NBSIR 73-229

^

Interim Report No. 6. Corrosion and

Creep Testing of Coated Reinforcing

Bars in Concrete

Nonmetallic Coatings for Concrete

Reinforcing Bars

James R. Clifton, Hugh F. Beeghly, Erik Anderson, Robert G. Mathey

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

April 1973

Interim Report for Period January - March 1973

Prepared for Federal Highway Administration

U. S. Department of Transportation

Washington, D. C. 20590

NBSIR 73-229

INTERIM REPORT NO. 6. CORROSION AND

CREEP TESTING OF COATED REINFORCING

BARS IN CONCRETE

NONMETALLIC COATINGS FOR CONCRETE

REINFORCING BARS

James R. Clifton, Hugh F. Beeghly, Erik Anderson, Robert G. Mathey

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

April 1973

Interim Report for Period January - March 1973

Prepared for Federal Highway Administration

U. S. Department of Transportation

Washington, D. C. 20590

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

ABSTRACT

The possibilities of protecting steel reinforcing bars embedded in con- crete from corrosion by using organic barrier-type coatings are being

investigated in this project. This corrosion is accelerated by the

chloride ions of the two most commonly used deicing materials, calcium

chloride and sodium chloride.

In this report, corrosion studies carried out on coated reinforcing bars

embedded in concrete are discussed. Methods of instrumenting creep-test

specimens are also explained.

The electrical potentials of coated reinforcing bars are not reliable

indicators of the corrosion state of the steel bars. The electrical

resistances of the coating films are more reliable indicators of the

performance of a coating material than the electrical potential measurements.

Key Words

Corrosion; creep testing; epoxy coatings; po ly (vinyl)chlorides

strain gages; steel reinforcing bars
CONTENTS

1. Project Information 1 2. Introduction 1

2 . 1 Background 1 2.2 Objectives 1 3. Discussion of Activities , 2 3.1 Corrosion Studies of Coated Reinforcing Bars

Embedded in Concrete 2 3.1.1 Materials and Fabrication of Test Specimens 2 3.1.2 Corrosion Test Methods 4

3.1.3 Results and Discussion 5 3.2 Creep Tests 6

3.2.1 Calibration of Springs 6

3.2.2 Strain Gages 7 3.3 Implementation 7 3.4 Talks Based on Project 8

3.5 Meetings Attended 8

3.5.1 Meetings Attended in Conjunction with the Project 8

3.5.2 Pertinent Meetings Held Between NBS Staff

and Industrial Representatives 8

4. Status of Project 9

5 . Problems 9

6. Work Planned for the Next Quarter 9

7. References 10

Appendix A 15
Interim Report No. 6

Corrosion and Creep Testing of Coated

Reinforcing Bars in Concrete

1. Project Information : Order No. 2-1-0614

Tit le ; Nonmetallic Coatings for Concrete Reinforcing Bars

Date Project Initiated ; September 17, 1971

Research Agency ; National Bureau of Standards

2. Introduction

2.1 Background ; The early deterioration of the concrete of bridge

decks, attributed to the corrosion of the steel reinforcing bars,

has become a major problem in highway maintenance during the past

decade. The annual cost of repairing these damaged bridge decks is

Over 70 million dollars according to estimates of the Federal Highway Administration.

The corrosion of the steel reinforcement is caused by chloride

ions from the two major deicing materials, sodium chloride and calcium

chloride. Chloride ions depassivate steel thereby promoting the active

corrosion of the steel.

A reasonable method to obviate the rapid corrosion of the reinforcement is to protect the bars with barrier-type of coating. The

present study was undertaken to ascertain the feasibility of using

organic coatings, especially epoxy systems, to protect steel reinforcing

bars.

2.2 Ob jectivesTo investigate the protective qualities of organic

coatings, especially epoxy systems, and to select the most promising

materials. The selection is based upon physio chemical testing with

consideration given to economics involved in coating and fabrication.

1
3 . Discussion of Activities

3.1 Corrosion Studies of Coated Reinforcing Bars Embedded in Concrete.

The protective qualities of epoxy and po lyviny Ichlor ide coating

materials have been previously assessed by partially immersing coated

reinforcing bars in aqueous solutions of 0.5 to 1.0 N NaCl. Performance

of the coatings was evaluated by measuring both the electrical

potential of the coated bar and the electrical resistance of the coating filrti.

Many of the coatings adequately protected the reinforcing bars limiting

corrosion to only a few isolated sites [1]. Because these coatings

may behave differently when in concrete the present corrosion study

was undertaken. Coated reinforcing bars embedded in concrete specimens

similar to those described by Stratfull [2,3], have been partially immersed

in an aqueous solution containing chloride ions. Any corrosion occurring is

being monitored by taking both electrical potential and resistance

measurements. The fabrication of test specimens and the method of

testing are described in the following discussion.

3.1.1 Materials and Fabrication of Test Specimens

The materials and methods used to fabricate the corrosion test

specimens were more thoroughly discussed in the previous report [4]

and are summarized in this report to give a complete discussion of the

tests .

2

I
The corrosion test specimens, figure 1, are concrete blocks,

2 7/8 X 4 7/8 X 15 inches, in which are embedded a reinforcing bar

concentric with the longitudinal axis of the block.

The mix proportion of the concrete was approximately 1:1.7:2.5

by weight of port land cement (type III), sand and coarse aggregate,

respectively. The sand was a siliceous aggregate and the coarse

aggregate was crushed stone. Maximum size of the coarse aggregate

was 3/4 inch. Water content of the concrete was about 5 1/2 gallons

per sack of concrete and the slump ranged from 3 to 5 inches.

Coating materials were applied by the applicators or manufacturers

handling the respective coatings, to No. 6 reinforcing bars furnished

by the National Bureau of Standards. Surfaces of the bars were blasted

to a white finish [5], coatings applied and cured, and then the bars

were returned for testing [1].

The coated rebars selected for corrosion testing coincided

essentially (when sufficient specimens were available) with those used

in the pullout tests [4]. These coating materials and their application

methods are described in table 1. The coating materials have been

assigned code numbers for laboratory identification purposes, with

the numbering sequence indicating the chronological order in which

the materials were received.

The corrosion-test specimens were cast in wooden forms, which were

lined with stripping oil, with the reinforcing bar in a horizontal

position. The specimens were removed from the forms after 2 days, moist

cured for 14 days, and stored at 50 percent relative humidity and 72°F

until tested (60 days)

.

3 .
A terminal was inserted into an end of each reinforcing bar so

that electrical connections could be made to a voltmeter or conductivity

bridge. The other exposed end of the reinforcing bar was covered with

a heavy coating, ca . 0.5 inch, of silicone sealant. Therefore, provided

the silicone sealant does not leak, the reinforcing bars are exposed

only to chloride ions permeating the protective layer of concrete.

3.1.2 Corrosion Test Methods

The corrosion- test specimens have been placed in a 105 gallon polyethylene- IJji^dL^ibe^ tank, 4 ft . X 2 ft . X 2 ft

.

The bars are in a vertical position with the lower ends protected by

silicone sealant fitted into 1 inch diameter holes drilled in 1 ft. x 1 ft.

spacing racks of 3/4 in. thick marine plywood. The racks rest on a sheet

of marine plywood laid on the floor of the polyester tank. Similar spacing

racks have been placed on top of the specimens (figure 2) . The marine

plywood and racks have been coated with an epoxy paint to prevent their

deterioration. Sufficient amount of a 3.5 percent sodium chloride solution

was transferred to the tank to cover the lower 13 inches of each specimen,

with the upper 2 inches of concrete being above the level of the solution.

Periodic measurements of electrical potential, millivolts (M.V.) vs. the

saturated calomel half-cell (S.C.E.) and resistance (ohms), vs. the platinum

electrode are being taken for each immersed specimen. The specimens also

are being inspected regularly for visual evidence of cracking or other signs

of failure. The tests will continue until either the concrete specimens

have failed, as evidenced by cracking of the concrete, or the project is

terminated. In the latter case, the concrete specimens will be split

so that the condition of the coatings can be visually assessed.

4
3.1.3 Results and Discussion

The electrical potentials and resistances of the corrosion- test

specimens are listed in table 2 for exposure periods of 24 and 1296

hours. The results obtained to date are in general agreement with

the protective ratings given in table 8 of Interim Report No. 4 [l].

The large potential shifts noted for specimens 18, 30B, and 40-Phos A

are attributed to sealing small holes in the silicone seals on the

immersed portion of the reinforcing bars. NOTE: Some difficulty has

been experienced with sealant failures. Efforts are being made to obtain

more satisfactory sealants.

Electrical potential measurements do not seem to accurately indicate

the corrosion state of the coated reinforcing bars. The uncoated bars have

potentials of ca. -296 M.V. which are in the passive range [3], while

many of the coated bars have muclj more active potentials. This same

phenomenon was noted earlier in the corrosion testing of uncoated and

coated bars immersed in 0.5 N NaCl [l], even though the uncoated

bars were badly corroded as compared to little or no corrosion of the

coated bars. It is felt the electrical potential measurements are not

reliable indicators of the corrosion conditions of coated reinforcing

bars.

Resistance measurements may possibly be more reliable indicators than

potential measurements, since the resistance values are primarily dependent

on the integrity of the coating films. The resistance of a film

will sharply decrease if holidays develop or decrease more slowly if

the film is deteriorating overall. The resistance of the protective

5
layer of water-soaked concrete is low [6,7], certainly much lower than the

resistance of a good protective coating on a bar. The corrosion-test

specimens giving the highest resistance measurements, listed in table 2,

also generally had the highest protective ratings.

No evidence of cracks developing in the concrete cover nor of rust

stains were observed,

3.2 Creep Tests

The work in the reporting quarter involved preparing the creep specimens

and apparatus for testing. The creep specimens consist of a 4 ft, length

of No. 6 reinforcing bar embedded in a 10 x 10 x 12 inch concrete prism

so that the rebar is concentric with the longitudinal axis of the prism.

The creep specimens are the same as the pull-out specimens described in

a previous report [4],

3.2.1 Calibration of Springs

The 24 steel springs which will be used to exert tensile stresses of

15 and 30 ksi (30,000 psi), within the steel reinforcing bars, were calibrated

Dimensions of these springs are: height of 8 inches; outside diameter of

5/14 inches; and the steel coils have a diameter of 1 3/16 inches.

The springs were calibrated using the device (figure 3) shown

in service in figure 4. The compressive displacement of the springs was

-4

measured with 1 x 10 in. micrometer dial gages. The load was exerted on

the springs with a 60,000 lb, capacity hydraulic universal testing machine.

Loads were in the range of 0 to 14000 lb, (14 kips) and dial gage readings

were taken at intervals of 1 kip between 0 and 5 kips and 8 to 12 kips,

while between 5 to 8 and 12 to 14 kips the intervals were 0.5 kips. Amounts

of displacement were determined from the average values of two dial gages

located diametrically opposite on the calibration device. The 24 springs

6
had nearly the same displacement response to loading as indicated by the

plot in figure 5, which shows the range in displacement for corresponding

load application,

3.2.2 Strain Gages

Strain gages, to monitor the tensional loads, are being attached to

the reinforcing bars approximately 3 inches from the concrete prism. The

gages. Model WK-06-500GB-350, were procured from Micro-Measurements,

Romulus, Michigan"^, These gages are reported to have only a small intrinsic

creep of 10 M^ (microstrain units)/year and therefore should be satisfactory

for the present study.

Sixteen of the 24 creep specimens have been instrumented with the

strain gages and the remainder will be instrumented during April 1973.

The methods that have been developed to attach the strain gages to the

reinforcing bars are described in Appendix A.

3 . 3 Implementation

The NBS staff has assisted the FHWA in the implementation portion

of the project by drafting preliminary performance specifications for

powder epoxy coated reinforcing bars, which will be used in the construction of experimental bridges. In the early implementation phase the NBS

staff also served as liaison between the FHWA and coating manufacturers and

applicators

.

1_/ Certain materials are identified in this paper in order to adequately

specify the experimental conditions. In no case does such identification

imply recommendation or endorsement by the National Bureau of Standards

nor does it imply that the materials are necessarily the best available

for the purpose.

7
3.4 Talks Based on Project

Talks based on the project have been given by Dr. James Clifton,

before the following organizations:

1. Committee on Performance of Concrete-Chemical Aspects,

Highway Research Board, January 22, 1973.

2. Committee on Corrosion. Highway Research Board, January 23, 1973.

3. NBS Composite Materials Seminar, February 1, 1973.

4. Research Session of the American Concrete Institute, March 7, 1973.

3 .5 Meetings Attended

3.5.1 Meetings attended in conjunction with the project.

1. Highway Research Meeting in Washington, D. C, January 22 to

26, 1973, by Robert Mathey, Hugh Beeghly and James Clifton.

2. American Concrete Institute Annual Convention, Atlantic City,

New Jersey, March 5 to 9 , 1973, by James R. Clifton.

3. Epoxy Coated Reinforcing Steel Meeting sponsored by the

Implementation Division of FHWA, February 21, 1973, Washington, D. C,

by Hugh Beeghly, Robert Mathey and James Clifton.

3.5.2 Pertinent Meetings held between NBS Staff and Industrial

Representatives.

1. Dr. Kiuchi of Republic Steel met with Hugh Beeghly on March 9, 1973.

2. Mr. Lang of H. C. Price met with Hugh Beeghly and James Clifton

on January 8, 1973 at NBS.

3. Hugh Beeghly and James Clifton met with coating and engineering

staff members of DuPont at Wilmington, Delaware on January 16, 1973.

8
4 . Status of Project

Except for delays in starting the creep tests of coated and uncoated

reinforcing bars, the project is progressing according to schedule. The

delays in the creep tests are primarily due to modifications in instrumentation, especially in the type of strain gages. Revisions in plans

by FHWA for loading and monitoring the creep specimens resulted in

extensive changes in the instrumentation used to measure the tensile

load in the steel rebars over a long period of time.

5 . Prob lems

It is the opinion of the NBS staff that both the creep and corrosion

testings of reinforcing bars embedded in concrete should be continued

until either the specimens fail or unequivocal test results are obtained.

This will necessitate continuance of these tests beyond the contract

expiration date of September 30, 1973.

6 . Work Planned for the Next Quarter

The remainder of the creep specimens will be instrumented and the

creep tests will be commenced.

The corrosion testing of the coated and uncoated reinforcing bars

embedded in concrete will be continued.

The following long-term studies will be completed:

(1) Chloride permeabilities of thin epoxy films.

(2) Corrosion testing of the coated and uncoated rebars in

3.5 percent aqueous NaCl.

(3) Weight stabilities of epoxy discs immersed in several

aqueous solutions.

9
References

J. R. Clifton, H. F. Beeghly, and R. G. Mathey , Interim Report

No. 4. Screening Tests for Evaluating Materials. National

Bureau of Standards Report 10960, 1973.

D. L. Spellman and R. F. Stratfull, Laboratory Corrosion Test of

Steel in Concrete, Research Report M & R 635116-3, Division of

Highways, State of California, 1968.

R. F. Stratfull, Half Cell Potential and the Corrosion of Steel

in Concrete, Research Report CA-Hy-MR-5 116- 7- 72-42 , Division of

Highways, State of California, 1973.

J. R. Clifton, H. F. Beeghly, and R. G. Mathey, Performance of

Coated Steel Reinforcement in Concrete. Part 1. Investigation

of Bond in Pullout Specimens, National Bureau of Standards

Report, in Press.

Steel Structures Painting Council Surface Preparation Specification

SSPC-Sp5-63, amendment 1971.

E. B. Rosa, B. McCollum and 0. S. Peters, Electrolysis in Concrete,

Technologic Papers of the Bureau of Standards, No. 18,(1919).

Adam M. Neville, Hardened Concrete: Physical and Mechanical

Aspects, Chapter 18, Electrical Properties, American Concrete

Institute Monograph No. 6, 1971.

10
Table 1 Long Term Corrosion Testing. Coatings on Reinforcing Bar

Specimens (No. 6 Coated Bars Embedded in Concrete)

Test Solution - 3.5% by Weight NaCl in H^O

Coat ing

Code No,

Quantity of

Specimens TypeJL

Coating

Thickness (mil)

Application

Method

1

2/ 1-1-

1-S

3/

Epoxy

,

liquid

Epoxy

,

liquid

Epoxy

,

liquid

Brush

Brush

Brush

Epoxy

,

primer

Brush

Epoxy

,

liquid

25 Brush

18 Epoxy- coal

tar, liquid

Brush

19 Epoxy

,

liquid

Dip & fused

25 Epoxy

,

powder

Electrostatic

spray

27 Epoxy

,

powder

Electrostatic

spray

28 Epoxy,

powd e r Electrostatic

spray

29 Epoxy,

powder

Electrostatic

spray

30

31

PVC

Epoxy

,

powder

17

9

Fluidized bed

Electrostatic

spray

38

39-Phos

Epoxy

,

powder

Epoxy,

powder

Electrostatic

spray

Electrostat ic

spray

11
Table 1 (continued)

Coating

Code No,

Quantity of

Specimens Type

Coating

Thickness (mil)

Application

Method

4/ 40-Phos -

40

41

2 Epoxy

,

5 Electrostatic

powder spray

2 Epoxy 5 Electrostatic

powder 2 spray

2 Epoxy, 3 Electrostatic

powder spray

Uncoated

— Unless otherwise indicated, coating material was applied to rebars with

surfaces blasted to a white finish.

2/ Same material as No. 1 but with different pigment.

3^/ S denotes coating material No. 1 mixed with sand.

4/ Phos. indicates that the blasted steel surfaces of the rebars were phosphatized

before the coating materials were applied.

12

I
Table 2

Electrical Potential and Resistance Measurements

of Corrosion-Test Specimens in 3.5 Percent NaCl.

Coating , Code No.-

1 A

B

EMF

(MV)

345 .0

408.8

Exposure Time (Hour)

24

Resistance

(ohms)

3.8 X 10^

7.0 X 102

EMF

(MV)

310.5

335 .3

1296

Resistance

(ohms)

3.8 X 10^

8.6 X 102

Protective , 2/ Rating

1-1

1-S

3

18

19

A

B

A

3

A

B

337.0

484.5

285 .6

260.3

339 .2

130.0

575 .6

484.0

438.0

2.5 X 10'

4.8 X 10'

3.1 X 10^

2.7 X 10^

2.4 X 10^

1.0 X 10^

6.0 X 10-

5.6 X lo;

6.1 X 10'

279.0

449.0

311.7

281.7

304.5

148.4

040.0

406.5

429.0

3/

2.3 X 10^

5.1 X 102

2.9 X 102

2.9 X 102

2.2 X 10-^ 1.3 X 10^

1.1 X 10^

5.1 X 102

6.6 X 10^

25

27 A

B

542.7

654.6

571.5

4.1 X 10'

1.3 X 10,

6.8 X 10-

408.5

638.7

569.0

4.4 X 10'

1.8 X 10,

5.4 X 10-

28

29

30

A

B

A

B

461.5

376.3

403.4

058.0

448.2

5.2 X 10^

6.4 X 10^

6.6 X 102

1.0 X 10^

1.5 X 10^

460.0

377.7

408.0

4.4 10'

059.0

007.03/

6.6 X lo;

5.2 X 10^

1.1 X 10^

1.7 X 10-

31 A

B

359.8

092.2

1.5 X 10;

9.8 X 10-

437.2

043.5

1.2 X 10

6.5 10'

38 392.7 3.2 X 10' 261.0 3.5 X 10^

13
Table 2 - continued

Coating , Code No.-

EMF Resistance

(ohms)

39-Phos A S 1 3 0 4.9 X

. ^2 10

B . 536.2 5 .0 X 102

40-Phos A Z. ^ • ^ 2.5 X

-, ^2 10^

40-Phos B 382.5 3.4 X 102

40 A 431 8 2.9 X 102

B J / / • u 2.8 X 102

41 A 540.5 6.0 X 103

B 575 .9 5.4 X 102

Uncoated A 334.2 2.7 X 102

B 264.0 2.6 X 102

EMF

(MV) Resistance(ohms)

Protective

Rating

396.3 4.5 X 3

401.5 4.2 X 10^

127.7^/ 2.6 X 102

102

2

386.2 3.1 X

408.4 3.6 X 102 3

331.2 2.7 X 10^

532.8

547.6

1.2

1.2

X

X

10^

10^

2

291.7 2.3 X 102 4

299.0 2.7 X 102

1/ A and B denote duplicate specimens

2/

' — Ratings from Table 8 of reference [1].

3/ — Large shifts in electrical potential attributed to sealing small holes

in the silicone seal.

14
Appendix A

Methods of Attaching Strain

Gages to Reinforcing Bars

A. Surface Preparation

I, The area of the bar to be cleared of deformation patterns will

start 1 3/4" from the surface of the concrete block and extend

to 4 3/4" from the block, thus leaving a 3" length by 1/2" wide

strip of smooth metal. On dummy and temperature compensating

bars, center the area lengthwise on the bar,

II. First use a coarse file to remove most of the deformation patterns.

III. Next use a fine file to smooth the bar being careful not to remove

any more metal than necessary,

IV, Finally, round the surface with 80 grit closekote aluminum oxide,

V, Degrease the area with either Chlorothene NU or Freon TP^^

VI, Final abrading of the surface is done with 320 grit silicon carbide

paper after thoroughly wetting the smoothed area with M-Prep

Conditioner A, When done, slowly wipe the surface dry with a

gauze sponge,

VII „ Repeat VI,

VIII. Apply alignment marks indicating where the gages will be located

as needed with a ballpoint pen, carefully, so that the gages will

be placed diametrically opposite on the rebars. DO NOT SCRIBE THE

METAL !

\J Certain materials listed in Appendix A are those suggested by the manufacturer of the strain gages and are identified in order to adequately

explain the method of attaching the gages. In no case does such identifica

tion imply recommendation by the National Bureau of Standards nor does it

imply that the materials are necessarily the best available for the purpose

15'
Appendix A - continued

IX. Repeatedly apply M-Prep Conditional A and scrub with a cotton

tipped applicator until a clean applicator is no longer discolored.

Remove all residue and M-Prep Conditioner A by slowly wiping with

a gauze sponge until the surface has no residues left.

X. Apply a liberal amount of M-Prep Neutralizer 5 to the areaand

scrub with a cotton tipped applicator. With a single s low

wiping motion of a gauze sponge, carefully dry the surface.

Caution - DO NOT wipe the gauze back and forth as this may

allow contaminants to be redeposited.

XI. Slip meter support and measuring bars over the rebar and fasten

as close to the concrete block as possible.

B. Strain Gage and Terminal Strip Attachment

I. Using tweezers, remove the gage from its acetate envelope, cut

leads to 1/4" and check with ohm meter. Place it, bond side

down, onto a chemically clean glass plate. The terminal strip

should be positioned next to it as the complete assembly will

appear on the bar. While holding the gage in position with an

acetate envelope, place a short length of Mylar JG tape over about

half of the gage and the entire terminal strip.

II. Remove the taped assembly by peeling the tape at a shallow angle

(about 30°) and tranferring it onto the specimen making sure that

alignment marks coincide with specimen layout lines. If misalignment does occur, lift one end of the tape at a shallow

angle until assembly is free. Realign and replace.

16
Appendix A - continued

III. Mix the 610 adhesive. Pour the contents of one "Curing Agent"

bottle into one "Part A" dispenser bottle with the aid of the

disposable plastic funnel. After replacing the brush-cap, shake

the bottle vigorously for 10 seconds. Allow the mixed bottle to

stand at least one hour before use. This mixed bottle of adhesive

has a shelf life of about six weeks at 75°F. One bottle should

last for many applications of gages.

IV. Peel back one end of the taped assembly (again, at a shallow

angle) so as to raise both the gage and terminal. By curling the

Mylar tape back upon itself it will remain in position, ready to

be accurately relaid after application of the adhesive. Install

both gages before going on to the next step,

V. Coat gage backing, terminal backing and specimen surface with a

thin layer of adhesive. DO NOT allow adhesive applicator to touch

tape mastic. Permit the adhesive to air dry for 5 to 30 minutes

(at 75°F and 50% relative humidity).

VI. Replace gage/terminal assemblies to their original positions over

the layout marks using only enough pressure to allow the assembly

to be taked down. Overlay gage /terminal areas with a piece of

thin Teflon sheet. If necessary anchor Teflon in position with

a piece of Mylar tape.

VII. Cut a 3/32" thick silicone gum pad and a metal back up plate to

a size slight ly larger than the gage/terminal areas and carefully

center these on the assembly areas. Clamp silicone pads and metal

plates to the rebar..

17
Appendix A - continued

C. Curing

I. Tip the specimen into an upright position, if not already. Slide

the wire screen cylinder over the rebar and down until it rests

on the concrete block.

II., Wind the heating tape around the outside of the screen cylinder.

Plug the heating tape into a variac in order to regulate the

temperature.

III. Slide the thermocouple in between the rebar and the screen to

monitor temperatures. The thermocouple should be as close as

possible to the rebar. Wrap the entire assembly with two layers

of aluminum foil and gather loosely at the top.

IV. Raise the temperature at the rate of 5°F to 20°F per minute up

to a maximum of 350°F to 400°F. Allow the specimen to cure for

1 1/2 hours. Next, decrease the temperature to about 150°F-250°F

and continue to cure for 2 more hours.

V. Upon completion of the above curing cycle, turn off the heating

tape and allow the temperature to drop to room temperature before

removing the heating assembly, clamping assembly and tape.

VI. After removing all tape, etc. wash the entire gage area with toluene

in order to remove all mastic residue and other contaminants <, Wipe

dry with a gauze sponge.

D. Wiring

I. Each lead wire must be exactly the same length; in the present case

30" long.

II. Both ends of the 430-FST four wire cable will' have the shielding and

outer coating of Teflon stripped 2" back from the end of the cable.

Each wire (red, black, white and green) will be stripped 1/4" on both ends

i 18
Appendix A - continued

III. Wiring diagram

STRIPS

IV. Solder the cable to the terminal strip using a small amount of ros

core solder and heat. Tape the cable to the rebar about where the

shielding ends with black plastic electrical tape. Next, solder

the strain gage leads to the terminal strip leaving them looped

up, again using just enough solder and heat. Take the black and

red leads at the output end o£ the cable, twist together and

solder. This pair of wires should be folded back against the

cable and taped down with black plastic electrical tape making

sure the ends are covered.

V. Check wiring with ohm meter. Look for excessive resistance

caused by faulty solder connections.

Coatings

I. Melt micro-crystalline wax (M-Coat W-1) and brush a thin layer

(1/16") over the gage and terminal strip, and complete around

the rebar.

II. Mix and apply a coating of M coat G making sure that all the wax

is covered. Allow to dry for 24-48 hours.

19
Captions for Figures

1. Coated Reinforcing Bar Embedded in Concrete- Corrosion-Test Specimen.

2. Corrosion-Test Specimens Immersed in 3.5 Percent NaC/

.

3. Apparatus for Calibrating Steel Springs.

4. Calibration Apparatus with Spring Loaded in Hydraulic Testing

Machine

.

5. Range of Displacement Response of 24 Steel Springs.

20






FORM NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 73-229

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Interim Report No. 6. Corrosion and Creep Testing of Coated

Reinforcing Bars in Concrete

Nonmetallic Coatings for Concrete

5. Publication Date

6. Performing Organization Code

7. AL'THOR(S) James R. Clifton, Hugh F. Beeghly, Erik Anderson,

Robert G. Mathey

8. Performing Organization

NBSIR 73-229

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

10. Project/Task/Work Unit No. 4616433

11. Contract/Grant No.

12. Sponsoring Organization Name and Address Federal Highway Administration

U. S. Department of Transportation

Washington, D. C. 20590

13. Type of Report & Period Covered Interim

Jan. - Mar., 1973

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. .'\BSTR.^CT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The possibilities of protecting steel reinforcing bars embedded in concrete from

corrosion by using organic barrier-type coatings are being investigated in this

project. This corrosion is accelerated by the chloride ions of the two most commonly

used deicing materials, calcium chloride and sodium chloride.

In this report, corrosion studies carried out on coated reinforcing bars

embedded in concrete are discussed. Methods of instrumenting creep-test specimens

are also explained.

The electrical potentials of coated reinforcing bars are not reliable indicators

of the corrosion state of the steel bars. The electrical resistances of the coating

films are more reliable indicators of the performance of a coating material than the

electrical potential measurements.

17. KEY WORDS (Alphabetical order, separated by semicolons) CorrOsion; creep testing; epoxy COatingS;

polyvinylchlorides ; strain gages; steel reinforcing bars

18. AVAILABILITY STATEMENT

I I UNLIMITED.

^FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

22. Price

USCOMM-DC 66244.P7I