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13 This chapter identifies, describes, and evaluates different forms of pavement marking removal as to their ability to remove work zone and permanent pavement markings effec- tively with minimal damage to the underlying pavement or visible character of the surface course. The removal meth- ods discussed are blasting, grinding, burning, laser, chemical, and masking. Each of these methods and the variants thereof are described in detail herein. Several of the methods are only seeing limited use and do not show much promise for expanded use, whereas other methods are showing increased interest and use. The advantages and disadvantages of the methods based on the literature and survey (Chapter 4) are also described herein. Blasting There are several different forms of blasting removal tech- niques, such as high-pressure water blasting, sand blasting, hydroblasting, dry ice blasting, shot blasting, crushed glass blasting, and soda blasting. With the advent of large truck- mounted mobile high-pressure water blasting systems that reach or exceed 30,000 pounds per square inch (psi), water blasting systems appear to have made vast improvements over their predecessors, which ranged from 1,000 to 10,000 psi. This method is more mobile, and not only is the marking removed, but the current systems have vacuum heads that suction up the water and the majority of the debris produced during the removal operation, which can average 2 mph. As a result, for sections of roadway requiring restripe in the same area, the pavement surface is already cleaned for restriping once the remaining residual water evaporates. Several pictures of pavement marking removal by the newer, larger truck-mounted mobile high-pressure (40,000 psi) water blasting system are shown in Figure 2. Figure 2a shows the bars that contain the nozzles and rotate while spraying the high-pressure water. The nozzles, bar rotation speed, water pressure, and forward velocity of the vehicle can all be adjusted for more or less aggressive removal. Figure 2b shows the high- pressure water blaster removing markings. The smaller hoses are for the supply water, whereas the larger hoses are for the vacuum suction system. Figure 2c shows the entire truck, the location of the supply water tank and return waste storage tank, and the smaller mobile utility cart that can be used for special removal applications, such as transverse pavement markings. Based on experience and findings in the literature (Berg and Johnson 2009, Ellis et al. 1999, Niessner 1979), the potential drawbacks to high-pressure water blasting are low tempera- ture (e.g., freezing conditions); residual surface moisture; and removal complications with open-graded asphalt surfaces. The low temperature and surface moisture concerns are really more of an operation consideration than a problem, whereby contractors would need to plan for the water evaporation prior to marking installation, and low temperature freezing situations would need to be considered. As for the open-graded asphalt and surface treatments, other blasting methods and even the most common removal method of grinding may also have similar difficulties on these surfaces. The high-pressure water blasting may also remove the surface layer of asphalt binders, which could lead to water infiltration, and the surface of the aggregate may become polished, which could lead to a ghost marking. The high-pressure water blasting also has the highest potential to do damage to pavement joints on asphalt or concrete. Sand blasting is another removal method that utilizes high-pressure air and a nozzle to blast sand aggregate against pavement markings to break up the pavement marking surface. The sand blasting technique is effective at removal, but it produces byproduct/debris consisting of sand, pave- ment marking materials, and pavement aggregate. While this method may not cause a large amount of surface scarring, this method may actually polish the surface of the pavement, which could result in a ghost marking from pavement sur- face contrast between the existing pavement and the polished pavement. A working pavement marking removal convoy C H A P T E R 3 Identification, Description, and Evaluation of Removal Processes
14 would require a supply vehicle with the aggregate sand, a vehicle with the blasting equipment, and a vehicle with an aggregate and debris collection system. There have been several other aggregate-based blasting methods developed similar to sand blasting. Health issues from silica in the sand have affected the use of sand blasting. Sand blasting is more effective at removing thin pavement marking systems such as paint compared to thicker systems such as thermoplastic. Soda and dry ice blasting also utilize high-pressure air and a nozzle. Both methods are effective at removing pavement markings with minimal surface effects with respect to either scarring or leaving a ghost marking; however, both methods are very slow (0.3 to 8.6 ft/sec), and the soda blasting pro- duces a considerable amount of dust that can greatly hamper visibility (Berg and Johnson 2009, Oregon DOT 2001). One of the primary advantages of dry ice blasting is that the only byproduct is the removed pavement marking material and loose pavement aggregate. The actual dry ice sublimates into a gas, and so only the dislodged material is the byproduct. Some additional drawbacks of both of these methods are that the working convoys require multiple vehicles and staff person- nel must conduct the removal on foot. These types of blasting are only effective on non-durable marking materials. Shot blasting is similar to sand blasting in the use of aggregate, but shot blasting accelerates with a conveyor rather than compressed air at velocities around 175 mph. There are truck-mounted mobile systems, and the blasting aggregate can be recycled, which adds to the speed of the operations while reducing the waste generated in the removal process. Shot blasting can use several different types of blast material, such as aluminum oxide, ground glass, or silicon carbide. Shot blasting can only be used in dry conditions, and typically only on a smooth surface. Undulations in the surface will lead to a loss of blasting media. Shot blasting is more effective at removing non-durable pavement marking systems compared to durable systems. Hydroblasting is a combination of sand and water blasting. High-pressure water blasting is often referred to as hydro- blasting, which can be confusing because they are technically not the same since hydroblasting combines sand and water to abrasively remove pavement markings, and in general, the operating pressures range from 5,000 to 10,000 psi (Migletz et al. 1994). While hydroblasting is effective, it has similar drawbacks to sand blasting with regard to the generation of larger quantities of debris versus water blasting, and it has a tendency to scar the surface of the pavement, although the scarring appears to wear away under traffic. Hydroblasting also appears to remove the asphalt binder coating the surface aggregate in AC, and it does poorly at removing thermo- plastic pavement markings (Niessner 1979). It also appears that the advent of high-pressure water blasting in a mobile truck platform may have replaced this removal method, at least for large-scale pavement marking removal. Grinding The term grinding is being used to describe grinding, milling, flailing, and scarifying, as each of these methods is often referred to as just grinding, even though the reference is often incorrect or at least lacking in description. Grinding can be used on any marking type, but scarring of the road surface is typical. Regardless of the design, all removal equipment utilizing grinding methods rotates an abrasive surface against the pavement marking. One method is to rotate abrasive disks or spindles fitted with teeth within the horizontal plane about a vertical axis similar to an orbital sander (Heydon 1997). Figure 3 shows an example of one orbital style removal system and its triple flailing style head. Another grinding method uses a drum setup of multiple blades/disks stacked side by side (see Figure 4), a drum with teeth, or a drum with a combination of smaller drums with teeth or disks stacked together. The disks will be made of metal or a composite material and have abrasive edges like a saw blade that may consist of teeth, or an abrasive surface, such as diamonds that are adhered over the outer edge of the disk. Cutting heads that utilize teeth are either steel tip, carbide tip, or diamond tip. Regardless of the design of the cutting head, the head is rotated along the cylindrical axis. The cylindrical a) Rotating heads b) Removing marking c) Full-size truck with smaller mobile unit Storage Tanks Mobile Unit Figure 2. High-pressure water blasting removal truck example.
15 axis will be placed perpendicular to the travel direction of the removal process and rotated in or against the direction of travel. Figure 5 displays a full-size flailing truck fitted with six drums with flailing heads, as pictured in Figure 4b. This truck system also has an incorporated vacuum system. Burning There are several different methods of removing pavement markings using burning, such as hot compressed air and excess oxygen (Bryden and Kenyon 1986, Kilgore 1980, Migletz et al. 1994, Niessner 1979). With the hot compressed-air method, high-velocity air is mixed with propane into a combustion chamber that vents out high-velocity heated gas at around 2,400 Â°F. The flame from the combustion is actually contained within the combustion chamber. The excess-oxygen system also utilizes propane, except the combustion is external and the flame makes direct contact with the pavement marking (Kilgore 1980). Propane and oxygen are mixed and ejected out of a nozzle, and the mixture is ignited. Then, additional pure oxygen is fed into the flame and applied over the mark- ing. This method reaches temperatures in excess of 4,500 Â°F. Burning methods are typically only used for specific tempo- rary tapes, typically foil, and for thin paint markings. Care Figure 3. Orbital flailing style system mounted on track steer. a) Walk-behind flailing unit drum b) Replacement flailing drum for truck Figure 4. Drum-style mechanical removal. Figure 5. Full-size flailing drum-style removal truck.
16 needs to be taken, especially on asphalt, to ensure the burning heads are not left in one place too long or pavement damage may occur. Typically, a second form of removal, vacuum or sweeper, is necessary to remove the burned debris from the roadway. Laser The laser removal method is still in the experimental phase. Innovations Deserving Exploratory Analysis (IDEA) Project 16 was one such research effort to evaluate and further develop a laser removal method (Pew and Thorne 2000). While the system developed on the project did not deliver comparable productivity with respect to pavement marking removal, it did show promise, though slow, for paint pavement markings. Chemical The chemical method consists of applying a remover over the pavement markings to be removed and allowing it to react prior to pressure washing off the line (Bryden and Kenyon 1986, Migletz et al. 1994, Niessner 1979). This method is effective on thin lines of paint around 0.010 to 0.020 inches (10â20 mil) in thickness, and so for thicker lines, multiple applications may be required. While it is effective, the method requires 10 or more minutes and at least two passes of equipment between the initial application and the pressure washing. Furthermore, the water and residue should be removed from the pavement, which may either be completed with additional water or vacuum removal. While this method works on both PCC and AC, the methodâs effectiveness is hampered by the porosity of the pavement surface, so open-graded AC may require multiple passes to remove the pavement markings. There were no systems found that would work on anything besides paint pavement markings. Also, depending on the chemical removal system, the asphalt may be damaged if left on too long, though newer chemical systems seem to have corrected this issue. Masking The masking of pavement markings is not necessarily removal of the marking itself but rather covering the mark- ing with something else to hide its presence. Markings can be masked with a new road surface across the entire road, a small area of surface treatment, or material just over the marking itself. The covering material needs to be similar to that of the surrounding road surface so that the covered area blends into the surrounding pavement and cannot be confused as a form of delineation. Other than a full or partial resurface, masking is a method whereby a material of similar color and surface characteris- tics to the roadway is applied over the pavement markings that need to be removed. Masking with removable, non-reflective, preformed tape that is approximately the same color as the pave- ment surface may be used where markings need to be covered temporarily (FHWA 2009). In the case of masking with tempo- rary tape, the tape itself would need to match the road surface color and be applied directly over the marking. The tape would be used (temporarily) to preserve the marking underneath to be reused later instead of removing the marking just to apply another one in a short time frame. The tape can also be used to cover markings that are in need of removal but have yet to be removed. The MUTCD prohibits masking using other mark- ing materials or for long-term use because of concerns that the marking being covered may become exposed in the future. Resurfacing is generally the most expensive method of pavement marking removal because the roadway requires an entire overlay. As a result, it is used the least, and when used, it is typically the final surface of the construction project. Resurfacing that is not planned for the entire roadway is typi- cally limited to lane-shift areas where markings cross lanes and removing them could lead to very confusing ghost markings. Another method is to cover the marking and the surrounding area (1 or 2 ft on either side) with a surface treatment similar to that of the surrounding road surface. Surface treatment refers to fog seal, slurry seal, microsurfacing, bituminous surface treat- ment, and other treatments, usually involving asphalt. They are primarily used for maintenance or interim roadway surface treatments. These types of surface treatments are described in Chapter 6. Summary Each of the removal methods are summarized in Table 3. Table 3 lists the reported advantages and disadvantages of each removal method. The advantages and disadvantages were gathered from the literature and the pavement marking removal survey (discussed in the next chapter). Table 4 is a re-creation of a table presented in the Roadway Delineation Practices Handbook that provides a previous perspective on the effectiveness of each removal method with respect to the pave- ment marking material being removed (Migletz et al. 1994). Table 4 has been updated with additional information gathered from literature and the pavement marking removal survey. The specific literature references are indicated where the research has either filled in gaps or improved upon the original research with new information. Where good is referenced in the table, it is an indication that the removal type can adequately remove the pavement marking. Where slow is referenced in the table, it indicates the marking can be adequately removed but at a slower speed than other removal techniques. A notable change is that high-pressure water blasting has significantly improved in that the operating removal pressures now range
17 Table 3. Advantages and disadvantages of pavement marking removal methods. Removal Method Advantages Disadvantages High-Pressure Water Byproduct does not create dust and is contained within the equipment. Lile to no scarring on PCC. With the excepon of drying me, the pavement surface is prepped for pavement marking reinstallaon. Relavely fast for a blasng method. Large vehicle mobile systems available with addional ulity carts for smaller nearby areas. Limited to above-freezing condions. May polish surface aggregate and/or clean the surrounding pavement, creang a color contrast. May remove some surface asphalt and fines that could lead to water penetraon. Potenal for damage to pavement joints. Currently not widely available, higher costs. Proper equipment operaon crical to achieve good results. Grinding Fast and economical. Depending on the system configuraon (effecve vacuum system installed to remove dust), dust created by removal can be contained. High availability. Damage to pavement surface. Scarring with full marking removal, minimizing damage to roadway may leave marking material behind. Orbital flailing may result in less noceable scarring than drum flailing due to tapered edges. Non-vacuum systems can create dust clouds and be hazardous. Sand Blasng Minimal pavement degradaon. LiÂle to no scarring. Hand-operated precision. Creates considerable byproduct. Creates considerable dust. No current large vehicle mobile system, therefore slower than mobile methods. Health hazards depending on blast media. Shot Blasng Minimal byproduct. Byproduct does not create dust and is contained within the equipment. Minimal pavement degradaon. LiÂle to no scarring. Shot recovery can be problemac especially on uneven surfaces. Cannot be used in wet condions. Can be slow especially for thicker markings. Can cause pavement damage on non-smooth surfaces. Limited availability of equipment. Soda Blasng Minimal pavement degradaon. Li le to no scarring. Hand-operated precision. Creates a moderate amount of byproduct. Creates considerable dust. No current large vehicle mobile system. Can be slow especially for thick markings. Only useful on some markings. Dry Ice Blasng Minimal environmental concerns with respect to debris generated. Minimal pavement degradaon. Marking can be completely removed. Hand-operated precision. Dry ice is a difficult medium to handle and store. Very noisy. Slow. No current large vehicle mobile system. Only useful on some markings. Hydroblasng Similar advantages to high-pressure water and sand blasng. Minimal pavement degradaon. Limited scarring. Similar disadvantages to high-pressure water and sand blasng. Creates considerable byproduct. No current large vehicle mobile system. Limited to above-freezing condions. Excess-Oxygen Burning Minimal pavement degradaon. Requires at least one addional pass to remove residue. Slow. No current large vehicle mobile system. Only useful on some markings. Laser Non-contact and should have li le to no wear, which reduces maintenance costs. Minimal pavement degradaon. Minimal environmental concerns. Slow. Requires at least one addional pass to remove residue. No current large vehicle mobile system. Only useful on some markings. â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ (continued on next page)
18 Removal Method Paint Thermoplastic Epoxy Tape Foil Tape High-Pressure Water Good (Berg and Johnson 2009; Ellis et al. 1999) Good (Ellis et al. 1999) Good (Berg and Johnson 2009) Good Ineffective Sand Blasting Good Slow Good Ineffective Very Slow Hydroblasting Good Slow Good Ineffective Ineffective Soda Blasting Slow (Berg and Johnson 2009, Cho et al. 2011, Oregon DOT 2001) Slow (Berg and Johnson 2009, Cho et al. 2011) Dry Ice Blasting Slow (Berg and Johnson 2009, Cho et al. 2011) Slow (Berg and Johnson 2009) Slow (Cho et al. 2011) Shot Blasting Good (13) Grinding Good (Berg and Johnson 2009, Cho et al. 2011, Ellis et al. 1999, Oregon DOT 2001)c Good (Ellis et al. 1999, Oregon DOT 2001)c Good (Berg and Johnson 2009, Ellis et al. 1999)c Ineffective Ineffective Hot Compressed-Air Burning Slow (Niessner 1979) Excess-Oxygen Burningb Thin Only Ineffective Ineffective Ineffective Good Laserb Slow (Pew and Thorne 2000) Chemicalsb Slow (Cho et al. 2011) Ineffective Ineffective Ineffective Ineffective Hand Removal Very Slow Very Slow Ineffective a Table modified from original table presented in the Roadway Delineation Practices Handbook (Migletz et al. 1994) based on more recent research. b Method requires a second pass to remove debris/residue, which could be another method such as high-pressure water. c Removal can be successful but typically results in pavement scarring. Table 4. Effectiveness with respect to pavement marking material.a Removal Method Advantages Disadvantages Chemical Byproduct does not create dust. Can get complete removal without scarring. Potenal to damage pavement surface if incorrect removing agents are used. Requires at least one addional pass to remove residue. Slow, need to wait for chemical to react then proceed with removal. No current large vehicle mobile system. Only useful on some markings. Hand Removal Detailed removal. Slow. Typically only for removable tapes. Masking No damage to road surface. Exisng markings can be temporarily covered with tape that matches the road surface color and texture, and later reused when the tape is removed. Removed areas can be masked to help blend in scarring or surface color changes. Can be used in lane-shiÂ areas to reduce driver confusion due to ghost markings or scarring. Can be expensive. Material may wear away exposing the markings being covered. Difficult to match color and texture with tape. Tape is for temporary purposes only. Cannot use marking materials other than tape to cover a marking. â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ Table 3. (Continued).
19 in excess of 40,000 psi and all of the equipment can be loaded on a mobile platform. These changes have made high-pressure water blasting more competitive with respect to effectiveness and cost versus grinding methods. In general, blasting systems tend to be able to remove all of the markings without leaving a deep scar but still may result in shadow lines from the removal process, whereas grinding tends to leave a scar in order to remove all of the markings. Grinding and blasting can both create dust and debris that need to be cleaned or vacuumed while marking removal is conducted to allow for a safe driving and work environment. Wet grinding and water blasting do not have issues with dust. Grinding tends to be faster and cheaper than the blasting techniques.