Science takes on potholes

• Building a better asphalt: New mixes will be tested on H-1 paving project

By Mike Leidemann
Advertiser Transportation Writer

Santo Calaro, a service worker at the asphalt plant of the Grace Pacific Makakilo facility, shovels a load of the Marshall mix asphalt being produced at the plant. That basic formula is used on most Hawai'i roads. Bruce Asato • The Honolulu Advertiser

The changes could smooth the pavement for drivers, prolong the life of existing roadways, reduce road construction delays and save taxpayers money in the long run, the officials said.

"We've been using road technology that hasn't changed much from the 1930s or 1940s, but the traffic keeps increasing and the trucks keep getting heavier," said Steve Ege, an engineer with the state Transportation Department's Materials Testing and Research Branch. "Sometimes that makes it seem like our roads are getting worse faster."

Robert Christe, who has driven an Island Movers delivery truck for 14 years, agrees.

"The roads have gotten worse since I started, especially the freeway with all those patch jobs," he said. "Sometimes, it's pretty spooky."

To deal with the problems, highway officials are planning several new efforts:

• A pilot program in which parts of Moanalua Freeway will be paved this year with three different asphalt mixes, allowing engineers to study which go down easiest and which last longest.
• A pavement preservation program designed to extend the life of existing roads three to seven years and reduce the amount of money the state has to spend on regular repaving.

Asphalt, which is extracted from petroleum, has been around for thousands of years. It was used as a waterproofing material in ancient Mesopotamia and Egypt and was first put to work on roads as early as 625 B.C. in Babylon. True asphalt pavement was first used in the United States in the 1870s, when parts of Pennsylvania Avenue in Washington, D.C., were covered with it.

Basic highway paving techniques have not changed much since 1930s, when an engineer named Bruce Marshall developed a mix of asphalt and crushed stone that was first used on roads in Mississippi, said Bob Wilkinson, president of Grace Pacific, the only company on O'ahu that produces asphalt paving materials.

That basic formula has been used on most Hawai'i roads since then, Wilkinson said.

While several alternative mixes, Superpave and Stone Matrix Asphalt, have become more widely available in the past 10 years, local and state officials have not rushed to put them into use here, he said.

However, Superpave, Stone Matrix and the Marshall mix all will be used in different parts of the road when the state Transportation Department begins work on Moanalua Freeway.

The test will provide the first opportunity to compare how the materials stack up against each other in terms of cost and longevity, said Erik Rhinelander, manager of quality control and research and development at Grace Pacific.

The materials, which take advantage of new polymers and blending techniques to improve the strength of the hardened pavement, could provide long-term help to state and county maintenance crews, who have been forced in recent years to reduce maintenance and increase the time between regular road reconstruction or repaving.

The new compounds cost 10 percent to 30 percent more than the old ones, but can last at least 30 percent longer.

"A lot of places are already agreeing that Stone Matrix Asphalt is the way to go," Rhinelander said.

Ultimately, the big savings come in lower labor costs as the life of the roadway is extended and the need for costly resurfacing projects — and the unpopular traffic delays they create — are reduced.

"The downside is the initial cost, but the upside is that over the life cycle of the pavement, costs will go down," Rhinelander said. "With the old way, you cut costs up front but end up paying more in the end."

That could be good news for state and county officials who are trying to extend the life of the existing pavements with new surveying, patching and repaving techniques, said Casey Abe, head of DOT's Materials Testing and Research Branch, which is in charge of the pavement preservation program.

Water and weight are the two big factors that do the most damage to Hawai'i roads, engineers say.

The volume and weight of cars and trucks have increased the wear and tear on old asphalt roads at a time when maintenance and repaving schedules have been cut back because of financial constraints, officials said. That creates more cracks and other damage, opening the way for water to get under the pavement, creating even more problems.

Using a laser mounted on the front bumper of computer-equipped van, engineers have begun making an annual survey of all state roads, providing a "roughness index" for every mile of state roadway, Abe said.

The index then allows state officials to determine which roads are most in need of repairs, repaving or reconstruction, he said. By attacking smaller, less expensive problems first, the department may be able to extend the life of some roads by three to seven years.

The fixes may be able to stop damage at the surface before it spreads to a road's underlying base, which is the most expensive part to replace or repair.

"We may be able to fix some cracks or other damage in time before they allow water to get underneath," Abe said. "That could mean saving millions of dollars."

City and state officials also have begun using a new pothole patching material called Wespro. Although almost 10 times more expensive than the "hot patch" mix that has been used for decades here, the new material goes down quicker and bonds better with existing roadways, even in wet weather, allowing the repair work to last longer.

Grace Pacific also has been using recycled asphalt and crushed glass in its new asphalt mixtures, helping to reduce waste and costs. State regulations allow a new batch of asphalt pavement to contain up to 10 percent recycled asphalt, but company officials say that figure probably could be safely increased to up to 30 percent without any reduction in quality.

Mike Bishop, a U.S. Postal Service delivery driver for nine years, says road professionals can appreciate the difference.

"They patched things up pretty well after the last big rain, but I'm sure we'll start to see problems again soon," he said, taking a break in Waikiki during Friday's heavy downpour. "I like that new pavement with the glass. It feels smoother and safer."

Ultimately, though, Hawai'i roads will have to be built differently to cope with the ever-increasing loads, he said.

"We'll have to improve on the base we use on new roads," he said. "If we know there's going to be a lot of heavy truck traffic in an area, we can plan and build accordingly."

Reach Mike Leidemann at 525-5460 or meleidemann@honoluluadvertiser.com.

Building a better asphalt: New mixes will be tested on H-1 paving project

In a pilot program, parts of Moanalua Freeway will be paved with three different mixes, allowing engineers to study which go down easiest and last longest.

Marshall mix

Developed in the 1930s and used throughout America and Hawai'i ever since. A mix of asphalt cement and three types of stone aggregate. A densely graded mix, compacted by up to 75 blows from 10-pound slide hammers. Advantages include wide availability and relatively low expense. Disadvantages: susceptible to cracks and rutting, allowing water to spread inside and create more damage.

Superpave

Developed under the Strategic Highway Research program and introduced in the United States in 1992. Changed the binding requirements for most asphalt mixtures, tailoring them toward specific climates and traffic loads. Compacted through gyration, rather than slide hammers, reducing damage to the stone content. Less resistant to rutting and other damage. Costs higher than the Marshall mix, but becoming more affordable.

Stone Matrix Asphalt

Developed in Europe to resist damage from stud tires and introduced in the United States in 1991. Uses polymers and fibers and increased asphalt content to strengthen bonding power. Allows for stone-on-stone contact in the mix — lasts much longer as a result. Best alternative for most heavily used roads and freeways. Costs between 10 percent and 30 percent more than other mixes.