03 September 2004
03 September 2004
A collaborative project produced new cost-effective blast resistant structures using pre-fabricated reinforced polyurea panels.
A joint development effort by The Sherwin-Williams Company; B & H Coatings, Inc.; Teijin Twaron USA, Inc. and TechFab LLC has resulted in a new, patent-pending construction technology that can be used to more easily and cost-effectively build blast-resistant structures, and retrofit existing structures, a potentially important development in defending against terrorism both in the U.S. and abroad.
The technology, which is nearly ready for commercialization, involves the use of pre-fabricated reinforced polyurea panels that elongate and stretch, acting as a safety net to contain blast pressure and flying debris.
John Durig, director, Sherwin-Williams General Polymers business unit, speaking on behalf of the consortium involved in the development effort, said, ""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. 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.
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 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. 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 pre-drilled 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 few strips of metal.""
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 fibres were used to create a non-woven grid manufactured by TechFab LLC. The fibres used were Twaron high modulus para aramid; a higher strength, higher elongation Technora para-aramid copolymer; and a Technora para-aramid copolymer/polyester fibre hybrid, each layered between two 90 mil layers of polyurea.
""Para-aramid fibres are commonly used in protective vests and other body armour,"" Durig said. ""The total thickness of the fibre-coating combination is less than 1/4-inch, and all variations performed equally well in Army testing.""
Sherwin-Williams signed an agreement last August with the U.S. Department of Defense to conduct blast testing. In three sets of tests begun in February by the U.S. Army Aberdeen Test Center at the Department of Defense's Aberdeen Proving Ground in Hartford County, MD, three panel variations were demonstrated to withstand blasts created by 70 pounds of C-4 explosives at a distance of 30 feet, 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 armour-piercing shells through a .45-caliber pistol at 20 and 40 feet, 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 clean-up will inevitably require decontamination. Additionally, the panels may assist in containing the spread of radioactivity.""
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.
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