Effectiveness Study of UNL's Pneumatic Crack/Joint Preparation Device
Record Type: DOT
Flexible and rigid pavement joints and cracks are sealed or filled to mitigate further damage caused by the infiltration of water and the buildup of foreign debris. “Materials and procedures for sealing and filling cracks in asphalt surfaced pavement” recommends crack sealing for 5 to 19 mm. Also, Unified Facilities Criteria (UFC) provides guidelines for crack preparation for sealing based on crack size. The traditional procedures for preparing roadway joints and cracks for sealing/filling are largely ineffective, labor intensive and/or dangerous. Currently, the Nebraska Department of Roads (NDOR) uses the following methods for crack preparation and problems of each method are discussed as follows: Air Blasting. Air blasting is the most common means of pavement crack preparation. A hose and a wand attachment supply the treated area with approximately 100 psi of compressed air pressure. This method effectively expels voids of dust and relatively loose small contaminants. However, air blasting is not an effective means of cleaning out large wedged in debris, as well as the thin layer of deicing chemicals that often coat the pavement of cold weather prone areas. Hot Air Blasting. The hot jet of air cleans the crack just as with simple air blasting, but takes it further by drying the area and warming the walls of the crack to promote sealant adhesion. However, hot air blasting introduces other problematic issues into crack preparation. Extreme caution must be taken to ensure the pavement is not overheated which will result in the asphalt binder to become brittle and lead to premature bond failure. Care should be taken to never allow for direct flame methods to be used as the charring effect will lead to a sooty residue and cause poor initial bonding. Hot air laces are noted to produce hot air in excess of 3,000 degrees Fahrenheit at velocities of 3,000 feet per second. The extreme safety concerns associated with hot air blasting translates to a high level of safety and maintenance training required by both the operator and crew. In addition, the heated surface can introduce more moisture when it cools down quickly. Although routing is the best approach among the methods above for cleaning cracks, it is not a solution for complete preparation for crack sealing. Routing only excavates narrow cracks and still leaves de-icing chemicals on both sides of the crack surface. The surface preparation is very important for better bonding between surface and sealing material. Also, routing which generally uses a 3/8” carbide-tipped rotary impact bit is not effective for cleaning de-icing chemicals in wider cracks unless multiple routing paths are used. Furthermore, several districts in the state of Nebraska hesitate to rout cracks because routing equipment is very heavy and makes it difficult to follow cracks unless they are straight. In fact, it often results in the creation of another crack while routing random cracks. Pulling such heavy equipment downhill or on a windy day often puts the operator in dangerous situations as well. In summary, the current typical practices used for crack/joint cleaning in NDOR clearly highlights the remaining problems of each process. Especially, none of the current practices can effectively remove de-icing chemicals, vegetation, or old seals. It is the research team’s intention to evaluate the University of Nebraska at Lincoln (UNL’s) new crack/joint cleaning and preparation device that solves the problems identified from the above procedures. The principal investigator's (PI’s) research team has developed an innovative crack/joint cleaning device through the funded project by the NCHRP IDEA program in 2010. The device utilizes a pneumatically powered rotary attachment (e.g., wire wheels, carbide cutter) to rout cracks or to clean stubborn vegetation and accumulated de-icing materials from pavement cracks of mid- to large size. Directly behind such rotary attachments, a set of air blasting nozzles is used to further expel fine grained particles. The basic concept of the innovation incorporates several traditional crack/joint preparation methods in one device: (1) wire brushing/routing/cutting and (2) air blasting. Through several field tests with some of selected maintenance groups in NDOR and the City of Omaha during the development period, its technical and economical feasibilities have been validated and very positive feedbacks were received. Directly behind the rotary attachment, variable directional air blasting nozzles on the device are used to further expel fine grained particulate like concrete dust, fine sand, and most importantly, winter de-icing chemicals from the walls and surfaces of the pavement cracks. The device was constructed with a high torque pneumatic motor, machined aluminum pipes and associated fittings, and a varied selection of industrial wire brush wheels, carbide router bits, and diamond cutting blades. The main objective of this research is to evaluate the effectiveness of the UNL’s crack/joint preparing device for improving the current crack/joint preparation practices and for possible adoption as a standard in NDOR. Although the device has been tested and validated with short-term use by the selected pavement maintenance groups in NDOR and the City of Omaha, the long-term effectiveness and benefits of this device has not been completely validated yet. The main focus of this project is to evaluate the technical and economic effectiveness of the UNL’s device compared to the NDOR’s current practices. No developmental efforts (e.g., adding additional functions or redesign of the system) will be made during the period of proposed research. If successful, this research will benefit the State of Nebraska in the following ways: (1) The proposed device will improve the crack preparation crew’s safety. The light-weight device has the ability to largely replace the current NDOR’s use of heavy router and (hot) air blasting in crack preparation. (2) The proposed device will significantly reduce the road maintenance cost by speeding up the crack/joint preparation process for sealing, saving equipment cost, reducing a crew size, and lengthening the life of sealed cracks/joints due to the improved quality of sealing. The device yields a low cost purchase price for the tool itself, while effectively and efficiently preparing pavement cracks and joints for sealer or filler, which will further reduce long-term pavement maintenance cost. Traditionally routing and crack cleaning tasks have to be completed by at least two different crew members. As the current design stands crew size can be decreased by one member, there is no need for a second individual to follow behind the attachment to finish cleaning out debris and fine particulate in cracks or on the pavement surface. Labor costs are often a primary constraint when it comes to construction, and road maintenance is no different. The cost savings of one less crew member has the potential to yield substantial cost savings. There is a clear benefit in regard to mechanical simplicity. The proposed device is powered by pneumatic means only. This allows for a decrease in maintenance cost due to the simplicity of air powered motors, rather than the traditional small gasoline engines used to power the portable rotary brushes. In addition, the device is easily attached to current air blasting mechanism, and or maintenance trucks equipped with air compressors making the upgrade costs as minimal as possible. This simple attachment is likely to be relatively small, needing no new storage space on work trucks or tow behind units. In summary, the PI highly expect that this device will be used on a higher percentage of pavement maintenance, yielding an increase in preventative maintenance and a decrease in new construction costs by formulating a more efficient way of effectively cleaning joints and cracks. According to the Montana Department of Transportation for every one dollar spent on preventative roadway maintenance four to ten dollars are saved in rehabilitation costs. Michigan found that for their state, rehabilitation and reconstruction costs fourteen times more per mile of roadway of the life the pavement than preventative care. These cost savings translate into tangible budget factors that could funnel state allocated money into other needed projects.
Start date: 2012/7/1
End date: 2013/12/31
Status: Active
Total Dollars: 89916
Source Organization: Nebraska Department of Roads
Date Added: 06/07/2012
Index Terms: Joint sealing, Crack filling and sealing, Deicing chemicals, Air blasts, Routing, Pavement maintenance, Pneumatic equipment,
|
