Presentation on theme: "Kevin Morris Market Director of Water and Wastewater The Sherwin-Williams Company."— Presentation transcript:
Kevin Morris Market Director of Water and Wastewater The Sherwin-Williams Company
Maintenance Challenge for owners More corrosive than in the past
Maintenance Challenge for owners Residential expansion The economy Age of structures Collapsing infrastructure combine with reduced income has forced municipalities and private businesses to seek solutions that offer the greatest life cycle expectancies.
More corrosive than in the past Less water in waste stream Longer transport times Slower flows Possible introduction of industrial waste
MIC takes place in 4 phases 1. Sulfur reducing bacteria (SRB’s) break down sulfates in the waste stream and produce hydrogen sulfide gas (H₂S) and Carbon Dioxide (CO₂). 2. The acidic gases (H₂S and CO₂) reduce the pH of the concrete from 12 to as low as 9. Sulfur oxidizing bacteria (SOB’s) attach to the surface as sulfates are produced.
MIC takes place in 4 phases 3. The SOB’s (Thiobacillus thioxidans) consume the H₂S and elemental sulfur and discharge sulfuric acid (H₂SO₄). The pH of the substrate continues to drop, accelerating microbial growth. As the bacteria colonize, more concentrated pockets of H₂SO₄ are created. 4. The acid attacking the concrete creates a layer of gypsum (calcium sulfate) that eventually allows structural failure to occur.
Available in a variety of chemistries and formulations Vary in functional characteristics and application requirements May require ancillary work to be performed prior to coating application
Provide a protective barrier to isolate the substrate from its environment to prevent corrosion from taking place. High Performance Coatings and Linings Cementitious Linings Resinous Linings
Cementitious Linings that are typically used for these types of applications are classified into three generic chemistries Microsilica Mortars Calcium Aluminate Mortars Microsilica Mortars Containing MIC preventing additives
Typically Portland Cement with the addition of fumed silica additives to create a more dense and chemical resistant cement liner. This class of mortar linings can provide up to a 2 times life cycle improvement of the substrate when compared to standard portland-based cements.
Utilize calcium aluminate cement rather than portland cement. Calcium Aluminates maintain a higher pH level that is less affected by the corrosive gases in the sewer system. Higher pH limits the growth of SOB’s thereby prolonging the life of the structure up to 4 to 5 times longer that standard portland-based cements
These mortars are the same as the standard microsilica mortars but with the addition of an additive intended to kill or impede the growth of the bacteria. These additives work to pierce the exoskeleton of the bacteria to kill it or form a solution that prevents the growth of the bacteria on the surface of the lining.
There are many benefits derived from the use of cementitious linings. Cost Ease of Application Tolerance of Substrate and Cure Conditions These linings will corrode as the original substrate did but at a much reduced rate over portland cement. These linings will not provide long-term protection to: Infiltration Cracks Freeze/Thaw Cycling
Resinous Linings are typically categorized into the three generic chemistries Epoxy Liners Neat Epoxy Resin Fiber Reinforced Epoxies Epoxy Mortars Polyurethane and/or Hybrid Polyurea Liners Pure Polyurea Liners
“Work Horse “ Chemistry for years in the market place. Ideally suited for application in these environments Excellent broad spectrum chemical resistance Unaffected by dampness or humidity They cannot handle elongation or crack bridging. Multiple means of application Sprayed Troweled Spin Cast Used as saturates with geo-textile cloths High Film Build properties Typically 60 – 250 mils DFT
Have been slow to gain recognition in the industry Excellent physical toughness and elongation over epoxies Require moisture tolerate epoxy primers to adhere to saturated surface dry concrete Spray applied at typically 60 – 250 mils DFT Can be applied through sophisticated rotary spray equipment.
Have been slow to gain recognition in the industry Ultimate physical toughness and elongation over epoxies Require moisture tolerate epoxy primers to adhere to saturated surface dry concrete Lowest permeability and abrasion resistance rating for all of the generic chemistries. Spray applied at typically 60 – 250 mils DFT Should be applied through sophisticated rotary spray equipment for tight spaces such as manholes.
Intended to bond directly to the substrate to which they have been applied. Failures provide an indication of issues and/or concerns with many facets of the application: Surface Preparation Application Operating Conditions Failures can manifest themselves as cracking, delaminations and/or blisters
Intended to bond directly to the substrate to which they have been applied but can disbond from the substrate and remain freestanding within the structure to which they were applied. Excellent for providing barrier protection against the environment inside the manhole. Can allow issues to take place behind the disbonded liner that cannot be visible to the owner, such as: Water Infiltration Continued Substrate Corrosion
Commonly polyvinyl chloride (PVC) sheet materials Ideally suited for application in these environments Excellent broad spectrum chemical resistance They can handle elongation or crack bridging through proper design. Common Installation During the production of precast or cast-in-place concrete structures Embedding into a mastic resin during rehabilitation of a structure Heat welded seams Failures with these liners are commonly application related and most commonly associated with the heat welding process at the seams.
Commonly constructed of a geotextile, saturated with a resin and forced cured by a suitable means. They can provide structural properties. Cannot handle irregular designs of structures Wrinkles are common place in the chimney area Difficult to properly terminated with lateral services lines or other portrusions Provide structural properties to the host structure.
Water Infiltration Regardless of which coating is used, measures must be taken to prevent water infiltration before application. Water is best stopped using reactive polyurethane resins that are activated by: Ground Water Leaking into the structure “Twin Streamed” through an “F” pipe assembly with water These polyurethane resins are commonly referred to as chemical grouts and are available as: Hydrophilic – The love of water Hydrophobic – The fear of water
Hydrophilic Flexible Foam or Gel Medium Expansion High Shrinkage Potential to Freeze in deep frost zones Rigid or Flexible Foam only High Expansion Low Shrinkage Unaffected by freezing Hydrophobic
Our infrastructure is in varying states of disrepair. Funding for these protection or rehabilitation of these projects is not increasing. Owners are looking for the most cost effective means of increasing the life cycle of these critical structures. Corrosion resistant coatings and linings provide the benefit of increased lifecycle by isolating the substrate from the service environment in which it has been placed.
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