While private and public efforts such as Portland’s Working Waterfront Loan Fund aim to provide financial assistance for maintenance, relief is also coming in the form of technological innovations in materials and design. These in innovations could revolutionize the way we design, build and maintain waterfront infrastructure.
The new materials are called composites, because they combine natural materials such as sawdust or hemp fibers with plastic compounds and engineering savvy. They are stronger, lighter and more resistant to harsh environmental stresses of ice, salt and wave action than today’s most commonly used materials. Not entirely by chance, the brains and skill driving this revolution reside at the University of Maine’s Advanced Structures and Composites Laboratory. Funded by grants and a share of the Research and Development bond issue approved by Maine voters, the lab houses $6 million in machinery that heats, stretches, compresses and extrudes materials to test their structural strengths and weaknesses.
The first test of composites to come out of the lab and hit the waterfront is a new 170- by 16-foot vertically laminated composite pier in Milbridge. Working with the Maine Department of Transportation (MDOT), Milbridge applied for and won a $180,000 grant from the Maine Science and Technology Foundation. That made a significant dent in the project’s overall $600,000 budget.
“One of the town’s piers was dilapidated and unsafe for people to walk on,” says Milbridge town manager Howard Kroll. “We have a huge commercial and recreational fleet. The new pier is up river, where it will serve as the town’s recreational and backup commercial pier.”
Its composite deck is a combination of thermoplastics and sawdust 21.5 feet long and 8.5 inches deep. The panels are reinforced with a thin laminate of patented composite material made of phenolic resin and synthetic fibers. Just one percent of the panel’s overall thickness, it is twice as strong as steel. The decking on the Milbridge pier has the same strength and stiffness as concrete, at a third the weight.
Habib Dagher, director of the Advanced Structures and Composites Lab, says the material went through rigorous testing in the lab before it became applicable in the real world. Composite materials are subjected to mechanical stress using the lab’s hydraulic equipment to mimic bending, twisting and impact stresses.
Environmental stresses such as repeated cycles of freezing and thawing, water damage, salt and UV exposure are mimicked in the lab’s 25-foot-long environment chambers, where temperatures can rapidly swing from -40 to 100 degrees and back, and humidity quickly changes from five percent to 95 percent. A day in the chamber can resemble years of weather and climate exposure.
“Our job is to make sure these materials have gone through enough torturing that they’ll survive in real natural environments,” says Dagher. For salty marine applications, corrosion resistance properties are critical. The composite performs better than steel or reinforced concrete because steel and concrete rebar corrode. “The life expectancy should exceed 70 years based on modeling,” he says. “Time will tell. There’s nothing like putting it out there to determine its durability. This is new technology. The Milbridge pier is the first like it in the world. There are no long-term durability examples.”
In Milbridge, Howard Kroll is reasonably enthusiastic about the hosting the first test of the new materials. “Without a doubt it’s the best infrastructure in town. A lot of communities will look at us as an example. It should stay for many years.”
Pilings: new fix to an old problem?
The new Milbridge pier is supported on concrete reinforced steel pilings. However, most piers typically involve constant maintenance, not new construction. Pilings are replaced one by one as they either rot or are attacked by marine borers. The current replacement for pilings is the familiar green pressure-treated southern pine piling. The old way of dealing with it — coating wood with creosote — has been banned since the 1980s due to creosote’s toxicity. Now the safety of conventional, chemical wood treatment is being seriously challenged. Most pressure-treated wood contains the toxic pesticide chromated copper arsenate (CCA) to deter decay and insects. But the Environmental Protection Agency (EPA) and public health advocates have grown increasingly concerned about CCA in light of two studies on arsenic exposure in humans. The first, conducted by the National Academy of Sciences’ National Research Council on arsenic in drinking water, concludes that long-term exposure to arsenic in drinking water translates into an increased risk of lung and bladder cancer. The second study, released in mid-November, says that arsenic-treated lumber exposes people to 25 times the arsenic levels known to increase lung and bladder cancers from drinking water. The Bush administration recently embraced more stringent arsenic standards for drinking water, and two government agencies are currently reviewing the risks posed by arsenic-treated wood.
“You don’t want to install CCA piles today,” says Roberto Lopez-Anido, professor of civil engineering at the University of Maine. In addition to CCA’s toxicity, Lopez says the pilings are not resistant to marine borers. “So the only solution today is not a good solution,” says Lopez.
Though few look back with nostalgia to the days of polluted harbors, the filthy water made harbors virtually uninhabitable for most forms of native marine life. It certainly rendered species like clams, lobsters, or fish inedible. But at least the wooden piers were safe from the gribbles.
Absent the toxic stew of untreated industrial runoff, harbors are finally safe again for marine pests that have been missing for hundreds of years. Limnoria lignorum, alias the gribble, is just one example of a pest that has returned to torment our marine infrastructure. Gribbles resemble an ordinary wood louse, 6 mm in length with seven pairs of legs and four pairs of mouthparts. Like Teredo shipworms, they feed aggressively on wooden pilings. Wood that is not penetrated by a preservative is consumed, turning pilings into little more than hollow wooden cylinders unable to support weight.
The return of Teredo and Limnoria to Maine harbors has waterfront managers scrambling to find new ways of dealing with a very old problem. The development of new resins and composite materials suitable for use in marine applications may one day present an environmentally sound solution, and that day not be far off.
Recently Lopez inspected five piers in Portland harbor and documented visible damage in over 50 pilings from Limnoria. Lopez is currently testing the viability of using composites to repair pilings in place, thereby eliminating the costly requirement of removing pier decking to remove old pilings and install new ones.
Lopez’s experiment involves wrapping pilings in multiple layers of strong composite sheathing, then pumping the void full of either concrete or polyurethane grout. The work is still in the preliminary phase, and Lopez hasn’t tried it in a real world application. But he is hopeful that by May the results will be positive. “Our hypothesis is that marine borer damage is a problem and there is no good solution to it. So we first want to prove that this method is sound from an engineering basis, to make sure it will pass all tests of strength, UV resistance, and test the properties of the two grout systems.”
He also wants to determine if his solution is economically viable. Though it may be more cost efficient to repair pilings in place than to replace them, he is coordinating with the University’s business school to study whether the product has economic potential. And if piling replacement does prove the only remedy, a piling constructed completely from composite materials is probably no more than two years off.
The race is on
The economic ramifications of the successful application of composites in commercial and industrial settings are enormous. The Advanced Structures and Composites Laboratory is collaborating with the state Department of Transportation to use composite material similar in concept to the Milbridge pier on roadway bridges. They are also working on a federal highway project to develop national design specifications for use of composite materials, and a chapter in the federal bridge code that will allow use of these materials in federal projects.
While the basic filler material — sawdust or natural fibers — makes up 60 or 70 per cent of the volume of composites, other factors such as resins and their properties play a major part in the performance of the end product. The race is on to develop the cheapest material with the best properties that can be extruded most efficiently. Some very large companies — BP Amoco and Dow Chemical, for example — come calling in Orono when they want to run trials of their experimental materials. “We’re the leader in composite technologies in the world, and the only lab in the country that has this extruder,” says the lab’s director Habib.
Whether composites are used in pilings, railings, shortspan beams, bulkheads, walls, decking or larger structural components, the success of these resins is poised to change modern construction. Every waterfront stands to gain.