Evaluating the Need to Seal Thermal Cracks in Alaska’s Asphalt Concrete Pavements
By: Anthony Mullin
The Alaska Department of Transportation & Public Facilities (AKDOT&PF) has promoted routine sealing (or in severe cases, patching) of all cracks in asphalt concrete (AC) pavements for many years. Crack sealing is a common maintenance practice for all pavement types in most areas of the United States. Based on many field observations made by AKDOT&PF research engineers over the preceding 30 years, a conjecture had developed that certain crack types may sometimes be ignored, i.e., left completely unsealed, for the life of the pavement with no negative effects. The research conducted for this study represents the first attempt in Alaska to verify or reject this conjecture through a systematic field study of a significant portion of Alaska’s paved highway system. While only thermal cracks are the subject of speculation data was collected on other types of cracks and pavement surface distresses as well. The field study was limited to one year and was conducted on interconnecting roads to include the Richardson, Alaska, Glenn, Tok Cutoff, Steese, Elliot, Parks, and Sterling. Evaluations were performed on 91 sections 0.1 mile long and are a minimum of 20 years old. The methods of evaluation were PASER, LTPP, and a Special Thermal Crack Evaluation system. These methods are qualitative, quantitative, and include many photographs with documented observations. References for the literature review describe fracture energy being a discriminating parameter to compare different asphalt mixes. Much has been written on the comparison of sealing techniques and materials but few references discuss how crack sealing affects metrics for overall ride quality. Finally, suggestions are given on what type and condition of thermal cracks to seal or not seal. It is the opinion of the authors that lessor thermal cracks in Interior Alaska do not need to be sealed. It is also suggested to perform further research on pre-saw cutting asphalt pavements such as had been done successfully in Fairbanks over 25 years ago.