Training Courses Teach TxDOT Personnel Best Practices in Seal-Coat Projects
The Texas Department of Transportation (TxDOT) maintains more than 79,000 miles of farm-to-market, ranch-to-market, state, U.S. and interstate highways. That’s more roadway than any other state. As resources are stretched thin, maintaining the roadways is a challenge. Seal coats — also known as chip seals — are simple, relatively inexpensive pavement surfaces that are highly effective if adequate care is taken in the planning and execution of the work.
Since 2007, the Texas A&M Transportation Institute (TTI) has provided TxDOT support with preparing, planning and teaching seal-coat training courses for its district personnel. The courses are based on a curriculum created from TxDOT’s Seal Coat and Surface Treatment Manual.
“We have two one-day training classes we usually teach back to back,” says TTI Research Engineer Cindy Estakhri, who manages TTI’s Recyclable Materials Program. “One class is designed for inspectors [i.e., practitioners], and the other focuses on planning and design [intended for engineers]. Our classes are meant to supplement and enhance participant understanding of seal-coat projects while on the job.”
The seal-coat training road show begins classes in the fall, when the weather cools off and the summer seal-coat season is complete. In a typical year, Estakhri — along with Jerry Peterson (director of TxDOT’s Asphalt and Chemical Laboratory) and Joe Graff (retired deputy director of TxDOT’s Maintenance Division) — travels around the state conducting a dozen or so classes a year that are usually filled with students.
“There are many factors affecting the success of a seal-coat project,” explains Estakhri. “For example, the type of asphalt used may not be appropriate for the environment or the amounts of aggregate, and aggregate applied may not be appropriate for roadway conditions. Both of these scenarios can cause immediate problems, so it’s helpful to have the experience of our instructors to explain how to do the job right the first time and avoid costly mistakes.”
Currently, the courses are undergoing revisions that include updated photos, slides and a series of videos explaining equipment inspection.
“Seal coats are a very important part of TxDOT’s preventive maintenance program,” says TxDOT Director of the Pavement Preservation Branch Magdy Mikhail. “Seal coats are approximately $2 per square yard versus $7–10 for an asphalt overlay, so they provide a major cost value benefit for taxpayers. The seal-coat training courses ensure we give our personnel the tools they need to properly maintain our roadway system.”
Implementation of New Specification for Asphalt Binders in Seal Coats
From the semi-arid northern plains to the humid subtropical piney woods, Texas is a vast state with a sprawling network of roads spanning multiple climates. While the temperature and landscape variances add to the giant state’s lore, they can also play havoc with roadway maintenance — namely the popular seal-coat surface treatment placed on 5,000 miles of roadways per year at a cost of approximately $300 million.
“The performance of a seal-coat surface treatment depends on several factors, climate being one of them,” says TTI Research Engineer Amy Epps Martin. “Inadequate binder properties when first placed in hot weather or when the first cold temperatures arrive can result in premature bleeding and aggregate loss, respectively. This results in poor performance and a roadway that should last six to eight years needing additional maintenance much sooner.”
The Texas Department of Transportation has sponsored multiple research projects with the goal of developing and validating a surface performance-graded (SPG) specification toward improved selection of seal-coat binders. “The selection of seal-coat binders is currently based on experience and traditional specifications that aren’t performance related and don’t directly consider climate,” notes Epps Martin. “The validated SPG specification directly considers the multiple climate zones in Texas through performance-based properties measured with the same equipment currently utilized for asphalt binders in hot-mix and warm-mix asphalt mixtures.” This SPG specification will replace existing seal-coat binder specifications and selection tables for in-service performance.
The Texas A&M Transportation Institute is working with TxDOT to implement the SPG specification in a four-year staged effort. In the future, a large seal-coat project in TxDOT’s Corpus Christi District and a smaller one in the Paris District will serve as initial test beds for the new specification. After the first year of in-service performance, the research team will evaluate the results and revise the specification as necessary. The Abilene, Amarillo, Austin, Brownwood, Corpus Christi and Paris Districts are planning to implement the SPG specification in 2016.
“The SPG specification is ready for implementation, and this effort will provide further validation with additional highway sections, corresponding climates and a wider variety of materials,” says TxDOT Deputy Director of the Construction Division Darren Hazlett. “It’s been a long time coming, but we’re hopeful this new specification will result in increased performance and reduced costs.”