Waterproofed tanks left standing after Japan’s catastrophic 2011 earthquake and tsunami have inspired Japanese researchers to develop a new coating that may protect other concrete structures hit by similar forces.
|Thousands of roads and other infrastructure were destroyed in Japan's earthquake and tsunami.|
A thin layer of the new spray-on plasticizing polyurea coating may help infrastructure and architectural structures retain their integrity even when jolted by natural forces, according to the developers.
The National Defense Academy of Japan, the Shimizu Corp., and Mitsui Kagaku Sanshi Co. Ltd. report that they have arrived at “commercial viability” of the coating as an effective reinforcement method for concrete.
The coating is being tested at the National Defense Academy, a four-year university-level military academy in Yokosuka, Kanagawa. Shimizu is a Tokyo-based general contractor with 11,137 employees. Tokyo-based Mitsui Kagaku Sanshi Co. is involved in the home and garden business, according to an online business report.
What’s at Stake
Identifying technologies to strengthen structures is a grave priority in Japan.
The 9.0-magnitude Great East Japan Earthquake and subsequent tsunami and landslides of March 2011 killed some 20,000 people. Most were tsunami victims.
Thousands of roads, bridges, dikes, railway structures, power plants and other infrastructure were damaged or destroyed in the disasters, as were more than a million homes.
The events destroyed the power grid in large areas of Northern Japan and laid waste to the primary and backup systems for controlling and cooling the reactors at the Fukushima Dai-Ichi Nuclear Power Station, leading to explosions, fires and significant releases of radioactive debris into the atmosphere.
Dylan McCord / U.S. Navy
Emergency vehicles cross the wreckage left by the Great East Japan Earthquake and tsunami. More than 1 million structures were affected.
One year after the disaster, still-incomplete damage reports put the direct and indirect economic losses at about $500 billion.
The polyurea plastic in development is formed by spraying an instantaneous mixture of petroleum and nitrogen compounds—a formula previously recognized for its absence of toxicity and its resistance to weather, UV-light and acidic/alkaline environments, among other characteristics, the researchers say.
Such formulations have previously been used for waterproofing and providing corrosion protection to structures, the developers say.
However, they also report that the coating offers remarkable resilience, allowing it to recover its original shape without fracturing, even after stretching to 200 percent of its original dimensions.
“Only now has this key characteristic drawn attention,” the developers said in a release.
From Trout to Testing
The companies said they realized polyurea’s “full potential” upon observing the waterproofed tanks coated with polyurea at a trout farm.
“These tanks remained miraculously intact even after being hit by the tsunami caused by the Great East Japan Earthquake,” the companies said.
“Field surveys indicated these tanks suffered no damage, despite clear evidence of being hit by three-meter-high tsunami waves laden with various objects such as trucks and boulders, while all other tanks and structures at the site were completely destroyed.”
Those observations prompted the companies to test the notion that a polyurea coating might effectively constrain and reinforce a variety of concrete structures.
Load and Impact Tests
In loading and impact tests carried out at the National Defense Academy, the organizations assessed two groups of reinforced concrete members, all measuring 1200 millimeters (mm) in length, 100 mm in width, and 120 mm in depth.
One group was left uncoated; the other was coated with a 2 mm layer of polyurea.
Cracks appeared in both groups when deflected by roughly 5 mm at the center, according to the companies. The cracks in the uncoated members expanded when the amount of deflection exceeded 40 mm, effectively destroying the member.
However, concrete members coated with polyurea remained intact, even when deflections approached 80 mm, the limit imposed by the test equipment. These members remained flexible under the load, like rubber, capable of withstanding loads that would destroy ordinary reinforced concrete.
“Remarkably, these members remained functional and intact, even though the concrete within the coating had shattered. Our study showed that the coating hardens rapidly—in 30 seconds—and that reinforcing effects materialize in 30 minutes,” the companies say.
The organizations are now looking to develop practical applications for the coating technology.
They say that using polyurea has the potential to halve the cost and slash the work time involved in reinforcing and repairing civil structures, while reducing the human and property loss of future disasters.
The developers say they will “continue to collect the data necessary to apply these findings to structures and designs, with the goal of establishing applicable and effective design methods at the earliest possible date.”