Patent Application
20140212647
The present invention relates to systems and methods for repair of concrete-based systems, and more particularly, to systems and methods that can be applied to repair and renew sewers, manholes and the like.
Afflicted by pipe failures, sewer backups and sewage spills, America's wastewater infrastructure is clearly showing its age. Most municipal systems are 75 to 100 years old, and nearly all are compromised to some degree by corrosion, overburdening and structural fatigue. Even as these existing systems are deteriorating, population demands are pressing upon cities to expand their wastewater collection capabilities.
More and more municipalities are addressing this growing health and environmental challenge by paying increased attention to rehabilitating corroded manholes. By most industry estimates, leaking manholes account for an estimated 20% to 30% of the unnecessary groundwater infiltration and inflow that overtax and threaten the sanitary sewage system.
A primary cause of corrosion in municipal sewer environments is MIC, or Microbiologically Induced Corrosion. MIC occurs when bacteria of the genus Thiobacillus, “concrete eating bacteria”, oxidize sulfur from hydrogen sulfide, “sewer gas”, and produce sulfuric acid as a by-product. Sulfuric acid is highly corrosive to concrete, steel and non-ferrous metals. When concentrated and heated by summer temperatures, it is extremely damaging to the concrete and non-ferrous metals used in most wastewater structures.
Construction materials in such environments quickly lose their ability to support loads, maintain their shape, transport liquids and function as designed. Manholes may be among the toughest environments encountered. Manhole restoration can take several forms. For many years, manhole rehabilitation consisted mainly of spot repair or patching, typically offering only a temporary solution to the inevitable acid attack.
Since the cost of repairing the components is typically much less than the cost of replacement, many techniques have been developed to repair and rehabilitate waste water system components. Conventional spray-applied epoxy, acrylic or polyurethane liners are known, as is the use of resin impregnated substrates, such as felt. The current spray-applied systems suffer from various issues, such as moisture, delamination, shrinkage and structural weakness problems resulting from the typical environment encountered in the repair operation.
The conventional systems often do not achieve good bonding to the manhole substrate. The conventional systems often do not purge the concrete for correct substrate preparation.
As can be seen, there is a need for an improved complete manhole repair system that repair damaged sewer manholes.
In one aspect of the present invention, a coating system for a concrete or brick surface comprises a surface preparation material applied to the concrete or brick surface; a primer layer applied to a surface prepared concrete or brick surface; a foam layer applied to the primer layer; and a polyurea layer applied to the foam layer.
In another aspect of the present invention, a repair system for an existing concrete or brick surface comprises a purge treatment applied to the concrete or brick surface; a primer layer applied to a surface prepared concrete or brick surface to a thickness from about 3 to about 5 mils; a foam layer applied to the primer layer to a thickness from about 1 inch to about 3 inches; and a polyurea layer applied to the foam layer to a thickness from about 50 to about 80 mils.
In a further aspect of the present invention, a method for repairing manholes comprises applying purge treatment to a concrete or brick surface of the manhole; applying a primer layer to a surface prepared concrete or brick surface; applying a foam layer to the primer layer; and applying a polyurea layer to the foam layer to an exterior thickness from about 50 to about 80 mils.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Broadly, an embodiment of the present invention provides a complete system and method for the repair and sealing of a sewer manhole. The process of the present invention includes surface preparation with steps to purge out embedded contaminants, application of a primer to the prepared and purged surface, application of a closed cell foam layer over the primer layer, and application of polyurea layer disposed on the foam layer. By first making sure the concrete is purged of contaminants, the system, when applied, cannot be damaged by the outgassing of contaminants from the coated concrete as may be possible with conventional systems. Moreover, the system of the present invention uses a 100% polyurea coating that provides appropriate flexibility, strength, and chemical resistance.
Referring now to
The system of the present invention, as described below, can be applied to either a new concrete/brick surface 22 or an old concrete/brick surface 20.
For a new concrete/block surface system 38, as shown in
For an old concrete/bock surface system 40, as shown in
Typically, the Nukote HPT is sprayed over all areas of concrete to be coated. A user can wait about 24 hours after application and contamination can be removed by hydro blasting, abrasive blasting, grinding or the like, until all particles that are visual are removed. This step can be repeated as needed before moving onto the next step.
Once the surface is prepared, either with Nukote HPT for the old concrete/brick surface 20 or with Nukote HLT for the new concrete/brick surface 22, a primer layer 28 can be applied over the surface 20, 22. The primer can be a two component, 1:1 ratio, rapid setting, non-sag, liquid applied, aromatic urethane polyurea primer having 100% solids. The primer can be, for example, Nukote EP Prime II primer, manufactured by Nukote Coating Systems. The primer layer 28 can be applied at a thickness from about 3 to about 5 mils.
A rigid closed cell foam layer 30 can be applied over the primer layer 28. This layer 30 is optional and can be applied depending on the amount of wall degradation or loss of the manhole, for example. The foam layer 30 can be made with various foams having, for example, a density of about three pounds. The foam layer 30 can be made with Nukote SPU foam, manufactured by Nukote Coating Systems, for example. The foam layer 30 can be applied in a thickness from about 1 inch to about 3 inches. In some embodiments, an epoxy grout can be used in place of the foam layer 30. The foam layer 30 can chemically bond to the primer layer 28.
A polyurea layer 34 can be applied over the foam layer 30 (or over the primer layer when the foam layer is not present). In some embodiments, a polyurea base coat layer 32 can be applied between the foam layer 30 and the polyurea layer 34. The polyurea layer 34 and the base coat layer 32 can be made from Nukote ST, manufactured by Nukote Coating Systems. Nukote ST is a 100% solids, spray applied, rapid curing polyurea. When present, the polyurea base coat layer 32 can be from about 20 to about 30 mils in thickness and the polyurea layer 34 can be from about 30 to about 50 mils in thickness. When the polyurea base coat layer 32 is not present, the polyurea layer 34 can be from about 50 to about 80 mils in thickness.
The polyurea coating is a highly elastic, waterproof coating that is resistant to chemicals and abrasion. The polyurea coating is fast to cure, has no VOCs and no odor. When coated with polyurea, concrete and steel substances can be submerged, buried and driven upon in just minutes. This fast reaction time is particularly appealing in municipal wastewater rehabilitation because it permits quick installation and a nearly immediate return to service.
Because of their elasticity, polyurea is ideal for concrete-dominated structures such as manholes, which tend to crack. These coatings have the ability to stretch and bridge gaps up to ⅛ inch. Polyurea coatings are not limited by extremes of temperatures and can maintain their flexibility as the substrate expands or contracts. The coating's elongation characteristics serve municipalities especially well that experience severe freeze/thaw cycles or frequent ground movement.
Polyurea coatings can be applied from 10 mils to 125 mils (⅛ inch) in one coat. Because only a single coat of these high build materials is required, labor and rental costs for scaffolding and other equipment can be reduced. The coatings also offer excellent adhesion. They are regularly tested at up to 2000 psi, compared with conventional epoxy coatings at 600 to 800 psi. Polyurea systems can cure under conditions of high moisture and humidity when the surface is properly prepared and primed with a penetrating, moisture-tolerant primer. In addition, because these coatings can be cured under cold and hot conditions (from −20° F. to above 350° F.), they can be applied throughout the entire year.
In some embodiments, the various layers can be color coded to assure that each subsequent coat completely hides the prior layer.
While the above description focuses on using the system and methods of the present invention on manholes, embodiments of the present invention can be used in various other areas, including wet wells, lift stations, dewatering buildings, odor control buildings, and the like.
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
