Patent Application
20090249724
1. Field of the Invention
The present invention generally relates to blast mitigation systems, including construction materials, such as coatings for application in building construction, and the methods for applying these coatings.
2. Background of the Invention
Blast-resistant construction became a priority for federal structures following the bombing of the Murrah building in Oklahoma City in 1993. The attacks in the U.S. on Sep. 11, 2001 further emphasized the need for such improvements to many of the existing government and non-government structures.
The General Services Administration (“GSA”) manages federal properties and classifies threat levels of buildings based on their usage. Those structures having the highest threat level require use of “Class E” blast-resistant materials in their outer walls. The Pentagon is an example of a Class E-type structure. Many buildings are not considered to be as critical. Therefore, they have lesser requirements for blast resistance, for example, Class C-type structures. Most of the Class C-type structures are reinforced concrete frame with masonry in-fill walls.
The present invention provides a system to protect the interior of a structure from projectile debris, which harm occupants when an exterior wall fails catastrophically in an explosion. One object of the present invention is to provide a “blast mitigation coating” (BMC) System acting as a “blast curtain” to keep the debris from moving into the structure and controlling the collapse of the wall. It does not provide additional structural support to prevent the walls from collapsing. However, it protects the interior of the building from the flying debris. Another object of the present invention is to provide a BMC System comprising a polymer or polymer mixture and a glass-fiber reinforced fabrics for application to the construction structures. For the Class C-type structures, BMC System would be applied directly to the interior of the masonry and then covered by an architectural interior treatment.
These together with other objects and advantages, which will become subsequently apparent in the details of composition and application of the BMC System as more fully hereinafter described.
Although a limited number of preferred embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its scope to the details of composition and application of the BMC System set forth in the following description. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the preferred embodiments, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents, which operate in a similar manner to accomplish a similar purpose.
One embodiment of the BMC system consists of a two-component trowel-applied polymer coating and a glass-fiber reinforcing fabric as described below.
Composition of BMC System:
Component A (50% of total weight of the coating): An organic polymer compound, which includes a waterproof, flexible polymer, micro-fiber reinforcement, and specialized fillers to enhance high-build installations and adhesion to masonry substrates. A typical formula is shown in the following table (Table I).
Component B (50% of total weight of the coating): A blend of portland cement and dry additives, which when mixed with Component A, provides a flexible adherent membrane with high tensile bond strength and water impermeability. Typically, Component B is dry type I Portland cement meeting ASTM C 150 standard.
BMC Mesh: Glass-fiber reinforcing mesh with a polymer coating to promote bond and compatibility with construction materials. For example, the mesh has the following characteristics:
22 oz/yd2 (0.678 kg/m2);
Leno Weave; and
Warp Strands/inch 8.
Implementation of BMC System:
At first, Component A and Component B are mixed. Once mixed, the mixture has a working time of approximately one (1) hour at 70° F. (20° C.) and 50% RH (relative humidity).
The mixture is applied by spray or trowel directly to a clean surface of masonry to form a coating. Enough material is applied to completely embed the mesh to be placed. The work area is limited to that the mesh can be embedded before the coating begins to dry.
The BMC Mesh is embedded in the coating. A trowel is used to fully embed the mesh and ensure intimate contact of the mesh to the coating. The BMC Mesh can be embedded with long dimension either horizontally or vertically. Adjacent embedded meshes overlap by a minimum of 2.5 inches (63.5 mm) along the edge. The mesh is embedded in one direction until the full wall surface is covered.
A second layer of coating is applied to the surface to receive the mesh by spraying or troweling. Sufficient material is applied to fully embed the mesh and provide for the desired finish texture. A second layer of mesh installation may begin immediately upon completion of embedment of the first layer of mesh.
A second layer of BMC Mesh is embedded in the coating. A trowel is used to embed the mesh fully in the coating. A second layer of mesh is embedded with long dimension perpendicular to the long dimension of the first layer of mesh. Each run of mesh overlaps the adjacent embedded mesh by a minimum of 2.5 inches (63.5 mm) along the edge. The entire wall surface is covered. Any wrinkles or bulges will be worked out of the mesh such that it is fully bonded and covered by the coating.
If required, a trowel will be used to smooth the surface. A thin “sweet coat” ( 1/32 inch [0.8 mm]) of the coating may be applied to smooth localized surface irregularities.
Another embodiment of the BMC system consists of two products: a component in the form of a trowel-applied polymer coating and a glass-fiber reinforcing mesh.
Coating—A proprietary organic polymer compound, which includes a waterproof, flexible polymer, micro-fiber reinforcement, and specialized fillers to enhance high-build installations and adhesion to masonry substrates. A typical formula is shown in the following table (Table II).
BMC Mesh—Glass-fiber reinforcing mesh with a polymer coating to promote bond and compatibility with construction materials. For example, the mesh has the following characteristics:
20 oz/yd2 (0.678 kg/m2);
Leno Weave;
Warp Strands/inch 8;
Weft Strands/inch 3.
A minimum of two layers of meshes are used. The coating is applied first to the substrate in a thickness that will accept the mesh and provide enough thickness to encapsulate it. The mesh is pushed into the coating with a trowel and the coating that comes through the mesh is spread with the trowel to completely encapsulate the mesh. Additional coating (the same product) is applied to the surface and a second layer of mesh is installed in a similar manner to the first, except the long dimension of the mesh is run perpendicular to the orientation of the long dimension of the first layer. The mesh is pressed into the coating and the coating that comes through the mesh is spread across the top to completely encapsulate the mesh. If surface irregularities need to be addressed to provide a smooth, flat surface, additional coating may be applied in a thin layer with a trowel. The mesh width is approximately 38 inches. Each piece of mesh should overlap the adjacent parallel piece by a minimum of 2.5 inches.
The first layer of coating must completely cover the substrate area to receive the mesh before any additional mesh is placed. This assures that there is coating between the mesh and substrate at all points. The minimum wet thickness (measured with the mesh in place and troweled smooth) is 0.075 inches (75 mils or 1.9 mm) for each mesh application. The minimum total thickness for two layers of mesh is 0.15 inches (150 mils or 3.8 mm). Note that the thickness of the mesh may be used to gauge the application thickness. The mesh pattern may be visible, but the color of the mesh should not be visible.
The conventional method uses a solvent-based two-component urethane material that produces hazardous fumes, requires special mixing and spraying equipment, and requires significant disruption of in-service facilities due to the odor produced and environmental concerns. The coating system of the present invention is water-based and environmentally friendly. The odor is minimum and no special equipment is required. The improvement provides a better method that will not only achieve at least the existing level of performance, but also result in functional improvement of the building at significantly reduced material and labor costs.
The embodiments of the present invention have successfully passed testing where two coating and reinforcement systems were applied to the interior side of the exterior masonry walls to determine if either or both of the BMC Systems comply with the Class C blast resistance requirements.
The test was performed by constructing an unreinforced, ungrouted 8-inch CMU (Concret-Masonry-Unit) wall on a test structure with the BMC System of the present invention applied thereon. The test method is “Standard Test Method for Glazing and Glazing Systems Subject to Airblast Loadings”, which is a GSA adaptation of ASTMF1642-96 standard. A 600 lbs ammonium nitrate and fuel oil bomb 165 feet away from the wall was detonated. The testing was performed by a GSA approved blast consulting firm, Applied Research Associates, Inc. (ARA). Quoting from the ARA report: “No formal test procedure currently exists for walls of this type, therefore the procedure for this test followed the GSA standard test protocol used for the testing of window systems.”
More specifically, in the testing for the first embodiment of the present invention, BMC system of the first embodiment of the present invention was applied to the interior surface of the CMU wall. After the blast, there were small cracks between CMU blocks. There was no measurable post-test deformation resulting from the ISC Medium Level of Protection (GSA Level C) loads in the test. There was no evidence of wall fragments entering the occupied space. Therefore, this BMC system should be suitable for use on external windowless walls in facilities requiring ISC Medium Level of Protection (GSA Level C).
In the testing for the second embodiment of the present invention, BMC system of the second embodiment of the present invention was applied to the interior surface of the CMU wall. After the blast, there were small cracks CMU blocks. Two small pieces of mortars were removed from the exterior surface of the wall. There was no measurable post-test wall deformation resulting from the ISC Medium Level of Protection (GSA Level C) loads in the test. There was no evidence of wall fragments entering the occupied space. Therefore, this BMC system should be suitable for use on external windowless walls in facilities requiring ISC Medium Level of Protection (GSA Level C).
| Number | Date | Country | |
|---|---|---|---|
| 60613758 | Sep 2004 | US |
