concrete repair: bridges and tunnels--epoxies
DESCRIPTION
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).TRANSCRIPT
Tran
spor
tatio
n Epoxy ApplicationsEpoxy Applications
ChemCo Systems
Concrete Repair: Bridges and Tunnels
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Civil uses
Major roles:• Repair and Protection
• Infrastructure Renovation– Bridges & Tunnels– Airports– Rail
• Structural Rehabilitation– Commercial, Industrial & Residential– Public & Private Sectors
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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).
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Salt: tough on steel and concrete
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Monitor crack movement (strain gauge)
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Specification for civil engineering
ASTM C881Standard 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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Properties: Viscositymeasure 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)
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Properties: Modulus of ElasticityRatio of stress to strain
High modulus rigid or stiff• Structural uses
– High creep resistance
Low modulus flexible• Impact resistant, less brittle
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Properties: Coefficient of Thermal Expansion(Thermal Compatibility {ASTM D648})
Materials change in size at varying rates upon being heated or cooledNeat epoxies expand/contract at a higher rate than steel or concrete
Filled epoxies behave more like concrete or steel
• Aggregate gradation is key criteria for filled epoxies (gap-grading is helpful)
Important factor for thick layers and bulk applications
EFFECT of BOND LINE STRESSES
50
45
40
35
30
25
20
15
10
5
0
CONCRETE 10x6-6
1 2 3 4 5 6 7 8 9
NEAT EPOXY (SAND FREE)
MAXIMUM EPOXY SAND LOAD
AGGREGATE/BINDER RATIO EFFECT ON THE THERMAL COEFFICIENT OF EXPANSION FOR AN EPOXY SYSTEM.
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
VariableHot Oil
BathEPOXY BEAM 1/2”x1/2”x5”
CONSTANT LOAD 264 psi
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Properties: Cure rate vs. temperature
CURE RATE OF EPOXY ADHESIVES
020406080
100120140160
30 40 50 60 70 80 90 100
Cure T empera ture Deg. F
Typical epoxy resinSlowerFaster
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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, scabblersDry--no standing water
• Some epoxies are designed for wet or underwater use
Prepare surface profile for good mechanical / chemical bonding
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Surface prep
Shotblasting
Hydroblasting
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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)
ASTM Bond Types: I, II, III, IV,V, VI, VII
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Why Repair Cracks?
Extend structural lifespanRepair settling from poor soilsEarthquake damage repair Cracked member unable to transfer design load
Fix spalls due to freeze/thaw cycles, unrepaired cracks, steel corrosionStop leakage in fluid containing structures (see above)Cracks are unsightly in architectural concrete
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Crack Treatment Considerations(for reinforced concrete used in structural applications)
0.100.004Water retaining structures (excluding pressure pipes)
0.150.006Seawater and seawater spray: Wetting and drying
0.180.007De-icing chemicals
0.300.012Humidity, moist air, soil
0.410.016Dry air or protective membrane
Tolerable crack width (mm)Tolerable crack width (in.)Exposure condition
ACI 224 guidelines for crack width
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Restore monolithic strength
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Structural Crack Repairs
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Injection: beams and columns
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Injection--tunnels
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Injection--Rail
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Injection--airports
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Injection--bridges
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Injection: pile caps
Mass pours (large volume single pours) can develop severe cracks associated with high heat buildup during cure
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Bridge--Gravity Feed Crack Repair
For concrete decks with high amounts of small crack networksGravity feedVery low viscosity systems use epoxies and HMWM (methacrylates)Open to traffic in 5 hrsRestore monolithic integrity to deckProtect reinforcing steel from corrosionAlso available in special long potlife version
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Spray Applied – Gravity feed
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
QC Check: Taking Cores
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Visual Inspection
Can penetrate cracks assmall as 0.002” (0.05 mm)
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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.
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Bonding: Hardened to Hardened
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Trowel Applied
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Set Precast Panel
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Spray Applied Concrete Bonder
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Fresh Concrete Pour (over epoxy)
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Bridge deck overlay delamination repair
Modification of structural crack injection practicesObserved more frequently in climates with high cold-to-hot temp ranges (Canada and parts of China)Fill voids between overlay and structural slabConsiderable savings compared to replacement of deck overlay
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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.
Polymer Overlays
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Broadcast overlay
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Seed with aggregate to excess
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Completed thin overlay
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Apply by Hand
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Place Segments
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Epoxy Squeeze-Out
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
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
External strengthening
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Why add Strengthening?
Insufficient reinforcement Corrosion of reinforcement Change in use Excessive deflections Structural/Fire damage Seismic upgrade
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Failed columns
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Beam damage
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
External fixes: Stitching
Mid 1960s drawing from US Army Corp of Engineers
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Plate strengthening used with epoxy injection
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Steel saddle (3-sides) over concrete beamused with epoxy injection
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Column grouting Steel (or rigid fiberglass) jackets
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Composite Systems
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Bridge Column Upgrade
Applying fairing epoxy to corner
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Test substrate adhesion (after surface prep)
ASTM D4541(Elcometer)
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Prime Substrate
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Saturate Fabric – Wet Lay-Up
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Apply Saturated Fabric
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Dry Lay-Up
Tran
spor
tatio
nEpoxy ApplicationsEpoxy Applications
ChemCo Systems
Reinforce Tension Zone with CF strips
Fiberglass bars inset in pre-cut channels used in a “stitching”technique are an alternative to strips