Selecting how long a given joint sealant will last before replacement — and what to include for the performance period in life-cycle costing — is not as easy as it may seem. Historically, the best reference has been the federal Strategic Highway Research Program’s (SHRP) H-106 work conducted in 1999 (see Web extra on page CS-52). The report documents the results of the research effort, which installed sealants at five locations and evaluated them for a mere seven years. Another limitation: This report only studied the reseal condition.
The Seal/No Seal Group recently reported on two unique studies at sites that allowed evaluations of sealants up to 21 years. One study was coordinated by pavement preservation product manufacturer Crafco, and took place at Fairchild Air Force Base in Spokane, Wash. The other study was at the Federal Highway Administration’s Long-Term Pavement Performance (LTPP) SPS-2 Experiment in Phoenix.
Fairchild Air Force Base
In 1989, the U.S. Army Corp of Engineers Construction Productivity Advanced Research (CPAR) conducted a sealant performance study consisting of both laboratory and field evaluations. The study evaluated both hot-pour and silicone sealants over a 10-year period (see Web extra). CPAR selected the Fairchild site because it had reported extreme temperatures ranging from -30 degrees F and 108 degrees F, which would sufficiently test the efficacy of the sealant products.
As part of the field evaluation, crews replaced existing sealants with new ones on the then 35-year-old runway. CPAR researchers then conducted seven different evaluations, with the final evaluation taking place after 117 months (10 years) in service.
In 2012, Crafco realized that many of the sealant test sections were still in service and performing well. As a result, a second “final” evaluation was conducted by the same personnel who conducted the earlier evaluations. They used the same techniques used previously, which were consistent with SHRP H-106 and National Transportation Product Evaluation Program (NTPEP) procedures still used today. This evaluation took place 21 years (250 months) after the original installations. Findings include:
- Asilicone sealant installed in a conventional manner and a low-modulus, hot-applied asphalt sealant installed using flush-fill geometry exhibited a performance period of more than 21 years.
- With the hot-applied asphalt sealants, the flush-fill installation geometry produced more than a 50% increase in sealant life as compared to the standard recess fill.
- Silicone sealants produced six times more joint spalling than hot-applied asphalt sealants.
- There doesn’t appear to be a correlation between silicone sealant extension ranging from 450% to 1000% and silicone sealant life.
These findings are not necessarily new, but they provide more conclusive evidence due to the longer evaluation period.