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

IntroductionUpon 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 systems flexible and chemical resistant properties as well as the relatively swift installation time.

Challenge:Excessive dynamic crackingOutdoor, uncovered serviceAverage temperature swings of 40F (4.4C) depending on time of yearNo moisture barrier under concreteLining must provide 100% containmentMust pass rigorous chemical resistance qualifications

Initial ApplicationThe 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.

Dynamic CrackingCrack in concrete surface that changes in width as the concrete moves

Typical Crack Repair:Routed CrackBacker RodElastomeric caulkBond breaker tapeFiberglass mattreinforcementPrimerChemical resistant Coating (2 layers)

Repair DecisionTwo options:1. Revise existing thin film system to include rigorous, multi-step crack repair or2. Choose a completely new coating systemThe decision was to choose a completely new coating systemA loose line comprising of a geotextile fabric coated with a polyurea

Polyurea Loose Liner SystemPolyurea applied over geotextile to form a loose, semi-floating linerGeotextile- synthetic fibers manufactured in a woven or loose non-woven mannerPolyurea-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.

Plural Component ApplicationPaint equipment that uses multiple positive displacement pumps to achieve a desired mix ratioMixes paint at correct ratio within mixing block or at gun by use of a static mixer to a single homogenous blendFor viscous paint, heated lines can be used

Mechanical Proportioning of Components A and B

*Manifold Mixer

*Mixing Block (isolated)

Cut-away of Plural Component Impingement Gun with Component Hoses Joined at the Tip

Liner Details

Liner consists of the following components:12 oz. (0.3 L) geotextile fabric with a 6 inch (15.24 cm) overlap at seamsMechanical anchor with 2 inch (5 cm) washersStainless steel batten strips80-180 mils (2032-4572 microns) polyureaSlow setting polyurea formulation

Polyurea Slow Set vs. Fast Set

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

Loose Liner ProsNo direct adhesion to concrete requiredMinimal surface preparation required only for metallic protrusionsHigh film build material permits adequate coating of crevicesLow film build is anything below 25 mils (635 microns)High film build is anything over 25 mils (635 microns)Contours around protrusionsRelatively swift installation due to fast cure time and plural component equipment use during installation

Loose Liner ConsUltrasonic dry film thickness (DFT) gages are not accurate over the polyurea/ geotextile systemSystem highlights all angulations and uneven surfaces

Lessons LearnedObserved formation of small voids around the edges of the anchor washersAvoided by sealing around mechanical anchor/ washers and edges of baseplates

Measuring DFTThe following method was used to determine DFT:3 x 5 steel panels placed within coating area prior to applicationOnce coated, panels were removed from liner using razor blades and patch was recoatedNumber of panels determined in accordance with SSPC-PA2 frequencies, with each panel representing one spot measurementPanels 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

SSPC-PA 2Procedure for Determining Conformance to Dry Coating Thickness RequirementsDescribes 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 measurementAn area measurement = 5 spot measurements

SSPC-PA 2For areas not exceeding 300 ft2 (30 m2)Measure each 100 ft2 (10 m2) areaFor areas greater than 300 ft2 (30 m2) and not exceeding 1000 ft2 (100 m2)Select three 100 ft2 (10 m2) areasFor 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

Lessons LearnedDevelopment of tie-in and termination detailsDistance between anchorsDistance of anchors from grout padsTerminations over baseplatesSealing uni-strut supportsManipulation of geotextile fabricIn corners of concrete curbsInside concrete sumps and trenches

Lessons LearnedFormation of Bird-Mouths between overlapping seamsDue to heat of the polyurea during application, the top layer of the seam lifted, forming a gap exposing bare concreteRepaired by sealing the seams using a slow setting brush-grade version of polyureaA 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

Lessons LearnedFabric Tenting- causing the fabric to be pulled taut, increasing stress in the immediate locationRepaired 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

SummaryPolyurea/ geotextile floating liners are viable solutions for extensively cracked concreteAllow for concrete movement without affecting coatingCapable of providing 100% containmentMinimizes surface preparation requirementsNo crack repair requiredContours around protrusions

Questions?

1-*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 areas1-*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 them1-*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.1-*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.