Multiple Coat Epoxy

Broom & Seed Bridge Overlay

I. BRIDGE SELECTION: When to use polymer concrete overlays

  1. Decks in good condition with few surface imperfections
  2. Less than 2 in. of clear cover over rebar
  3. High permeability in the concrete cover
  4. (in excess of 2,000 coulombs AASHTO T-277)
  5. Excessive cracking (non-moving)
  6. lmproper air entraining and air void system in cover
  7. Decks with patches (to extend life of patched areas)
  8. Decks needing improved ride quality

II. PREPARAT1ON OF BRIDGE DECK

  1. Evaluate bridge deck for delaminations and chloride contents of concrete.
  2. (If delaminations are so extensive or the concrete is so badly deteriorated that a great deal of concrete must be removed, deck replacement may be a better, more cost-effective repair)
  3. Repair delaminations, potholes and cracks.
  4. Clean test areas of deck by shotblasting to remove all surface contaminants, i.e. laitance, curing compounds, asphalt and sealers.
  5. Test surface for bondability by performing one of the following tests:

1.  ACI. 503R

2.  VTM 92

3.  ICRI Surface Preparation Level 5-7

4.  ASTM 965 Pavement Macro Texture Depth of 0.40 mm

  1. Evaluate results of test.
  2. If surface passed bondability test (the cleaning method, materials and installation procedure is approved), proceed with entire bridge deck cleaning by shotblasting.
  3. Check for surface moisture. The deck must be dry prior to placement of the overlay. Water vapor rising from the surface is a potential problem. A sheet of transparent plastic affixe~1 to the concrete surface will reveal the presence of moisture after 6-24 hrs., depending on temperatures, cloud covet, etc. (ASTM D-4263)
  4. H.. Final removal of all dust or debris should be done with oil-free compressed air, not brooming!

III. SELECTION OF EPOXY & AGGREGATE

A. Epoxy Binder Characteristics

PROPERTY REQUIREMENTS TEST METHOD

Viscosity 7-25 poises ASTM D2393, Brookfield RVT

Spindle No. 3 at 20 rpm

Gel time 15-45 min. ASTM C8B1, para. 11.2 modified

Compressive strength Minimum of 6.9 MPa ASTM C579 modified

(1,000 psi) at 3 hrs. (with plastic inserts):

Minimum of 34.4 MPa

(5.000 psi) at 24 hrs.

Tensile strength (neat) 13.8-34.4 MPa ASTM D638

(2,000-5,000 psi) at 7 days

Elongation (neat) 30-80% at 7 days ASTM D63B

Adhesive strength Minimum of 1.7 MPa ACI 503R, Appendix A, VTM 92

(mixed with aggregate) (250 psi) at 24 hrs.

Permeability to chloride ion Maximum of 100 coulombs AASHTO T277

at 28 days

Absorption Maximum of 1% at 24 hrs. ASTM D570

Thermal compatibility No delamination of overlay ASTM C884

(mixed with aggregate)

Infrared spectrum To be established for each AASHTO T237, para. 4

component for each mfr.

Note: Values are based on specimens or samples cured or aged and tested at 75°F (24°C).

B. Aggregate Characteristics

1.  Aggregate shall be angular grained silica sand or basalt having less than 0.2% moisture and free of dirt, clay, etc.

2.  The silica sand and basalt shall have a minimum MOHS scale hardness of 7 unless otherwise approved,

3.  The silica sand and basalt shall conform to the following gradation:

PERCENT BY WEIGHT OF PASSING INDICATED SIEVE

No. 4 Sieve No. 8 Sieve No. 16 Sieve No. 30 Sieve

100% 20-75% Max. 5% Max 1%

IV. PLACING THE EPOXY OVERLAY

A.  Check air, surface and components’ temperatures. The temperature limitations as specified by the manufacturer for the epoxy and aggregate should be strictly adhered to. The deck and air temperatures must be appropriate.

B.  Mix epoxy according to manufacturer’s recommendations.

C.  Apply neat epoxy with notched squeegee.

D.  Broadcast aggregate after epoxy has leveled. A guide of minimum epoxy and aggregate coverage for each course follows:

MINIMUM EPOXY & AGGREGATE COVERAGE RATES

EPOXY RATE AGGREGATE RATE

Course 1 Not less than 40 sq. ft./gal. 10 lbs./sq. yd.

(1 L/m2) (5.4 kg/m2)

Course 2 Not less than 20 sq. ft./gal. 14 lbs./sq. yd.

(2 L/m2) (7.6 kg/m2)

E.  Allow to cure.

F.  Repeat above steps for course 2. See table below for average temperatures of overlay components and minimum curing times for each course.

MINIMUM CURING TIMES OF EPOXY OVERLAY COURSES

Average Temperatures of Overlay Components

60-64°F 65-69°F 70-74°F 75 –79°F 80-84°F 85+°F

16 –18°C 19-21°C 22-23°C 24 –26°C 27-29°C 29+°C

Min.Cure Time

Course 1 4 hrs. 3 hrs. 2.5 hrs. 2 hrs. 1.5 hrs. 1 hr.

Course 2 5-6 hrs. 5 hrs. 4 hrs. 3 hrs. 3 hrs. 3 hrs

V. LIMITATIONS OF OPERATION

  1. Provide a technical representative of the epoxy manufacturer on the job site during the placement of both courses of epoxy overlay.
  2. The representative is to provide technical expertise to the contractor and the engineer regarding safe handling, placement and curing of the epoxy overlay.
  3. No power driver tools heavier than a 30 lb. chipping hammer should be used during deck preparation.
  4. Do not open the first course to traffic!!

VI. CORRECTION OF UNBONDED OR DAMAGED AREAS

A.  Repair newly overlaid areas that are discovered to be unbonded by tapping or chain drag and areas of the overlay that were damaged by the contractor's operation.

B.  Saw cut the unbonded or damaged areas to the top of the deck surface, remove the overlay with small air tools (30 lb. max) or shotblasting.

C.  Replace with overlay following the standard placement procedures at no additional compensation.

VII. SOURCES

A.  David A. Meggers, P.E., Research Development Engineer, Bureau of Materials & Research, Kansas Department of Transportation, Topeka, Kansas.

B.  Guide Specifications for Polymer Concrete Bridge Deck Overlays, AASHTO-AGC-ARTBA, Task Force 34, Oct. 1995.

C.  Michael M. Sprinkel, P.E., Research Manager with Virginia Transportation Research Council.