Testing Polyurea Application for Excessively Cracked Concrete

Testing Polyurea Application for Excessively Cracked Concrete

Have you ever had to coat a concrete containment area that was so severely cracked it would take months to properly repair? Add in speed bumps such as lack of a vapor barrier and fully installed equipment and you have one major headache. Solution: A polyurea “loose” liner.

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 “bandage” over the damaged concrete to provide 100% containment.

Polyurea/ Geotextile systems are commonly recognized as on grade liners for disposal sites, reservoirs, and tank farms. After evaluating various options, the polyurea/ geotextile liner was selected on a trial basis due to its system’s flexible and chemical resistant properties as well as the relatively swift installation time. The liners ability to be molded around protrusions and minor surface preparation requirements made this system highly desirable.

This webinar will outline the trials and challenges of modifying the membrane liner to accommodate stringent chemical resistance criteria, poor concrete conditions, and hundreds of pre-installed obstacles. From detailed design to installation mock-up, the pros, cons and lessons-learned are discussed.

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 the 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 like 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 i the relatively swift installation time.

Challenge:
• Excessive dynamic cracking
• Outdoor, uncovered service
• Average tcwqqcemperature swings of 40°F
(4.4°C) depending on the 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 nova lac 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 the concrete surface that changes in width as the concrete moves
CCDT^

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

Liner Details
The 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
-80-180 mils (2032-4572 microns) polyurea
• Slow setting polyurea formulation

Polyurea Slow Set vs. Fast Set
• Slow Set -Fast Set
-To touch-20 min. • To touch-20

  • Light traffic- 4 hrs. min-
    -To cure- 36 hrs. • Light traffic-1
    -Pot life-8-10 min. hr

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 the Xformation 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 minim
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 measurement

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 ft;
    m2) 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