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.
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
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.
Dynamic Cracking Crack in concrete surface that changes in width as the concrete moves
Typical Crack Repair: Routed Crack Backer Rod Elastomeric caulk Bond breaker tape Fiberglass matt reinforcement Primer Chemical resistant Coating (2 layers)
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
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.
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
Mechanical Proportioning of Components A and B
11 Manifold Mixer
12 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 seams –Mechanical anchor with 2 inch (5 cm) washers –Stainless steel batten strips – mils ( microns) polyurea –Slow setting polyurea formulation
Polyurea Slow Set vs. Fast Set Slow Set –To touch- 20 min. –Light traffic- 4 hrs. –To cure- 36 hrs. –Potlife min. –Fast Set To touch- 20 min. Light traffic- 1 hr. To cure- 24 hrs. Potlife- 3-5 min.
Mock-up It is a good idea to perform a full scale mock-up over a representative area prior to applying full system
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
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
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
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
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
SSPC-PA 2 For areas not exceeding 300 ft 2 (30 m 2 ) –Measure each 100 ft 2 (10 m 2 ) area For areas greater than 300 ft 2 (30 m 2 ) and not exceeding 1000 ft 2 (100 m 2 ) –Select three 100 ft 2 (10 m 2 ) areas For areas exceeding 1000 ft 2 (100 m 2 ) –Measure as in second bullet, but for each additional 1000 ft 2 (100 m 2 ) area, arbitrarily select and measure one additional 100 ft 2 (10 m 2 ) area
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
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
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
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