Lessons Learned in Coating Water and Wastewater Treatment Structures

Presented by: Randy Nixon Corrosion Probe, Inc. www.cpiengineering.com

Learning Outcomes:

• At the end of this webinar, you will be able to: • Explain real life common errors that occur with lining concrete wastewater substrates.

• Provide practical solutions of how to avoid premature failures.

Chronological Examination of Common “Errors” During a Typical Concrete Lining Project

1.Material Selection Phase 2.Surface Preparation Phase 3.Restoration/Resurface phase 4.Lining Application Phase 5.Testing and Repair Phase

Material Selection Phase

• Consider H 2 S, CO 2 , and Methane gas concentrations in headspace conditions.

• Consider pH of headspace surfaces based on pH measurements.

• Consider permeability resistance of conditioned coatings and linings – Swat Test.

Material Selection Phase

• Good film build properties required.

• Good abrasion resistance.

• Moisture tolerance during application and cure.

• Consider extent of cracking – reflective cracking problems – select flexible linings when cracking is extensive.

FAILURE ANALYSIS: REFLECTIVE CRACKING -1997 VIRGINIA • •

Epoxy lining (sprayed) installed in 1992 Rectangular sludge storage tank with vertical cracking every 8 to 10 feet

EXPERIENCE • • • • •

Reflective cracking is more prevalent in rectangular tanks than in round tanks.

Less through-wall vertical shrinkage cracks in round tanks.

Less movement in round tanks.

Shell-type structures like round tanks are much more rigid than rectangular structures.

Round and domed tanks are much more resistant to movement – fewer reflective cracks in rigid linings.

FACTORS AFFECTING REFLECTIVE CRACKING • • • •

Thermal disparity across walls or roof .

Flat roofs – more cracking than in domed roofs.

More cracks in outdoor tanks than indoors.

Below grade tanks have less reflective cracking – irrespective of geometry – due to lower Δt across walls.

LESSONS LEARNED • • •

Selection of flexible linings vs. non-flexible linings should be based on presence and frequency of through-section cracks.

Careful assessment of propensity for reflective cracking should be made.

If few through-wall cracks exist, localized treatment methods can be effective at those cracks.

Surface Preparation Phase

•Laitance not thoroughly removed.

•Sufficient profile not achieved.

•Voids and bug holes not opened or exposed.

•Protrusions not removed.

•Existing lining materials not thoroughly removed.

• Existing contamination not thoroughly removed.

•Surface pH below 8.0.

Laitance Not Removed • Thin, weak layer of aggregate fines including unreacted concrete constituents which is poorly adhered to the substrate.

•Disbondment of the lining system.

Laitance Not Removed

Residual Laitance Following Preparation by UHPWJ Residual Laitance Following Preparation by Abrasive Blasting

Failure to Achieve Sufficient Profile

•To get proper adhesion a surface profile is needed on the concrete substrate. The following test methods can be used to achieve this: •ICRI Technical Guideline 310.2

•9 CSPs •ASTM D7682, Standard Test Method for Replication of and Measurement of Concrete Surface Profiles Using Replica Putty

Failure to Achieve Sufficient Profile

• SSPC-SP 13/NACE No. 6 describes a concrete surface profile by comparison with various grades of sandpaper •Fine •Medium •Coarse

Failure due to inadequate concrete surface profile

Inadequate concrete surface profile causes lining delamination

Voids/Bug Holes not Opened/Exposed •A result of air bubbles entrapped during placement and compaction.

•Small regular or irregular cavities, usually not exceeding 15 mm (0.6 inches) in diameter while voids can be significantly larger.

Cross Section of Bug Holes

Other Often Overlooked Conditions

• Surface Irregularities – e.g., protrusions.

– Mechanically removed by chipping or grinding.

• Residual lining material remaining in voids.

• Contamination - e.g., chlorides and sulfates.

• Surface pH too low (below 8.0).

– A pH of less than 8.0 would suggest the presence of acid salts.

• Concrete not sufficiently hydrated.

– A pH greater than 12.5 – new or green concrete.

• Extent if cracking due to restrained drying shrinkage not considered.

PART 1 .

ACID ATTACK AND SULFATE ATTACK H 2 SO 4 + Ca(OH) 2  CaSO 4 + 3H 2 O . Sulfuric Acid + Calcium Hydroxide Calcium Hydroxide + Water . (25% of hydrated (or Gypsum) Portland Cement)

Figure 1

DEEPER IN CONCRETE: SULFATE REACTIONS

CaSO 4 + 2 H 2 O + C 3 A 3CaO.Al

2 O 3 .3CaSO

4 .3H

2 O

Calcium Sulfate Dihydrate + Tri-Calcium Aluminate  Calcium Aluminate Trisulfate 32-Hydrate ( ettringite)

Figure 2

KNOWING THE DEPTH OF ACIDIC AND SULFATE ATTACK: •

Crucial to required depth of concrete removal to prevent on-going deterioration beneath protective linings.

Large areas of ceiling with lining delamination Back of delaminated lining Substrate

pH INDICATIONS • • • •

Newly hydrated concrete – cement paste pH = 12.5 plus pH reduction to less than 12.0 – loss of potassium and sodium hydroxides pH reduction below 10.0 – loss of calcium hydroxide pH reduction below 8.0 – loss of calcium silicate hydrates and possible on-going acidic reactions in paste

Depth Below Exposed Substrate

⅛” ¼” to ½” ½” to ¾”

pH Measurements

6.0 to 7.0

Loss of CSHs 9.0 to 10.0

Loss of Calcium Hydroxide 11.0 to 12.0

Loss of Sodium and Potassium Hydroxide

GAGING DEPTH OF SULFATE ATTACK • • •

Mean sulfate concentration in Type I and Type II Portland cement is about 3% (by percent weight of cement) Sulfate measured as SO 3 Small amount of calcium sulfate (gypsum) added for set control

Restoration/Resurfacing Phase

• Substrate not thoroughly cleaned of dust and debris.

• Substrate too wet or too dry.

• Unsuitable application conditions.

• Post application curing not properly performed.

• Cracks and joints not properly treated.

• Bugholes and air voids not filled resulting in out-gassing and pinhole formation in the applied lining or coating system.

Improperly surfaced concrete causes out-gassing and major pinhole problems

Substrate Too Wet / Too Dry

METHOD Anhydrous Calcium Chloride INDUSTRY STANDARD

ASTM F 1869

LIMITATIONS

  only for horizontal surfaces requires a minimum of 60 hours

Plastic Sheet RH Probes Electronic Meters

ASTM D 4263 ASTM F 2170  requires 16 hours  hole must be cored (destructive) None  measures at or just below surface

Flexible polyurethane lining failure – moisture related

Moisture caused polyurethane lining to not cure properly and disbond

Micro photograph of water reacted with isocyanate in flexible polyurethane lining

Microphotograph of failed polyurethane lining in digester

Unsuitable Application Conditions • Material temperature

– May vary between components – controls viscosity

• Surface temperature • Air Temperature • Relative Humidity • Dew Point

Unsuitable Application Conditions

• Materials should not be applied in direct sunlight • Materials should not be applied if the substrate temperature is ascending – Air entrained within the concrete expands as temperatures rise, causing outgassing • Pinholes • Craters

Other Often Overlooked Items • Post application curing of cementitious repair materials

– Periodically wetting or maintaining a wet cure with fabric or burlap to insure that sufficient water is available for proper hydration

• Cracks and joints not properly treated

– Cracks can and will reflect through many lining systems

• Ample ventilation helps avoid most concrete dry-out problems provided concrete has hydrated for several months.

• Heating and D.H. can cause problems if not properly managed and operated.

Concrete Cracking

Spray Applied Epoxy Reflecting Crack Problems

Lining Application Phase

•Inadequate or nonexistent lining terminations •Unsuitable substrate moisture content •Unsuitable application conditions •Repair/restoration material not abraded •Storage and mixing

CEMENTITIOUS MORTARS • • • •

Many manufacturers say no preparation required and broom brush finish ok Leaves a weak, laitance rich layer Leads to lining disbondment failure - from curing stresses - cohesive failure plane within weak repair mortar Troweled or floated finishes provide more uniform CSP when blast cleaned

Shows typical broom finish on cementitious repair mortar Shows troweled/floated mortar finish (post-blast cleaned)

Shows post-blast cleaned, broom finished repair mortar Post-blast cleaned shotcrete mortar – float finished vs. ICRI comparators (uniform CSP 5 achieved)

Installation of 1 ½” to 3” cementitious shotcrete repair mortar – trowel finished Post-blast condition of cementitious shotcrete mortar

Inadequate or Nonexistent Lining Terminations •Terminations in immersion service are susceptible to edge lifting and undercutting •Lining system should be terminated within a chase or saw cut

Edge Lifting/Disbondment at Termination

Other Often Overlooked Items

• Substrate moisture content – Excessive moisture is detrimental and must be constantly controlled and monitored as conditions change • Materials improperly stored • Materials improperly mixed • Repair/Restoration material not abraded or prepared – Laitance must be removed prior to application of the chemically resistant lining

Flexible polyurethane lining – cohesive failure within cementitious mortar (New Jersey) Cohesive bond failure within cementitious mortar for epoxy sludge tank lining (Florida)

Off Ratio Material

Off Ratio Material

Look for patterns

Testing and Repair Phase

• Dry film thickness testing • Adhesion testing • Holiday detection • Repairs

LEARNINGS • • • •

Always test substrate integrity first – use ASTM C1583… should be 350 to 400 psi minimum (hammer sound also) Always test repair mortar integrity – use ASTM C1583 - results should be similar to substrate tests Calibrate mortar adhesion results via substrate results Lining adhesion to mortar – ASTM D7234… should be 400 psi or higher

Adhesion Testing •ASTM D7234

Dry Film Thickness Testing

• Non-Destructive – SSPC-PA 9, Measurements of Dry Coating Thickness in Cementitious Substrates Using Ultrasonic Gages – ASTM D6132, Standard Test Method for Nondestructive Measurement of Dry Film Thickness of Supplied Organic Coatings Using an Ultrasonic Gage • Destructive – ASTM D4138, Standard Practices for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive Cross Sectioning Means

Holiday Detection

Do not repeat high voltage holiday detection over entire surface.

How Best To Avoid

• Engage the services of a competent Engineering firm to develop the technical specifications.

• Avoid utilizing boilerplate or recycled specifications. – Reference performance based standards.

• SSPC Paint 44, Liquid Applied Organic Polymeric Coatings and Linings for Concrete Structures in Municipal Wastewater Facilities • Pre-qualify the Applicator.

– SSPC-QP 8, Standard Procedure for Evaluating the Qualifications of Contracting Firms that Install Polymer Coatings and Surfacings on Concrete and Other Cementitious Substrates.

How Best To Avoid

• Encourage/solicit active participation from the manufacturer of the lining material including periodic site visits.

• Engage the services of a qualified third party to provide full time quality control, either in conjunction with the applicator’s in-house QC or independently.

– SSPC CCI Certified Inspector

References

• Preparing and Lining Concrete for Immersion Service: Steps and Procedures to Avoid Failures, Randy Nixon and Robert Maley with Corrosion Probe, Inc., SSPC GreenCoat 2013.

Summary

• When applying coatings in wastewater facilities careful consideration must be given to the substrate condition, ambient conditions, presence of moisture, and coating selection.

• Pay attention to details!

Top Ten List

1. Proper material selection is about understanding the chemical, physical, and thermal exposure conditions, the expected substrate conditions (i.e. cracking, extent of bugholes, etc.) and conditions under which application will occur.

2. Good surface preparation is about decontamination, adequate profile for the coating system, and degree of cleanliness.

3. For concrete, coating or lining film quality is all about proper surface preparation to remove protrusions and open-up bugholes followed by complete filling and resurfacing prior to coating application.

Top Ten List (continued)

4.

5.

6.

7.

Cementitious filler/surfacers need to be abraded to ensure sound coating/lining adhesion.

The key to suitable application conditions include ambient air temperature and humidity control as well as adequate substrate dryness. Ventilation generally solves concrete dry out problems provided high MVT issues are not present.

Proper detail treatment of concrete is crucial to coating/lining system performance at joints, cracks, transitions, and terminations.

Do not apply coatings and linings on concrete when substrate temperatures are rising. This causes out-gassing problems and pinhole formation.

Top Ten List (continued)

8.

9.

Especially when plural component applied coatings are used, watch-out for off-ratio problems which result in intracoat and intercoat failures. Look for spray/scaffolding patterns when discovered.

Adhesion testing is a useful tool, but we must be careful not to over-emphasize its importance as repeatability can be a problem and technique can result in poor results.

10. Holiday Detection must be properly conducted and must not be repeated over all surfaces after repairs are made. ONLY perform to confirm efficiency of repairs.

• Questions?????