High-pressure Water Speeds Markings Removal

Construction projects and certain maintenance activities initiated by the Ontario Ministry of Transportation (MTO) require that pavement markings be removed and/or repainted to maintain safe road delineation for Ontario drivers. Markings that are no longer applicable or no longer define the path of travel must be removed, masked or obliterated as soon as practical. MTO recently assessed a new ultra high-pressure water blast line removal technology that promises to enhance pavement marking removal operations.

Traditionally, markings are removed by soda-blasting or grinding. Soda-blasting is the most commonly used technique in which markings are broken loose by high pressure sodium bicarbonate (baking soda). While this method is effective and environmentally safe, it can be a noisy and time-consuming process that may cause pavement scarring. Furthermore, soda-blasting is not useful for removing durable marking materials such as thermoplastic. Grinding, in which rotating steel cutters dig up the pavement surface and markings, is the more cost-effective of the two line removal methods, but has a high potential to damage road surfaces. It should be noted that different methods are selected for each removal operation based on a number of factors, including the length of removal required, noise pollution, the time available for lane closures, the surrounding environment and cost issues.

MTO's Maintenance Office, in conjunction with the Materials Engineering and Research Office, recently had the opportunity to evaluate a new method with the potential to improve long-line removal operations: ultra high-pressure water blast technology. A contractor licensing this technology approached MTO in the fall of 2003 and trial demonstrations were scheduled for October 2003 to determine if this technology would be appropriate for use on MTO projects.

The water blast system, developed by the U.S.-based NLB Corporation, is new to Canada but has been used with great success in most American states. The system consists of a nozzle assembly device mounted to the front of a truck carrying a high-capacity water tank, vacuum recovery system and pumping unit (the truck may also tow an additional water supply). The mobile nozzle assembly, with adjustable speed and positioning options, follows lane markings and bombards the surface with extremely high-pressured water, effectively removing both typical and durable pavement markings. Water blasting offers a number of advantages over soda-blasting and grinding, the primary benefit being that it leaves the surface intact and unharmed. Furthermore, the system is environmentally safe, quiet, fast and efficient, requires only one operator, features simple controls, and also makes use of a vacuum recovery system to collect water and debris. Most water blast removals require only a single pass to produce a clean, dry road surface ready for repainting. The time requirements for water blast removal are comparable to grinding and superior to soda-blasting. Water blasting serves as an effective supplement to current removal methods, and is ideal for long-line projects.

The demonstrations took place on October 23-24, 2003, at three locations: the MTO facility on Arrow Road in Toronto, MTO's pavement marking test deck on Highway 401 in Belleville, and on the Avenue Road off-ramp on the 401 westbound Collector lanes. The Arrow Road and Belleville trials took place during the day, and used the water blast technology to remove lane lines from asphalt and concrete. The equipment removed markings at a rate of 10-17 m/minute, and successfully removed 95-100% of paint and thermoplastic markings without any significant surface damage. Representatives from various MTO offices who attended the demonstration were impressed by the efficiency of the operation and the effectiveness of the vacuum recovery system.

"I feel confident that the performance of this water blast system will make it an excellent addition to MTO's Designated Sources for Materials (DSM) list for long-line removal operations," said Vic Ozymtchak, Maintenance Officer.

The Avenue Road night trial, which involved the removal of a solid line down the middle of an off-ramp, produced similar results. Soda-blasting, which typically takes 3-4 hours to complete, was originally planned for use in this operation. The water blast technology removed the entire 250m line in only 40 minutes.

"Due to the low cost, and quick, clean removal of water blasting, I would recommend that this method be used as much as possible," commented Tyler Neill, Contract Control Officer in charge of the Avenue Road demonstration.

Upon review of the trials, the NLB product was found to exhibit high-quality performance capable of advancing MTO's long-line removal projects, making them more efficient and cost-effective. On January 19, 2004, the product was added to the Ministry's DSM list, authorizing it for use on highway contracts throughout Ontario. The Maintenance Office is currently arranging for the demonstration of other high-pressure water blast systems to add to the DSM for future implementation.