Thermoplastic Field Guide
Thermoplastic is a pavement marking material that is a 100% solid, environmentally and user safe compound. A mixture of glass beads, pigments, binder, and filler materials, thermoplastic, as its name suggests, becomes liquid when heat is applied.
Glass Beads - provide the retroreflectivity necessary for its bright night time appearance
Pigments - provide the color and opacity
Binder - a mixture of plasticizer and resins that provide toughness, flexibility, and bond strength while holding all the components together
Fillers - such as calcium carbonate, sand and/or other inert substances that provide bulk
Thermoplastic Types:
Two basic types of thermoplastic are available. The two, hydrocarbon and alkyd, take their names fromtheir binder types. Hydrocarbon thermoplastic is made from petroleum-derived resins.
• Hydrocarbon tends to be more heat stable, with more predictable application properties, than alkyd
• Because it tends to break down under oil drippings and other automobile contaminants, hydrocarbonis recommended for long-line, skip lines and edge-line applications and not for high-traffic areaswhere cars are stationary.(Such as stop bars, crosswalks, turn arrows)
Alkyd thermoplastic is made from wood-derived resins that is resistant to petroleum products.
Alkyd thermoplastic exhibits some advantages over hydrocarbon materials such as:
• higher retroreflective values
• being oil impervious
• being more durable
Alkyd is recommended for inner-city markings and other high-traffic areas where petroleum drippings are common.
Both hydrocarbon and alkyd thermoplastic are available in granular or block form, packaged in 50-pound bags or boxes. The application properties of each should have a guaranteed shelf life of one year when stored inside at a temperature less than 100° F.
Hot applied thermoplastic is prepared for road application in a melting kettle where the granular or block material is introduced and heated until it liquefies at temperatures exceeding 400° F. An agitator blends the ingredients until thermoplastic is transferred into a screed, ribbon or spray device where it is then shaped into its specified width and thickness as a line, legend or symbol.
Glass beads are immediately applied to provide initial retroreflectivity.
When applied on asphaltic surfaces, thermoplastic material develops a thermal bond via heat-fusion. When applied on Portland Concrete Cement and on oxidized or aged asphaltic surfaces, and a recommended sealer is properly applied, a tenacious mechanical bond is achieved.
Providing that all necessary conditions are met concerning temperature of material and substrate, absence of moisture, road preparation and minimum thickness, you can achieve excellent performance using thermoplastic pavement marking compounds. Typical performance life ranges from 4 to 8 years depending on roadway conditions.
Correct application of thermoplastic:
Temperature is the most important factor in the proper mixing, melting and bonding of thermoplastic.
• Heated to a temperature between 400 and 440° F and agitated properly, the thermoplastic compound becomes a homogenized liquid.
• Applied at this temperature, the thermoplastic melts into the upper surface of the asphalt, forming a thermal bond.
• When installed on porous surfaces, such as open-graded asphalt or tined concrete, the hot liquid thermoplastic fills all voids, creating a good mechanical lock on concrete.
Thickness of the applied thermoplastic should be as specified. A minimum thickness of 90 mils is important to the material's ability to hold the heat necessary for good bonding. The thermal bonding that occurs when application is at the proper thickness ensures the thermoplastic's durability and long-term retroreflectivity, A minimum thickness of 30 mils is required to hold the heat necessary for proper bonding when recapping a line because of poor reflectivity or inadequate thickness.
Being raised above the road surface, combined with the retroreflectivity produced by the glass beads makes thermoplastic more visible from a distance and at night. The thickness also contributes to improved retroreflective performance in wet conditions and the exceptional durability of the product.
The amount of glass beads, both mixed in with the compound and dropped on the installed line, must be correct.
• Drop-on beads must be applied evenly and adhered to a depth of 50 to 60%.
• Apply at 8 to 10 lbs / 100 ft2.
• Proper application thickness, temperature and formulation, in conjunction with correct bead coatings, ensure that bead depth is accurate.
• Intermix beads shall be mixed in the thermoplastic in accordance with agency's specification.
Equipment:
Application equipment should meet the criteria of the specification. The engineer may be responsible forapproving such equipment, whether it be mobile or portable, prior to the start of work.
Melting Kettle(s) must be capable of :
• Heating thermoplastic material to its application temperature evenly, without scorching.
• Maintaining temperatures above 400’ F. The heating mechanism of the kettle should employ a heattransfer medium consisting of oil or hot air.
• A temperature gauge must be visible on the outside of the kettle to indicate the temperature of thethermoplastic material. The material gauge must not be confused with the heat transfer medium (oiltemperature)gauge.
• Material temperatures should be monitored frequently with an external, calibrated thermometer Proper application temperatures should always be checked at the point of application.
Mixing and Agitating Equipment - Melting kettles and portable applicators:
• Must be equipped with material agitators.
• Must be capable of thoroughly mixing the material at a rate which will ensure even disbursement and uniform temperatures throughout the material mass.
Priming Equipment
On pavement surfaces that are to be primed before the application of the thermoplastic material, theprimer material shall be sprayed on the surface at the specified rates recommended by the manufacturer ofthe primer/sealer material. All of the priming equipment should be inspected and checked to ensure thatit is completely operational and capable of disbursing the primer/sealer at the rate prescribed by themanufacturer.
Glass Bead Dispenser
Both mobile and portable thermoplastic application equipment are required to be equipped with a drop-onor a pressure-type bead dispenser. The glass beads are to be evenly dropped-on to the hot thermoplasticstripe immediately after its application, embedding and anchoring at a depth of 50 to 60%. The purposeof the glass beads is to provide initial night time retroreflectivity of the pavement marking which, withoutthem, would be barely visible to the motorist, The bead dispenser shall be inspected frequently to ensureproper operation and to ensure uniform rates of each application over the entire marking surface.
Dispensing Devices
There are various devices used to screed/extrude thermoplastic material onto the pavement. The deviceshould be positioned such to protect it from the wind.
Ribbon Dispensers are heated and suspended above the road surface, applying a forced-extrusion,well-defined thermoplastic line.
Spray Dispensing Devices - Thermoplastic spray pattern shall result in a uniformly thick, well.defined and securely-bonded stripe as specified. Compressed air must be dry when mixing with themolten thermoplastic.
Screed Extrusion Devices - The dispensing shoe rides directly on the road surface and a continuosline is formed by a three sided die with a control gate set to a pre-determined thickness.
Successful Performance:
Because bond failures are application related, they can be minimized by proper application controls. This can be accomplished through correct and frequent inspection at the project site. The following guidelinesare intended to assure successful installation performance.
Marking Location - To minimize damage from snowplow blades and from substrate failure, thermoplastic markings must be:
• placed directly on the lane, preterably 2 inches from the shoulder and construction joints.
• Do not apply edgeline markings directly over the joint formed between the roadway and the adjoining shoulder.
• Do not apply skip line markings over the longitudinal joint between travel lanes.
Equipment - A daily inspection of equipment should be made to ensure that is operable and within thespecification requirements. Breakdowns of equipment during the day may cause thermoplastic materialsor primers to be subsequently held too long or heated improperly. This can result in parts of the jobfailing to meet the overall specifications and longevity requirements of the road marking materialintermitent malfunctions of equipment can also cause inconsistent performance of small sections of laneines within a limited area, Continuous uniform operation of all equipment used to make thermoplasticapplications is of extreme importance. Keep equipment clean and free of material residue buildup.
Materials - Material specifications should be reviewed completely, It is the function of the governmenttesting laboratory to determine whether or not the material meets the requirements of the materialspecifications, Field samples of material may be retained by the project engineer for quality verification.
Material packaging shall have accurate batch number designations, The material type and formulationshould be distinctively shown on the container: 1) Alkyd or Hydrocarbon and 2) Extrude or Spray.
Although alkyd and hydrocarbon materials will fuse to one another on the road, they areincompatible in a melting kettle, Failure to completely clean out kettles during material change.overs can cause severe equipment problems, DO NOT MIX ALKYD AND HYDROCARBONMATERIALS!!!
Pavement Surface - Pavement surfaces must be clean, dust free and dry. Remove poorly adhering.existing markings and curing compounds. Air and surface temperatures shall be at least 50' F and risingduring applications.
Heavy deposits of existing painted pavement markings, polymer trafic tapes, and built-up roadsideaccumulations of dirt, etc., will all require removal. In some cases, an air blast or manual or mechanicalbrooming will be sufficient to clean the surface, In others, more effort or different methods such asabrasive-blasting, water blasting or mechanical removal will be needed.
New thermoplastic applications should successfully bond to worn existing thermoplastic lines or preformthermoplastic markings. Do not apply thermoplastic over existing tape markings.
All pavement should be more than visibly dry, oisture is the most detrimental factor in bondingSubsurface moisture can be present in amounts sufficient to affect proper bonding, Early morning dewand fog conditions will usually cause dampness. If excess pavement moisture exists, it will usually resultin blistering the hot-applied marking. Blisters will form as surface bubbles which may or may not haveburst open. They are easily spotted, and if the condition occurs, marking operations should be stoppeduntil the pavement dries. The only way to be certain, whether moisture is present is to conduct a test.There are numerous ways to test for moisture.
• Tape a 12 inch square sheet of thin plastic to the road surface, being careful to seal all edges, After15 minutes, examine the bottom of the sheet and the road surface. If more than a sparse amount ofmoisture is present, do not apply thermoplastic.
• Place an 18 inch piece of tar paper on pavement and apply thermoplastic heated to 420’F on topWait two minutes and lift tar paper. Check underside. If moisture is present, do not apply.
Air Temperature - Thermoplastic should only be applied if the air temperature is 50 F and rising. Besure to account for wind chill factors, If the temperature falls below 50 F, then striping operation shouldbe halted.
Primer Application - Use the thermoplastic manufacturer's recommended primer:
• on all Portland concrete
• on asphalt surfaces that are more than two years old, oxidized and/or have aggregate exposed
If specified prior to the thermoplastic application, the primer must be applied to all pavement surfaces atmanufacturer's recommended application rates, It must set for the specified cure or evaporation timeprior to thermoplastic being applied.
Primed pavement surfaces must be striped within the specified set time or within the same working day.If the primed surfaces are not striped within these time limits, they must be reprimed prior to thethermoplastic application at the prescribed rate denoted by the manufacturer. If an approved epoxyprimer is used, proportional mixing must be checked and thermoplastic application must occur beforeepoxy has cured.
Improper primer/sealer application will cause bond failure between the thermoplastic and substrate.Improper application may also result in physical degradation of the thermoplastic material by excessivepinholing and blistering of the line. This degradation may occur through extraction of the binder by thesolvent system contained in the primer/sealer promoted by improper drying time and application rates.