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Sewer Infrastructure Rehabilitation. Kevin Morris Market Director Water & Wastewater. Learning Objectives. Causes of Deterioration of Concrete in Municipal Infrastructure Stopping Inflow & Infiltration Structural Rehabilitation Materials Chemical Resistant Coatings and Linings.
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Sewer Infrastructure Rehabilitation Kevin Morris Market Director Water & Wastewater
Learning Objectives • Causes of Deterioration of Concrete in Municipal Infrastructure • Stopping Inflow & Infiltration • Structural Rehabilitation Materials • Chemical Resistant Coatings and Linings
Causes of Deterioration • Structural Fatigue • Corrosive Gases • Microbial Induced Corrosion (MIC) • Old Age
Causes of Deterioration Structural Fatigue • Caused by: • Traffic Loading • Freeze/Thaw Cycling • Soil Movement • Erosion or Cavitation
Causes of Deterioration Corrosive Gases • Hydrogen Sulfide – H2S • Corrosive to metal and concrete • Reduces the pH level • Converts to sulfuric acid when it comes in contact with Sulfur Reducing Bacteria (SRB’s)
Causes of Deterioration Corrosive Gases • Carbon Dioxide • Slow deterioration of the substrate • Naturally occurring • Acts to reduce pH of the substrate • Carbonated concrete
Causes of Deterioration Microbial Induced Corrosion (Four Phases) • Phase 1 • Sulfur reducing bacteria (SRB) break down sulfates in the waste stream and produce hydrogen sulfide (H2 S) and carbon dioxide CO2.
Causes of Deterioration Microbial Induced Corrosion • Phase 2 • The acidic gases H2S and CO2 act to reduce the pH of concrete from approximately 12 to as low as 9. • Sulfur oxidizing bacteria (SOB’s) attach to the surface as sulfates are produced.
Causes of Deterioration Microbial Induced Corrosion • Phase 3 • The SOB’s are known as Thiobacillus Thioxidans. They consume H2S and discharge sulfuric acid H2SO4 • The pH continues to drop and microbial growth accelerates creating more H2SO4
Causes of Deterioration Microbial Induced Corrosion • Phase 4 – Final Phase • Acid attack of the concrete creates a layer of gypsum (calcium sulfate). As organisms reproduce additional acid is produced. • Eventual structural failure
Stopping Inflow & Infiltration • Purpose: • Lower the cost of wastewater being treated at the plant. • Lower the cost of equipment maintenance associated with abrasive soils in the waste stream. • Protect the environment for Sanitary Sewer Overflows (SSO’s) or Combined Sewer Overflows (Cso’s)
Stopping Inflow & Infiltration • Process • Treated through trenchless technology applications • Utilizing polyurethane grout injection
Stopping Inflow & Infiltration • Why should you use polyurethane grouts? • Lowest cost permanent repair procedure. • Little disruption to the community. • Grouting seals leaks and fills voids. • Can be performed in house or contracted out.
Stopping Inflow & Infiltration • Grouting is a Non Structural repair, if the manhole/pipe are in good sound condition grouting is all that is needed to seal leaks, fill voids, extend the structures life, lower repair costs. • Grouting, in many cases, may be needed to stop infiltration prior to the application of coatings and linings.
Stopping Inflow & Infiltration • Possible Applications • Leak Repairs • Manholes, Storm Sewers, Treatment Plant Tanks,Tunnels, Box Culverts, Dams, Seawalls & Pipe joints. • Stabilization • Manholes, Roadways, Seawalls , Pipe lines &Tank Slabs.
Stopping Inflow & Infiltration • Chemical Grouts are broken down into 4 basic categories. 1. Acrylamide 2. Acrylate 3. Acrylic 4. Polyurethane **Acrylamide and Acrylate grouts are the primary chemical grouts used for Mainline sewer grouting**
Stopping Inflow & Infiltration • Polyurethane Chemical Grouts are broken in to two categories. • 1. Hydrophobic • 2. Hydrophilic
Hydrophobic Resins Rigid and Flexible Resin + Catalyst Good Bond Repeals Water Low Shrinkage High Expansion Adjustable Set Times Foam Stopping Inflow & Infiltration Hydrophilic Resins • Flexible • Resin only • Great Bond • Absorbs Water • Medium to High Shrinkage • Medium Expansion • Foam or Gel
Typical Problems Here are four products designed to solve problems in Manholes: Polyurethane foam A flexible Polyurethane for cracks and pipe penetration. Hydrophobic: A Polyurethane capable of shutting off gushing leaks and f filling voids. Gel : A Polyurethane gel that will seal leaks and stop infiltration through the walls. OAKUM: A dry jute rope when soaked in Polyurethane is capable of filling large cracks. Grouting Leaks in main line pipes can easily be accomplished using Acrylates or Acrylamide grouts.
Using Oakum Apply Oakum in Joint Soak Oakum In Resin Dip Oakum with Resin in Water
Structural Rehabilitation Materials • Cementitious Repair Mortars • Portland Cement with Admixtures or Calcium Aluminates • Sprayed or trowel applied • New product mixes allow radial spray with no entry into manhole • Will degrade as the original surface did
Structural Rehabilitation Materials • Portland Cement • This is the most commonly used cement during the precasting and/or cast-in-place production of today’s wastewater components. • Relatively Inexpensive • Easily Located • Susceptible to MIC • Long cure times before topcoating
Structural Rehabilitation Materials • Microsilica Repair Mortars • Microsilica repair mortars utilize portland cement to create the cement paste but also contain a fumed silica admixture to create a more dense substrate. • Chemical Resistant / Lower Permeability • Can be used as a stand alone liner in a mild H2S environments. • Faster cure times for topcoating • Susceptible to MIC • Lower cost than Calcium Aluminate Mortars
Structural Rehabilitation Materials • Calcium Aluminate Repair Mortars • There are two common types of calcium aluminate mortar commercially available today. • Pure Calcium Aluminate Mortars • Where the aggregate is a coarsely ground version of the cement dust • Calcium Aluminate Mortars • Where the aggregate is silica sand
Structural Rehabilitation Materials • Calcium Aluminate Repair Mortars • Multiple manufacturers in the U.S. • The principle behind Calcium Aluminates is that they maintain a higher pH that prevents they colonization of the Thiobacillus bacteria. • The paste will erode exposing the chemically inert silica sand. Eventually the sand will fall out of the surface of the repair mortar*.
Structural Rehabilitation Materials • Calcium Aluminate Repair Mortars • Available from only 3 manufacturers in the U.S. • The principle behind Calcium Aluminates is that they maintain a higher pH that prevents they colonization of the Thiobacillus bacteria. • The paste will erode at the same rate as the aggregate*.
Structural Rehabilitation Materials • Pure or Fused Vs. Calcium Aluminate Mortars • In a test conducted in Germany to replicate an 8-year service life in a sewer system the weight loss difference between these 2 products was approximately 1%. Contributed to the previous statements marked with an*.
Structural Rehabilitation Materials • Calcium Aluminate Mortars • Offer an improved life cycle over other repair mortars • Fastest cure time for topcoating • Require humidity to properly cure • Susceptible to MIC but a reduced rate • Can be used as a stand alone liner in moderate H2S environments.
Chemical Resistant Coatings & Linings • Protect the surrounding environment • Provide a longer life cycle for the substrate they are protecting • Provide an excellent infiltration barrier • Available chemistries include: • Epoxy • Polyurethane • Polyurea
Chemical Resistant Coatings & Linings • Epoxy Coating and Linings • Epoxy coatings have been the industry standard since municipalities began lining manholes and provide performance properties that will satisfy the requirements of many rehabilitation projects. Epoxies are not the cure or fix for every situation and should be considered based on the structure, location, use, and environment during application.
Epoxy Coatings & Linings Cons • Rigid films • Subject to Blush • Exothermic Reaction could cause microfracturing Pros • Moisture tolerance • High film builds • High strength • Low/No Odor • Chemical Resistance • Variable formulations • Epoxy Resins • “Hot Pot” Spray • Plural Component Spray • Epoxy Mortars • Hand trowel • “Hot Pot” Spray
Chemical Resistant Coatings & Linings • Polyurethane Coating and Linings • Polyurethane chemistries have gained market acceptance over the last several years. This generic chemistry offers the greatest flexibility of formulation to fit the desired needs of the end user and excellent chemical resistance.
Polyurethane Coatings & Linings Cons • Do not tolerate moisture well during application or initial cure • Plural Component Spray • May require a primer Pros • Flexibility of formulation • Flexible • Rigid • Hand Applied Repair Grades • Improved elongation • Fast cure times • Abrasion Resistance • High film builds
Chemical Resistant Coatings & Linings • Polyurea Coating and Linings • Polyurea or Hybrid Polyurea chemistries are the newest technologies to have gained market acceptance. This technology may be one of the most difficult for an end user to evaluate due to the formulation variances. These variances can effect performance and chemical resistance.
Polyurea/Hybrid Polyurea Coatings & Linings Cons • Do not tolerate moisture well during application or initial cure • Plural Component direct impingement application • Chemical resistance • High tensile strength • Primer may be required Pros • Fast dry times • High film builds • Used for linings and chimney seals • Physical Toughness • Excellent Abrasion resistance • Elongation
Inspection and Holiday Inspection • Required to test liner for discontinuity • Moisture in substrate sufficient for reading • High Voltage – > 20.0 DFT • 100 volts per dry mil
Spark Testing Polyurethane Elastomer Installation For manhole rehab.
Summary • There are numerous products and methods available for the lining and rehabilitation of sewer infrastructure. • Physical performance characteristics vary greatlyacross the numerous chemistries. • Products should be selected based on the needs of the end user. • Uniform monolithic films aid in prevention of chemical attack.