Pavement Marking
    Materials
    Practices
    Specifications
    Evaluation
    Technologies
    References
    Acknowledgment
 
Pavement Marking: Technologies in use
1._General
2._Equipment_Used_in_Pavement_Marking_Industry
    2.1_Type_of_Retro-reflectometers
    2.2_Multi-purpose_gauge
    2.3_Digital_marking_gauge
    2.4_Road_marking_control_kits
3._Application_Techniques_of_Pavement_Marking
    3.1_Glass_Bead_Application
4._Evaluation_Techniques_for_Marking_Materials
    4.1_Retro-reflectivity_Performance_Evaluation_Techniques
    4.2_Degradation_model_of_retro-reflectivity
    4.3_Pavement_Marking_Thickness_Measuring_Techniques
5._Pavement_Marking_Removal_Techniques



1. General

Transportation agencies adapt new technologies to improve their traffic control devices, and increasingly search for more sustainable technologies. Being one of the important components of traffic control system, pavement marking also requires new technologies at same level. Technologies are used to evaluate marking materials, to apply markings, to remove materials, and finally, to measure performance parameters in service condition. Before discussing technologies, a brief description of all major equipment used in pavement marking industry for material evaluation, construction and assessment existing markings is described.

2. Equipment Used in Pavement Marking Industry

After reviewing different transportation agencies (Alberta, Saskatchewan, British Columbia, New Brunswick,  Irelands and UK) specifications, the following general requirements are summarized for traffic paint application equipments:

  • The choice of pavement marking application or installation through equipments should be based on recommendations of marking material manufacturers.
  • For applying solvent based traffic paint, water-borne traffic paint, thermoplastics and polymeric material; spray equipment can be used.
  • All equipment should conform to MUTCD requirements.
  • The equipment should be capable of achieving required thicknesses and widths as a uniform stripe with sharp edges
  • Line paint equipment should be equipped with a glass bead dispenser and should be able to apply beads uniformly at the recommended rate
  • Equipment shall have mounted storage boilers capable of heating up to specified temperature and maintaining the temperature throughout the operation. 
  • Radio communication system is suggested
  • Adequate traffic control and signs should be provided

Commonly used equipments are:

  • Spray equipment consists of boiler, thermometer, spray guns, beads dispenser and traffic control signs.  Spraying equipment can be either self contained units or truck mounted
  • Pilot trucks are equipped with overhead revolving amber beacon, a sequential arrow, a rear-mounted caution sign.
  • The manual screed equipment consists of a hopper which feeds to a thermoplastic rectangular screed at the base. The machine is fitted with a manual stirrer and screed cut-off. The machine is not normally equipped with glass beads to the marking surface.
  • Extrusion equipment is a mechanically propelled extrusion method of thermoplastic application as pavement marking. This equipment contains glass beads dispenser and simultaneously applied beads to the surface of the marking line.

2.1 Type of Retro-reflectometers

  • The Laserlux® CEN 30 (figure 7) is the most commonly used mobile retro-reflectometer. This complete and sophisticated equipment measures the retro-reflectivity of pavement markings using a scanning laser source. It follows American Society for Testing and Materials (ASTM) E1710 30-meter geometry with 6+inches of ground clearance. It provides real-time pavement marking reflectivity and can be used for both day and night at variable traffic speeds

Figure 7 : The vehicle is equipped with Laserlux® CEN 30 type of mobile retro-reflectometer (Source: Road Vista, 2006)

  • ZRM 1013+ Retro-reflectometer RL & Qd is a portable retro-reflectometer suitable for both night and day visibility. It performs independently during night and daytime, on the road or in the laboratory.
  • RoadVista model 1200F: This portable retro-reflectometer designed for use in field measurements of raised retro-reflective pavement markers.
  • ZRM 1021 Reflectometer: This portable meter is suitable to determine day visibility of pavement marking
  • StripeMaster and StripeMaster II: These portable meters measure retro-reflectivity of pavement markings as per ASTM E1710 and EN 1436 30-meter geometry. It can be used to measure on wet (per ASTM E2176 and ASTM E2177) or dry surfaces. It contains removable wheels for extended measurements and stabilizer to work in case of rough surface.
  • Model 930C Laboratory/Field Retro-reflectometer is a portable meter. It is suitable for evaluating new retro-reflective materials and signs as well as determining degradation resulting from weathering at different observation and entrance angles.
    (
    Road Vista, 2006, Innopave Group, 2006)

2.2 Multi-purpose gauge

The gauge is used to test film thickness, to assess adhesion of single and multi layers applications. One such gauge is ZMG 2150 Multi-purpose gauge manufactured by Innopave Group.

2.3 Digital marking gauge

Figure 8 shows a digital gauge which can be used to measure the dry film thickness of road markings.

Figure 8 : A Digital marking gauge of model ZMM 5000 (Source: Innopave Group, 2006)

2.4 Road marking control kits

This kit is very useful for quality assurance works of pavement marking installations. It is used to ensure appropriate temperature requirements, humidity, film thickness, reflective beads amount and their embedding need. The following Table 18 listed the equipments used by NTPEP in their material evaluation program.

Table 18 : Represents equipment historically used on NTPEP PM Test decks (Best Practice Manual, 2006)

Equipment

Recommended

Testing Equipment

 

Retro-reflectometer

LTL X LTL 2000Y

Spectrophotometer

Color-Guide(Gardner)

Film Thickness Gauge

Dry Film Thickness Gauge (0-200 mils / 0-5 mm) integral - ferrous

Surface Temperature Gauge

Raytek ST Pro Series Infrared Thermometer with Laser Guide

Weather Station

Davis, Complete Weather Monitor II (includes software for downloading results to a database)

Handheld Computer

 

Other Equipment

 

Gas Generators

Honda Super Quiet

Balances

 

Weight Stations

 

Lap Top

 

Note:  ASTM specifications call for a 1500 gram balance with an accuracy of 0.1 grams. Chosen balance is designed for outdoor use and extremes in temperature. They should be adjustable to level, equipped with a tare function, easily read, reliable calibration, and with a large top (panels being weighed are 12” by 12”).

Table 19 consists of monitoring and measuring control devices, recommended by the UK, National Highways Sector Schemes for Quality Management in Highway Works.

Table 19 : Requirements for the Control of Monitoring and Measuring Devices: (BS EN ISO 9001: 2000 clause 7.6) (Adapted from NHSS, 2006)

Equipment

Specification

Calibration Control

Calibration Frequency

Thermometers and temperature control equipment

Equipment must operate within a tolerance of ±10ºC at working temperature

Calibration traceable to national standards

3 monthly (may be extended to 12months upon demonstration of continued calibration accuracy)

Pressure measuring equipment

Appropriate British or International standard

Calibration traceable to national standards

Annually

Thickness/height measuring equipment

Maximum allowable error at any point in working range value +5%

Calibration traceable to national standards

Annually

Measuring wheels, tapes and rules

Maximum allowable error ±1% of the measurement range undertaken (upon purchase only)

Verification check when signs of wear or damage appear

Checks as required

3. Application Techniques of Pavement Marking

Depending on type of marking material and application equipment, the following type of applications techniques have been mentioned in the UK based National Highways Sector Schemes (NHSS), (2006) for markers and beads:

  • Spray
  • Extrusion
  • Hand screed
  • Hand cart screed (PRAM)
  • Raised rib
  • Embossed
  • Embossed
  • Preformed
  • Permanent tape

3.1 Glass Bead Application

The following four types of method are used to apply glass beads in pavement markings as retro-reflectivity requirements:

  • Air assisted
  • Mechanical metered feeder
  • Gravity fed
  • Hand applied

4. Evaluation Techniques for Marking Materials

National Transportation Product Evaluation Program (NTPEP), operated by AASHTO, conducts tests for commercially available pavement markings against other proprietary engineered products in order to develop qualified product lists. Some of the state agencies perform much of their own research in agency operated facilities (Migletz, and Graham, 2002). The field (test deck) and laboratory tests are performed according to AASHTO and ASTM standards. To evaluate fluid traffic markings on a NTPEP pavement test deck, ASTM D 713 standard is followed. To measure the retro-reflectance of samples, LTL 2000 or LTL-X Retro-reflectometers are used. As a durability performance evaluation, appearance/color is determined through a combination of a color-measuring instrument (NTPEP, Best Practices Manual 2006). Evaluations are done thorough out the life cycle; after every thirty days for the starting year and 120 days from second year. Evaluations include daytime/nighttime color, retro-reflectivity, durability, and wet night retro-reflectivity for each product evaluated. A photo-log is also maintained. Besides field tests, laboratory evaluations are also performed according to a number of ASTM and AASHTO tests specified for the type of material. If applicable, an infrared scan is done on some material as well.

4.1 Retro-reflectivity Performance Evaluation Techniques

To evaluate retro-reflectivity, transportation agencies have been using mobile and hand-held retro-reflectometers. Correlation of the results obtained from mobile and hand-held retro-reflectometers were found within 8%. Visual inspection preferably aided with a magnifying glass can be effective to evaluate reflectorised marking (Migletz, and Graham, 2002).
The retro reflectivity of pavement markings degrades over time due to a variety of factors. The visibility of pavement markings at dark is dependent on their retro reflectivity.
A study by Loetterle et al. (2004) identified that the minimum acceptable level of retro-reflectivity ranges from 80 to 120 mcd/m2/lux. A comparison study by Parker and Meja (17) between objective measures (retro-reflectivity measurements) and subjective evaluations (on a 5-point scale; 5 - very clearly visible, 4 - visible with no difficulties, 3 - visible with some difficulties, 2 - visible with great difficulties, and 1 – invisible) found a high correlation between retro-reflectivity and visibility ratings. The study concluded that the relationship between the objective and subjective measures was non-linear.
Survey results of Migletz and Graham (2002) study revealed that all the agencies surveyed had been using some combination of objective and subjective evaluations to analyze the retro-reflectivity and performance of long-term pavement markings. ASTM has adopted 30-meter geometry as the standard for measuring pavement marking retro-reflectivity; which is also used by the European Committee on Standardization (CEN). Figure
9
illustrates the entrance and observation angles associated with 30-meter geometry.


Figure 9 : Entrance and observation angles for 30-meter geometry, from the Highway Innovative Technology Centre (2001)

Bahar et al (2006) stated that in subjective evaluations inspectors should examine existing marking, apply engineering judgments, and assign rating following an established guideline. The tables 20 and 21 summarizes variety of objective and subjective tests that usage by various agencies across Canada and US, respectively.

Table 20 : Presents a summary of agencies using three objective evaluations with a Retro-reflectometer (Bahar, Masliah, and Tan, 2006)

Note: N = Number of transportation agencies that responded to survey
a Dry performance of pavement markings - measurement of pavement-marking retro-reflectivity, day or night
b Luminance contrast ratio - relative difference in retro-reflectivity between pavement-marking and the adjacent pavement surface
c Wet performance of pavement markings - measurement of pavement-marking retro-reflectivity, day or night, during condition of rain

Table 21 : Degree of usage of various subjective evaluations, from Migletz and Graham (2002)

Note:
N = Number of transportation agencies that responded to survey
a Dry performance of pavement markings - subjective evaluation made at night using vehicle headlights during dry conditions (e.g., using a scale of 1 to 10)
b Pavement marking durability - subjective evaluation of a material's resistance to wear and loss of adhesion to pavement surface over time (e.g., percentage of material remaining on a scale of 1 to 10)
c Bead retention - subjective evaluation of retro-reflectivity and bead distribution during the daytime under sunny conditions (e.g., using the sunlight-shadow technique with a pass-fail rating)
d Color scale - subjective evaluation of marking color (e.g., using a scale of 1 to 10)
e Wet performance - subjective evaluation made at night using vehicle headlights during wet conditions (e.g., using a scale of 1 to 10)
f Pocket microscope - a microscopic evaluation of bead distribution, embedment, and damage
g Pavement marking color - subject

4.2 Degradation model of retro-reflectivity

In his study, Thamizharasan et al. (2003) identified three common patterns of decay of retro-reflectivity with elapse of time. These patterns are shown in figure 10. Figure 10 A represents that retro-reflectivity of newly placed pavement markings increases as glass beads become exposed after some period of road use. Once the retro-reflectivity attains maximum value, then it starts decreasing. Figure 10 (B) shows that older (older than 300 days) markers loose their retro reflectivity over time. Finally, figure 10 (C) shows that pavement marking is significantly affected by some activities such as remarking or snow removal operations in winter.

(A)

(B)

(C)

Figure 10 : Retro-reflectivity degradation pattern of new (A), established (B), pavement markings, and degradation due to snowploughing (C), from Thamizharasan et al. (2003)

4.3 Pavement Marking Thickness Measuring Techniques

Hawkins et al.  (2006) commented that pavement marking thickness was one of the primary inspection measurements. A comparison study of relative accuracies of thermoplastic thickness, measured with calliper and needlepoint micrometer have been conducted by investigators. This Texas based study results showed that needlepoint micrometer could be used to measure between the beads; however, only top of bead could be measured with calliper. The differences between measurements with the two methods were significant.  The average measurements from calliper were 20.5 mil. These measurements were 16.7 mil thicker than that of needlepoint micrometer for large and small bead samples. The research findings are summarized as follows:

  • A needlepoint micrometer should be used to measure thickness of the thermoplastic from the top of the surface
  • Use of calliper as thickness measure of thermoplastic is discouraged
  • Each measurement should be taken three times
  • Measurement should be taken across diagonally as shown in figure 11.

Figure 11 : Locations for Measuring Marking Thickness (Hawkins et al. 2006)

5. Pavement Marking Removal Techniques

Any degraded or unacceptable pavement marking should be removed for safety reasons of road users, and new marking should be applied. The followings are the most common methods/ techniques found in transportation agencies guidelines and literatures (Alberta, 2003; NHSS, 2006 & Pavement Marking, 2006):

  • Sandblasting
    • Wet abrasive blasting: hydro blasting, or vacuum blasting.
    • Dry abrasive blasting
  • Forced Air Abrasive (Shot Blasting): Abrasive particles are projected by ‘high Pressure’ air at the pavement marking which remove it. If the pavement surface contains porous/thin layer, total removal of marking materials is only possible by this method. Equipment operates with high noise (105dba) for this method
  • Hot Compressed Air (HCA) Lance is another method of mechanical removal of markings. Hot compressed air is used to vaporize marking, but no flame is used to avoid burning of markings. Applied temperature may damage thin bituminous road surface, so these situations should be avoided. HCA operates with high noise (120dba), and may create fume and smoke.
  • Mechanical Scabbling grinds the marking from the surface, but total removal could damage the surface. It is mainly used for removing bulk amount of marking, and produces substantial amount of debris. The equipment used in this process is very noisy, operates at 90dba which could rise up to 104dba.
  • Mechanical/hand Chipping –only suitable for temporary removal of studs and tapes. (Alberta, 2003; NHSS, 2006 & Pavement Marking, 2006).

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