Initial results of one study indicate hot-pour rubberized asphalt allows less water to infiltrate joints than silicone self-leveling and preformed compression sealants. Photo: SNS Research Committee
By Tom Bagsarian
A group of highway contractors and manufacturers that's been studying how sealing joints affects long-term pavement performance reports significant progress.
Joints are sealed to keep:
- Dirt and debris out of joint wells so pavement can expand and contract as necessary
- Water from trickling into and weakening pavement sublayers.
As of 2000, about three-quarters of state DOTs sealed new pavement. Two-thirds resealed joints and 14% didn't reapply sealant after repairs. But as states attempt to balance their budgets, DOTs are considering revising their specifications.
This brought a backlash.
“We don't believe owners have enough answers to automatically eliminate sealing,” says Scott Eilken, owner of Quality Saw and Seal Inc. of Bridgeview, Ill., and co-chair of The Seal/No Seal Group (SNS). He knows resource-strapped managers would rather spend $1 million on new pavement than on an activity that may not be necessary. But, he says, “we're in a lot of trouble if you start eliminating [sealing] across the country and in 20 years our pavements start failing.”
Launched about three years ago to prove or disprove that theory, the online clearinghouse focuses primarily on concrete but also gathers research on asphalt conducted by state DOTs from California to Minnesota and academic centers like the University of Iowa's National Concrete Pavement Technology Center. Members include Crafco Inc., Dow Corning Corp., Hilti Corp., and W.R. Meadows Inc.
“The industry didn't have a lot of information,” Eilken says. “Places across the country have done test sections, but they're never monitored long enough to truly gauge whether [sealing] is a good thing or a bad thing.”
Various states treat the issue differently. Wisconsin, for example, doesn't seal joints. “Their roads aren't any different,” Eilken says. “But at what point do they become worse? What if maintenance costs increase? We want to show owners so they can make an educated decision.”Hot-pour is least permeable
In fall 2010, the Texas Transportation Institute kicked off research intended to quantify the degree to which sealant type, condition, and joint well configuration keep moisture from compromising the structural integrity of pavement sublayers.
Transportation Institute researchers are establishing the infiltration rates of joints partially and completely sealed with hot-pour rubberized asphalt (average life: seven to 10 years), silicone self-leveling (average life: 12 to 15 years), and preformed compression (average life: 20 to 25 years) compared to untreated joints. They mimicked various rainfall intensities by flooding sections of a test track at Texas A&M University's Riverside Campus in Bryan to various depths and widths, then measured moisture as it trickled through joints and collected in a series of catch buckets. They're also using ground-penetrating radar to detect moisture levels below the slab.
In January 2011, preliminary results of “Effect of Joint Sealant Condition on Moisture Infiltration and Erosion Potential” found that hot-pour sealant had the lowest infiltration rate when the opening of sealant is less than 1 mm. Work is continuing to establish the flow rates of 3/8- and ½-inch joint wells, and how various levels of dirt and moisture in wells affect bond quality.Other research topics
The group is also working with material scientists to develop testing procedures to determine pavement cleanliness, dryness, and proper adhesion. The industry doesn't have tools to measure if a joint is dry or clean enough to install sealants. Another area of study is the impact of hazardous material spills on unsealed pavement.
The group's first effort to demonstrate the long-term effectiveness of sealants on pavement performance has not yet yielded results.
In 2009, Crafco hot-pour and silicone sealants were installed on eight sections of Route 59 near Joliet, Ill., on 9¾-inch dowelled concrete placed on a 12-inch base. The results of those sections, which opened to traffic in November of that year, will be compared to those of two unsealed sections of the same road. A year later, Walsh Construction of Chicago conducted smoothness testing with a profilograph.
“That gives us a base of how smooth the roadway was at the beginning,” Eilken says. “Then we'll retest and monitor how it's progressing.”
Skeptics might wonder how objective the group might be in reporting the results of these various tests.
“No question about it — we've trying to protect our industry,” Eilken says. “There are pros and cons on our website. We will not allow it to be a shaded opinion. We want the opportunity to bring the information to the table so owners can make an educated decision. Right now, that information isn't there.”
— Bagsarian is editor of CONCRETE SURFACES, a sister magazine of PUBLIC WORKS. This article first appeared in the June 2011 issue, and was updated in March 2012.