This invention relates to a clear polymeric coating that can, be applied to elements of infrastructure substrate, such as building foundations made of steel, stone, concrete or other structural materials, and bridge structural elements made of concrete, steel, or other structural materials, to protect the surface of those substrates and to provide the ability to visually inspect the physical condition of the substrates.
Destructive forces are increasingly affecting the integrity of elements of civil engineered and architecural infrastructure, such as building foundations, bridge support columns, utility towers, culverts and the like. Damage and destruction from causes such as weather and its remediation, age, normal wear and tear, seismic events, malicious or military explosive detonations, and vehicle collisions can diminish the strength of such infrastructure elements. Degradation of weakened and deteriorating structures, especially those of cured solid construction material such as concrete and cement, is often manifest as spalling, in which surface cracks appear and propagate and the surface layers chip and flake off.
A traditional method of protecting, against deterioration is to coat the completed surface with a thin layer of a coating material. Conventional coating materials typically are opaque. Although the coating may be less than ten mils thick for paints and as much as 120 mils thick for polyurea coatings, rust, cracks and chips in the substrates cannot be observed by visual inspection because of coating opacity. Testing for structural defects thus requires application of expensive, technologically sophisiticated analytical instrumentation. A transparent protective coating applied to structural surfaces would reduce the need for such instrumentation by enabling visual inspection for for surface defects developing beneath the coating surface. The transparent polymer of the invention enables such visual inspection of the substrate surface.
Moreover, while concrete, as a construction material, has excellent compressive strength, tensile strength is low, which explains one reason concrete typically is reinforced. Reinforcement often is installed in cage-like arrangements to help compromised structures maintain more of their load bearing capacity than they would if the pieces of cracked concrete were to fall away from the structure.
The surface coating of the present invention supplements traditional concrete reinforcement by adding a small, yet helpful, enhancement to the tensile strength of the concrete. In addition, even when spalling and other deterioration occurs, a portion of the strength of the infrastructure element can be maintained if the compromised pieces of the structure remain a part of the structural unit. A resilient, high-tensile strength exterior coating can provide another element that increases the overall resistance of the structure to failure.
Provided herein is a transparent polymeric composition that can be applied as a coating onto the surface of a substrate. The substrate may comprise or consist of metal, wood, stone, concrete or other structural materials utilized as supports for buildings, bridges, tunnels, piping (above or below grade), storage tanks, chemical emission stacks, material silos, dams, retaining walls, and the like. The clear coating can protect the substrate and its coated surface from environmental insult, including degradation from dirt, pollution and weather. The coating also possesses elastomeric properties that allow the coating to deform with the substrate structure. The coating therefore provides a resilient, high tensile strength reinforcement to substrates used in infrastructure elements, particularly those elements comprising concrete. Because the coating is clear, the coating features the ability to view surface defects in the underlying substrate to facilitate straightforward visual inspection.
As used herein, “transparent” or “clear” refers to the property of the composite or composition material wherein an object can be adequately visually viewed through the material for the purpose for which the viewing is intended. “Substrate” refers to any structural element, particularly an element that enables buildings and infrastructure to better withstand the forces that they were intended to withstand and resist. Such substrates especially include, although are not limited to, concrete, stone, steel, wood, plastic, glass, laminates and the like.
The polymer of the invention provides a visually transparent protective coating to new or existing structures that would benefit from the ability for persons, including those responsible for inspection of the structures, to visually observe or inspect the coated surface of the substrate of the structure through the clear polymer. As used within the scope of the present invention, the structure comprises a substrate to which the visually clear protective polymer is applied. The structure may include, but is not limited to, a building, a foundation, a road, a bridge, pipe, a utility tower, and the like, or the structure may comprise a part of an assembly for which a freely suspended or fastened amount of cured polymer is incorporated, such as used in place of window glass, as a structural component, or as a safety shroud around equipment that requires visual observation of a function of operation requiring protection for the observer from that function of operation.
The polymer described disclosed herein is a polyaspartic polymer containing urea groups (—NCON—) within some or all repeating units of the polymer chain. Esters, ethers, amides and urethanes also may be present in the polymer chain. The polyaspartic polymer is typically produced by reaction of a diisocyanate with an amine functional polyaspartic acid ester.
A preferred polyaspartic polymer composition for use according to the invention is formed by reacting aliphatic polyisocyanate resin, including 1,6-hexamethylene diisocyanate, with an amine functional polyaspartic acid ester and a polycarbonate diol. Preferred amine functional polyaspartic acid esters are selected from the DESMOPHEN® NH family of products (Covestro, North America, Pittsburgh, Pa.). These include DESMOPHEN NH 1220, 1420, 1520, and 1521. Representative 1,6-hexamethylene diisocyanate includes DESMODUR® N 3200, N 3300 and N 3900 (Covestro, North America, Pittsburgh, Pa.). Examples of polycarbinate diols include DESMOPHEN C XP 2613 and 2716 (Covestro, North America, Pittsburgh, Pa.). In addition, the use of polysiloxane resins and hybrids can be incorporated to enhance certain physical properties. A preferred polyaspartic polymer composition for use in this invention utilizes the formulations of isocyanate and polyol components of Table I.
1= isocyanate to isocyanate-reactive material ratio = 1.09
2= Desmodur N3900
3= Desmophen NH 1420
4= Desmophen C XP 2716
As an aid to degassing the mixture, 0%-1.0% of a defoamer such as Byk 066N (Byk USA, Walingford, Conn.) may be added to the mixture. Additionally, 0%-3% acetone may be added to aid in degassing.
The preferred polyaspartic polymer was prepared as follows. All materials were maintained and mixed at about 70° F. The two non-isocyanate components, as well as any optional added defoamer and acetone, were mixed to form a homogenous blend. The isocyanate component was added to the container and agitation continued until a homogeneous mixture was achieved. The resulting mixture was degassed by placing in a vacuum chamber and vacuum was drawn to a pressure below 0.4 in Hg. Vacuum was maintained until essentially all entraped air had been removed from the mixture. This process also evaporated the majority of the acetone from the mixture. The uncured mixture in liquid form was coated onto the surface of a substrate. Coating can be accomplished by any conventional coating technique such as casting, pouring, brushing, transfer roll coating, spraying, doctoring and dip coating.
A preferred method of applying the polyaspartic acid polymer to a surface comprises the use of a plural component spray system, such as a Graco XP70 (Grace, Inc., Minneapolis, Minn.). Two-component spray applicators traditionally are used to apply two-component polyurethane foam or polyurea. Applying the present components to the use of two-component applicators, the homogenous blend comprising the non-isocyanate components is filled into one reservoir of the spray foam applicator system, while the isocyanate component is added to the second, separate reservoir of the system. The polymer is applied to a substrate by mixing the non-isocyanate component blend and the isocyanate component in the equipment mixing chamber just before application. In addition, a blocking agent, such as dimethylpyrazol (Wacker Chemie AG, Munich, Germany) can be used to inhibit the reaction between the isocyanate components and other reactive components, thereby allowing the mixture to be used as a single component coating. A single component coating can be sprayed with single component spray equipment, such as a Graco DH230 (Graco, Inc., Minneapolis, Minn.).
The polyaspartic polymer employed according to this invention provides exceptional clarity and also boosts the tensile performance of concrete, cement and stone to which it is applied.
In other preferred embodiments the polyaspartic polymer can be applied to fracturable substrates such as metal, wood, brick, masonry, concrete, cement, and glass. In such embodiment, the polymer system acts as an elastomeric polymer which envelopes the surface of the substrate. After fracture of such substrate due to earthquake, shock, impact, torsion, deterioration, friction, vibration, environmental degradation age and the like, the polyasrartic polymer can bind pieces of fractured surfaces to reduce crumbling and add structural reinforcement to a shattered structure of those fractured pieces. By holding pieces in place, the polyaspartic polymer can reduce dirt, dust and debris in the field near the site of fracture, and can provide additional residual strength to the structure.
This can be very helpful, for example, in the field of civil engineering where polymeric protection to concrete support structures for bridges and concrete building foundations is required. Commonly concrete structures are conventionally surveyed for damage by visual inspection. These structures are either uncoated or coated with conventional opaquely pigmented coatings. After fractures are detected, surface penetrating radar is used to further evaluate the nature of those fractures. Coating these structures with clear polyaspartic polymer according to this invention allows quicker surveying of these structures without resort to sophisticated, slow and expensive analytical instruments. Preferably, the thickness of the coating of polyaspartic polymer is substantially uniform over the surface area of the structure. The thickness should be at least about 10 mils, and preferably at least about 20 mils. The maximum thickness is usually determined by the cost of material utilized. The thickness should be at most about 500 mils, preferably at most about 400 mils, more preferably at most about 200 mils, and most preferably at most 150 mils.
The preferred polyaspartic polymer was prepared as follows. All materials were maintained and mixed at about 70° F. The two non-isocyanate reactants, as well as any added defoamer and acetone, were mixed well to form a homogenous blend. The isocyanate component was added to the container and agitation continued until a homogeneous mixture was achieved. The resulting mixture was degassed in a vacuum chamber at a pressure below 0.4 in Hg. Vacuum was maintained until most entraped air had been removed from the mixture. This process also evaporated the majority of the acetone from the mixture. The uncured mixture in liquid form was coated onto the surface of a substrate and allowed to cure.
Polyaspartic polymer compositions were prepared as described above using material compositions as formulated in Table II below. The compositions were formed into sheets from which samples were cut using ASTM standard D412 die C. The resulting samples were tested according to ASTM standard test D412. Results are described below and presented in Table II.
1equivalent weight %
2percent of total isocyanate and reactant mass
The demonstrated maximum strength of only 2600 psi is insufficient carry a significant tensile, load prior to failing.
Although specific forms of the invention have been selected in the preceding disclosure for illustration in specific terms for the purpose of describing these forms of the invention fully and amply for one of average skill in the pertinent art, it should be understood that various substitutions and modifications which bring about substantially equivalent or superior results and/or performance are deemed to be within the scope of the following claims.
This application claims benefit to U.S. provisional application 62/114,532, filed Feb. 10, 2015, which, is incorporated herein by reference.
Number | Date | Country | |
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62114532 | Feb 2015 | US |