1. Polyurea Application for Excessively Cracked Concrete
Presented by: Kristin Leonard, SSPC Protective Coating Inspector, SSPC Concrete Coating Inspector, Bechtel Materials Engineering Technology

2. Introduction
Upon installation of a typical thin film coating system, extensive dynamic cracking was discovered in concrete chemical secondary containment structures. After multiple failed attempts to repair cracks using standard coating products, the decision was made to proceed with equipment installation in hopes of maintaining schedule while the coating details could be evaluated. With this additional hurdle, the challenge was made to develop a coating system that delivered chemical resistance while acting as a “band aid” over the damaged concrete to provide 100% containment. After evaluating various options, a polyurea/ geotextile liner was selected on a trial basis due to the system’s flexible and chemical resistant properties as well as the relatively swift installation time.

3. Challenge: Excessive dynamic cracking Outdoor, uncovered service
Average temperature swings of 40°F (4.4°C) depending on time of year
No moisture barrier under concrete
Lining must provide 100% containment
Must pass rigorous chemical resistance qualifications

4. Initial Application
The initial application included the thin film epoxy novalac system applied direct to prepared concrete prior to installation of equipment.
After coating application, cracks were noticed propagating through the coating system.
Multiple repair attempts were made using standard coating products with no success.
Coatings work was stopped and a concrete specialist was brought in to evaluate the defects.

5. Dynamic Cracking
Crack in concrete surface that changes in width as the concrete moves

6. Typical Crack Repair: Chemical resistant Coating (2 layers) Primer
Bond breaker tape
Fiberglass matt
reinforcement
Elastomeric caulk
Backer Rod
Routed Crack

7. Repair Decision Two options:
1. Revise existing thin film system to include rigorous, multi-step crack repair or
2. Choose a completely new coating system
The decision was to choose a completely new coating system
A loose line comprising of a geotextile fabric coated with a polyurea

8. Polyurea “Loose Liner” System
Polyurea applied over geotextile to form a loose, semi-floating liner
Geotextile- synthetic fibers manufactured in a woven or loose non-woven manner
Polyurea-a type of elastomer that is derived from the reaction product of an isocyanate component and a synthetic resin blend
The isocyanate can be aromatic or aliphatic in nature.

9. Plural Component Application
Paint equipment that uses multiple positive displacement pumps to achieve a desired mix ratio
Mixes paint at correct ratio within mixing block or at gun by use of a static mixer to a single homogenous blend
For viscous paint, heated lines can be used

10. Mechanical Proportioning of Components A and B
A Plural Component Coating Application System is:
*An application system that heats 100% solids coatings to a desired temperature and properly proportions their two components prior to mixing
*A system focused on the application of two- component 100% solids coatings (e.g., Part A and Part B)
*A process where components are mixed until application is begun
*A system that has mobile equipment for better access to hard to reach areas

11. Manifold Mixer
Pre-heating, Proportioning, and Mixing Before Transfer to Gun
*Piston proportioning pump used
*Mixed components are pumped from machine mixer to gun
*Coatings with short pot life must be applied immediately
*After interrupting application, residual mixed coating must be cleaned from gun and lines with solvent to prevent damaging them

12. Mixing Block (isolated)
Heated Components Mixed at Remote Mix Manifold
*Piston proportioning pump used
*Individual components (parts A and B) mixed at manifold and pumped to gun
*Distance from manifold to gun may limit acceptable pot life
*After interrupting application, residual coating must be cleaned from manifold, spray hose, and gun with solvent to avoid damaging them
In most cases when a mixing block is used, you only have to solvent clean from the mix block (after where A & B are mixed) to the gun on a daily basis. However, some equipment manufacturers may recommend a complete solvent clean weekly or at the end of a job or if materials are changed out.

13. Cut-away of Plural Component Impingement Gun with Component Hoses Joined at the Tip
Heated Components Mixed at Gun Tip (Polyurethanes and Polyureas)
*Piston proportioning pump used
*Individual components mixed at gun tip (impingement)
*Harder to monitor mix ratio
*Pot life can be very short (e.g., a few seconds)
*After interrupting application, only gun tip must receive mechanical or air purging
Note: This type of mixing equipment is typically used for spraying polyurethanes and polyurea materials.

14. Liner Details Liner consists of the following components:
12 oz. (0.3 L) geotextile fabric with a 6 inch (15.24 cm) overlap at seams
Mechanical anchor with 2 inch (5 cm) washers
Stainless steel batten strips
mils ( microns) polyurea
Slow setting polyurea formulation

15. Polyurea Slow Set vs. Fast Set
To touch- 20 min.
Light traffic- 4 hrs.
Light traffic- 1 hr.
To cure- 36 hrs.
Potlife min.
To cure- 24 hrs.
Potlife- 3-5 min.

16. Mock-up
It is a good idea to perform a full scale mock-up over a representative area prior to applying full system

17. Loose Liner Pro’s No direct adhesion to concrete required
Minimal surface preparation required only for metallic protrusions
High film build material permits adequate coating of crevices
Low film build is anything below 25 mils (635 microns)
High film build is anything over 25 mils (635 microns)
Contours around protrusions
Relatively swift installation due to fast cure time and plural component equipment use during installation

18. Loose Liner Con’s
Ultrasonic dry film thickness (DFT) gages are not accurate over the polyurea/ geotextile system
System highlights all angulations and uneven surfaces

19. Lessons Learned
Observed formation of small voids around the edges of the anchor washers
Avoided by sealing around mechanical anchor/ washers and edges of baseplates

20. Measuring DFT The following method was used to determine DFT:
3” x 5” steel panels placed within coating area prior to application
Once coated, panels were removed from liner using razor blades and patch was recoated
Number of panels determined in accordance with SSPC-PA2 frequencies, with each panel representing one spot measurement
Panels were measured using a magnetic thickness gage, labeled on back, and kept as part of inspection records.
Patch area was easily repaired leaving minimal physical evidence

21. SSPC-PA 2
Procedure for Determining Conformance to Dry Coating Thickness Requirements
Describes a procedure for determining shop or field conformance to a specified coating dry film thickness (DFT) range on ferrous and non-ferrous metal substrates using nondestructive coating thickness gages (magnetic and eddy current)
A minimum of 3 gage reading = 1 spot measurement
An area measurement = 5 spot measurements

22. SSPC-PA 2 For areas not exceeding 300 ft2 (30 m2)
Measure each 100 ft2 (10 m2) area
For areas greater than 300 ft2 (30 m2) and not exceeding 1000 ft2 (100 m2)
Select three 100 ft2 (10 m2) areas
For areas exceeding 1000 ft2 (100 m2)
Measure as in second bullet, but for each additional 1000 ft2 (100 m2) area, arbitrarily select and measure one additional 100 ft2 (10 m2) area

23. Lessons Learned Development of tie-in and termination details
Distance between anchors
Distance of anchors from grout pads
Terminations over baseplates
Sealing uni-strut supports
Manipulation of geotextile fabric
In corners of concrete curbs
Inside concrete sumps and trenches

24. Lessons Learned Formation of “Bird-Mouths” between overlapping seams
Due to heat of the polyurea during application, the top layer of the seam lifted, forming a gap exposing bare concrete
Repaired by sealing the seams using a slow setting brush-grade version of polyurea
A 2 inch (5.08 cm) wide line of polyurea was applied between the layers of geotextile seams, then firmly pressed using a smooth seam roller

25. Lessons Learned
Fabric Tenting- causing the fabric to be pulled taut, increasing stress in the immediate location
Repaired by modifying the order in which the anchors are installed, calling for the exterior baton strip to be fully installed prior to any anchor bolts being set in the base mat

26. Summary
Polyurea/ geotextile floating liners are viable solutions for extensively cracked concrete
Allow for concrete movement without affecting coating
Capable of providing 100% containment
Minimizes surface preparation requirements
No crack repair required
Contours around protrusions

27. Questions?