sewer infrastructure rehabilitation

Sewer Infrastructure Rehabilitation

Kevin MorrisMarket Director Water & Wastewater

• Causes of Deterioration of Concrete in Municipal Infrastructure

• Stopping Inflow & Infiltration• Structural Rehabilitation

Materials• Chemical Resistant Coatings

and Linings

Learning Objectives

• 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


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)


Corrosive Gases• Carbon Dioxide– Slow deterioration of the

substrate– Naturally occurring– Acts to reduce pH of the

substrate– Carbonated concrete


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.


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.


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


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


• 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


• 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.


• 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.


• 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.


• 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 **Acrylamide and Acrylate grouts are the primary chemical grouts used forused forMainline sewer grouting**Mainline sewer grouting**

• Polyurethane Chemical Grouts are broken in to two categories.– 1. Hydrophobic– 2. Hydrophilic


Hydrophilic Resins• Flexible• Resin only• Great Bond• Absorbs Water• Medium to High

Shrinkage• Medium Expansion• Foam or Gel


Hydrophobic Resins• Rigid and Flexible• Resin + Catalyst• Good Bond• Repeals Water• Low Shrinkage• High Expansion• Adjustable Set Times• Foam

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

Soak OakumIn Resin

Dip Oakum withResin in Water

Apply Oakum in Joint

Insertion of Wall Spear

Insertion of Ports

Shutting Off High Flow Leaks

Complete encapsulation

• 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


• 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


• 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


• 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*.


• 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*.


• 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*.


• 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.


• 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

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

Cons• Rigid films• Subject to Blush• Exothermic Reaction

could cause microfracturing

• 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

Pros• Flexibility of

formulation– Flexible– Rigid– Hand Applied

Repair Grades• Improved elongation• Fast cure times• Abrasion Resistance• High film builds

Cons• Do not tolerate

moisture well during application or initial cure

• Plural Component Spray

• May require a primer

• 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

Pros• Fast dry times• High film builds• Used for linings and

chimney seals• Physical Toughness– Excellent Abrasion

resistance– Elongation

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

• Required to test liner for discontinuity

• Moisture in substrate sufficient for reading

• High Voltage – > 20.0 DFT • 100 volts per dry mil

Inspection and Holiday Inspection

Spark Testing

Polyurethane Elastomer Installation

For manhole rehab.

• There are numerous products and methods available for the lining and rehabilitation of sewer infrastructure.

• Physical performance characteristics vary greatly across the numerous chemistries.

• Products should be selected based on the needs of the end user.

• Uniform monolithic films aid in prevention of chemical attack.

Summary

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sewer infrastructure rehabilitation

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