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Thermal cracking is one of the most prevalent asphalt concrete (AC) pavement distresses in northern states and countries. Every year in Alaska, a substantial amount of funding is spent on sealing cracks according to the practices of the Alaska Department of Transportation and Public Facilities (ADOT&PF) Maintenance and Operations (M&O) division. However, to date there are no specific guidelines available that clearly outline the best timing for crack sealing or even what conditions necessitate crack sealing in a consistent manner. There is a need to evaluate the effectiveness and best practices for using the crack sealing techniques on AC pavements in Alaska. In response to this research need, a pavement preservation project was conducted and found that although crack sealing is a very common practice in Alaska, it is unclear how and why M&O decides to seal cracks since some are sealed and some are not. This motivated further evaluation of 91 field sections that represent the various climate regions of Alaska. A new survey method, “special thermal crack evaluation (STCE) ”, was developed to answer critical questions related to road thermal cracks and to provide guidance for crack sealing practices. The new STCE method was conducted along with two other field survey methods, the Long Term Pavement Performance (LTPP) program and the Pavement Surface and Evaluation Rating (PASER). Results between methods were then correlated. Finally, regression analyses were conducted to determine factors that significantly influence crack development and crack sealing practices in Alaska. Significant influencing factors on crack development include pavement temperature, freezing index, and rut depth. Crack frequency, freezing index, pavement age, PASER rating, PASER transverse crack severity level, and certain STCE questions can significantly contribute to the decision making for current sealing practices. It was found that the STCE method could generate direct recommendations on crack sealing practices. STCE, in combination with the LTPP and PASER methods, provides specific analysis about asphalt thermal cracking and sealing of these cracks so that informed decisions can be made for a positive impact on ADOT&PF’s maintenance budget. It is recommended to use STCE along with the LTPP and PASER methods and to use the findings of influencing factors of this study to develop more specific plans for future crack sealing practices.
The primary purpose of this study was to develop criteria to improve the effectiveness of Utah's flexible pavement crack sealing practice. The methodology involved field measurements of seasonal variation in crack width and in-depth interviews of Department members at various levels of management in maintenance, materials, construction, and research. Other states were queried by questionnaire in order to obtain a comparative base on with to evaluate Utah's practice. Findings indicate that flexible pavement cracking is a significant problem in the Far West, Rocky Mountains, Great Lakes, and New England. Criteria to determine when to seal (fill) cracks, and materials or techniques to be used vary widely. Choice of materials if affected by storage requirements and equipment available. Prepackaging of materials especially designed for crack sealing has resulted in improvements in control of mix and material properties; further gains can be anticipated as mix design improves and material specifications become more exact.. Low temperature and freeze thaw cycles significantly affect the amount of thermal cracking and the performance of crack sealant. Poor rideability, increased pavement deterioration, obscured traffic markings, lowered skid resistance can result from inappropriate selection and installation of crack sealants. Ductile sealants such as Crumb rubber/asphalt cement mixes, in combination with routing appear to offer substantial gains in sealant life and performance. These gains are partially offset by increased installation cost and hazard to the operator. Existing data is insufficient for benefit/cost analysis.
Transverse thermal cracking is one of the most common pavement distresses on asphalt pavements in cold climates. Transverse cracks are costly to maintain and unpleasant to drive over. The State of Alaska Department of Transportation and Public Facilities must seal cracks every summer to prevent further road damage from occurring. A simple solution that is gaining support is the precut technique where saw cuts are installed perpendicular to the road centerline shortly after construction to help relieve thermal stresses that cause cracking. This technique has effectively reduced the effects of natural transverse thermal cracking in other states as well as in Fairbanks, Alaska. This study investigates two road construction projects that include precuts with variable factors including three precut spacing intervals, five precut depths, and five pavement structures. Costs to install precuts are also compared against the cost to maintain a section without precuts in a preliminary cost effective analysis. Crack survey data from both projects have revealed that precutting does reduce transverse thermal cracking. Shorter precut spacing, placing precuts where natural cracks existed prior to construction, deeper precuts, and stronger pavement structures provided the best results. Further observations and more accurate cost data are recommended for an absolute determination of cost effectiveness.
Sealing or filling cracked asphalt pavements to prevent the intrusion of water into the pavement structure has long been an accepted practice of the Montana Department of Transportation. The goals of this research are to establish the most economical and effective method of sealing pavement cracks for Montana; and to better determine the role of crack sealing within Montana pavement management system (PMS). This study has involved the construction of 4 experimental test sites within larger crack sealing projects. These test sites have included combinations of 11 sealant materials and 6 sealing techniques. Monitoring of the test sites includes visual inspections (for all of the sites) and nondestructive structural readings and surface distress identification under Montana PMS (for one test location). An estimate of the useful life of each crack sealing method has been determined from these investigations. This report presents information on project history, the project methodology used for evaluating and analyzing the performance of sealed cracks, and the results of the cost effectiveness analysis. Final results are presented for the 4 test sites: Conrad, Dutton, Tarkio, and Helena (Seiben). Results show that similar performance has been observed for all materials with ASTM D 5329 cone penetrations in excess of 90. In general, routing of transverse cracks improved the performance of the sealants. Routing does not appear necessary for centerline longitudinal cracks. Notably, router operators seem to prefer the shallow reservoir configuration as compared to square reservoirs. The test site established near Helena provided the most reliable and useful data. As such, a detailed review of the final performance from 4 1/2 years of service is summarized. In general, the highest failure rates occur during the coldest period of the year, and much of this distress exhibits a tendency to heal after exposure to the summer heat and traffic. An eclectic forecasting model has proven useful in predicting the life of crack sealing operations for those methods that did not show complete failure during the evaluation period. Structural evaluations using a Falling Weight Deflectometer did not prove an advantage for any particular sealing technique or sealing material nor did they prove the benefit of sealing cracks in asphalt pavements. Therefore, conducting a life cycle cost analysis was impractical because no structural or ride benefit was proven at this site. However, a cost effectiveness analysis was performed and the averaged results showed that, overall, Crafco 522 was the most cost effective material and the Shallow and Flush was the most cost effective fill technique. However, the crack sealing approach that has the highest cost effectiveness as calculated herein (defined as the ratio of effectiveness to cost) may not offer the best value, if this effectiveness is in excess of that required to protect the pavement from premature damage. More research is necessary to substantiate the need for higher performance materials and techniques.
In 1980, a Vanguard High Pressure Water Blaster capable of providing 10 gallons of water per minute at 2000 psi was purchased to evaluate water blasting as a crack cleaning method prior to crack filling on asphalt concrete pavements. Afer some iniital trials demonstrated its effectiveness of removing dirt, debris and vegetation, it was included in joint and crack maintenance research on Iowa 7 in Webster County. The objective of the research was to evaluate six crack preparation methods and seven "sealant" materials. The cleaning and sealing was performed in the spring of 1983. Visual evaluations of the performance were made in the fall of 1983 and spring of 1985. Compressed air and/or high pressure water did not adequately prepare cracks less than 3/8 inch wide. Routing or sawing was necessary to provide a sealant reservoir. The water blaster was more effective than compressed air in removing dirt, debris and vegetation but this did not yield significant improvement in sealant adhesion or longevity. Periodic crack filling is necessary on ACC surfaces throughout the remaining life of the pavement.