Publication Number: FHWA-SA-97-024
Date: June 1997

Narrow Joints Lead to Big Savings

What do you get when you narrow the width of transverse joints in portland cement concrete pavements? A savings of as much as $4 million. That's the amount the Arizona Department of Transportation (DOT) expects to save by allowing joints as narrow as 3 mm (1/8 in) on 160 km (100 mi) of new concrete pavements to be built in the State.

In the past, Arizona specified that joints in concrete pavements had to be 3/8 in (10 mm) wide. Narrower joints have three big advantages over the DOT's old specification-they can be cut with one pass of a saw, not two, reducing labor costs; less sealant is needed to seal the joints, saving money on materials; and sealing the joints takes less time, reducing labor costs even more. The exact width of the joints is not critical, according to Larry Scofield of Arizona DOT. "There's nothing magic about the size," he says. "We just want a single saw cut and minimal damage to the concrete."

The lower labor and materials costs translate into a savings of about 3 percent of the total cost of new concrete pavement, Scofield says. That may not sound like much, but it adds up fast. The new specification is being tried on new pavements in the Phoenix and Tucson metropolitan areas. Scofield predicts that the overall costs will be between $2 million and $4 million lower than with the old specification, and when the seals eventually need to be replaced, the DOT will likely save about the same amount of money.

Arizona DOT adopted the new specification in response to the findings of the western States sealant experiment. The experiment expanded on two complementary experiments begun during the Strategic Highway Research Program (SHRP). The first focused on innovative materials for repairing joint seals in concrete pavements; it evaluated how well sealant materials held up, but did not consider their effect on pavement performance.

The second experiment was part of the long-term pavement performance (LTPP) program's specific pavement studies on preventive maintenance treatments for concrete pavements (SPS-4). This experiment focused on the effect of joint seals on pavement performance, without considering the performance of the seals themselves.

The western States sealant experiment combined the goals of these two experiments. It is designed to evaluate the effect of joint sealant performance on the performance of concrete pavements.

Arizona DOT developed the design for the western States sealant experiment and built a test section on U.S. 60 near Mesa in 1991. Colorado, Nevada, and Utah built similar test sections.

The western States sealant experiment began to pay off after just a few years. By 1995, Arizona DOT had concluded that silicone sealant performs equally well in joints as narrow as 3 mm (1/8 in) and as wide as 10 mm (3/8 in). This finding appears to run counter to conventional practice and the recommendations of silicone sealant manufacturers, Scofield says. He points out that "Arizona DOT doesn't disagree that a wider joint may theoretically be better, but it isn't necessary with the sealant materials available today." Seal installation, not joint width, he says, "may be one of-if not the-most important variable in sealant performance."

Arizona isn't the only State to change its specification: narrow joints are now being specified for concrete pavements in Colorado and Utah (see sidebar).

The sealant experiment will eventually yield information on the relationship between seal performance and pavement performance. For example, a test site on State Route 202 in Phoenix will help Arizona DOT learn about the life-cycle costs of different joint sealant materials, the use of less expensive hot-pour materials to repair silicone seals in existing pavements, and the ability of contractors to work with narrow joints.

According to Scofield, it cost only $25,000 to construct the experiment on U.S. 60-a tiny fraction of the amount Arizona DOT will save from switching to the new specification.

To find out more about the study and to learn how to set up a test section in your State, contact Larry Scofield at Arizona DOT (phone: 602-407-3131; fax: 602-256-6367; email: lscofield@dot.state.az.us). For more information on the LTPP program's experiments on joint seals, contact Shahed Rowshan at FHWA (phone: 703-285-2527; fax: 703-285-2767; email: shahed.rowshan@fhwa.dot.gov).

Like Arizona, the Utah Department of Transportation (DOT) has taken the results of the western States sealant experiment to heart, adopting narrow, 3-mm-wide (1/8-in) transverse joints for concrete pavements. However, Utah is using hot-pour asphalt joint sealant, not the more expensive silicone sealant used in Arizona.

Utah will use the new specification on the massive project to rehabilitate and expand Interstate 15, the main north-south route through Salt Lake City. The 4-year, $1.38-billion project, part of the city's preparations for the 2002 Winter Olympics, is the largest design-build contract let in the United States. The specification will also be used on 260 lane-km (162 lane-mi) of other pavement projects this year.

Darrell Giannonatti of Utah DOT says the narrow joints may do more than save money on labor and materials-they could also improve pavement performance. "Making joints with one saw pass reduces the microfracturing that occurs from cutting," he says. "The result is less raveling and spalling along the edge of the joint."

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