Pavement Preservation Journal - Winter 2012 - (Page 41)
Texas DOT Develops Crack Sealing Field Manual
By Dr. Yetkin Yildirim, P.E.
avement cracking inevitably develops in virtually all pavement surfaces, and is the primary mode of deterioration for asphalt pavements. Cracking is observed in a variety of forms: transverse, longitudinal, block and alligator. All types of cracks should be treated promptly as they contribute to accelerated pavement service life reduction. Cracks allow moisture to penetrate to a road’s base, which can cause serious damage. Neglecting pavement cracks typically leads to far more serious conditions, such as potholes, crack growth, spalls, secondary cracks and base failure. The main causes of cracking are thermal variations and excessive loading, which are expected and unavoidable. Because of this, it is important that road maintenance personnel are able to apply crack sealant efficiently, effectively and in a timely manner. In pursuit of this goal, the Center for Transportation Research at the University of Texas has developed a field manual for the Texas Department of Transportation (TxDOT) to provide a quick reference guide for cracks and crack sealing procedures. CHOOSE RIGHT ROAD First, for crack sealing to be effective, the right road must be chosen for the maintenance procedure. Crack sealing will not be able to repair serious structural failures, so the road in question must remain in good to fair condition in order to be a viable candidate for crack sealing. Additionally, roads that are scheduled to receive full-width seal coating or asphalt overlays will require crack sealing for cracks wider than 1/16 in. before subsequent operations. It also is important for maintenance personnel to identify which cracks are not suitable for crack sealing. For example, alligator or fatigue cracking is indicative of more serious structural conditions that will not be improved with the sealing of surface cracks. Once a proper candidate has been identified for crack sealing, further considerations must be taken into account before initiating the procedure. First, ambient temperature and the current weather conditions are important factors in the execution of crack seal applications. Crack sealing generally should be completed during cold months, when cracks are at their widest (ambient temperature around 45 to 65 deg F). During these times the sealant can more easily penetrate the cracks. Second, maintenance personnel must remain mindful of safety concerns. Materials that are used in crack sealing can be hazardous to both workers and commuters. Hot-pour sealants are applied at approximately 350 deg F, so caution must be taken in sealant application.
Additionally, traffic control must be taken into account in planning and execution of crack seal applications. The traffic control plan should take into account expected traffic volume, sealant curing time, and planned time between sealant application and removal of traffic control devices. METHOD OF APPLICATION With these concerns in mind, maintenance personnel next must select the method of sealant application. This selection will depend on the movement and physical characteristics of the crack. Appropriate candidates for typical crack sealing are cracks which have horizontal or vertical movement of less than 1/10 in. Typical crack sealing should also be used for cracks that have moderate or no edge deterioration. For cracks with movement greater than 1/10 in., routing procedures are required. Crack routing involves cutting along the crack to provide a uniform, rectangular reservoir in which the sealant is placed. This procedure creates uniform, smooth edges, which result in improved adhesion of the sealant material. Finally, once all of these preliminary concerns have been taken into account, execution of the sealant procedure can begin. First, the crack in question must be cleaned and dried. This cleaning will optimize adhesion between the sealant material and the pavement surface. Most crack seals that fail do so as a result of loss of adhesion, so cleaning is of utmost importance to the longevity of the sealant. Cleaning of the crack is achieved with high-pressure air blasting (away from traffic), and drying is completed using a hot air lance. When sealing large cracks, it is important that the sealant does not drain to the bottom of the crack. To prevent this, backer rods may be placed in the cracks before application of the sealant. When sealing wide areas, aggregate should be placed on top of the fresh sealant in order to maintain safe surface friction. Traffic should not be reopened to the construction area until the sealant has fully cured. If, however, traffic must be allowed on the area before curing finalizes, then blotting should be used, the application of fine aggregate or sand to the uncured sealant in order to prevent tracking from vehicle tires. Following these guidelines for crack seal project selection and construction procedure will greatly improve the efficiency of effectiveness of pavement maintenance practices. The crack sealing field manual developed by the Center for Transportation Research can be accessed in its entirety at www.utexas.edu/research/ctr/pdf_reports/0_4061_P3.pdf Yildirim is director, Texas Pavement Preservation Center.
Winter 2012 pavement preservation journal 41
Table of Contents for the Digital Edition of Pavement Preservation Journal - Winter 2012
Lee Road Preservation Study Unique to NCAT Research
San Antonio Condition Surveys
When Managing Pavements, Manage Friction As Well
Language Affecting Pavement Preservation in MAP-21 Will Benefit Preservation Community, Road Users
Lebanon, Ohio Uses FDR to Quell Refl ective Cracks
Texas DOT Develops Crack Sealing Field Manual
Implementation of International Road Management Systems
Index of Advertisers
Pavement Preservation Journal - Winter 2012