A Global Need

In monitoring the conditions that lead to corrosion of steel-reinforced concrete, the ECi-2 addresses a multi-billion-dollar world-wide problem – and one that exacts a grim toll in human life.

iStock_000029182392_ExtraSmallThe estimated cost to repair reinforced concrete structures runs $200 per square meter of exposed surface. In the United States, the annual direct cost of corrosion in highway bridges alone is roughly $8.3 billion, including maintenance, repair, replacement, and the cost of capital. Indirect costs, including traffic delays and lost productivity, may run 10 times that number.

But corrosion is more than an economic issue. In June 1983, a 100-foot section dropped out of the Mianus River Bridge in Greenwich, Connecticut, U.S.A., killing three motorists and critically injuring three others. The steel pins that joined sections of the bridge had decayed. In May 2000, in Concord, North Carolina, U.S.A., more than 100 people were injured when steel strands corroded in a pre-stressed concrete pedestrian bridge and the structure collapsed onto the highway below.

eciRebarWhen a structure is first built, the concrete itself protects steel reinforcement by providing both a physical shield and an alkaline environment. This causes a passive film of iron oxide to form over the rebar, preventing further corrosion. Over time, however, chlorides from de-icing salts and sea water may permeate the concrete and depassivate the steel. They penetrate the iron oxide film, and set up corrosive electric circuits within the structure. Carbon dioxide also poses a threat, reducing concrete’s alkalinity and weakening its protection for embedded rebar.

Once corrosion begins, it’s self-sustaining. As steel rusts, its corrosion products occupy three to six times the volume of the original rebar. This stresses the concrete, generating cracks, delaminations, and spalls. These, in turn, provide new means for water and chlorides to reach the steel, which then corrodes even faster.

None of this is visible until late in the process, however, when cracks form. This is unfortunate, as visual inspection has long been the mainstay of structural maintenance. Supplementing the human eye, some maintenance engineers have cut concrete samples for analysis. But this is destructive and expensive, and it disrupts the use of a structure.

Historically, engineers have also installed analog probes into concrete. But these have generally measured only one or two factors in corrosion. This has limited their usefulness and reliability. Probes have also faced challenges in delivering data. Many require inspectors to tour a structure, plugging a reader into each probe by hand. Others transmit their readings to a datalogger. Because their signals are analog, however, they’re vulnerable to electro-magnetic interference. This has made it difficult for probes to transmit reliable data for more than 30 feet. Worse, it’s obliged structure owners to install a multi-thousand-dollar datalogger to receive the readings from each probe.

iStock_000025925511_ExtraSmallThe ECi-2 solves these problems. By contrast with prior generations of corrosion monitors, it measures five key factors in corrosion – open circuit potential, linear polarization resistance, resistivity, chlorides, and temperature. This reveals correlations among the causes and signs of corrosion, yielding a fuller, more certain picture of the threat.

The ECi-2 also integrates processing electronics with its sensors and electrodes. Consequently, it can transmit all readings digitally, protecting the integrity of these data and making it possible to connect numerous ECi-2 monitors to a single datalogger, hundreds of feet away. This can save tens of thousands of dollars in support electronics. It also helps protect the datalogger, which can now be housed in a more sheltered location.

From the datalogger, ECi-2 corrosion readings can be downloaded to a computer or transmitted to an office by wireless transceiver and cellular modem. Already digital, ECi-2 data can readily flow into a structural management system.

The ECi-2  generates a comprehensive, continuous stream of data on corrosion conditions, and transmits these remotely, economically, and on demand to the owners and managers of a structure. This makes it possible to anticipate problems, save money on maintenance, and prevent catastrophic failures. In all of these ways, the ECi-2 helps address a multi-billion-dollar world-wide problem.