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49 As part of this research project, the removal of pavement markings was studied in the field. The field study consisted of two different study types. The first study type was controlled pavement marking removal evaluations where the research- ers controlled the marking types, road surfaces, and removal methods used. The second study type was the evaluation of pavement marking removal operations as part of planned highway maintenance or construction as they occurred or after they were recently completed. The field study design and resulting field evaluations are described in this chapter. Removal Combinations to Evaluate The removal combinations that were evaluated were based on combinations of the type of removal process, type of mark- ing material, and type of road surface. The general idea was to test some of the most commonly removed marking materials on the most typical road surfaces. The removal processes that were tested were some of the most commonly used methods and those that show the most promise to be an effective means of marking removal. It was not feasible to evaluate every type of pavement marking removal, on every road surface, for every type of pavement marking during this research project. The survey and various pieces of literature that were reviewed served as the sources of information on marking materials, road surfaces, and removal types that should be considered for evaluation. The survey and literature also supplemented the results of the field study for removal types, road surface types, and material types that were not evaluated. The project panel also provided guidance on what pavement marking removal techniques to evaluate. Responses from the survey indicated the most common forms of marking removal and on what types of markings. Both the water blasting and grinding methods were very common among the responses, with no responses indicat- ing that these methods were no longer used. The use of shot blasting and sand blasting were also indicated in some of the responses, but it was also indicated in several other responses that these methods are no longer used. A combination of grind- ing and blasting was indicated by only a few survey responses, but this method may offer an effective means of marking removal. From the survey, the respondents indicated that their preferred removal techniques seemed to be either water blasting or grinding. Some survey respondents also indicated that their preferred method, which sees limited use due to other factors (typically cost), was water blasting. The survey responses also indicated the combinations of road surfaces and pavement markings where removal occurred. Asphalt and PCC road surfaces had many more responses than did surface treatments. Paint and thermoplastic were the two marking materials with the highest frequency of removal, which makes sense since they are by far the two most com- mon marking materials. Tape and several plural component markings (epoxy, polyurea, and urethane) were also indicated by several responses. Ideally, all road surface types would be evaluated for some of the marking types that are typical on each. The most common pavement marking types were evaluated, as was temporary tape since it is often used in work zones. The temporary tape evaluation was based on a review of data from the NTPEP. The data and discussion are included in Chapter 6. Table 51 pres- ents the combinations of marking materials and road surfaces used to conduct the field study. The Y in the table indicates that the listed combination of road surface type and pavement marking type was evaluated. The areas with a dash were not evaluated because these situations are less common. The mark- ing removal methods that were evaluated are as follows: ⢠Grinding: â Carbide tipped drum, flailing, full-size truck-mounted system. â Carbide tipped drum, flailing, hand-operated system. â Carbide tipped rotary/orbital flailing system, mounted to skid steer. C H A P T E R 5 Field Study Design and Evaluation
50 ⢠High-pressure water blasting, current state-of-the-art full- size truck system. ⢠Combination testing. The combination testing was a light pass from the full-size flailing truck followed by the high-pressure water blasting. This combination system was intended to take advantage of the pros of the two systems while minimizing the cons. Criteria to Measure the Effectiveness of Removal Techniques The effectiveness of pavement marking removal can be established in several ways, and thus a compromise of the various measures will be needed to determine which method is truly the most effective removal technique for a given situ- ation. Based on various factors for each given situation, the impact of each of the measures that affect the effectiveness of a removal technique may vary. The measures for which the effectiveness of pavement marking removal can be estab- lished are the following: ⢠Quality of the actual marking removal itself: â Scarring depth. â Changes to the roadway surface characteristics. â Percentage of marking material removed. â Retroreflectivity characteristics. ⢠Speed at which the marking is removed. ⢠Cost of the marking removal. ⢠Environmental impact. ⢠Availability of the removal equipment. ⢠Required skill of the operator and room for operator error. In the survey, respondents were asked if they had any mea- sures of effectiveness to determine the quality of marking removal, such as amount of scarring to the pavement, amount of marking material remaining, and damage to joints or sealer. Most responses indicated that there were no measures used and that only a subjective evaluation was conducted. Subjec- tive evaluation of the removal quality is not ideal compared to a quantitative measure since a quantitative measure should be equitable and repeatable. Developing a quantitative measure of the removal quality was brought up in the survey responses as something that would be beneficial. Depth of scarring is one of the factors that will affect the quality of the removal and thus the effectiveness of the removal technique. Depth of scarring was indicated as a criterion for quality of marking removal in several state specifications and also in several responses to the survey. Several states call out a maximum allowable scarring depth, but survey respondents did not indicate how well this is enforced if at all. As shown in Figure 7, an electronic depth gauge, or an accurate depth measuring device, can be used to quantify the depth of scar- ring. An issue with measuring scar depth is that the scar is not typically uniform across the removal width, resulting in an undulating surface that makes measurement more diffi- cult. In addition to the depth of scarring, the quantity of the removed marking is also a key component to effective mark- ing removal. The percentage of marking material removed may be quantified with analysis of photos taken from directly over the marking or subjectively evaluated from over the marking or from a driverâs perspective. Photo analysis of the removal percentage can be difficult due to the removal processes pol- ishing the roadway surface, resulting in the surface aggregate being of similar color to the removed marking. This was especially true for the grinding removal techniques on the surfaces that were evaluated. In addition to the electronic depth gauge, the research team used retroreflectometers, a colorimeter, a laser texture scanner Road Surface Type Pavement Marking Material Type Paint Thermoplastic Plural Component Permanent Tape Temporary Tape Asphalt Y Y - - Y PCC Y Y Y Y Y Table 51. Combinations of marking materials and road surfaces to evaluate. Figure 7. Electronic depth indicator.
51 (see Figure 8), and a charge-coupled device (CCD) photom- eter to capture data at the pavement marking removal sites. The researchers collected data on the removed area and the adjacent road surface area. The goal of the measurements was to determine if it is possible to quantify the changes to the roadway surface characteristics and the retroreflectivity char- acteristics of the removed marking area. The retroreflecto- meters were used to measure retroreflectivity in mcd/m2/lux. The colorimeter was used to measure surface brightness (Y) using illuminant D65. The laser texture scanner was used to estimate the texture depth of the surface. The CCD photo- meter captured luminance images during both the day and night (see Figure 9). The camera was positioned at driver eye height in a vehicle 32 m away from the markings. The 32-m data collection distance was selected to achieve a similar geometry to that of standard retroreflectivity measurement while allowing all of the markings across the lane width to be captured in a single image. At night, the markings were only illuminated with the vehicleâs headlights. During the day, a combination of CCD luminance measurements were taken with the sun in various positions to see its impact on the vis- ibility of the removed areas. The researchers also explored taking CCD luminance images in wet conditions, but the natural weather did not cooperate. Water was brought to the removal sites, but the artificial wetting of the removed areas did not seem realistic, so the data were not analyzed. Beyond the quality of the removal itself, there are also the factors of speed at which the marking is removed, cost of the marking removal, availability of the removal equipment, required skill of the operator and room for operator error, and environmental impact. Each of these factors also plays a role in determining the effectiveness of a removal technique. Obviously, the quality of the marking removal is one of the major factors, but each of these additional factors can limit the effectiveness of a removal technique. As indicated, the impact of each of these different measures may vary for dif- ferent situations. If cost or speeds are more important than some of the other factors, then those measures should be weighted more heavily in the decision as to which removal method is most effective for a given situation. The researchers collected removal speed information during the testing. The other factors are discussed in other sections of this report. Field Removal Operations The research team felt a multifaceted field research plan would take advantage of facilities and research areas available to help cover the desired pavement marking, road surface, and removal type combinations. There were three key areas where the field removal operations occurred: (1) pavement marking test decks on open highways, (2) the closed-course at Texas A&M University Riverside Campus, and (3) construction or maintenance projects that have pavement marking removal occurring on them. The pavement marking test deck areas and closed-course Riverside Campus were controlled field studies where the research team controlled what removal methods were used, and on what markings and what surface. The evaluations at construction or maintenance areas were not controlled. The research team observed what was occur- ring or had occurred at these locations. Pavement Marking Test Deck Removal The first area where field evaluations of pavement mark- ing removal took place was at pavement marking field test decks that had previously been studied by the Texas A&M Transportation Institute (TTI). These test decks had various marking materials installed on them for 3 years, which would better represent in-service marking compared to a newly applied marking material. The test decks were on both asphalt and PCC surfaces. The test markings were placed longitudi- nally in the lane in 20-ft long sections. Each removal method at each test deck was used to remove two of the pavement marking sections. The removal operators were instructed to remove the markings in two different ways. The first marking was to be removed as well as possible without damaging the Figure 8. Laser texture scanner. Figure 9. CCD image analysis of flailing removal of paint on asphalt.
52 road surface (light removal). The second marking was to be removed to the point that little material remained while try- ing to minimize damage to the road surface (heavy removal). These pavement marking test decks provide an area where direct comparisons between removal methods could occur. Figure 10 is an image of one of the pavement marking test areas on the PCC test deck. The PCC test deck had modi- fied urethane, thermoplastic, methyl methacrylate (MMA), polyurea, preformed thermoplastic, and permanent tape pave- ment markings. The PCC test deck had a transverse diamond- grooved surface finish, with the depth of the grooves varying between the different marking sections. Figure 11 is an image of one of the pavement marking test areas on the asphalt test deck. The asphalt test deck had high-build paint, preformed thermoplastic, thermoplastic, and waterborne paint pave- ment markings. Closed-Course Pavement Marking Removal The second area where field evaluations of pavement marking removal took place was at the Texas A&M Univer- sity Riverside Campus (see Figure 12). The Riverside Cam- pus already had numerous thermoplastic markings applied to its concrete runways that were removed as part of this project. These thermoplastic markings were typically applied in 0.4-mi long sections. This allowed the researchers to get a better measurement of the speed of removal compared to the 20-ft long sections at the pavement marking test decks. The Riverside Campus also had sections of side-by-side water- borne paint on both concrete and asphalt surfaces similar to the field test decks, except the markings were each 45 ft long. Each removal method removed several of the paint markings from each surface and one of the long thermoplastic mark- ings. When removing the thermoplastic markings, the first 0.1 mi was used to get the removal system optimally setup for removal and speed. The speed of removal was measured over the last 0.3 mi. Construction and Maintenance Project Pavement Marking Removal The third area where field observations of pavement mark- ing removal occurred was at construction and maintenance projects that were having or recently had pavement marking removal occur on them. The research team only acted as an observer at these field locations to note pros and cons of the removal techniques, to speak with the removal crews, and to see where improvements could be made. These field obser- vations provided supplemental information to the removal that the research team conducted on the pavement marking test areas. The researchersâ goal was to evaluate each of the removal techniques that were used for the test area removal in actual field removal operations. Unfortunately, only the Figure 10. Pavement marking test deck on PCC surface. Figure 11. Pavement markings test deck on asphalt surface. Figure 12. Closed-course Texas A&M University Riverside Campus old PCC surface.
53 full-size flailing truck and high-pressure water blasting tech- niques were observed in the field. There were no operations occurring where a dual removal technique (e.g., grinding fol- lowed by high-pressure water blasting) was used, nor could arrangements be made to observe the orbital flailing method. Controlled Test Deck Marking Removal Evaluation During and after each field trial, whether it was on the closed-course Riverside Campus or the highway test decks, the effectiveness of each marking removal technique was evaluated. The effectiveness of the removal was based on how well the marking was removed, the condition of the pave- ment where the removal occurred, the cost effectiveness of the removal, and the environmental impact of the removal. The criteria to measure the effectiveness of removal tech- niques included the means of acquiring quantitative values for assessing the success or failure of each trial. The evalu- ation criteria that were necessary to collect during the field evaluations were factors associated with the quality of the removal itself, such as scar depth; changes to the roadway surface characteristics; and retroreflectivity characteristics. The speed at which the marking was removed was also col- lected. In addition to the quantitative data, the removal of the markings was also rated based on visual appearance. The visual ratings were removal degree and removal rating. The degree of removal was based on the percentage of pavement marking material removed and used a 0 to 10 scale, with the rating value equating to the amount of material removed, e.g., 9 = 90 percent of material removed. The removal rating was a rating based on the overall appearance of the removed area compared to the surrounding road surface. The removal rat- ing considered the amount of material left, the scar depth, the changes to surface characteristics, and the change in color of the removed area. The removal rating was based on a 1 to 5 scale, with 5 being the least noticeable difference from the surrounding pavement and 1 being the most noticeable. The data were collected and analyzed to determine the feasibility of using the criteria to assess the quality of pavement marking removal and to compare the removal techniques. The pros and cons of each removal technique for each marking type removed on each pavement surface were also documented. The removal at each test area was documented with video and pictures and assessed with the evaluation criteria. Fig- ure 13 provides an example of the high-pressure water blast- ing removal on the PCC test deck. This was a full-size water blasting truck with a high-powered vacuum recovery system. The system typically ran around 32,000 psi, and the nozzles in the two removal heads were in an aggressive removal setup. The nozzles can be adjusted to increase or decrease removal capabilities. This is where operator experience and removal testing at the start of a project are necessary to achieve the best setup possible. The operators indicated they typically use this setup, so the researchers chose it for testing since they did not have the ability to remove numerous markings while test- ing different head configurations. It would have been ideal to test different configurations at the field test sites, but it was just not feasible. The operators also indicated that the rota- tional speed of the removal heads and the forward speed of the truck were two other variables for the high-pressure water blasting removal. Figure 14 provides an example of the orbital flailing removal on the asphalt test deck. This was a skid steer-mounted unit with a vacuum system to control dust. The system had three removal heads. Being a skid steer-mounted unit, it was at an inherent disadvantage to the two other full-size truck- mounted removal systems when considering the speed of the removal, but all other factors should be considered equal. Figure 13. High-pressure water blasting on PCC test deck. Figure 14. Orbital flailing on asphalt test deck.
54 The height position and downward force of the removal unit, the forward velocity of the vehicle, and the condition of the removal heads were the major variables for the orbital flailing removal. Figure 15 provides an example of the flailing removal method on the closed-course PCC test deck. The flailing truck was a full-sized truck with a vacuum system to control dust. The system had three removal units that each contained two removal drums of flailing teeth. Similar to the orbital removal method, the height position and downward force of the removal unit, the forward velocity of the vehicle, and the condition of the removal heads were variables in the flail- ing systemâs removal. The combination testing was a pass from the full-size flail- ing truck followed by the high-pressure water blasting. This technique was only used on the pavement marking materials that were considered thicker materials, such as thermoplas- tic, preformed thermoplastic, MMA, and tape. The combi- nation testing used the flailing truck to remove the bulk of the material without damaging the road at a higher-than- normal removal speed. After the flailing truck removed the bulk of the material, the high-pressure water blasting truck was used to remove the remnants at a higher-than-normal removal speed. The research team felt it would be difficult to remove much of the thinner materials, such as paint, high- build paint, polyurea, or modified urethane, without possi- bly doing damage to the road surface, so this technique was not used on those marking types. The hand-operated flailing unit was only used on the closed-course test deck. The hand- operated units are very common units but are typically only used for small removal projects. The focus of this research was for larger-scale removal projects, so the small hand-operated units were not included at all field locations. The following subsections of this report document the removal evaluations at each of the controlled test decks. The summary of all data collected can be found in Appendix D. PCC Test Deck Six different pavement marking materials were removed using the four removal techniques on the PCC pavement marking test deck. The transverse diamond-grooved surface allowed some of the marking materials to get down into the grooved areas, increasing the difficulty of the removal on this particular surface. Two of the removed materials on the PCC deck are highlighted here in the body of the report, with gen- eral comments about the other removed materials. The sum- mary data from all of the markings removed can be found in Appendix D, Table D-1. The results of the pavement marking removal on the PCC deck were documented photographically. Figure 16 and Figure 17 provide images of the removal results of the modified urethane and thermoplastic pavement markings. The pictures of the four removal methods show the mark- Figure 15. Flailing on PCC closed-course test deck. Figure 16. Modified urethane removal on PCC images. a) High-Pressure Water Blasting b) Orbital Flailing c) Flailing
55 ing closely from a low angle and from directly above. These figures provide a visual look at the quality of the removal from the perspectives of the percentage of material removed and how the pavement surface was impacted. The pictures provided are of the heavy removal where the goal of the removal was to remove the marking to the point that little material remained while trying to minimize damage to the road surface. For both pavement marking material types on the PCC sur- face, the high-pressure water blasting removed nearly all of the material while doing little damage to the road surface. The high-pressure water blasting resulted in a slight removal of the very top of the surface, but the resulting surface texture change was not as apparent compared to the other removal types. The orbital flailing method removed most of the material except that which was in the grooves of the road surface. The orbital flailing impact to the road surface was limited to sur- face discoloration caused by polishing the top of the surface, making it appear lighter in color than the surrounding sur- face. The flailing method removed the majority of both mark- ing materials but resulted in the most noticeable change to the surface texture. The flailing removal left a visible groove that removed some of the road surface and resulted in a much lighter surface color that was easily discernible from the sur- rounding surface. The combined removal was only used on the thermoplastic and removed all of the marking. The com- bined removal did result in a greater change to the surface texture than expected. The first pass using the flailing removal removed most of the marking while doing little damage to the road surface. The second pass using the high-pressure water blasting removed the little remaining material but also removed more of the road surface material than when the water blasting was used by itself, even though the speed was about twice as fast. It is likely that the uneven surface resulting from the flail- ing method, combined with the flailing method doing some un intended damage to the road surface, allowed the high- pressure water blasting to damage the surface further. The PCC test deck had an MMA pavement marking that is noted for its hardness and durability. Figure 18 is a close- up of the end of the high-pressure water blasting removal area where some marking material remained. The picture Figure 17. Thermoplastic removal on PCC images. a) High-Pressure Water Blasting b) Orbital Flailing c) Flailing d) Combined Removal Flailing and High-Pressure Water Blasting Figure 18. Close-up of high-pressure water blasting removal of MMA on PCC.
56 shows the etching of the surface that the water caused. At the edge of the removal area, the individual water jet paths can be seen, but in the center area, the removed area is smooth except for the slight indentations that were left from the dia- mond grooving. The removal of the other four materials on the PCC deck had similar visual results to the modified urethane and thermo- plastic markings. The high-pressure water blasting typically removed all of the marking while leaving a minimal scar and little difference in the surface texture. The orbital flailing was able to remove most of the markings, except that which was in the grooves, and did little damage to the surface, but it did result in some surface discoloration. The flailing removal damaged the PCC surface the most when it removed all of the marking; if material was left behind, the damage was less. The combined removal resulted in slightly more surface damage than the high- pressure water by itself but resulted in a smoother surface and less discoloration than the flailing removal by itself. Figure 19 and Figure 20 provide a sample of the CCD images for the modified urethane and thermoplastic removal on the PCC test deck. The CCD images were taken during the day, looking away from the sun, and at night. The CCD images provide a driverâs perspective of the visibility of the marking removal. The modified urethane remaining in the grooves is apparent in the night image. The visibility of the flailing removal area is also very apparent compared to the other removal methods. The remnants of the thermoplastic removal that were not adequately swept up are also very apparent in the night image, indicating the need for proper cleanup of removed materials (see Figure 20). The high-pressure water blasting removed most if not all of the marking with mini- mal surface damage, and the removal area appeared to show minimal contrast with the surrounding pavement both day and night and thus received high removal ratings. Table 52 summarizes the data collected at the removal of the modified urethane and thermoplastic markings on the PCC deck. The data include the removal with each method and whether it was light or heavy removal. The data also include the measures of the adjacent road surface for comparison purposes. Included with the measured quantitative data are the qualitative values of degree of removal and removal rating. The summary data can be viewed and evaluated in many dif- ferent ways. The ability of the different removal techniques to remove a marking can be compared to each other, or the ability of the removal technique to remove different mark- ings can be compared. Evaluating the data across the different road surfaces should also be done. When comparing the removal speeds, the full-size removal trucks were faster than the skid steer-mounted orbital flailer, but it is expected that if multiple orbital flailers were used in sequence, like the flailing truck, comparable speeds could be maintained. The removal speeds of the flailing truck and high- pressure water blasting truck were close for most material types, with the flailing truck typically being a little faster. The flailing was a little slower than the high-pressure water blasting on the preformed thermoplastic material. The combined removal was able to yield high-pressure water blasting speeds that were typi- cally twice as fast as when the water blasting was used alone. When evaluating the data, comparing the removed area values to the road surface values will give a representation of how much the surface texture and reflectance characteris- tics differ. The bigger the difference between the values, the more noticeable the removed area will be from the surround- ing pavement. On the PCC surface, the high-pressure water blasting results in the smallest difference from the surround- ing road surface with regard to the reflectance measures of retroreflectivity, luminance day and night, and measured brightness for all markings except for the MMA. In general, the orbital flailing and high-pressure water blasting resulted Figure 19. CCD images of modified urethane removal on PCC. a) Day Image b) Night Image HPW Flail HPW Flail Orbital Light Light Heavy Heavy Light HPW Flail HPW Flail Orbital Light Light Heavy Heavy Light Figure 20. CCD images of thermoplastic removal on PCC. a) Day Image b) Night Image HPW Flail Combined Flail Orbital Heavy Heavy Heavy Heavy HPW Flail Combined Flail Orbital Heavy Heavy Heavy Heavy
57 in similar scar depths that were less than those of the flail- ing method. The estimated texture depths were more vari- able across the removal types. Even though the high-pressure water blasting surface looked relatively smooth, the estimated texture depth numbers increased over that of the road sur- face, indicating a more highly textured surface. The flailing and high-pressure water blasting estimated texture depth val- ues were higher than those of the orbital flailing. The orbital flailing appeared to smooth the surface out with some texture numbers that were lower than the surrounding pavement. Asphalt Test Deck Four different pavement marking materials were removed using the four removal techniques on the asphalt pavement marking test deck. The asphalt surface was slightly open, allowing some material to get down below the surface and thus increasing the difficulty of the removal on this particular surface. In addition, the gradation of stone in the asphalt mix resulted in a large variety of aggregate sizes near the surface including a large quantity of smaller aggregate and fines. Two of the removed materials on the asphalt deck are highlighted here in the body of the report with general comments about the other removed materials. The summary data from all of the markings removed can be found in Appendix D, Table D-2. The results of the pavement marking removal on the asphalt deck were documented photographically. Figure 21 and Fig- ure 22 provide images of the removal results of the high-build paint and thermoplastic pavement markings. The pictures of the four removal methods display the marking closely from Marking Type Removal Method Removal Rate (ft/hr) Degree of Removal Removal Rating Measured RL (mcd/m2/lux) CCD Luminance (cd/m2) Measured Brightness (Y) Scar Depth (in.) Estimated Texture Depth (mm) Day Night Modified Urethane Road Surface 26 1434 0.696 28.34 0.457 Orbital Flailing Light 1980 7 3 78 1829 1.733 39.17 0.03 0.478 Orbital Flailing Heavy 1020 9 4 66 1520 1.617 47.72 0.04 0.597 High- Pressure Water Light 6000 9 5 47 1289 1.076 31.41 0.02 0.761 High- Pressure Water Heavy 4020 10 5 31 1417 0.806 28.23 0.04 0.657 Flailing Light 4500 8 3 66 1657 1.545 40.78 0.05 0.706 Flailing Heavy 4200 8 2 64 1795 1.555 40.09 0.09 0.66 Thermoplastic Road Surface 30 548 0.74 30.37 0.655 Orbital Flailing Light 3600 7 4 51 683 1.339 49.56 0.01 0.594 Orbital Flailing Heavy 3000 9 5 46 687 1.179 41.72 0.02 0.506 High- Pressure Water Light 5160 9 4 36 586 0.927 30.23 0.01 0.753 High- Pressure Water Heavy 4020 10 5 37 542 0.982 30.83 0.02 0.853 Flailing Heavy 5160 10 3 50 658 1.349 39.39 0.04 0.731 Combined 4800 grind, 7980 HPW 10 4 41 618 1.058 34.64 0.01 0.908 Table 52. PCC test deck evaluation summary.
58 Figure 21. High-build paint removal on asphalt. a) High-Pressure Water Blasting b) Orbital Flailing c) Flailing
59 Figure 22. Thermoplastic removal on asphalt. a) High-Pressure Water Blasting b) Orbital Flailing c) Flailing d) Combined RemovalâFlailing and High-Pressure Water Blasting
60 a low angle and from directly above. These figures provide a visual look at the quality of the removal from the perspec- tives of the percentage of material removed and how the pavement surface was impacted. The pictures provided are of the heavy removal, where the goal of the removal was to remove the marking to the point that little pavement mark- ing material remained while trying to minimize damage to the road surface. For both pavement marking material types on the asphalt surface, the high-pressure water blasting removed most of the marking material, but unlike the PCC, there was some damage to the road surface. The high-pressure water blasting resulted in the removal of some asphalt, small aggregate, and fines from the top of the surface. The larger aggregate was not removed, nor was a dug-out groove formed, but the asphalt and fines around the larger aggregate were removed, resulting in an easily visible change in the surface texture. The removal of the asphalt and fines may lead to the eventual loss of the larger rock and future pavement degradation in the removed area. The orbital flailing method removed all the material except that which was in the grooves of the road surface. The orbital flailing impact to the road surface was not as great as the high-pressure water blasting, with the only damage being a polishing of the aggregate, but the removal was not 100 per- cent. If the marking material was removed at 100 percent, the pavement would have inevitably received some damage. The flailing method removed the majority of both mark- ing materials but also resulted in a noticeable change to the surface texture. The flailing removal left a visible groove that removed some of the road surface and resulted in a much lighter surface color that was easily discernible from the surrounding surface. The combined removal was only used on the preformed thermoplastic and removed most of the marking but left some in the voids. Not all of the material was removed because the high-pressure water blasting truck was going at a speed to minimize damage to the road surface. The combined removal did result in a much greater change to the surface texture than expected. The first pass using the flailing removal removed most of the marking while doing little damage to the road surface. The second pass using the high-pressure water blasting removed the little remain- ing material but appeared to also remove more of the road surface material than when the water blasting was used by itself, even though the speed was about twice as fast. Simi- lar to the PCC surface, it is likely that the uneven surface resulting from the flailing method, combined with the flail- ing method possibly doing some unintended damage to the road surface, allowed the high-pressure water blasting to damage the surface further. The removal of the other paint and thermo plastic materials on the asphalt deck had similar visual results to the high-build paint and preformed thermo- plastic markings. Figure 23 and Figure 24 provide a sample of the CCD images for the high-build paint and thermoplastic pavement markings on the asphalt test deck. The CCD images were taken during the day (looking both toward and away from the sun) and at night. The CCD images provide a driverâs perspec- tive of the visibility of the marking removal. From the daytime images, it is clear that the position of the sun in relationship to the viewing position of the removed area can affect the vis- ibility of the removed area. For both materials, when looking toward the sun, the removed areas look darker than the sur- rounding pavement and do not stand out as much as when the sun is behind the viewer. When the sun is behind the viewer, the removed areas look lighter than the surrounding pavement, and for the flailing and orbital flailing methods, they stand out quite a bit. The material left on the pavement surface is also much more noticeable when the sun is behind the viewer. From the night images, the material left in the surface voids is apparent. The high-pressure water blasting heavy removal was conducted on a double-wide line, and the entire width was not removed prior to taking the CCD images or other measurements. That is the reason why there Figure 23. CCD images of high-build paint removal on asphalt. a) Day Image Looking South b) Day Image Looking North c) Night Image HPW Flail HPW Flail Orbital Heavy Light Light Heavy Heavy HPW HPW Orbital Heavy Light Light HPW Flail HPW Flail Orbital Heavy Light Light Heavy Heavy HPW HPW Orbital Heavy Light Light Orbital HPW HPW Light Light Heavy Orbital Flail HPW Flail HPW Heavy Heavy Light Light Heavy
61 is excess material on the edges of the heavy high-pressure water removed area in Figure 24. Table 53 summarizes the data collected at the removal of the high-build paint and preformed thermoplastic markings on the asphalt deck. The data include the removal with each method and whether it was light or heavy removal. The data also include the measures of the adjacent road surface for comparison purposes. Included with the measured quantita- tive data are the qualitative values of degree of removal and removal rating. Comparing the removal speeds revealed that the full-size removal trucks were faster than the skid steer-mounted orbital flailer, but it is expected that if multiple orbital flailers were used in sequence, like the flailing truck, comparable speeds could be maintained. The removal speeds of the flailing truck and high- pressure water blasting truck were close for the material types tested on asphalt. The combined removal was able to yield high-pressure water blasting speeds that were typically twice as fast as when the water blasting was used alone. On the asphalt surface, the high-pressure water blasting resulted in the smallest difference from the surrounding road surface with regard to the reflectance measures of retroreflec- tivity, luminance day away from sun and night, and measured brightness for all markings. For the luminance day toward sun, the results differed between removal method and mark- ing type. In general, both the high-pressure water blasting and flailing resulted in large scar depths that were less than those of the orbital flailing method, but a higher percentage of the material was removed. The high-pressure water blast- ing had the greatest scar depth when removing the preformed Figure 24. CCD images of thermoplastic removal on asphalt. Orbital Flail Combined Flail HPW Heavy Heavy Light Heavy Orbital Combined HPW Light Light HPW Flail Combined Flail Orbital Heavy Light Heavy Heavy HPW Combined Orbital Light Light HPW Combined Orbital Light Light HPW Flail Combined Flail Orbital Heavy Light Heavy Heavy a) Day Image Looking South b) Day Image Looking North c) Night Image Marking Type Removal Method Removal Rate (ft/hr) Degree of Removal Removal Rating Measured RL (mcd/m2/lux) CCD Luminance (cd/m2) Measured Brightness (Y) Scar Depth (in.) Estimated Texture Depth (mm) Day (Toward Sun) Day (Away from Sun) Night High-Build Paint Road Surface 9 3002 1554 0.2851 7.15 0.901 Orbital Flailing Light 2400 6 2 66 3570 3026 1.423 20.3 0 0.6 Orbital Flailing Heavy 780 8 3 47 3025 2744 0.906 26.51 0.04 0.789 High-Pressure Water Light 3600 10 3 20 2330 1611 0.361 10.39 0.06 2.552 High-Pressure Water Heavy 3300 10 3 18 2136 1703 0.42 9 0.07 4.236 Flailing Light 5160 8 3 59 3404 3162 1.022 20.65 0.1 0.942 Flailing Heavy 3300 9 3 41 3131 2937 0.795 29.45 0.11 0.862 Preformed Thermoplastic Road Surface 9 2523 1744 0.343 9.97 1.062 Orbital Flailing Light 480 4 2 64 3694 4911 1.692 30.45 0 2.405 Orbital Flailing Heavy 420 5 2 69 3727 4851 2.241 36.55 0.02 1.746 High-Pressure Water Light 1800 10 2 12 1737 1481 0.316 5.53 0.18 3.783 High-Pressure Water Heavy 1620 10 2 21 1870 1550 0.477 5.03 0.2 5.091 Flailing Light 3120 4 2 74 498 6411 2.337 53.93 0.1 0.862 Flailing Heavy 1200 10 2 42 2761 3678 1.605 19.23 0.16 2.364 Combined 3600(f), 3660(hpw) 9 1 41 2288 1839 0.853 6.6 0.18 4.195 Table 53. Asphalt test deck evaluation summary.
62 thermoplastic marking. The estimated texture depths were more variable across the removal types. The high-pressure water blasting surface texture depth differed the most from the surrounding surface. Again, the orbital flailing appeared to smooth the surface out with some texture numbers that were lower than the surrounding pavement, but the material in the road surface voids was not adequately removed if full removal was required. Closed-Course Test Deck Two different pavement marking materials on two surfaces were removed using the five removal techniques on the closed- course test deck. The relatively smooth surface of the PCC did not allow marking materials to get down into any deep grooved or tined areas on this particular surface, resulting in an easier surface for removal than the previously described PCC pavement marking test deck. The closed-course PCC surface was very dirty, though, which greatly increased the color differences after removal. The asphalt surface was slightly open, allowing some material to get down below the surface and thus increasing the difficulty of the removal on this particular surface. In addition, the gradation of stone in the asphalt mix was uniform and of smaller-sized aggregate. All removal from the closed-course test deck is discussed in the body of this report. An additional data summary table can be found in Appendix D, Table D-3, with the rest of the controlled test deck data. The results of the pavement marking removal on the closed- course deck were documented photographically. Figure 25 through Figure 28 provide images of the removal results of the paint and thermoplastic pavement markings on the concrete and asphalt surfaces. The pictures of the five removal methods show the marking closely from a low angle and from directly above. These figures provide a visual look at the quality of the removal from the perspectives of the percentage of material removed and how the pavement surface was impacted. The pictures provided are of the heavy removal, where the goal of the removal was to remove the marking to the point that little material remained while trying to minimize damage to the road surface. The high-pressure water blasting removed all of the paint off the PCC surface. There was little damage to the road sur- face; the surface color change was the only noticeable differ- ence. The orbital flailing of the paint on PCC removed most of the marking except that which was located in some of the lower portions of the surface. There was little damage done to the PCC surface from the orbital flailer. The flailing and hand flailing removal removed all of the paint marking material off the PCC, but this resulted in some surface scarring. All three flailing methods resulted in a greater change in surface color than the high-pressure water blasting. The flailing methods resulted in a removed area that was whiter than the surround- ing pavement. The high-pressure water blasting removed all of the paint off the asphalt surface. There was some damage to the road surface; some surface fines and asphalt were removed from the surface, resulting in a rougher texture with a darker color than the surrounding road surface. The orbital flailing of the paint on asphalt removed most of the marking except in areas where the machine was moving forward too fast. There was little damage done to the asphalt surface from the orbital flailer other than a slight discoloration of the surface that was whiter than the surrounding road surface. The heavy flailing and hand flailing removal removed all of the paint marking material off the asphalt, but this resulted in some surface scar- ring. The light flailing removed most of the marking material but not all. The light flailing had less surface damage than the heavy flailing. All three flailing methods resulted in a lighter surface color than the surrounding road surface, whereas the high-pressure water blasting resulted in a darker surface. Old yellow thermoplastic pavement markings were also removed from the closed-course PCC surface. These markings were 0.4 mi in length, which allowed some adjustment during the removal. The high-pressure water blasting removed all of the thermoplastic marking while doing little damage to the road surface. The orbital flailing removed most of the marking with little damage to the road surface but was unable to remove most of the yellow stain on the PCC. The flailing removal removed most of the marking and did not scar the surface. The combined removal had a similar finish to that of just the high-pressure water blasting itself. The high-pressure water blasting, flailing, and combined removal all resulted in a noticeable change in surface color. The flailing color change was the most noticeable. Figure 29 shows the remnants of the thermoplastic pave- ment marking on the closed-course PCC after the initial pass with the flailing removal technique. After the pass with the flailing truck, the high-pressure water blasting technique removed the remnants as the second part of the combined removal of this marking. The finished results can be seen in Figure 28. Table 54 provides the summary of the data collected from the closed-course removal. Comparing the removal speed revealed that the skid steer-mounted orbital flailer was much faster than the hand-operated flailer, but both were much slower than the full-sized removal trucks. The removal speed of the high-pressure water blasting truck was faster for the paint removal on PCC and similar in speed to the flailing truck on the asphalt surface. The flailing was able to remove the thermoplastic on the PCC faster than the high-pressure water blasting. The combined removal of the thermoplastic on PCC was able to yield high-pressure water blasting speeds that were over three times as fast as when the water blasting was used alone.
63 a) High-Pressure Water Blasting b) Orbital Flailing Figure 25. Paint removal on closed-course concrete. c) Flailing d) Hand Flailing
64 c) Flailing Light (most removed) d) Flailing Heavy (all removed) Figure 26. Paint removal on closed-course asphalt. a) High-Pressure Water Blasting b) Orbital Flailing
65 Figure 27. Thermoplastic removal on closed-course concrete pt. 1. a) High-Pressure Water Blasting b) Orbital Flailing
66 Figure 28. Thermoplastic removal on closed-course concrete pt. 2. a) Flailing b) Combined RemovalâFlailing and High- Pressure Water Blasting
67 For the thermoplastic removal on the PCC surface, the high-pressure water blasting and combined removal resulted in the smallest difference from the surrounding road surface with regard to the retroreflectivity and measured brightness. None of the removal methods left any measurable scar, but the surface texture of the PCC was changed slightly depend- ing on the removal method used. For the paint removal on PCC, the high-pressure water blasting resulted in the small- est difference between the road surface and the removed area for retroreflectivity, day and night luminance, and measured brightness. The orbital flailing and high-pressure water blast- ing had the least amount of scar damage when removing the paint from the asphalt. The high-pressure water blasting had the greatest change in texture of the removal areas when the paint was removed from the PCC. For the paint removal on asphalt, the high-pressure water blasting resulted in the smallest difference between the road surface and the removed area for retroreflectivity, day and night luminance, and mea- sured brightness. The orbital flailing had the least amount of scar damage when removing the paint from the asphalt, whereas the heavy flailing had the deepest scar damage. The high-pressure water blasting had the greatest change in tex- ture of the removal areas when the paint was removed from the asphalt. A graphical representation of the CCD luminance read- ings for the long-line thermoplastic removal can be found in Figure 29. Combined removal remnants prior to high-pressure water blasting of thermoplastic on concrete. Table 54. Closed-course test deck evaluation summary. Marking Type Removal Method Removal Rate (ft/hr) Degree of Removal Removal Rating Measured RL(mcd/m2/lux) CCD Luminance (cd/m2) Measured Brightness (Y) Scar Depth (in.) Estimated Texture Depth (mm) Day Night Thermoplastic on Concrete Road Surface 17 13.57 0.883 Orbital Flailing Heavy 2340 8 2 38 32.41 0 0.589 High-Pressure Water Heavy 3960 10 4 26 23.91 0 1.059 Flailing Heavy 7620 9 3 41 36.5 0 0.572 Combined 27,120(f), 14,280(hpw) 10 4 25 27.12 0 0.801 Paint on Concrete Road Surface 17 3143 0.451 13.57 0.854 Orbital Flailing Heavy 720 9 3 86 8790 1.855 44.77 0.01 0.597 High-Pressure Water Heavy 4320 10 4 26 5196 0.698 24.34 0.01 1.014 Flailing Light 4320 9 3 76 9093 1.664 38.29 0.08 0.676 Flailing Heavy 2700 10 2 43 7869 1.062 29.88 0.09 0.58 Hand Flailing Heavy 240 10 2 49 8147 1.247 40.98 0.07 0.569 Paint on Asphalt Road Surface 22 5043 0.765 15.51 0.588 Orbital Flailing Heavy 1260 8 4 48 5407 1.381 25.3 0.06 0.815 High-Pressure Water Heavy 3360 10 4 20 3194 0.571 12.56 0.1 1.331 Flailing Light 6660 8 3 45 5515 0.935 31.95 0.13 0.951 Flailing Heavy 3540 10 2 115 7381 2.1551 36.22 0.2 0.748 Hand Flailing Heavy 300 7 2 74 6385 1.746 27.97 0.12 0.875
68 Appendix D, Figure D-1 and Figure D-2. The first figure rep- resents the luminance along the marking at various distances when viewing the removed area looking toward the sun. The data indicate the flailing removal resulted in the marking that had the highest luminance readings, meaning it would be more noticeable than the others based on the reflectance of light off the removed area. There was no trend in the data as the lines were viewed at further distances. The second figure is of the same removal areas but at night under only low-beam illumi- nation. Again, the flailing removal resulted in the highest lumi- nance readings, meaning it would be the most noticeable of the removed areas. As expected, the nighttime luminance readings for all the removed areas decreased as distance increased. Overall Assessment of Controlled Test Deck Removal Evaluation Data There are several things to take away from the controlled test deck removal evaluations. For pavement marking removal, there is not one removal system that works for every mark- ing on every road surface and does a perfect job. Where one removal technique may have an advantage on one road sur- face or material type, it may have disadvantages on other material types or road surfaces. In addition to the quality of the removal that was evaluated in this chapter, the costs of the removal and the environmental impact need to be considered. The researchers collected many different types of data, attempting to yield a data set that could quantitatively rate the quality of the removal. The data set could then be used to compare the different removal techniques on the different road surfaces and markings. The quantitative data could also be compared to the qualitative data to see if a subjective rating of the removal could be an adequate technique to determine the quality of the removal. The previous sections in this chap- ter discuss some of the data collected and how they relate to the marking removal. In addition, the research team compared the collected data to see if any trends could be observed to aid in evaluating pavement marking removal. In Appendix D, Figure D-3 through Figure D-17 provide summary compari- son charts of the data collected at the various test decks. Figure D-3 through Figure D-5 show a comparison of the retroreflectivity of the removed areas versus the degree of removal and removal rating for all the evaluated markings at each of the three test decks. The data show that there was not a strong relationship between measured retroreflectivity and removal rating at any of the test decks. The same holds true for the degree of removal except on the asphalt test deck. On the asphalt test deck, there was good correlation between the measured retroreflectivity and degree of removal. In general, retroreflectivity alone is not a good measure to evaluate the degree of removal or to determine the quality of pavement marking removal. Figure D-6 through Figure D-8 show a comparison of the CCD night luminance versus measured retroreflectivity and measured brightness versus measured retroreflectivity on the dual y-axis graph. A good relationship between the different measures is apparent. This would suggest that it is acceptable to use retroreflectivity as the only quantitative photomet- ric measure, as it is the easiest to measure, and not consider measuring CCD luminance at night or measuring the bright- ness (Y). Figure D-9 through Figure D-11 show a compari- son of the CCD night luminance versus removal rating and measured brightness versus removal rating on the dual y-axis graph. There is not an apparent relationship between the mea- sures, indicating that CCD night luminance and measured brightness (Y) are not great predictors of an assessed removal rating. This would mean these measures alone do not correlate well with the researchersâ subjective rating of the quality of the marking removal. Figure D-12 through Figure D-14 show a comparison of the scar depth versus degree of removal and estimated texture depth versus degree of removal. In general, the scar depth did not correlate very well with the degree of removal, indicating that it is not necessary to create a deep scar to attain a high degree of removal. The same holds true for the estimated tex- ture depth in that it is not necessary to change the texture in order to achieve a high degree of removal. Figure D-15 through Figure D-17 show a comparison of the scar depth versus degree of removal and estimated texture depth ver- sus removal rating. There does appear to be some correla- tion between these measures and the removal rating on the concrete and asphalt test decks, but not on the closed-course evaluation. It makes sense that there would be some correla- tion because the qualitative removal rating is based in part on the visual observance of these measures. Since these are not the only measures considered in the removal rating, it should be expected that there may be some differences. The scar depth and estimated texture depth along with retroreflec- tivity are good measures to quantitatively evaluate the quality of pavement marking removal. Field Observations of Removal Operations In addition to the controlled test deck pavement marking removal, the research team also evaluated pavement mark- ing removal at several other field sites. The field sites were selected to evaluate similar removal to what occurred on the test deck areas for comparison purposes and to view things that were not able to be captured on the test decks. In total,
69 six different sites were visited, and each presented a unique set of circumstances that provided beneficial findings to the research. Removal 1: Flailing Thermoplastic on PCC and Asphalt Members of the research team accompanied a contractor conducting night work on an interstate highway. The work being conducted consisted of removing and replacing pave- ment markings on both asphalt and transverse tined PCC surfaces. The removal technique was a state-of-the-art full- size flailing truck with vacuum system to control dust. The marking material being applied was epoxy, which is not com- patible with the currently applied thermoplastic markings requiring the removal of the thermoplastic. Though this was a remove and replace job, the incompatibility of the marking materials still required a large portion of the existing mark- ings to be removed to ensure a good bond of the new marking with the road surface. Figure 30 provides a view from behind the removal truck just after it had removed a lane line marking. Figure 31 pro- vides a look from directly above the removed area. Approxi- mately 90 percent of the marking was being removed with minimal damage to the road surface. The material that remained was typically only in the grooves created from the transverse tined PCC surface or in the voids of the asphalt surface. The contractor indicated that this was his workersâ typical remove and replace setup and that they try to do as little damage to the road surface as possible because the grooves will hold water and damage the road. Also, markings placed in areas with a deep groove are easily flooded by the water and are less visible. The contractor indicated that they do not change their operations much if the markings are to be permanently removed other than adjust the system slightly to remove as much of the material as possible while causing minimal damage to the road. The contractor indicated that they typically remove markings with this system between 0.5 and 3 mph. Their speed during this removal was timed at approximately 0.75 mph while removing the lane line markings. They increased speed in the gaps between the mark- ings, but it was not always a consistent speed. The material that was not sucked up by the vacuum system was blown off the marking area using a compressed-air system on a separate vehicle. The new stripes were then applied. The observations at this field site were similar to the results that were found on the controlled test deck removal. Removal speed for this material type with this type of removal method was similar. The resulting surface changes were similar, with both the asphalt and PCC having slight grooves from the flailing teeth. The material that remained was below the pavement surface in the grooves or voids in the pavement surface. Any additional effort to remove the remaining material would result in creating a deeper groove in the road surface. Removal 2: High-Pressure Water Blasting Thermoplastic on Asphalt After speaking with a contractor, the research team was made aware of a recent removal area where a high-pressure Figure 30. Full-size flailing truck removing thermoplastic on PCC (behind). Figure 31. Flailing truck removal of thermoplastic on PCC (above).
70 water blasting system was used. The high-pressure water blast- ing system was used to remove newly installed thermo plastic markings on a new asphalt overlay. The removal was neces- sary due to incorrectly aligned markings. After the removal, new markings were replaced in the area where the removal occurred but not in the same exact location. Members of the research team visited the removal site to see the results of the removal. Figure 32 and Figure 33 provide views of the removal area looking toward and away from the sun. Figure 34 provides a closer view from above the removed area. The removal resulted in more than 95 percent of the material being removed. The material that remained was in the bottom of the voids of the asphalt surface. The vacuum recovery sys- tem recovered most of the removed marking material, but some still remained in the low spots of the asphalt surface. The high-pressure water blasting system not only removed the marking, it also removed the asphalt off the top surface of the aggregate and some from between the aggregate. The removal of the asphalt resulted in a very noticeable color contrast between the removed area and the surrounding pavement. As seen in the figures, the direction the removal is viewed from also plays a role in how visible the removed area is. Looking toward the sun, the color difference and the thermoplastic material that were not vacuumed up are not as noticeable as they are when looking away from the sun. The observations at this field site were similar to the results that were found on the controlled test deck removal. The high- pressure water blasting removed the thermoplastic marking very well with minimal material remaining. The resulting surface changes were actually better on this asphalt site com- pared to the controlled removal areas. The large aggregate size at this site likely reduced the ability of the removal sys- tem to remove the fines like it did on the controlled test deck removal sites. The color change between the removed area and the surrounding pavement was very noticeable at this site. However, being that the alignment was only slightly changed, the impact on drivers would be minimal. In other cases of similar removal that may have a greater negative impact on drivers, corrective measures such as a fog seal over the removed area could be a good way to blend the removed area into the surrounding pavement as well as replace some of the asphalt that was removed. Figure 32. Water blasted thermoplastic on new asphalt surface (toward sun). Figure 34. Water blasted thermoplastic on new asphalt surface (close-up). Figure 33. Water blasted thermoplastic on new asphalt surface (away from sun).
71 Removal 3: High-Pressure Water Blasting and Flailing Thermoplastic on Asphalt The same contractor also made the research team aware of a second area where his crew had recently completed a pave- ment marking removal project. At the next location, both a hand-operated flailing machine and a high-pressure water blasting system were used to remove thermoplastic on an asphalt surface. Both the markings and the asphalt surface at this location were older than the previous location. The high- pressure water blasting system was used to remove a portion of the thermoplastic markings, and the hand-operated flailing machine was used to remove a separate area of thermoplastic markings. The removal of these markings was necessary to convert a two-way left-turn lane into turn bays for a new traf- fic signal that was being installed. Members of the research team visited the removal site to see the results of the removal. Figure 35 and Figure 36 provide a wider view and a closer view of the area removed by the high-pressure water blasting system. The removal resulted in more than 90 percent of the material being removed. The material that remained was in the bottom of the voids of the asphalt surface. The vacuum recov- ery system recovered most of the removed marking material but some still remained in the low spots of the surrounding asphalt surface. In contrast to the removal on the new asphalt section where the removed area was lighter in color than the surround- ing pavement, the removal here was darker in color than the surrounding pavement. Being that the asphalt was older, it had faded, and the area under the marking was protected from this fading. When the marking was removed, the dark sur- face under the marking was exposed. The high-pressure water blasting system did little damage to this asphalt surface, with minimal removal of asphalt or surface fines. Figure 37 provides an image of the removed area where the hand-operated flailing machine was used prior to the newly applied markings. In the left portion of the removed area, the removed yellow dash line is still partially visible because of the material left at the bottom of the voids in the asphalt surface. The removal did scar the asphalt surface and was still unable to get all of the marking material. Unlike the water blasting, the flailing polished the rock, creating a lighter-colored surface compared to the surrounding area. The observations at this field site were similar to the results that were found on the controlled test deck removal. The high-pressure water blasting removed the thermoplas- tic marking very well with minimal material remaining. The Figure 36. Water blasted thermoplastic on asphalt surface (close view). Figure 35. Water blasted thermoplastic on asphalt surface (wide view). Figure 37. Hand flailed thermoplastic on asphalt surface.
72 resulting surface changes were again better on this asphalt site compared to the controlled removal areas. The larger aggre- gate size and reduced amount of fines in the mix at this site likely reduced the ability of the removal system to remove the fines, like it did on the controlled test deck removal sites. The flailing removal also provided similar results with some surface damage, with some marking still remaining below the surface. The color changes from both removal methods are unavoidable and can be corrected initially with a light fog seal, or just given time to age and blend in with the rest of the sur- rounding pavement. Removal 4: High-Pressure Water Blasting Paint on a Surface Treatment The research team evaluated the use of the high-pressure water blasting system while removing waterborne paint on an old surface treatment roadway. Figure 38 provides an example of the water blasting system in action. Since it was waterborne paint being removed, the system was able to remove all of the material at approximately 2 mph. Fig- ure 39 provides a closer view immediately after removal. As seen in the image, the road surface is wet immediately after removal. The ambient conditions will determine how fast the pavement is able to dry and be ready for a new marking to be applied. The vacuum system did a good job vacuum- ing up most of the removed materials and water. The water blasting did erode the top of the surface treatment slightly, resulting in a more undulated surface than the surrounding pavement. One of the biggest things to note is the cracks in the roadway were in some areas greatly eroded by the water blasting. Protection of joints on jointed PCC pavements and areas on asphalt where there is cracking may be necessary to reduce damage. Removal 5: Removal on PCC The research team visited a work zone area that was a prime example of an area where pavement marking removal resulted in an undesirable finished product. The removal occurred as part of construction phasing realigning the road- way. The material removed was thermoplastic, and a full-size flailing truck was used for the removal on the tined PCC surface. The removal was effective in that the material was adequately removed but ineffective in that the removed area was very apparent compared to the surrounding road surface. The change in alignment resulted in the removed marking leading motorists into a concrete barrier near a merge area. Though the new alignment was striped with new markings, the removed area could have potentially been mistaken as guidance, leading to a crash or, at a minimum, to a greater driver workload because of the added complexity of the driv- ing scene. The research team captured the results of this removal with video and pictures while driving through the work zone area. Figure 40 and Figure 41 provide two images of the removal area approaching the merge area as the lanes move to the left. In the images, the removal is apparent, as the removed areas cross the lanes and run in different directions than the new lane configuration. There is little to be done to reduce the change in surface color by any removal technique on a PCC surface such as this. High-pressure water blasting will clean the removed area, making it stand out from the surround- ing area, as seen in the closed-course controlled test deck Figure 39. Removed area immediately after water blasting. Figure 38. Water blasting paint on surface treatment.
73 removal. Any of the grinding techniques will also clean and polish the surface, resulting in a removed area that will stand out from the surrounding pavement surface. One thing to reduce the impact of the surface color change is to remove a larger area so that the removed areas are less likely to be noticed as removed markings. The research team spoke with a high-pressure water blast- ing contractor and found that his system is sometimes used to clean areas to create a more uniform surface appearance. The high-pressure water blasting system can be set to a less aggres- sive setting to not damage the road surface, and the removal heads can be operated parallel to each other to create a wider removal area. After the removal of the markings, the water blasting system could then be set up to just clean the sur- rounding pavement where the marking removal surface color changes may be problematic. Figure 42 and Figure 43 are copies of Figure 40 and Figure 41 but have been edited to show what a more uniform surface appearance may look like. The additional road surface cleaning will take additional time and money but may reduce driver confusion, which could reduce crashes especially if the phase of work is over a long period. Removal 6: Removal on Asphalt The research team visited another area of work zone activ- ity that was a prime example of an area where pavement marking removal resulted in an undesirable finished product. The removal occurred as part of several construction areas where phasing resulted in lane shifts. The material removed was thermoplastic, and a full-size flailing truck was used for the removal on the asphalt surface. The research team Figure 40. Ghost markings due to surface color changes near merge area. Figure 41. Ghost markings due to surface color changes at merge area. Figure 42. Photoshopped uniform surface color changes near merge area. Figure 43. Photoshopped uniform surface color changes at merge area.
74 captured the results of this removal with video and pictures while driving through the work zone areas. Figure 44 pro- vides an image of the removal area on a tangent section. From the image, the scarring to the asphalt surface is apparent, as is the marking material that remains on the surface. The con- tractor was trying to limit the damage to the road surface, but the amount of marking left on the road is undesirable. The DOT specified the use of wider pavement markings in this work zone to help reduce confusion between the removed markings and the new markings. The standard markings for Figure 44. Removed lane lines and wider markings. Figure 45. Wider and continuous markings in lane shifts. this roadway are 6 inches wide, whereas the work zone mark- ings are 8 inches wide. In addition to wider markings, this DOT also uses con- tinuous markings through lane-shift areas instead of broken line markings. Figure 45 provides an example of the wider- than-normal and continuous-lane line markings through the lane-shift area of the work zone. Again, the removal of the preexisting markings in this area does not appear to be very good, but the added guidance by the wider and continuous markings should be beneficial to drivers.
