Examples of maintenance, rehabilitation and repair of transportation structures including bridges and tunnels using epoxy products for structural repair and protection. ASTM C881 catagories are explained. ChemCo Systems, Redwood City, CA manufactures epoxies for these applications (www.chemcosystems.com).
2. Epoxy Applications
Transportation Civil uses
Major roles:
• Repair and Protection
• Infrastructure Renovation
– Bridges & Tunnels
– Airports
– Rail
• Structural Rehabilitation
– Commercial, Industrial & Residential
– Public & Private Sectors
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3. Epoxy Applications
Transportation Corrosion = spalling
Iron oxide (corrosion product
commonly called rust)
occupies about 7 times the
volume of a similar mass of
steel. The formation of rust
generates high internal forces
leading to spalling.
Spalling is more common in
applications with insufficient
cover (depth of concrete over
the steel reinforcement).
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6. Epoxy Applications
Transportation History of Epoxies
1936 First epoxy patents
1940s-50s Bakelight introduces commercial
applications (electrical and jewelry)
1948 First use as construction
adhesive (hardened-to-hardened
concrete bonding)
1954 Caltrans uses bonding agent for
traffic markers
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7. Epoxy Applications
Transportation History of Epoxies
late 1950s Patching, bolt grouting, crack injection and
overlays more common.
1959 U.S. Army Corp of Engineers issues
specification
1959 PG&E dam successfully repaired using
meter/mix pump and structural epoxy from
Adhesive Engineering
1978 ASTM* C881 spec. published
*American Society of Testing and Materials
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8. Epoxy Applications
Transportation Specification for civil engineering
ASTM C881
Standard U.S. specification for epoxy bonding
systems for concrete
AASHTO* M-235 used by U.S. transportation
design engineers as specification for epoxy bonding
AASHTO M235 = ASTM C881
*American Association of State Highway and Transportation Officials
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9. Epoxy Applications
Transportation
Properties: Viscosity
measure of a material’s resistance to flow—common unit is
centipoise (cps)
Water = 1 cps
Motor Oil = 100 - 500 cps
(similar to some unfilled epoxies)
Peanut Butter = 250,000 cps
(similar to some epoxy pastes)
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10. Epoxy Applications
Transportation
Properties: Modulus of Elasticity
Ratio of stress to strain
High modulus rigid or stiff
• Structural uses
– High creep resistance
Low modulus flexible
• Impact resistant, less brittle
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11. Epoxy Applications
Transportation Properties: Coefficient of Thermal Expansion
(Thermal Compatibility {ASTM D648})
Materials change in size at Filled epoxies behave more like
varying rates upon being heated concrete or steel
or cooled • Aggregate gradation is key criteria
Neat epoxies expand/contract at
for filled epoxies (gap-grading is
helpful)
a higher rate than steel or
concrete Important factor for thick layers and
bulk applications
EFFECT of BOND LINE STRESSES
50
45 NEAT EPOXY (SAND FREE)
40
35
30
25
MAXIMUM EPOXY SAND LOAD
20
AGGREGATE/BINDER
RATIO EFFECT ON THE
15 THERMAL COEFFICIENT OF
EXPANSION FOR AN EPOXY SYSTEM.
10
5
CONCRETE 10x6-6
0 1 2 3 4 5 6 7 8 9
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12. Epoxy Applications
Transportation Properties: Heat deflection temperature (HDT)
Temperature an adhesive polymer deflects under 3 point
load
120ºF is minimum value for ASTM C881 load bearing
structural use
Cold temperature curing may undermine HDT performance
Special adhesives available offering higher HDTs for high
temperature use
Creep is potential problem if use temp > HDT
CONSTANT LOAD 264 psi
Variable
Hot Oil
Bath
EPOXY BEAM 1/2”x1/2”x5”
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13. Epoxy Applications
Transportation Properties: Reactions are exothermic
Epoxies produce heat during cure
Temperature dependent
Mass dependent
Can undermine product performance in bulk
applications
Exotherm may increase apparent shrinkage
upon cure
• Thick cross-sections and bulk uses should
consider special low exotherm systems
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14. Epoxy Applications
Transportation Properties: Cure rate vs. temperature
CURE RATE OF EPOXY ADHESIVES
160
140
120 Typical epoxy resin
100 Slower
80 Faster
60
40
20
0
30 40 50 60 70 80 90 100
Cure T e mpe ra ture D e g. F
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15. Epoxy Applications
Transportation Advantages
Low shrinkage
Tolerates moisture after cure
Mechanical and chemical bond
• Very high bond strength
Cost effective repair vs. complete removal /
replacement
Chemically inert
Long storage life of A and B components
Repair is considered permanent
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16. Epoxy Applications
Transportation
Limitations
Thermal incompatibility
• Minimal concern with thin glue line
Creep
• Minimal concern with thin glue line
Vapor barrier
Proper mixing and ratio is critical
Short open time for some formulations
Clean-up requires solvents
Cure and viscosity is temperature sensitive
ChemCo Systems
17. Epoxy Applications
Transportation Surface Preparation
Clean and free of
contaminants (remove loose
substrate, laitance, dirt, dust,
grease, oils, chemical spills)
Metal shot blasting
machines, sand blasting,
“dust-free” diamond grinding,
hydroblast, scarifiers,
scabblers
Dry--no standing water
• Some epoxies are
designed for wet or
underwater use
Prepare surface profile for
good mechanical / chemical
bonding
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19. Epoxy Applications
Transportation ASTM Bond Types: I, II, III, IV,V, VI, VII
ASTM C-881 (or AASHTO M-235)
Crack Repair – pressure injection or gravity feed
(Types I & IV)
Concrete Bonding (Types II & V)
Low mod overlays and spall/joint repair (Type III)
Segmental Bridge Adhesives (Types VI & VII)
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20. Epoxy Applications
Transportation Non-ASTM Specification Uses
Miscellaneous Epoxy Products
• Base plate grouts
• Mortars for patching
• Coatings
• Control joints and wire loops
– Airport runway lighting (see right)
– Traffic control
• High strength grouts
• Polymer concrete
• Handicapped access warning strip adhesives
Adhesive Anchoring (ICC-ES/AC308)
External Structural Strengthening
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21. Epoxy Applications
Transportation
ASTM C-881 used in crack repair
Type I – Non-load bearing, bond hardened
concrete to hardened concrete
Type IV – Load bearing, bond hardened concrete
to hardened concrete
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22. Epoxy Applications
Transportation Why Repair Cracks?
Extend structural lifespan Fix spalls due to freeze/thaw
cycles, unrepaired cracks,
Repair settling from poor
steel corrosion
soils
Stop leakage in fluid
Earthquake damage repair
containing structures (see
Cracked member unable to above)
transfer design load Cracks are unsightly in
architectural concrete
ChemCo Systems
23. Epoxy Applications
Transportation Crack Treatment Considerations
Some moving cracks may re-
appear after injection
Cracks with hydrostatic pressure
(i.e., running water) are frequently
epoxy treated, but may also be
candidates for urethane grouting if
non-structural
Vertical / Overhead applications –
Injection technique
Horizontal applications – Gravity-
feed or injection
Voids and honeycombed concrete
may require special low exotherm
epoxy
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24. Epoxy Applications
Transportation Crack Treatment Considerations
(for reinforced concrete used in structural applications)
ACI 224 guidelines for crack width
Exposure condition Tolerable crack width (in.) Tolerable crack width (mm)
Dry air or protective membrane 0.016 0.41
Humidity, moist air, soil 0.012 0.30
De-icing chemicals 0.007 0.18
Seawater and seawater spray: 0.006 0.15
Wetting and drying
Water retaining structures (excluding 0.004 0.10
pressure pipes)
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32. Epoxy Applications
Transportation Injection: pile caps
Mass pours
(large volume
single pours)
can develop
severe cracks
associated
with high heat
buildup during
cure
ChemCo Systems
33. Epoxy Applications
Transportation Bridge--Gravity Feed Crack Repair
For concrete decks with
high amounts of small
crack networks
Gravity feed
Very low viscosity
systems use epoxies and
HMWM (methacrylates)
Open to traffic in 5 hrs
Restore monolithic
integrity to deck
Protect reinforcing steel
from corrosion
Also available in special
long potlife version
ChemCo Systems
37. Epoxy Applications
Transportation ASTM Standard C-881 (continued)
Type II – Non-load bearing, bond freshly mixed
concrete to hardened concrete
Type V – Load bearing, bonding freshly mixed
concrete to hardened concrete
Typical Applications:
• Introduction of newly poured concrete for
large area repairs.
• Primers for overlays (Type III) & patch repairs
with epoxy and cementitious mortars.
ChemCo Systems
38. Epoxy Applications
Transportation Concrete Bonding
Requirements for “fresh to hardened”
• Achieve monolithic structural bond of new
material to old concrete
• Epoxy must have proper viscosity to maintain
uniform film thickness of 20 mils
• Epoxy must be tacky when new concrete or
new material is placed
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44. Epoxy Applications
Transportation Bridge deck overlay delamination repair
Modification of structural crack injection practices
Observed more frequently in climates with high cold-to-hot temp
ranges (Canada and parts of China)
Fill voids between overlay and structural slab
Considerable savings compared to replacement of deck overlay
ChemCo Systems
45. Epoxy Applications
Transportation ASTM Standard C881
(cont.)
Type III – Bond skid
resistant materials to
hardened concrete
(low modulus)
• Binders in epoxy
mortars used on
traffic bearing
surfaces (overlays)
• Impact resistant joint
nosing repair on
bridge decks
• Handicapped access
warning strips
ChemCo Systems
46. Epoxy Applications
Transportation Polymer Overlays
What is an Overlay?
• A resurfacing of an existing horizontal surface
(bridge deck or parking structure)
Function of overlay
• Protects structure
• Provides non-skid surface
• Extends life of the structure
Properties
• Low modulus.
• Medium viscosity.
• Excellent adhesive properties.
• Long term abrasion resistance.
ChemCo Systems
50. Epoxy Applications
Transportation ASTM Standard C-881 (continued)
Segmental bridges
Type VI – Bonding / sealing segmental precast
elements with internal tendons (temporary post
tensioning applied)
• Normal Set
Type VII – For use as a nonstress carrying sealer
for segmental precast elements (temporary post
tensioning not applied)
• Slow Set
ChemCo Systems
51. Epoxy Applications
Transportation
Segmental Bridges
Technology first developed in France
and Switzerland in the 1940’s
Early projects left segment joints dry
Epoxies used since early 1970’s for
sealing segments
ASBI (American Segmental
Bridge Institute)
• Developed a standard epoxy
specification
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52. Epoxy Applications
Transportation Functions of Epoxy Resin (Segmental use)
Lubricant - allows segments to slide easily into
place during construction
Distributes compressive/shear stresses across
each joint
Provides water-tight seal between segments
Prevents loss of cementitious grout at joints when
pumped through cable ducts
Specific temperature ranges often used
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56. Epoxy Applications
Transportation External strengthening
Early applications used steel plate
Change in use
Used in seismic upgrades
Steel and fiberglass forms used on columns
Steel saddles on beams
Epoxy resin and hand-applied composite fiber
wrapping technologies are popular today
Fabrics are glass or carbon fiber
ChemCo Systems
57. Epoxy Applications
Transportation
Why add Strengthening?
Insufficient reinforcement
Corrosion of reinforcement
Change in use
Excessive deflections
Structural/Fire damage
Seismic upgrade
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71. Epoxy Applications
Transportation Reinforce Tension Zone with CF strips
Fiberglass bars inset
in pre-cut channels
used in a “stitching”
technique are an
alternative to strips
ChemCo Systems