane (line lead-lag layout).

Contrast markings are suitable for use at any location where the visibility of the pavement markings is poor, usually due to a light-colored pavement surface. Because of the increased expense for application of contrast markings, they are often used only for white lane lines on divided highways with light-colored pavements.

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Heated-in-Place Thermoplastic (Shortline Applications)

Heated-in-place thermoplastic is a preformed thermoplastic that has been shaped by the manufacturer into its final shape and thickness and includes a top layer of beads. These materials must conform to DMS-8240 and are classified by TxDOT in this specification as Type C. They are very durable markings and are used primarily for shortline applications, including transverse lines, words, and symbols. These materials do not have any pre-applied adhesive, and bonding to the pavement is achieved by placing the material in the desired location and heating the material with a torch. A manufacturer recommended sealer should be used on hydraulic cement concrete or old asphalt. Application includes five general steps:

Cleaning the surface.
Removal of moisture.
Layout of the material.
Heating the material (in some cases the pavement surfaces must also be heated).
Checking for proper bond using a chisel or similar device.

Figure 2-16 shows a typical preformed thermoplastic application.

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Figure 2-16. Typical preformed thermoplastic application.

Specific application requirements may vary with manufacturer, and therefore manufacturer specifications should always be followed. As with any thermoplastic application, the presence of pavement surface moisture or an improperly cleaned surface will cause insufficient bonding leading to failures.

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Retroreflective Raised Pavement Markings

Reflectorized raised pavement markers (RRPMs) are high-impact plastic markers approximately 4 inches square and 3/4 inch high with one or two retroreflective faces. RRPMs are used to provide retroreflectivity, delineation, and guidance and to enhance the reflectivity of pavement markings.

RRPMs may serve as a positioning guide or a supplement to pavement markings. The TxDOT standard is to install RRPMs using position guidance on all roadways with centerlines. Position guidance placement is used to show the driver where the centerline or lane lines of the roadway are located. Supplemental markings are installed along the outside of the solid centerline. The spacing and location of the markings are intended to inform the driver if passing is allowed and also mark the lane line location. The spacing and location of the RRPMs can be seen on the PM and FPM �standard sheets.

The RRPMs should be maintained and replaced periodically to ensure that the driver is getting the expected benefits of the markers. Routine maintenance of the markers should be performed when fewer than two markers are visible when spaced at 80 feet or fewer than three markers are visible when spaced at 40 feet. Table 2-18 shows TxDOT’s suggested replacement cycle for RRPMs.

Anchor: #i1014947Table 2-18. Suggested Replacement Cycle for RRPMs
Roadway ADT	Replacement Cycle
greater than 50,000 ADT	1 year
greater than or equal to 10,000 ADT	2–3 years
less than 10,000 ADT	3–4 years

RRPMs should be applied to the roadway surface using either bitumen or epoxy adhesives. Bitumen adhesives are normally used on asphalt surfaces, and epoxy is normally used on concrete roadways. Any adhesives used must meet TxDOT DMS specifications for epoxy or bitumen and must be installed in accordance with the manufacturer’s recommendations.