Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
132 possibly shorter service life, complications to winter maintenance procedures; and, maintenance patching difficulties, susceptibility to high stress sites, and requirement of minimizing the drainage path length to allow water passing through the layer to enter the drainage system. 1.29 Corrigan, S., K. W. Lee and S. A. Cardi. âImplementation and Evaluation of Traffic Marking Recesses for Application of Thermoplastic Pavement Markings on Modified Open Graded Friction Course.â TRB 2001 Annual Meeting CD-ROM. Transportation Research Board. National Research Council. Washington, D.C. 2001. 1.29.1 General This paper describes a study carried out to develop a specification for longer lasting and better performing thermoplastic pavement marking materials on âmodifiedâ open-graded friction courses (OGFC). The authors indicate the durability problems that result from the use of snow plows on these markings on OGFC mixes, and then describe three different techniques used for enhancing the durability. Corrigan et al indicates that the new technique consisted of applying thermoplastic pavement marking on recessed and semi-recessed areas of OGFC, and comparing their performance with that of markings on non-recessed areas. The durability was measured at different times through several years, in terms of markings retained, and the performance was measured in terms of retro reflectivity, under dry and wet night conditions. The authors mention that even though the non-recessed conventional inlaid markings were found to have a higher retro reflectivity compared to the recessed markings, the higher snow plow damage of the non-recessed markings, especially in curved sections, warrant the use of recessed markings. Based on durability, the life cycle cost of the recessed markings was found to be lower than that of the non-recessed markings. However, more research is needed on modifying the properties of the marking materials, such as size of glass beads, to increase the retro reflectivity of the recessed markings to acceptable levels. 1.29.2 Benefits of Permeable Asphalt Mixtures No information on benefits of porous asphalt mixtures has been provided. 1.29.3 Materials and Design No information on materials and design of porous asphalt mixtures has been provided. 1.29.4 Construction Practices Corrigan et al mentions that snow plow damage of thermoplastic pavement marking strips on OGFCs has been a significant problem in Rhode Island. The heated theromoplastic materials (at 400-440oF), when applied on the porous OGFC, penetrate about 1/8th inch into the surface and forms a strong bond with the OGFC materials. During snow removal in winter maintenance period, plows hit the pavement material and scrape off part of the OGFC as well as the pavement markings. The authors argue that if
133 the markings are applied over a constructed recess, along the surface, then the snow plows would pass over the recess and not cause any damage to the marking and the pavement materials. Corrigan et al mentions that although there have been studies with recessed markings, snow plow resistant markings and inlaid preformed tapes, these studies have produced mixed results and that no study has been conducted with modified OGFC. In the study reported in this paper, based on a newly developed specification and application methods, recessed markings were used in OGFCs on a 1,000 ft tangent section, a 500 ft exit ramp section, and a 500 ft curved section. Each test section included three types of recesses and a non-recessed control. The authors mention that in addition to the durability and performance comparisons, a study of cost associated with equipment and labor to produce the recessed markings as well as a life cycle cost study were conducted. The details of construction of the test sections are summarized in Table 73. Table 73: Details of Test Sections with Different Markings Condition Marking Comments Sunny, 48οF A gasoline powered pavement cutter equipped with a 6-inch carbide tipped blade was used to create the 6-inch wide traffic marking recesses. The debris was removed from the finished traffic marking recesses with a gasoline-powered blower. The white Alkyd thermoplastic skip stripes were applied to the traffic marking recesses with a small portable thermoplastic applicator. The molten thermoplastic was loaded from the Vulcan melting kettles into the portable thermoplastic applicatorâs storage reservoir (kept heated at 400 to 440οF). The thermoplastic was then applied to the traffic marking recesses though an extrusion die. The glass beads were uniformly applied onto the extruded markings by a gravity drop-on glass bead dispenser, located just behind the extrusion die. Drops of moisture were observed on the backing of the removed tabs even though it had been 4 days since the last precipitation had occurred. The region received the first significant snowfall of the season the day after the installation. This was the first time permanent inlaid marking tape has been used as traffic marking skip stripes on Modified OGFC in Rhode Island. 1.29.5 Maintenance Practices No information on maintenance practices of porous asphalt mixtures has been provided. 1.29.6 Rehabilitation Practices No information on rehabilitation of porous asphalt mixtures has been provided. 1.29.7 Performance Corrigan et al mentions that the performance of the different sections was evaluated on the basis of percentage retained after a certain time and the retro reflectivity numbers
134 under dry and wet night conditions. The details of testing procedures are summarized in Table 74. Table 74: Testing of Durability and Retro Reflectivity for Recessed and Non- Recessed Pavement Markings Property Test Method Durability Percentage retained method, defined as the nominal area of the marking minus the area of loss, divided by the nominal area, and multiplied by 100. Durability evaluations for the stripes within the 1,000 ft tangent test section were conducted on December 5, 1996, December 30, 1996, April 7, 1997, July 30, 1997, November 19, 1997, July 2, 1998, December 7, 1998, and June 30, 1999. The average durability for each type of recessed traffic marking was determined by averaging the percent retained of the six skip stripes within each grouping category. The evaluations within the 500 ft exit ramp test section were performed on December 5, 1996, December 30, 1996, April 7, 1997, July 30, 1997, November 19, 1997, July 2, 1998, December 7, 1998, and June 30, 1999. The evaluations within the 500 ft curved test section were conducted on December 5, 1996, January 6, 1997, April 9, 1997, July 30, 1997, November 19, 1997, July 2, 1998, December 7, 1998, and June 30, 1999. Retro reflectivity The Retroflex 1500 pavement marking retroreflectometer with a 30 meter fixed geometry was chosen to evaluate the retroreflectivity of the traffic markings. A total of four retroreflectivity measurements were taken on each skip strip, two measurements 3 ft from the leading edge and two measurements 6 ft from the leading edge. These measurements were then averaged to obtain a single representative retro reflectivity value for each stripe. Three evaluations were conducted within the 1,000 ft tangent test section during dry daylight conditions. Two evaluations were conducted during dry night conditions. The retro reflectivity was determined by averaging the measurements of the six skip stripes; The July 30, 1997 evaluation was conducted at night with simulated wet conditions. The retro reflectivity of the traffic markings during wet conditions was simulated by uniformly pouring water over the traffic marking stripes. The retro reflectivity readings were then taken approximately 60 seconds after the initial wetting of the stripe. The December 7, 1998 evaluation was conducted during a night with light scattered showers that tapered off as the wet night evaluation progressed. The retro reflectivity evaluations for the stripes within the 500 ft exit ramp test section were performed on December 30, 1996, April 9, 1997, and November 19, 1997 during dry daylight conditions. Dry night evaluations were performed on July 2, 1998 and June 30, 1999. The reflectivity for each type of recessed traffic marking was determined by averaging the readings of the four skip stripes within each grouping category (three skip stripes for the non-recessed). The evaluations within the 500 ft curved test section were conducted on Jan 6, 1997, April 9, 1997, and November 19, 1997 during dry daylight conditions. Dry night evaluations were performed on July 2, 1998 and June 30, 1999. Corrigan et al mentions that a significant amount of reduction in retro reflectivity was recorded for all different types of marking within the first three years of winter. The results are summarized in Table 75.
135 Table 75: Results of Durability and Retroreflectivity Evaluations Durability (wear), average percent retained Types of markings Time Tested Section Fully Recessed Semi Recessed Tapered Recessed Non- Recessed Permanent Inlaid Marking Tape 1,000 ft, high speed lane > 97% > 97% > 97% 95% 50.8%*; 68.3%** 1,000 ft middle lane > 98% > 98% > 98% --- --- 500 ft ramp > 97.0% > 97.0% > 97.0% 88% --- Over three winters 500 ft curve > 97.0%* > 97.0%* > 97.0%* --- 31.2%*, 42.5 % **; 81%*** Retroreflectivity, mcd/m2.lux 1,000 ft, high speed lane 415 395 406 413 593 1,000 ft middle lane 402 388 427 391 649 500 ft ramp 358 303 285 199 --- Initial 500 ft curve 329 316 324 333 205 1,000 ft, high speed lane 125, 70% 117, 70% 128, 69% 125, 70% ---, 80% 1,000 ft middle lane 119, 70% 106, 73% 115, 73% 124, 68% 134, 79% 500 ft ramp 90, 75% 96, 68% 107, 62% 148, 26% --- After three years, reduction 500 ft curve 112, 66%, 108, 66% 107, 67% 103, 69% 143, 30% * at the end of the first winter maintenance season, ** at the end of one snowplowing, *** at the end of third winter maintenance season (after repair after the first winter maintenance season) In general, Corrigan et al note that the durability of recessed markings is better than non recessed and permanent inlaid marks. In terms of retro reflectivity, the authors mention that significant reduction was noted within the first three winter maintenance periods, and that the retro reflectivity readings, both initial and reduced, are found to be higher for the non recessed marks. In discussing the results of statistical analysis of retro reflectivity results from different markings, Corrigan et al makes comparison between non recessed and recessed sections
