Experiments in Composite Bridges – Part 2
(This is Part 2 of a two-part article. Part 1 appeared last week.)
The deteriorating state of US bridges has been the subject of much attention. Countless, near- hysterical stories in the news media over the past decade or so have struck fear into the hearts of everyday Americans because such a huge percentage of our bridges are rated “structurally deficient” or “functionally obsolete.” (BTW, these are both defined terms in the bridge inspection business, and neither of them means what they sound like to the layman. Neither of them means the bridge is unsafe or is going to collapse any moment, although the media, who are as ignorant of the true definitions of these terms as the rest of the lay public, often make it sound like disaster is imminent.)
The main locus of most bridge deterioration is the deck. Usually made of concrete, the deck is exposed to the weather, and often gets covered with salt or de-icing chemicals during the cold months. When the salt gets dissolved in melting ice, is can seep into cracks in the concrete and cause rapid corrosion of the steel reinforcement in the concrete. The rust that forms occupies more volume than the steel that preceded it, and this expansion cracks the concrete, allowing more water infiltration, more corrosion, and on and on.
The search for a better bridge deck has been a major preoccupation of state and federal department’s of transportation for the past couple of decades. As mentioned in Part 1 of this article last week, there was a significant amount of experimentation with glass fiber composite bridges and bridge decks in the 90’s and early 2000s. Since these composites are not subject to corrosion, and show generally excellent weather resistance if they are properly protected from ultraviolet light, FRP was a natural avenue of investigation.
Both the bridges described last week were made by Hardcore Composites of New Castle, DE. The “hard core” in the refers to the common technology of the two bridges: the use of composite-wrapped foam cells as the core of a sandwich panel. The size of the cells varied depending on the span (and therefore the thickness) of the bridge, but the concept was the same.
For the Iowa bridge, (of which there is a more detailed description available) the foam cores are described as “bottles” presumably meaning that they are hollow inside. The bottles are rectangular blocks, 8” x 16” x 36”, with the 36” dimension oriented vertically in the bridge structure and comprising most of the depth of the bridge.
Each bottle was wrapped in a single ply of e-glass and infused with vinyl ester resin. This made them hard, as opposed to unwrapped foam that would be considerably softer.
The bottles – 600 of them for the Iowa bridge – were then all stacked in a tight configuration, and joined by FRP skins across the top and bottom. Each skin consisted of seven plies of e-glass composite. Special variations in the bottles were made at the locations of the lifting lugs and at the holes provided for fastening rods that joined the two panels together. A wear surface was added to the top skin over the seven plies of composite. In New York, it was 10mm of polymer concrete. In Iowa, it consisted of a 3/8” layer of abrasive epoxy.
In the case of the Iowa bridge, this arrangement weighed about 17,000 lbs. for each panel, or 34,000 for the entire bridge. It was about 35% of the weight of the steel temp bridges it was replacing. Both bridges were able to handle not only car traffic, but fully-loaded dual axle dump trucks. One such test documented the weight of the truck at 52,000 lbs, or roughly three times the weight of the panel that was supporting it.
Both were put into real-world traffic service, although one, only very briefly. As mentioned last week, it is unclear what ultimately happened to either of the bridges. The Iowa bridge was removed shortly after installation due to damage and delamination. The New York bridge apparently was in service from 1998 to 2012, but I have found no record of it after that.
The fate of Hardcore Composites is something of a cipher, too. Hardcore was owned by Master Builders Inc., which became SKW-MBT. An investor group led by Zoltek acquired 30% of Hardcore in 2000, with an option to buy the rest within two years. It is unclear if that option was exercised, but Zoltek was still involved with Hardcore as of 2004. A description of the company dating from about 2000 indicates that they had supplied ten FRP bridges to various DOTs. Hardcore also supplied FRP decks for a number of bridges in Ohio. Hardcore filed for Chapter 11 bankruptcy in 2004, and actually supplied the Iowa project after that date, but I have been unable to find any later reference to the company. SKW-MBT was absorbed into BASF, and perhaps Hardcore went with it. But after 2004, the trail – at least on the internet – goes cold.
There are at least two important things that can be learned from these projects. The most impressive take-away is that composite materials can be used for extremely demanding structural applications. There is hardly anything in the built environment that gets as brutal wear as a bridge. A material that can stand up to that can work on buildings, as well. Composites have established themselves are suitable for decorative applications and non-structural cladding, but the bridge experience suggests that FRP can be both a finish material and the support for that finish.
The other significant lesson concerns the Company that made these two bridges, and its fate. Like many of the companies that are fabricating composites for architectural applications, they came into the construction world from an different industry. (A large proportion of the companies fabricating architectural composites today came from boat-building.) They knew their way around the materials, but they were unprepared for the customs and practices of the construction industry.
In a short article published in Composites World in October 2004, Hardcore president W. Scott Hemphill describes how the technology succeeded, but the company was done in by their unfamiliarity and unpreparedness for the economics and pace of construction.
“Securing performance bonds and excessive amounts of insurance coverage strained not only our budgets, but also our internal resources. We soon found that months and, sometimes, years of delay between project initiation and actual delivery (and subsequent payment) was the norm, not the exception. Our best planning and budgeting fell short when applied to a process that includes “pay when paid” clauses, ten percent retainages and 90- to 120-day payments.
Although we successfully completed all our projects, including the largest use of composites in civil infrastructure to date (the wind fairings on New York City’s Bronx-Whitestone Bridge), these external factors steadily and ruthlessly wore away at us until we were forced to seek Chapter 11 bankruptcy protection. It is easy, especially for our competitors and those directly affected by this action, to blame our problems on poor management and business practices. And ultimately, they are correct. By not fully understanding the arena that we would be doing business in, we were unprepared for the toll it would take on all our resources, especially financially. I proffer this not as an excuse, but as a lesson for our brethren in the composites industry.”
(Images sourced as noted)