A new, patent-pending construction technology that can be used to build blast-resistant structures and retrofit existing structures more easily and cost-effectively has resulted from a joint development effort by The Sherwin-Williams Co; B & H Coatings, Inc.; Teijin Twaron USA, Inc, and TechFab LLC. The technology, which is nearly ready for commercialization, involves the use of prefabricated reinforced polyurea panels that elongate and stretch, acting as a safety net to contain blast pressure and flying debris. It has potential importance in defending against terrorism both in the U.S. and abroad.
"The concept is to catch the explosive force on the inner side of the structure, and to protect life within against flying debris and collateral damage," said John Durig, director, Sherwin-Williams General Polymers business unit, speaking on behalf of the consortium involved in the development effort. "We fully expect the technology to be useful for the protection of embassies, military installations, waterworks, nuclear plants -- any place that might be subject to a terrorist attack." The Israeli government and Turkish military already have expressed interest, he said.
Blast-Resistant Panel Technology
According to Durig, the technology is similar to that used in the post-9/11 reconstruction of government buildings. However, additional benefits are provided by prefabricated reinforced polyurea panels because they require less material, are easier to install, and are less expensive to use. "Blast-resistant panels allow the coating -- the critical element for blast-resistance -- to be shop-applied rather than sprayed-in-place," Durig said. "The technology also may contribute to preventing progressive collapse.
"Spraying polyurea at the construction site results in potential quality control problems and requires the use of expensive application equipment, specially trained applicators, ventilation, isolation of the installation areas, respiratory equipment for applicators, and protection of the surrounding areas from overspray. The use of panels eliminates these issues," Durig said.
The prefabricated panels are quality tested in-shop and delivered to the job site ready for installation, where they are applied with mechanical fasteners inserted through predrilled holes in steel reinforcing strips. "Blast-resistant panels can be applied in the presence of other trades, making construction scheduling much easier," Durig said, "especially since panel installation requires minimal training -- only a power drill, some screws, and a few strips of metal."
Blast Testing
Sherwin-Williams signed an agreement last August with the U.S. Dept of Defense to conduct blast testing. In three sets of tests begun in February by the U.S. Army Aberdeen Test Center at the
Dept of Defense's Aberdeen Proving Ground in Hartford County, MD, three panel variations were demonstrated to withstand blasts created by 70 lb of C-4 explosives at a distance of 30 ft, while the control wall was reduced to rubble. The videotaped tests show the test-structure walls remained standing after the blasts. A third round of blast testing is planned. The technology was also proven to meet ASTM E-84 requirements for a Class A fire-rating.
Tests conducted by the inventor, Bruce S. Hall of B & H Coatings, Inc, showed the panels also demonstrate ballistic performance. When fired upon with 12 rounds of 230-grain armor-piercing shells through a .45-caliber pistol at 20 and 40 ft, no shells penetrated the panel system.
Tests on polyurea coatings performed in the late 1990s under the direction of Los Alamos Technical Associates, Inc, of Richland, WA, demonstrate that nuclear contamination can be mitigated with a single water rinse, and that the polyurea coating is radiation resistant. "This may be extremely significant in the event of a 'dirty bomb' attack," Durig said, "because cleanup will inevitably require decontamination. Additionally, the panels may assist in containing the spread of radioactivity."
Panel Construction
Polyurea coatings are a class of fast-cure, waterproof coatings that are resistant to many chemicals. According to Durig, the particular polyurea elastomer used in the technology is unique because of its balanced elongation, flexibility, and tensile strength properties, which allow the coating to expand and stretch like a balloon that will not break, even when subjected to high levels of blast pressure and flying debris. Sherwin-Williams, based in Cleveland, through its General Polymers business unit in Cincinnati, provides the polyurea coating used in the panels.
In the three variations of panels tested, three different fibers were used to create a non-woven grid manufactured by TechFab LLC. The fibers used were Twaron® high modulus para aramid; a higher strength, higher elongation Technora® para aramid copolymer; and a Technora para aramid copolymer/polyester fiber hybrid, each layered between two 90 mil layers of polyurea.
"Para aramid fibers are commonly used in protective vests and other body armor," Durig said. "The total thickness of the fiber-coating combination is less than ¼-inch, and all variations performed equally well in Army testing."
Next Steps
The companies involved are moving quickly to commercialize the technology and to make engineering firms, military and government specifiers aware of the breakthrough. Sherwin-Williams will take the lead in bringing the technology to market.
