MTO Researches Saw and Seal
Marty Drinkwine, Cimline Incorporated
Recently the Ontario Ministry of Transport (MTO) began a series of field evaluations on the benefits of the Saw & Seal method of cracksealing.
This evaluation began about two years ago when the MTO initiated investigation into alternatives to Routing & Sealing, which is the current provincial standard. Discussions with agencies outside of Ontario revealed that many were having great success with the sawing process. This indicated to The Ministry that some further research and physical study could be worthwhile in evaluating ways to possibly improve their cracksealing specifications.
Cracksealing has long been recognized by the MTO as a very cost and results beneficial practice to pursue in prolonging provincial infrastructure. Generally it is executed at 1/6th the cost of conventional pavement rehabilitation and reconstruction methods. It does, however, lack the profile of more costly and complex processes and tends to get overlooked by most agencies and contractors. This, juxtaposed with its incredible reliability at pennies per metre. Like any process this dependability is reflective of the practices, materials and overall commitment to quality.
Earlier this year, Chris Raymond - Senior Bituminous Engineer, began to co-ordinate a plan to test the comparative benefits of the various practices with the emphasis on Sawing versus Routing. With the assistance of Gord Start - S/W Region Technical Services Supervisor and Steed & Evans the primary maintenance contractor, a suitable test area was chosen. The route selected was along Highway #3 between Tillsonburg and St. Thomas. This route was divided into several sections; each detailed to provide comparative data.
These detailed sections would each comprise several examples of a specified series of preparation and application steps. As an example, one section may require a 25 X 20 mm saw joint in HL3 with a 190 sealant and no over-banding. Another section may be identical but with sandblasting and over-banding steps included. To ensure reliable comparisons could be made, one section would adhere to the current provincial Routing & Sealing specification.
With the information laid-out and organized, attention to selecting an experienced contractor and equipment was required. After some deliberation, The Bridge Tite Group from Schomberg, Ontario was chosen. This company specializes in waterproofing, sandblasting, joint preparation and sealing.
Discussions between MTO and their Michigan counterparts revealed that equipment selection also had some bearing on the success they had achieved with the Saw & Seal process. After speaking to contractors, and in order to make a more accurate comparison, MTO chose to specify the same saws and blades as used in Michigan. This led to a call to Cimline Incorporated of Plymouth, Minnesota the leading manufacturer of cracksealing equipment in North America. Cimline and Heat Design, the Ontario authorized dealer, agreed to make a PCS-25 Saw, PCR-25 Router and support personnel available at no charge for the purposes of the tests. All that remained was to schedule the project, and after some adjustment the work was completed between September 27 28, 2005.
The most significant difference between the Sawing and Routing processes is the accuracy of the cut. The saw blade, with multiple teeth rotating at high speed ensures a clean, almost surgical cut. This provides for smooth, well-defined walls and base to the cut groove. Such precision limits peripheral damage and makes for a more verifiable sealant reservoir. By contrast, routing makes a less precise cut with a 'Star' shaped cutter, which permits easier chasing of meandering cracks.
Regardless of the desired cut, it is universally agreed that removing contamination and moisture is critical to joint life. During these tests a sandblasting process was employed to remove dirt and contaminant from the cracks. As a comparison, a number of cracks were blasted and sealed without the use of cutting equipment. A Heat-Lance was also used in one test section to examine the effectiveness of pre-drying to gather comparative data.
With the successful completion of documenting and sealing the various test sections, a monitoring phase was initiated. During the following months and years (possibly 2 or 3), these various cracks will be observed and measured to determine the effectiveness of the processes employed. As that data is gathered, the MTO will analyze and interpret it according to a predetermined set of criteria. According to Raymond, the MTO wants to provide contractors with a reasonable application criterion to improve overall reliability of the process. It is also hoped that when the data has been reviewed that the findings could be presented to the Canadian Technical Asphalt Association (CTAA) for broader consideration and discussion.
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