NATL INST OF STANDARDS & TECH R.I.C.

A1 11 00992841

/NBS building science series TA435 .U58 V65;1975 C.1 NBS-PUB-C 1974 s

v> BUILDING SCIENCE SERIES 65

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

r\0. Lp^

Nonmetallic Coatings for

Concrete Reinforcing Bars
The Building Science Series

The Building Science Series disseminates technical information developed at the National Bureau of Standards on

building materials, components, systems, and whole structures. The Series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems. These publications, similar in style and content to the NBS Building Materials and Structures Reports (1938-59),

are directed toward the manufacturing, design, construction, and research segments of the building industry, standards organizations, and officials responsible for building codes. The material for this Series originates principally in the Center for Building Technology of the NBS Institute for Applied Technology. The publications are divided into three general groups: Building Systems and Processes;

Health, Safety and Comfort; and Structures and Materials. For further information regarding these publications

please contact the Scientific and Professional Liaison Section, Center for Building Technology, Institute for Applied Technology, National Bureau of Standards, Washington, D.C. 20234.

LSee mailing list announcement on last page J
National Bureau of Standards SEP 2 1975

. oss Nonmetallic Coatings for

m Concrete Reinforcing Bars

James R. Clifton, Hugh F. Beeghly,

and Robert G. Mathley

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Sponsored by

U.S. Department of Transportation Federal Highway Administration

Offices of Research and Development

Washington, D.C. 20590

U.S. DEPARTMENT OF COMMERCE, Rogers C. B. Morton, Secretary

NATIONAL BUREAU OF STANDARDS

Issued August 1 975
Library of Congress Catalog Card Number: 75-600058

National Bureau of Standards Building Science Series 65

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 65, 42 pages (Aug. 1975) CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1975

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 • Price $1.00 Stock Number 003-003-01394

Catalog Number C13.29/2:65
Contents

1. Introduction 1 1.1 Project objective 1 1.2 Background information 1 1.3 Project program 1

2. Coating Materials 2

2.1 Selection of coating materials 2

2.2 Curing methods and specimen preparation 2

2.2.1 Two-component liquid systems 2

2.2.2 One-component liquid systems 2

2.2.3 Powder systems 2

2.2.4 Reinforcing bars coated by applicators 4

3. Reinforcement and Concrete Specimens 4

3.1 Reinforcement 4

3.2 Concrete 5

3.3 Test specimens 5

3.3.1 Pullout specimens 5

3.3.2 Creep specimens 5

3.3.3 Corrosion-test specimens 5

3.3.4 Fabrication and curing of specimens 5

4. Evaluation of Coating Materials, Experimental Methods and Results 6

4.1 Chemical resistance 6

4.1.1 Epoxy disk specimens 6

4.1.2 Immersion studies of coatings on reinforcing bars 7

4.1.3 Chloride permeability 7

4.2 Impact and abrasion resistance of epoxy coatings on steel plates 10

4.3 Inspection of coatings on steel reinforcing bars 10

4.4 Physical testing of coatings on reinforcing bars 10

4.4.1 Bend tests 10

4.4.2 Impact tests 12

4.4.2.1 Dropping coated bars on concrete 12

4.4.2.2 Falling weight method 12

4.4.3 Hardness determination 15

4.4.3.1 Pencil hardness 15

4.4.3.2 Indentation method 15

4.5 Electrochemical tests 15

4.5.1 Applied voltage studies 15

4.5.2 Electrical potential and electrical resistance measurements 17

4.5.2.1 Coated reinforcing bars in 3.5 percent solution of sodium chloride 17

4.5.2.2 Coated reinforcing bars embedded in concrete 17

5. Bond Strength and Creep Determinations 20

5.1 Pullout studies 20

5.1.1 Pullout test procedures 20

5.1.2 Results of pullout studies 21

5.2 Creep studies 24

5.2.1 Creep test procedures 24

5.2.2 Results of creep studies 26

5.2.2.1 Slip-time relationships 27

5.2.2.2 Slip values at 45 days 27

iii
Page

6. Discussion 29

6.1 Evaluation of coating materials 29

6.1.1 Chemical resistance of coating materials 29

6.1.2 Physical durabilities of coatings 29

6.1.3 Corrosion protective qualities of coating 30

6.1.4 Bond strengths and creep characteristics of coated bars in concrete 30

6.2 Proposed qualification criteria for coating materials 30

6.3 Implementation of epoxy-coated reinforcing bars 31

7. Conclusions and Recommendations 32

7.1 Conclusions and recommendations 32

7.2 Recommended further studies 32

8. References 32

9. Appendix A. Firms submitting coating materials for evaluation 33

10. Appendix B. Conversion factors of U. S. units to SI units 34

List of Figures

1. View of reinforcing bars 4

2. Typical stress-strain characteristics of reinforcing bars 4

3. Weight stabilities of cured specimen disks 7

4. Permeability cell 9

5. Concentration of chloride ions passing through epoxy films 9

6.A. Applied voltage test at beginning of test 16

6.B. Results of application of 2 volts for 30 minutes 16

7. Measurement of electrical potential of coated reinforcing bars 17

8. Measurement of electrical resistance of coatings on reinforcing bars 17

9. Electrical potential and resistance measurements of reinforcing bar

coated with material No. 1 immersed in 3*4 percent NaCl 18

10. Electrical potential and resistance measurements of reinforcing bar

coated with material No. 25 immersed in 3Y2 percent NaCl 18

11. Electrical potential and resistance measurements of reinforcing bar

coated with material No. 31 immersed in Sy2 percent NaCl 18

12. Corrosion-test specimen with coated reinforcing bar embedded in concrete block 18

13. Corrosion-test specimens immersed in 3.5 percent solution of NaCl 20

14. Pullout specimen on electromechanical testing machine 20

15. Schematic of pullout specimen 20

16. Applied load to reinforcing bar in pullout

specimens versus free-end and loaded-end slip 22

17. Schematic of creep specimen 25

18. Creep specimen loaded to a tensile stress level of 30,000 psi 25

19. Schematic of creep test frame 25

20. Apparatus for calibrating steel springs for the creep study 26

21. Range of displacement response of 24 steel springs used in the creep study 26

22. Free-end and loaded-end slips in creep specimens 27

iv
List of Tables

Pag*

1. Description of coating materials 3

2. Properties of reinforcing bars 5

3. Properties of deformations 5

4. Weight changes of cured epoxy disks immersed in aqueous solutions 6

5. Immersion studies of coatings on reinforcing bars 8

6. Permeability of chloride ions through epoxy films 9

7. Abrasion and impact resistance of cured epoxy coatings on steel panels 10

8. Inspection of coated steel reinforcing bars 11

9. Results of bending coated reinforcing bars 13

10. Drop resistance and impact resistance of coatings on rebars 14

11. Indentation hardness of coatings on reinforcing bars 15

12. Electrochemical studies of coated reinforcing bars 16

13. Electrical potential and resistance measurements of

corrosion-test specimens in aqueous solution of 3.5 percent NaCl 19

14. Pullout data 23

15. Creep of coated and uncoated bars in concrete prisms (at 45 days) 28

16. Proposed criteria for qualifying coating materials 31

v
Summary

The objective of this project was to determine the feasibility of using organic coatings, especially

epoxies, to protect steel reinforcing bars embedded in concrete of bridge decks and buildings from

corrosion accelerated by chloride ions. The study was to include the selection and procurement of promising coating materials; evaluation of the physicochemical durabilities of coatings as well as their protective qualities; and the determination of whether coated reinforcing bars would adversely affect the structural integrity of concrete bridge decks and buildings.

The coating materials were restricted to organic formulations, with the exception that the pigments

could be of inorganic composition, and the selection was done on a generic basis. The most important

criteria for selection were: inertness towards the constituents of cement paste and also chloride ions; creep characteristics; film integrity and protective qualities; and bond to steel. Altogether 47 different commercially available materials, of which 36 were epoxies, were evaluated. Most of the epoxy coatings studied in this project had satisfactory chemical resistance to test solutions chosen to simulate the aggressive materials likely to be present in concrete bridge decks and

buildings. Exceptions were some solvent-containing liquid epoxy systems which experienced large

weight changes when immersed in the test solutions. Many of the epoxy coatings even as thin films, were found to be essentially impervious to chloride ions. The abrasion resistances of all but two epoxy coatings were judged to be acceptable. Good cor- relation between the impact resistance (determined by the falling weight method) and the bend test was obtained. Brittle materials failed in both tests and conversely flexible materials had acceptable

impact resistances and experienced minimal damage in the bend test. A large variation was observed

between the relative flexibilities of epoxy coatings. However, in general, the powder epoxy system had

better flexibilities than the liquid epoxy systems. Polyvinyl chloride coatings had excellent flexibilities even in film thicknesses up to 35 mils. The hardness determinations indicated that epoxies are tougher

materials than the polyvinyl chlorides which were tested and, therefore, should be more resistant to the abuse reinforcing bars normally experience.

Powder epoxy coatings were observed to provide more uniform coatings with fewer holidays than

the liquid epoxy materials. Liquid epoxies tended to flow-off of the tops of the deformations of rein- forcing bars during curing and accumulated in the low-lying regions between deformations, thus leaving

the deformations either bare or thinly covered. In most corrosion studies carried out in the project,

corrosion was observed to initiate at the deformations. The powder epoxy coatings, when properly

applied and having a film thickness greater than 4 mils, adequately protected reinforcing bars from

corrosion.

The effect of coated reinforcing bars on the structural integrity, of bridge decks and buildings was

assessed by pullout and creep studies. Epoxy coated reinforcing bars, with average film thicknesses

between 5 and 11 mils, had acceptable bond strengths to concrete as measured in the pullout tests. All but two of the nine epoxy coatings that were included in the creep studies, had acceptable creep rates,

i.e., creep rates comparable to those of uncoated bars. The polyvinyl chloride coated bars had unacceptable bond and creep characteristics. Considering flexibility, bond strength, creep charactertistics, and minimum corrosion protective

requirements, it is concluded that the optimum film thickness of epoxy films on steel reinforcing bars

is 7 ± 2 mils. Four powder epoxy coatings were found to be the best candidates for protecting steel reinforcing

bars from corrosion. It is recommended that these four coatings be further evaluated in experimental

bridge decks and building construction.

vi
Nonmetallic Coatings for Concrete Reinforcing Bars

James R. Clifton, Hugh F. Beeghly, and Robert G. Mathey

This work was undertaken to ascertain the feasibility of using organic coatings, especially epoxies, to protect the steel reinforcing bars embedded in concrete of bridge decks from rapid

corrosion. This corrosion is caused by the chloride ions from the most commonly applied deicing

salts, sodium chloride and calcium chloride. Altogether, 47 different coating materials were

evaluated to some extent, consisting of 21 liquid and 15 powder epoxies; 5 polyvinyl chlorides; 3 polyurethanes; 1 polypropylene; 1 phenolic nitrile; and one zinc rich coating. The chemical and

physical durabilities, chloride permeabilities, and protective qualities of coatings were assessed. The bonds between coated and uncoated bars and concrete were measured by both pullout and

creep tests. The results indicate that both epoxy and polyvinyl chloride coatings, if properly applied, should adequately protect steel reinforcing bars from corrosion. However, only the epoxy coated bars had

acceptable bond and creep characteristics when embedded in concrete. The powder epoxy coatings

overall performed better than the liquid epoxies, and four powder epoxy coatings have been

identified as promising materials to be used on reinforcing bars embedded in concrete decks of experimental bridges. Key words: Bridge decks; chloride ions; corrosion; deicing salts; epoxy coatings: organic

coatings; polyvinyl chloride coatings; steel reinforcing bars.

1 . Introduction

1.1. Project Objective

This project was undertaken to determine if organic

coatings, especially epoxies, could be used to protect

steel reinforcing bars in concrete of bridge decks and

buildings from rapid corrosion.

1.2. Background Information

The deterioration of concrete bridge decks, in 5-10

years, has become a major problem during the past

decade [1—7].

1 The annual cost of such repairs on inter- state highways has been estimated to be more than $70

million in 1972. Often, this early deterioration has been

attributed to accelerated corrosion of the steel reinforc- ing bars induced by chloride ions from deicing materials [8,9]. Use of the two most commonly applied deicing

materials, calcium chloride and sodium chloride, has

increased substantially since the early 1960's [10]. Normally, steel is passive towards corrosion when in an environment of high basicity (pH of about 13) as

in portland cement concrete [11]; chloride ions, however, are able to depassivate steel and thereby promote

its active corrosion [11—12]. The resulting insoluble corrosion products occupy a substantially larger volume

(possibly more than a tenfold increase) than the steel from which they were formed; and as a consequence

large pressures may be exerted within the concrete which eventually cause the cracking and spalling of the

concrete. Spellman and Stratfull reported [14] that as

little as 1 mil of steel being converted into its characteristic corrosion products can cause the cracking of a %-in. thick concrete layer. Similar problems are en- countered with buildings constructed along the ocean and salt-water lake shores. Coating reinforcing steel with protective materials

has been considered previously as a practical means of reducing the rapid corrosion of the bars. Much atten- tion has been given to protecting reinforcing bars with

metallic zinc [15-16]. Recent studies [17-18], however,

1 Figures in brackets indicate the literature references on page 32.

suggest that zinc may be susceptible to rapid corrosion

by chloride ions in basic environments and, therefore,

possibly may not provide the necessary long-term protection for steel bars. Cadmium [19] and nickel [20]

have been reported to be satisfactory coatings for rein- forcing steel. Their cost, however, may be prohibitively

high. The use of organic types of barrier coatings for protecting reinforcing bars has been recommended

[21-22]. Tripler and co-workers evaluated a few nonmetallic coatings and suggested that an epoxy-coal tar type of coating could have potential as a protective

coating for reinforcing steel [20]. 1.3 Project Program

The program of this project was established to in- clude: the selection and procurement of promising

coating materials; evaluation of the physicochemical

durabilities of coatings as well as their protective qualities; and the determination of whether coated reinforc- ing bars would affect the structural integrity of concrete bridge decks. The coating materials were evaluated according to the five-part scheme outlined below.

The first part, chemical resistance of coatings, consisted of preliminary screening tests performed to choose the most promising materials. Then these

selected materials were subjected to the more exhaustive testing phase, parts 2 to 5. The tests in parts 2 to 5 were performed on coated reinforcing bars which

had been coated in the factory by the applicators or manufacturers handling the respective materials.

1. Chemical Resistance of Coating

A. Resistance to water, calcium chloride, calcium

hydroxide, calcium sulfate and fresh portland cement paste.

B. Chloride permeability.

2. Film Integrity of Cured Coatings

A. Coverage characteristics; variations in film thickness; etc.

1
B. Application methods.

C. Preparation of steel substrate prior to coating

application.

3. Physical Durabilities of Coatings on Rebars

A. Abrasion and impact resistances.

B. Flexibilities determined by bending coated re- bars.

4. Electrochemical Measurements of Coated Rebars

Immersed in Sodium Chloride Solutions

A. Applied voltage studies.

B. Electrical potential of coated bar.

C. Electrical resistance of coating film.

5. Bond Tests of Coated Rebars Embedded in Concrete

A. Pull out.

B. Creep.

2. Coating Materials

2.1. Selection of Coating Materials

The coating materials to be evaluated were restricted

to organic formulations, with the exception that the pigments could be of inorganic composition, and the

selection was done on a generic basis. The most important criteria for selection were: inertness towards

the constituents of cement paste and also chloride ions; creep characteristics; film integrity and protective

qualities; and bond to steel and concrete. The coatings selected for evaluation are listed in table

1 (also included are a few unsolicited materials submitted by the respective firms who handle them), and all are of commercial origin. The coating materials have

been assigned code numbers for identification purposes. The code number sequence has no significance other than indicating the chronological order in which the materials were received. The polyurethanes and epoxies each consist of two

components, a resin and curing component, and are

classified as thermosetting materials because their cure

(polymerization) is accelerated by the application of

heat. Once cured, thermosetting materials normally re- tain their shapes up to their decomposition temperatures. The other coatings in table 1 are classified as thermoplastics as they soften and change shape far be- low their decomposition temperatures when heated. Thermoplastics usually are one component systems.

Emphasis in this study has been given to the thermosetting materials and especially epoxies because these materials seem to best satisfy the established criteria. Altogether 36 epoxy coatings, both powder and liquid

systems, have been evaluated. The terms powder and

liquid refer to the uncured state of epoxy coatings;

when cured, i.e., polymerized, they form hard solids. Some materials, especially powders, were submitted

only in the form of cured films on steel reinforcing bars.

2.2. Curing Methods and

Specimen Preparation

2.2.1. Two-Component Liquid Systems

The epoxy liquid systems consist of two components

which must be mixed in the proper ratio to attain the optimum degree of polymerization. In the present work,

the ratio of curing component to epoxy resin, and the mixing and curing times, were closely controlled and were the same as those specified by the manufacturers'

accompanying instructions. The epoxy resins and cur- ing components were mixed at room temperature, ca. 75 °F, relative humidity of ca. 50 percent, using either an electric stirrer for solvent-free systems or a metal

spatula for solvent-containing systems. The two component urethane materials and the zinc-filled coatings were similarly mixed.

Test specimens of the coating materials were cast immediately after mixing was completed and, in addition, steel plates and steel reinforcing bars were coated

with thin films. Specimen discs of 2*4 in in diameter

with thickness of ca. % in (thicknesses of solvent con- taining systems were reduced to %B in) were cast using

aluminum weighing dishes as molds. The disks were

stripped from the molds after a curing period of seven

days.

Wet films of 3—7 mils 2 thickness were formed by

applying the coatings with a Baker roller film applicator

to the gel side of photographic paper or to sheets of Teflon.3 The cured films were stripped from the photographic paper after being immersed in water at room

temperature for 16 hours. Cured films were easily

stripped from Teflon sheets using a thin-bladed spatula.

Coating materials were applied to 4 x 4 x 0.050 in cold

rolled steel plates and to No. 6 steel reinforcing bars 4 using a paint brush. The steel plates had been degreased

previously using mineral spirits, and the reinforcing

bars had been sand blasted to a near white surface [23].

2.2.2. One-Component Liquid Systems

The two one-component liquid systems, a polyvinyl

chloride (PVC) and a phenolic nitrile, were hardened

by the evaporation of solvents. Test specimens were formed as previously described for the two-component

systems.

2.2.3. Powder System

No mixing of the epoxy powders was necessary since the two components are contained within each powder

particle. The powders were applied to steel and Teflon

substrates preheated to ca. 400 °F in an electric oven by

immersing the substrates into a fluidized bed [24] of the powders.

2 One mil equals 0.001 in. exactly.

3 Certain instruments and materials are identified in this paper in order to adequately specify the experimental conditions. In no case does such identifica- tion imply recommendations or endorsement by the National Bureau of Stan- dards or the Federal Highway Administration, nor does it imply that the material or instruments are necessarily the best available for the purpose.

4 No. 6 steel reinforcing bars have a nominal diameter of % in.

2
Table 1. Description of coating materials

Code Percent a Number T1 ype Uncured State Solvent Com merits

1 Epoxy—Polyamide b Liquid

-100 0 Used for concrete overlays. 2 Epoxy-Polyamide Liquid

-100 0 Has been previously tested as coating for steel rebars. 3 Epoxy—Polyamide Liquid

-100 0 Pri mer. 4 Epoxy-Modified amine Liquid

-100 0 Primer.

5 Epoxy-Polysulfide Liquid

-100 0 Used to bond fresh concrete to old concrete. 6 Epoxy—Modified amine Liqu id

-100 0 Topcoat.

7 Epoxy Liquid

-50 50 Water emulsion activated system. 8 Epoxy—Polyamide Liquid

-60 40

9 Epoxy—Polyamide Liquid

-50 50 Primer.

10 Epoxy—Ketamine Liquid

-100 0 High viscosity. 11 Epoxy-Ketamine Liquid

-100 0

12 Epoxy Liquid

-ca. 100 nil Cures at relative humidity above 50 percent. 13 Epoxy Liquid- 1 nn

-ca. 100 nil Limited flexibility. 14 Vinvyl Liquid

on -zU 80 Primer paint. 15 Epoxy—Polyamide Liquid

-oU 50 Epoxy paint. 16 Epoxy-Polyamide Liquid- cn Epoxy paint. 17 Epoxy Liquid

i nn -tuu nu Low viscosity.

1 P Coal-tar epoxy Liquid

l nn -tuu Protective overlay on concrete pavements.

1 0 Epoxy Liquid

-40 One component; cures by heating. ZU Epoxy Powder Only coated rebars have been received.

01ZIZZ99ZD93

Epoxy

Epoxy

Polyvinylchloride

Polyvinylchloride-Plastisol

Epoxy

Polyvinylchloride

Epoxy

Epoxy

Epoxy

Polyvinylchloride

Epoxy

Powder Only coated rebars have been received. Only coated rebars have been received. Only coated rebars have been received. Only coated rebars have been received.

Powder

Powder

9,1 Z<* Powder

9CZO Powder

26 Powder Only coated rebars have been received. 27 Powder

28

90 Powder

30 Only coated rebars have been received. Same material as No. 22 but coated rebars submitted from a different applicator and

also the pure powder was submitted.

31 Powder

32 Epoxy

Polyurethane

Powder

03 Liquid L/niy coateu reriars nave oeen received. o4 Phenolic nitrile Liquid- i n -J.U on Adhesive for metals. 3C Polyurethane Liquid—-100 \j Elastomer, elongation—600%.

36 Polyurethane Liquid

-100 0 Elastomer, elongation—550%.

37 Epoxy Liquid

i nn -1UU n\j Adhesive for metals. 38 Epoxy

Epoxy

Epoxy

Epoxy

Powder

39 Powder

Powder

41 Powder Only coated rebars have been received. 42 Epoxy Powder Only coated rebars have been received, same

materials as No. 41, but different application

procedure. 4o Epoxy

Zinc in a zinc silicate binder Powder44 Liquid--80 20 Metallic zinc filler and liquid base are mixed, hardens by solvent evaporation. 45 Coal-tar epoxy Liquid Unknown One component, epoxy resin and coal tar, no

curing components. 46 Epoxy-Polysulfide

Polypropylene

Liquid

47 Powder Only coated rebars have been received. Coat- ing very brittle. a Solvents comprised the listed percent of liquid materials.

b Materials identified as 1-1 and 1-S in tables 13 and 14 denotes a different pigmentation of material No. 1 and material No. 1 mixed with small amount of sand, respectively.

i

3
Then the coatings were cured in the electric oven under the conditions specified by the manufacturers.

When allowed to cool to room temperature, the cured

epoxy films were easily removed from the Teflon substrate by using a thin-bladed spatula. Both No. 6 steel reinforcing bars and 4 x 4 x 0.050 in cold-rolled steel plates were coated with the powders.

Specimen disks could not be satisfactorily fabricated

from the epoxy powders, because when sufficient masses

to make %6 in thick disks were heated to their specified curing temperatures, porous solids that had ex- panded over 100 percent were produced. Even four-fold reduction of the masses did not yield satisfactory

specimens. Only one powder epoxy did not exhibit this expansion phenomenon. Possibly, some of the curing

components are vaporized at the curing temperatures

causing the formation of porous structures in the thick

castings. However, no difficulties were encountered

when films that were less than 20 mils thick were formed from the powder epoxies.

2.2.4. Reinforcing Bars Coated by Applicators

The coating materials that were judged (on the basis of preliminary screening tests which included: resis- tance to chemicals; cure time; film integrity; and

evaluation of relative brittleness) to have the most

promise as potential protective coatings for steel rein- forcing bars were subjected to further testing using

bars coated by the applicators or manufacturers sub- mitting the respective coatings. No. 6 steel reinforcing

bars, grade 60, four feet in length having two different deformation patterns, were supplied to each applicator.

The surfaces of the bars were usually cleaned, often by

sandblasting; coating applied and cured; and the bars

returned to the National Bureau of Standards for evaluation.

3. Reinforcement and

Concrete Specimens

3.1. Reinforcement

The tensile reinforcement in the pullout, creep, and

corrosion tests consisted of No. 6 deformed bars hav- ing either a barrel (B) or diamond shaped (D) defor- mation pattern as shown in figure 1. The bars were randomly selected and may not all have been the same

heat. A 4 foot length of each type of bar was tested to rupture in tension. The yield strengths determined by

the "0.2 percent offset" method were 67,600 psi for No. 6 rebars (D) , and 62,500 psi for No. 6 rebars (B)

These bars did not exhibit a well-defined yield point,

however, their stress-strain relationships (fig. 2) were

linear up to a stress of about 64,000 psi for the (D)

rebars and approximately 62,000 psi for the (B) re- bars. Tensile properties of the bars are listed in table 2. The yield, tensile strengths and deformations of the bars met the requirements of ASTM A 615-72 [25] for Grade 60 bars. The properties of deformations were

determined from three coupons of each type of bar and

are given in table 3.

FIGURE 1. View of No. 6D (upper bar) and No. 6B (lower bar) reinforcing bars. D denotes diamond shaped deformation pattern and B indicates barrel pattern.

80xloV

70-

STRAIN (In/In)

FIGURE 2. Typical stress-strain characteristics of reinforcing

bars.

4
Table 2. Properties of reinforcing bars 3.3. Test Specimens

Bar size and type

Area, As

(in 2

)

Perimeter, Zo

(in)

Yield a strength

fi/ (psi)

Proportional

limit (psi)

Tensile

strength

(psi)

Modulus of

elasticity, E„

(106 psi)

Elongation

in 10 in (per- cent)

No. 6D b No. 6B c 0.441 0.434

2.35 2.34 67,600

62,500

63,900

61,800

95,700

95,200

30.7 28.411.2

8.2

a Yield strength was determined by the "0.2 percent offset" method.

b D denotes diamond deformation pattern.

c B denotes barrel deformation pattern.

Table 3. Properties of deformations a

Average Bar size Width of Average Average projected Bearing and type gap spacing height length Area

(in) (in) (in) (in) (in.2 /in) No. 6D b 0.064 0.300 0.040 2.22 0.296 No. 6B c 0.047 0.402 0.038 2.25 0.212

a Methods of measuring properties of deformation and defini- tion of terms are given in reference 25. b D denotes diamond deformation pattern.

c B denotes barrel deformation pattern.

3.2. Concrete

The concrete was procured from a transit-mix concrete company. The mix proportions of portland cement

(type I), sand, and coarse aggregate were approximately 1:1.7:2.5, by weight. The sand was a silicious aggregate and the coarse aggregate was crushed stone. Maximum size of the coarse aggregate was % in". Water

content of the concrete was about 51/2 gallon per sack

of cement and the slump ranged from 3 to 5 in. Al- though the concrete contained an air entraining admixture, the air content ranged from only 1 to 3 percent.

Three batches of concrete were used to cast the pullout

specimens and the corrosion test specimens.

Six standard 6 x 12 in cylinders were cast from each

batch of concrete along with the pullout specimens. The

cylinders were stored and cured in the same manner as the pullout specimens, and their compressive strengths were measured at the same time the specimens were

tested. The compressive strength was determined in ac- cordance with ASTM C39-66 [26]. The average compressive strengths at 27 to 29 days were 6160 psi for concrete batch No. 1, 6620 psi for batch No. 2, and

5730 psi for batch No. 3. The ranges and coefficients of variation [27] of the strength of the concrete cylinders were 226 psi and 1.5 percent, 136 psi and 0.8 percent,

355 psi and 2.3 percent for concrete batches Nos. 1, 2, and 3, respectively. The creep specimens were cast from

two additional batches, batch No. 4 and 5 of concrete, which had average compressive strengths at 28 days of 5494 psi and 5665 psi. The range of the strength of the concrete cylinders and coefficient of variation were 442 psi and 4.1 percent and 285 psi and 2.5 percent,

respectively.

3.3.1. Pullout Specimens

The pullout specimens were 10 x 10 x 12 in concrete prisms with the reinforcing bar concentric with the longitudinal axis of the specimens, so that the length of embedment of the bar in concrete was 12 in. I hi development length of the deformed bar was selected based on previous studies at NBS [28] and because the current ACI Standard 318-71, "Building Code Require- ments for Reinforced Concrete" slates that the development length should not be less than 12 in [29]. The

pullout specimen was designed so that the loaded-end

slip reached a value of 0.01 in corresponding I stress of approximately one half of its tensile strength

when uncoated bars were embedded in the specimen.

Splitting of the concrete was minimized by reinforcing

the specimen with a cylindrical cage of 2 x 2 —l2/\-> welded wire fabric. The cages had a diameter of 8 in extending the. length of the specimen and were concentric with the reinforcing bar.

3.3.2. Creep Specimens

The creep specimens were the same as the pullout

specimens except that the lower 23 in of the bars were

threaded, thread size of % in diam with 18 threads per

in to permit loading of the specimen assembly. Alto- gether 24 creep specimens were cast from concrete batches Nos. 4 and 5 in the same wooden forms used

to cast the pullout specimens.

3.3.3. Corrosion-Test Specimens

The corrosion test specimens were concrete blocks 2% x 4% x 15 in in which were embedded a 24 in length of No. 6 reinforcing bar concentric with the longitudinal axis of the block. The bars protruded out

of the concrete blocks with exposed ends of 1 in and

8 in. The end of the block with the 1 in of bar protruding which was to be immersed in the salt solution, was

first coated with an "underwater" type of epoxy which

bonded firmly to the concrete. Then the 1 in exposed

end of the bar and the epoxy were coated completely

with a heavy layer of silicone rubber. The bond of the rubber to steel and to the epoxy was very good, although

its bond to concrete in a salt solution is poor. A termi- nal was inserted into the long end of each reinforcing

bar so that electrical connections could be made to a voltmeter or conductivity bridge.

3.3.4. Fabrication and Curing of Specimens

All concrete pullout specimens were cast with the reinforcing bar in horizontal position in wooden forms

which were lined with stripping oil. The specimens were removed from the forms after 2 days and moist cured

for 14 days with wet burlap and room cured at 73 °F

and 50 percent relative humidity until tested. Two pullout specimens with uncoated reinforcing

bars were fabricated from each of concrete batch Nos. 1 and 2 and one such specimen was cast from batch No. 3. Duplicate specimens were fabricated for each

coating material from the same batch of concrete with

the exception that only one pullout specimen was fabri- cated that contained coating No. 1—S.

5
The corrosion test specimens were fabricated from

the same batches of concrete as the pullout specimens.

Coated bars selected for corrosion testing coincided

(when sufficient specimens were available) with those used in the pullout test.

4. Evaluation of Coating Materials

Experimental Methods and Results

Descriptions of the test methods used to evaluate coating materials are given in this section along with

the experimental results. Not all of the 47 coating materials which were evalu- ated were subjected to the same degree of testing; some were quickly judged not to be acceptable for such

reasons as: gel times for two component systems longer

than eight hours, coatings Nos. 10 and 11; poor film

integrity and excessive entrapped air in the cured state, Nos. 12 and 13; the tendency of some thermoplastics

to soften at 140 °F, Nos. 14 and 47; rubber-like expansion qualities (500 to 600 percent elongation) of two

urethanes, Nos. 35 and 36 (these two coating would not pass the pull-out and creep requirements) ; and extreme

brittleness of some epoxy systems, Nos. 5 and 13.

4.1. Chemical Resistance

4.1.1. Epoxy Disk Specimens

Disk shape castings of cured epoxy specimens (these

epoxies are liquids in the uncured state) were immersed

in the following: water; an aqueous solution of 3M

CaCl2; an aqueous solution of 3M NaOH; and a solu- tion saturated with both Ca(OH)2 and CaS04 '2^0,

and containing 0.5M CaCk. These test chemicals were

selected because they are, with the exception of NaOH,

present in concrete of bridge deckings and are probably

the major chemicals most potentially deleterious to epoxy coatings. Ca(OH)2 is a reaction product of portland cement and water; it stabilizes the siliciate gels

which are important constituents of durable concretes. CaS04 '2H20 is often added as a set-regulator to portland cement and also is frequently present in soil drainage water. CaCb is one of the two most commonly

used deicing materials. Since the solubility of Ca(OH)2

is low (0.2M at 25 °C), 3M NaOH was used in an

accelerated-type of test to determine if hydroxide ions are detrimental to the long-term embedment of epoxy

coatings in concrete. Water, in itself, can have a deleterious effect on coat- ing materials. It was felt that these test solutions are probably as aggressive or even more aggressive than

those encountered in concrete. Therefore, materials

performing well in the immersion tests will probably

not be degraded by long-term embedment in concrete. The specimens were immersed in water for 1 to 2 min

and wiped dry before measuring the original weights

prior to the immersion studies. Original weights of the disks varied from ca. 20 grams for solvent containing

systems to ca. 50 grams for the solventless epoxy sys- tems. The temperatures of the test solutions were

75 ± 1 °F. The immersion data are listed in table 4. In some

cases two separate castings were made, indicated by

two sets of data with different immersion times. In

general, the specimens had average weight changes in the four test solutions that were under 4 percent. The

three materials experiencing the largest weight changes, Nos. 7, 8, and 9, contained solvents in their uncured

states. The surfaces of both No. 7 and No. 9 changed

from smooth to rough textures during the immersion

period. No visually apparent surface deterioration was

observed with the other epoxy specimens.

Table 4. Weight changes of cured epoxy disks immersed in aqueous solutions

Code

number

Immersion

time (weeks)

Percent weight changes

Water 3M

CaCb

3M

NaOH

Saturated Ca(OH)2

saturated CaS04*2H20

and 0.5M CaCl2

66 £4.0 9 3 1 7 9 ^ 53 4.2 1.2 3.9 4.6

2 66 4.2 2.5 3.6 5.2 53 0.7 % Q 9 7 O.o

3 uu -2.3 -2.4 1.8 -3.0 53 _QO.Z9 O.J 0.3 7t _q q

4 uu 2.9 1.5 2.1 2.6 53 9 ^ 1 9 9 9 9 d.

c. UU 1.5 1.3 2.1 2.1 53 1 ft n ft U.O nU. 7i 11. 7i

ftu 66 3.7 1.8 2.8 3.6 53 3.0 1.5 2.5 3.2

7 66 16 19 13 18

8 66 -9.1 -6.3 -2.7 -5.5

9 66 -6.8 -10 5.3 -13

12 64 1.5 1.0 2.1 2.0

13 64 3.3 1.0 2.5 2.5

16 57 -0.8 -2.3 0.4 -2.0 53 -3.6 -4.2 0.9 -4.5

17 59 3.3 1.0 3.0 3.9 53 2.6 1.2 2.7 2.6

18 59 0.8 0.2 0.9 0.9 53 1.0 0.5 1.0 1.1

The weight changes versus immersion times are

plotted in figure 3 for epoxies Nos. 3, 4, 7, and 16,

which represent the different behaviors of the epoxy

specimens. No. 4 is typical of most of the specimens,

with a modest weight increase irrespective of the test solution; in contrast No. 16 has a gradual loss of weight

in all four test solutions. No. 7 had the largest weight

change of all the epoxies tested with weight increases ranging from 13 to 19 percent; which essentially occur- red during the first month of immersion. No. 3 experienced a gradual weight loss except when immersed in the NaOH solution.

6
I

LU Q> > in ~* O

3.0r

2.0-

1.0-

Code No. 3

3.0,-

-2.0

-3.0. 4 6 8 10 12 14 IMMERSION TIME (MONTHS)

16

I

C3 Water

Sat Ca(0H)2+Sat CaSC>4 + 05M CaCl2 3M NaOH 3M CaCk

4 6 8 10 12 14 IMMERSION TIME (MONTHS)

16

30.0

in -Tt a

-i^ o

20.0

I0.(

UJ5 <u . 10.0

£ -20.0

-30.0,

Code No. 7

4 6 8 10 12 14 IMMERSION TIME (MONTHS)

16

Code No. 16

4 6 8 10 12 14 IMMERSION TIME (MONTHS)16

FIGURE 3. Weight stabilities of cured specimen disks, fabricated from four liquid epoxies, immersed in aqueous solutions. A weight increase probably can be attributed to absorption of the test solution by the epoxy specimen

;

while loss in weight can be attributed to dissolution of

the specimen in the test solution, or in the case of solvent-containing systems, the loss of entrapped sol- vent. It is felt that epoxies exhibiting minor weight

changes, i.e., average under 4 percent, will not be de- graded by long-term embedment in concrete.

4.1.2. Immersion Studies of Coatings on

Reinforcing Bars The chemical resistances of the powder epoxy and

polyvinyl chloride systems were investigated by immersing coated reinforcing bars, supplied by applicators, in aqueous solutions of the following: 3M NaOH;

saturated Ca(OH) 2 ; and 3.5 percent {0.7M) NaCl.

Many of the liquid epoxies, usually applied by the staff of the National Bureau of Standards using brushes, were

also included in these immersion studies. The coated

bars were visually inspected for evidence of softening

and color changes of the coating, disbonding between the coating and steel surface, and for number and size of corrosion sites. Temperatures of the test solutions were

75 ± 1 °F. The results after one year of immersion

are described in table 5. The NaCl solution had a more deleterious effect on

the coatings than the Ca(OH)2 and NaOH solutions,

with the NaOH solution being the least aggressive. Only

one coating, No. 11, gave any indication of being de- graded by the long-term immersion in SM NaOH. The

greater discriminating effect of Ca(0H)2 versus NaOH

is an interesting phenomenon since the pH of both solu- tions (pH of saturated Ca(OH) 2 is 12.6 and of 3M

NaOH is 14.5) should be sufficient to passivate steel. The causes of this phenomenon are not presently obvi- ous and this is an area worthy of additional studies. Coatings with ratings of 1 or 2 (Nos. 22, 23, 24, 25,

30, 31, and 41) adequately protected the reinforcing

bars from corrosion when immersed in any of the test solutions. Four of the coatings with ratings of 1 or 2, Nos. 22, 25, 31, and 41 were powder epoxies; other coatings with high ratings, Nos. 23, 24, and 30, were

polyvinyl chlorides with heavy film thicknesses ranging

from 15 to 35 mils.

4.1.3. Chloride Permeability

If coatings are to be effective in protecting steel rein- forcing bars, the intrinsic chloride permeabilities of the coatings must be low. Little if any data on the permeability characteristics of epoxy films to chloride ions

have been reported previously.

The chloride permeability characteristics of thin

films (3—7 mils) of cured epoxies were determined

using permeability cells of the type shown in figure 4. Films selected for study were carefully handled, and

examined for any defects prior to installation in the

cell. The cell consisted of two glass compartments sepa7
Table 5. Immersion studies of coatings on reinforcing bars (test period of one year)

Aqueous test solutions Code Applied by a 3M Saturated 3.5 Percent (0.5M) Rating b number NaOH Ca(OH) 2 NaCl

1 MFR No change Few rust spots 8 rust spots 9O

1-1 MFR No change Few rust spots 10 rust spots QO 1-2 MFR No change Few rust spots 7 rust spots 6 2 NBS No change Few rust spots 6 rust spots 9O 3 NBS No change Few rust spots 7 rust spots

A4

2 & 3 NBS No change Few rust spots 3 rust spots z 4 NBS No change Few rust spots Severely rusted on ridges 96 5 NBS No change Few rust spots Severely rusted on ridges A4

6 NBS No change No change severely rusted on ridges 4

10 MFR No change No change 18 rust spots

ra

11 MFR Coating cracked No change Severely rusted cD & disbonded. Color leached from epoxy.

14 MFR Severely rusted A4

15 MFR 3 rust spots; poor bond 3 16 Mr n No change 9O

17 NBS No change 20 rust spots

A4

18 NBS No change 6 rust spots Badly rusted; coating softened rO

19 MFR No change Badly rusted Very badly rusted ; most of coating gone

r5 20 MFR Light rust spots under coating; bond very poor

96

21 MFR 12 rust spots 3 22 MFR No change No change JNo change i 23 Mr K No change No change

No change JNo change 1 24 MFR No change No change

No change except 1 rust spot and

small blisters

i 25 Mr K No change No change Z

26 MFR Rusted badly cO 27 MFR No change No change No change except few rust spots

T"> . I 1 Jl , r. i Rusted badly; coating sottened

6 28 MFR No change Badly rusted

A4 29 MFR No change

No change Few rust spots Very badly rusted A430 MFR No change AT 1 . p 11 . , No change except 5 small rust spots Z 31 MFR No change No change No change except 1 rust spot 1 32 MFR No change No change Rusted badly 93 33 MFR No change No change Rusted severely. Tubercles Vi i» high 96 34 NBS Rusted badly 5

35 NBS Large rusted areas 5 36 Large rusted areas

co 37 NBS Large rusted areas 5 38-Blast Mr K No change Rusted Badly rusted

A4 38-Phosp MFR No change Rusted badly T» 1111 . * J" . 1 Rusted badly; coating sottened 5 39-Blast MFR No change No change except few rust spots Rusted 3

39-Phosp A;! T7D Mr K No change No change except

slight softening Rusted 4

40-Blast MFR No change Rust spots Badly rusted o0 40-Phosp MFR No change Rust spots; coating softened Badly rusted; coating softened 4

41 MFR No change No change 15 rust spots 2 42 MFR No change No change

Badly rusted 10 rust spots 3 Un- MFR Slightly rusted Badly rusted 5 eoated

a MFR denotes the firm handling the material applied the coating to reinforcing bars and submitted the coated bars to NBS for evaluation. NBS denotes coating applied by the staff of the National Bureau of Standard.

b Rating sequence in order of decreasing protective qualities 1<2<3<4<5.

rated by an epoxy film sandwiched between two glass

plates, each having centered 1 in diam holes. One compartment contained 175 ml of SM NaCl and the other 115 ml of distilled water. The activity of chloride ions

passing through the epoxy membrane was measured

using a Model 401 Orion Specific Ion Meter, along with

a Model 94-17 Orion Chloride Electrode, and a Model

90—02 Orion Double Junction Reference Electrode. Activity measurements were converted into concentration values of mole per liter with a conversion diagram,

constructed by plotting measured chloride ion activities versus known chloride ion concentrations.

The data for 15 different epoxies are listed in table

6. Many of the epoxy films, Nos. 1, 3, 17, 19, 31, and

39, appear to be essentially impervious to chloride ions

(at least during the listed exposure times) . The accumulative concentrations of chloride ions passing through

epoxy films are plotted versus time in figure 5 for

8
FIGURE 4. Permeability Cell. Components: A. Compartment containing distilled water;

B. Epoxy film sandwich between two glass plates each having

centered one-inch diameter hole ; C. Component containing 3M NaCl

six different epoxy films. Generally, the chloride per- meability rates were highest during the first six weeks

of exposure. An exception is the film of No. 38 which

initially seemed to be impervious to chloride ions,

however, after about six weeks its permeability rate began to sharply increase and after 39 weeks the accumulative concentration of chloride passing through

the film was about 3 x 10~3M. Two other films, Nos. 13 and 16, also permitted sufficient chloride ions to migrate through so that the concentration in the compartment originally containing distilled water

approached or reached the chloride ion threshold concentration of 0.02M which has been reported [30] to induce the corrosion of steel embedded in portland

cement-concrete.

Table 6. Permeability of chloride ions through epoxy films

Concen- Code Thickness Exposure trations a Perme- number thickness time (moles per ability (mils) ( weeks

)

liter) Units b

1 3 50 c <5x 10-5 <2.5 x 10-6 2 3 23 1 x lO^1 9.7 x 10-6 3 3 16 <5 x 10"5 <8.5x 10-6 4 3 23 1 x 1(H 9.7 x 10-6 6 3 23 lxl(H 9.7 x 10-6 11 3 12 4 x 10-3 7.5 x lO^4 13 3 21 1 x 10-2 5.0 x 1(H

16 7 23 2x10-3 6.2 x 10-4

3 10 8x 1(H 2.3 x 10-1 17 3 50 <5x 10-5 <2.5x 10-6 19 7 37 N. C.d 29 10 37 N. C. 31 10 37 N. C. 38 2.5 39 3 x 10-3 1.8 x 10-5 39 2.5 39 N. C. 40 2.5 39 6x10-2 3.2 x 1(H

a Concentration of chloride ions in the chamber originally containing only distilled water.

b Permeability units are: (grams per day) /exposed area

(in 2

) /film thickness (mils); i.e., theoretically square inch and a film thickness of one mil.

c Millivolt readings were near the region of distilled water and

the lower limit of the chloride ion concentration was estimated.

d N. C. denotes that no changes from the original millivolt values were measured.

16 24 TEST TIME (WEEKS)

FIGURE 5. Concentration of chloride ions passing through epoxy films of materials Nos. 2, 13, 16, 31, 38, and 39.

Film thicknesses were 3 mils.

9
4.2. Impact and Abrasion Resistance of

Epoxy Coatings on Steel Plates

In the preliminary screening phase of the study,

the impact and abrasion resistances of coatings on

steel plates were determined to assess the ability of coatings to withstand harsh treatment. Both direct and reverse impact resistances of cured

epoxy coatings on 4 x 4 x 0.050 in cold-rolled steel plates were determined by the falling weight method

outlined in ASTM Designation G14-69T [31]. A

Gardner Laboratory impact tester was used along with

a four pound hammer.

The impact data are presented in table 7. The

reverse impact was found to be more severe than the

direct impact and probably gives a better indication

Table 7. Abrasion and impact resistance of cured epoxy coatings on steel panels a

Abrasion Code Film Impact resistance b resistance c number thickness

(mils) Reverse Dirct Weight loss per impact impact 1000 cycles

(in lb) (in lb) (mg)

1 7 20 90 71

2 7 4 dl20 56

3 8 40 160 107 4 5 4 40 70

5 7 8 20 58

6 6 4 20 71

11 6 89

16 5 8 50 148

17 6 7 50 58

18 7 12 110 52

19 1 >160 >160 51 4 160 160 25 7 4 60 70 28 8 40 60 88 29 8 50 60 57

31 6 20 80 35

38 7 20 80

39 8 20 40 90

40 11 20 ( e

) 41 7 85

a Epoxy coatings applied to 4x4x0.050 in steel plates (cold

rolled).

b Four pound hammer used.

c Taber CS-10 wheels, with 1000 g load per wheel.

d Bond at the steel-epoxy interface severed at 10 in lb. e Coating shattered off of steel panel.

of the flexibility of a coating. Reverse impact values lower than 40 in-lb are judged to be indicative of

brittle materials. It is felt that the impact values for some powder materials (Nos. 25, 28, 29, 31, and

38—40) are too low and are not reliable indicators

of their properties. Possibly, the low values can be

attributed to poor adherence to the surface of the

steel plates used in this impact test. The bend testing of coated reinforcing bars, and also impact tests on

coated bars, discussed later, are considered to yield more reliable results.

The abrasion resistance of epoxy coatings on similar

steel panels were determined in accordance with ASTM

Designation D1044—56 [32] by using a Taber Abraser

and Taber CS—10 wheels with lOOOg load per wheel. After each 200 cycles the wheels and specimens were

gently cleaned with a soft bristle brush. The abrasion

data are given in table 7 in units of weight loss in mg per 1000 cycles. Two of the solvent containing

materials, Nos. 3 and 16, had weight losses over 100

mg indicative of poorer abrasion resistances than

the other epoxy coatings tested.

4.3. Inspection of Coatings on

Steel Reinforcing Bars

The coatings applied to reinforcing bars by the applicators were inspected immediately after receipt for the following: film thickness, number of holidays per

unit bar length (4 ft.), and for their general appearance. The film thicknesses were measured with a Mikrotest Model 790000 Magnetic Gage, and the number of holidays was determined with a 67l/£ volt holiday detector. The results of the inspection are listed in table 8. In general, the powder epoxy coatings yielded films of more uniform thicknesses and with fewer holidays

than the liquid epoxy coatings. However, the films of both powders and liquid epoxies have excessive

numbers of holidays 5 (more than 10) when their film thicknesses are in the range of 1—4 mils.

4.4. Physical Testing of Coatings on

Reinforcing Bars

The abilities of coatings on reinforcing bars to withstand rough handling were assessed on the basis

of bend tests, impact tests, and hardness measurements. These tests were carried out either on the same speci- mens listed in table 8 or on companion specimens.

4.4.1. Bend Tests No. 6 bars coated by applicators were bent at a 120° angle with a radius of curvature of ca. 3 in using a Green Lee Tool Company Model 770 Bar

Bender. Portions of the bars coming in contact with

the bending machine were protected with rubber tub- ing of iy2 in o.d. and % i.d. to avoid mechanical

damage to the coating, so that any cracking in a coat- ing occuring during the bend test could be attributed to strain failure of the coating. The tests were performed

at 72 ± 1 °F. Cracking and disbonding took place on the area of some bars that was under tension during the bending

(table 9). The four different polyvinyl chloride coated

rebars (Nos. 23, 24, 26, and 30) gave excellent per- formances even though their film thicknesses ranged

from 2 to 35 mils. A greater variation was observed for

5 Holidays are defined as pinholes normally not visually discernible.

10
Table 8. Inspection of coated steel reinforcing bars a

Code number

Application

method

Film

thickness

(mils) No. of holidays per 4 foot bar

Visual inspection and comments

1 Brush 4-5 40 Deformation not well coated and slightly exposed Accumulation of epoxy in low lying regions.

2 Brush 5-15 ca. 10 Deformations not well covered—long uncovered regions. Material is brittle.

3 Brush 2-5 ca. 30-40 Deformations appear to be well covered.

4 Brush 10-20 none Deformation not well defined as the epoxy is concentrated

in the low lying region between the deformations.

5 Brush 10-15 too many to estimate Longitudinal deformations are not well covered. Excess epoxy in regions between the deformations.

10 Brush 10 ca. 10 Susceptible to abrasion; coating easily comes off of rebars. Rough texture. Epoxy accumulated between deformations.

11 Brush 10-12 none Coating easily chips off of rebar. Regions where deformations are not well covered. Evidence of epoxy dripping from bar.

16 Electrostatic spray gun 2-4 40 Deformations not well covered; accumulation of epoxy in low lying areas.

17 Brush 4 too many to estimate Tops of deformations not well covered. Brittle material

that easily chips off steel substrate.

18 Brush 4 too many to estimate Bad adhesion to steel. Abrades easily off of rebar.

1 o Single dipping 1 40 Good coverage; well defined deformation pattern. No bad

dipping regions observed.

22 Fluidized bed 25 none except at ends Uniform built-up film. Large thickness characteristic of

fluidized bed application.

23 Fluidized bed 25 none except at ends Uniform built-up film. Thermoplastic coating.

24 Fluidized bed 35 Deformation pattern is hidden. Thermoplastic.

25 Electrostatic spray gun 6-11 none Good coating material. Some bad spraying techniques; bars were sprayed from one direction giving the underside of the deformations a thin coating.

26 Electrostatic spray gun 2-3 ton mfltiv tn pQtimatp Top of deformations not covered, ^^hen received, coated

rebars were sticky. Thermoplastic.

27 Electrostatic spray gun 8 High gloss coating. Even build-up. Very tough coating

that did not chip off.

28 Electrostatic spray gun 1-2 cannot estimate Either very high number of holidays or electrical conducting 111— m<rmpnt<s "-.HI' II ' nmifrh 1 •

1 Ml_ I tpvturp 1 .

1 !

1

29 Electrostatic spray gun 1-2 cannot estimate Either very high number of holidays or electrical conducting pigment. Deformations do not appear to be well

coated. Tough coating that is not susceptible to chipping.

30 Fluidized bed 15-18 none Thermoplastic coating. Deformation pattern hidden, possibly due to tendency of material to flow when cured at elevated temperatures.

31 Electrostatic spray gun 8-9 none Good even built-up film. Deformations well covered. Tough

oc\'A t i n (t tnnt ic Tint QiiQppnt i n 1 p tn rhinninff

32 Electrostatic spray gun A.—(\ 4- O

Aflll cr»i lp tt-QC Tint »* Am ni'pn nnH pn a 1 1 Tl <t PliiIK PI TY1 P nit -Mill SCdlc Was IluL ICUlUVCli tlllli (.Udllllj. t.Hij_'5 luiiic %jn easily due to disbonding between the mill scale and the

steel rebars.

33 Brush 3-4 too many to estimate Coating easily damaged and chips off of rebar.

11
Table 8. Inspection of coated steel reinforcing bars—Continued

Code

number

Application

method

Film

thickness

(mils) No. of holidays per 4 foot bar

Visual inspection and comments

38 Electrostatic spray gun 2-4 ca. 30-40 Deformations not well covered. Some bars were phosphatized.

39 Electrostatic spray gun 2-4 ca. 30-40 Holidays located on deformations. Some bars were phosphatized.

40 Electrostatic spray gun 2-4 10 Tough coating that is not susceptible to chipping; some

bars were phosphatized.

41 Electrostatic spray gun 3-7 1 Good coverage. Bar heated prior to application of powder

coating.

42 Electrostatic spray gun 3-4 too many to estimate Same material as No. 41, but powder applied to cold

rebars.

43 Electrostatic spray gun 3-4 too many to estimate Material readily abrades off of rebar.

a Number 6 steel reinforcement bars coated by applicators or coating producers. Unless otherwise stated, the mill scale was

removed by sandblasting.

the epoxy coated rebars as some performed well while

a few were classified as failing. Generally, the epoxy

coatings which did not perform well were either the most brittle epoxies or their cured film thicknesses were

over 10 mils. The effect of the film thickness is well

illustrated by comparing the coated reinforcing bars Nos. 22 and 31, which were both coated with the same material applied by different application methods. No. 22 has a film thickness of ca. 25 mils (applied by

the fluidized bed technique) while the film thickness

of No. 31 was ca. 8—9 mils (applied using an electrostatic spray gun). When bent, substantial cracking was observed in the film of No. 22, while No. 31 was completely free of cracking.

Another factor affecting the bending characteristics of coated reinforcing bars is the type of surface preparation of the substrate prior to application of the

coatings. In two series of coated reinforcing bars, No. 28B and No. 32, epoxy coatings were applied to unpre- pared surfaces which were still covered with mill scale. Almost total disbondment was observed when each

series of bars was bent; while the epoxy adhered te- naciously to the mill scale, the mill scale was disbonded

from the steel substrate. A portion of the coated rebars Nos. 38, 39 and 40 were both sand blasted and phosphatized prior to being coated while the remainder were just sand blasted. The sand blasted coated rebars gave no indications of coating failures when bent while

the phosphatized bars were susceptible to varying

amounts of failure in the coatings.

The temperature of the steel substrate, when being

coated, can affect the flexibility of the cured epoxy

coating. For example, Nos. 41 and 42 rebars were

coated with the same material. However, No. 41 rebars were heated to 342 °F and immediately coated while No. 42 rebars were at ambient temperature when

coated. The epoxy coating was then cured at 319 °F

on both sets of rebars. Excellent flexibility was

exhibited by No. 41, whereas No. 42 cracked badly

when bent.

4.4.2. Impact Tests The resistance of coatings on reinforcing bars to impact were determined by dropping bars on concrete and by the falling weight method.

4.4.2.1. Dropping Coated Bars on Concrete An 18 in length of coated No. 6 reinforcing bar was

dropped on a slab of concrete so that impact occurred

lengthwise as follows:

1. A single bar was dropped one meter from a

horizontal position to the concrete.

2. The same bar was dropped from a height of two meters.

3. A companion specimen was taped loosely between two bare No. 7 bars of the same length and the assembly was dropped from a height of 2 meters

to the concrete slab.

4. The bars were inspected after each drop for the following types of damages:

A. Shattering of the coating to expose bare metal.

B. Cutting of the coating to expose bare metal.

C. Cracking of the coating. D. Disbonding of the coating from the steel substrate. The coatings were rated on a relative basis and

the results are given in table 10.

4.4.2.2. Falling Weight Method The test methods outlined in ASTM Designation

G14-69T [31] were followed. A Gardner Laboratory

impact tester was used along with a four pound

hammer. Impact occurred on the low-lying areas between the deformations.

12
Table 9. Results of bending coated reinforcing bars a

Code NumberFilm

thickness (mils) Results of 120° bend "

1 4-5 Slight cracking near edge of deformation, length of cracks were ca. Vb in.

2 5-15 Complete failure in bend area. Almost complete disbonding.

3 2-5 Few small cracks ca. % in long. Good performance.

4 20-30 Severe cracking at almost every transverse deformation in bend area. Lengths of crack- were

l/

2 to % in.

5 40-50 Severe cracking at deformations. Cracks were ca. ^8 in wide and undercutting disbondment

between the films and steel took place.

1U Severe cracking which extended from longitudinal deformation. Disbonding between the coating and steel was observed.

ii 10-12 Same as No. 10.

16 2-4 Very fine cracks, good performance.

17 4 Cracking started at 20° bend. Total disbondment in area under tension. Complete failure.

18 4 No cracking, excellent performance.

19 4 No cracks, excellent performance.

22 25 Substantial uuuciuuiiiu crackinf? i ii i\im_ extending VAil/iluiu^ from l l \J 1 longitudinal tn Innixitiidinal rlpfnrmntinn enmp rlieKnnrlinn

1

1 MMi.iiiMiiii.il l \J 1U1 ILi LUU III ul UCI Ul IllillUJIl, Ulvll I.J I M I 1 1 1 Li between the coating and steel was observed. 23 25 No cracks, excellent performance.

24 35 No cracks, excellent performance.

25 6-11 lVTanv many oinaii small (\ CAi_ a. ^/o in lnnfr^ tllin rraplcs pnnsl rlprpf] as mn/lpratp prapkinor /y ill lung / i iiiii v_iavi^o, LUIJ3iul/ltu tlo Iliuuciuic ' I I r. I ' 1 . .

26 2-3 No cracks, excellent performance.

27 8 Substantial cracking extending from longitudinal to longitudinal deformation. Some disbonding was observed

28 1-2 A. Slifiht cracking, good performance.

B. Substantial cracking and disbonding observed. d

29 3-4 No cracks, excellent performance.

30 15-18 No cracks, excellent performance.

31 8-9 No cracks, excellent performance.

c 32 4-6 Complete failure as total disbonding in bend areaj probably attributable to disbonding between

mill scale and steel.

33 3-4 No cracks, excellent performance.

38 A d 2-4 No cracks, excellent performance. B d 2-4 Severe cracking on every deformation in area under tension during bending.

39 A d 2-4 No cracks, excellent performance. B d 2-4 Two or three small cracks. Good performance. 40 A d 2-4 Excellent performance ' no cracking. B d 2-4 Failure. Phosphate coating adhered poorly to the steel substrate. Cracking of epoxy coating in complete area under tension during bending.

41 e 3-7 Excellent performance, no cracking.

42 f 3-4 Substantial cracking. 43 3-4 Slight "popping off" of coating. Good performance.

a Number 6 steel reinforcement bars coated by applicators or coating producers. Unless otherwise stated the mill scale was removed by sandblasting.

b Crack rating in order of decreasing performance: Excellent > Good > Moderate > Substantial > Severe > Complete failure.

c Mill scale was not removed.

d Surface of A sandblasted prior to application of coating material. Surface of B sandblasted and phosphatized prior to coating

application.

e Bars heated to 190 °C prior to applying powder coating.

f Same coating material as 41, but applied to cold reinforcing bars.

13
Table 10. Drop resistance a and impact resistance b of coatings on rebars

Code

number a Film

thickness (mils)

Impact resistance Drop

resistance I ' 1 1 1 1 1 '. 1

J— ' 11 c area ( in 2

) Type and severity of damage

12 5-15 0.110 Not tested. Shattering and disbonding of coating propagating from area of impact.

Good

Poor

3 2-5 .028 Only indentation in coating and rebar at impact area. Good

4 10-20 .082 Shattering and disbonding of coating propagating from area of impact. Poor

5 10-15 .383 Large amount of shattering and disbonding of coating surrounding

area of impact. Poor

10 10 .079 Shattering and disbonding of coating at impact area. Poor

11 10-12 .188 Shattering and disbonding of coating propagating from area of impact. Poor

16 2-4 .038 Slight shattering and disbonding of coating at impact area. Fair

17 4 .028 Slight shattering and disbonding of coating at impact area. Fair

18 4 .038 Slight shattering and disbonding of coating at impact area. Fair

19 1 .028 Only indentation in coating and rebar at impact area. Fair

22 25 .234 Large amount of shattering and disbonding of coating surrounding

area of impact. Excellent

23 25 .077 Large indentation in coating. Excellent

24 35 .110 Large indentation in coating. Excellent

25 6-11 .049 Shattering and disbonding of coating at impact area. Good

27 8 .077 Coating shattered at area of impact with slight propagating of shattering from impact region. Good

28 1-2 .038 Slight shattering and disbonding of coating of impact area. Fair

29 1-2 .028 Slight shattering and disbonding of coating of impact area. Good

30 15-18 .110 Large indentation in coating accompanied by slight cracking at impact area. Poor

31 8-9 .110 Shattering and some disbonding of coating at impact area. Excellent

32 4-6 .049 Cracking in coating at impact area, slight cracking extending from

impact region. Fair

33 3-4 .028 Shattering of coating at impact area. Good

38 2-4 .038 Shattering of coating at impact area, slight cracking extending from impact region. Excellent

39 2-4 .028 Only indentation in coating and rebar at impact area. Excellent

40 2-4 .079 Shattering of coating at impact area, slight disbonding extending from impact region. Excellent

41 3-7 .038 Shattering of coating at impact area, slight cracking extending from impact area. Good

42 3-4 .028 Only indentation in coating and rebar at impact area. Good

43 3-4 .038 Smashing of coating at impact area, slight cracking extending from

impact region. Good

a Coated reinforcing bars dropped from heights of 1 and 2 meters on concrete.

b Falling weight method ASTM Designation G-14 with impact of 120 in-lb.

c Relative rating: Excellent > Good > Fair > Poor.

14
The type and extent of damage to the coating caused

by an impact of 120 in lb. was visually assessed and

also the area of damage was measured (table 10). It

is felt that with an impact of 120 in lb. the area of damage should not exceed 0.15 in 2 for an acceptable

coating.

The criteria of 0.15 in 2 permissible area of damage

was only exceeded in three cases, namely, by coatings Nos. 5, 11, and 22. Both No. 5 and No. 11 were

previously classified as brittle materials on the basis of

their performance in the bend test. The poor perfor- mance of No. 22 probably can be attributed to its large

film thickness, ca. 25 mils; the same material with a film thickness of 8—9 mils, No. 31, had acceptable impact

resistance. There is a fairly direct correlation between the results of the drop and impact tests with a few exceptions

such as coating No. 22. Although the results of the impact test are easier to quantitatively evaluate, the drop test more closely simulates the rough handling

coated reinforcing bars will probably experience.

4.4.3. Hardness Determination

The hardness value of a coating gives an indication

of the relative resistance of the coating to the type of mechanical damage which results in scratching, cutting,

indentation, etc. of the film. The hardness of coatings on reinforcing bars was determined by the pencil

method and the indentation method.

4.4.3.1. Pencil Hardness Pencil hardness values were determined using a

series of lead pencils that covers the range of H to 8H, with steps of one hardness increment. The hardness

is designated as the softest lead that imparts a scratch

in the coating. All of the epoxy coatings had ratings

above 8H; while the polyvinyl chloride coatings were

softer, with hardness values of H for polyvinyl chloride

coatings Nos. 24 and 30, and a value of 8H for coating No. 23.

4.4.3.2. Indentation Method The microhardnesses of coatings on steel reinforcing

bars were also measured by the indentation method to determine the Knoop Hardness number, which is more

quantitative and reproducible than the pencil hardness. An apparatus of the type described in ASTM Designation D1474—68 [33], following the methods outlined

therein, with a 10 g load, was used for this determination. The Knoop Hardness Number (KHN) is calculated with the equation

:

KHN = ~ =

Ap VCp

where L is the load applied to the indenter in kilo- grams; 1 is the measured length of the long diagonal

of the indentation in the coating in millimeters; Cp

is a constant with the value of 7.028 X 10"2

; Ap is the projected area of the indentation. The results for five coatings on rebars are given in table 11. No. 30 is a polyvinyl chloride and has a

relatively low hardness of 6.7 KHN, wliilc the othei four coatings are powder epoxies having hardnesses

above 18 KHN. As previously discussed, No. 22 and

No. 31 are rebars coaled with the same epoxy material

applied by different methods which yielded different film thickness. The film thickness of No. 22 is ca. 25

mils and the film thickness of No. 31 is ca. 8 mils. The

microhardness was determined to be 20.7 KHN for both

coating films, therefore, it seems that the microhardness of the coating film alone was being measured and

not the composite hardness of the coating and the steel substrate.

Table 11. Indentation hardness of coatings on reinforcing bars

Code Hardness number KHN a

22 20.7 29 19.8 30 6.7 31 20.7 39 21.2 Knoop Hardness Number.

4.5. Electrochemical Tests

Electrochemical tests were undertaken to quantitatively rate the relative performance of coatings exposed

to solutions corrosive to steel embedded in concrete.

4.5.1. Applied Voltage Studies The effects of electrochemical stresses on coatings on

reinforcing bars were assessed by applied voltage

studies. Such stresses can be induced in the field by

cathodic protection devices, stray currents, or by cor- rosion processes. The cathode and anode were No. 6

reinforcing bars, 6 in long, both coated with the same

material. The electrolyte was an aqueous solution of 7 percent NaCl. A potential of 2 V was applied and the electrodes were visually observed periodically for evolution of hydrogen gas at the cathode and for evidence

of corrosion products of iron at the anode. Before

immersion, any bare ends or obvious mechanically

damaged areas on the electrodes were covered with a

film of silicone rubber, and no intentional holidays were induced. The sources of any corrosion, therefore, were holidays in the films. The applied voltage method

also serves as a sensitive holiday detector and can be

used to ascertain whether holidays are developing in a

film because of degradation of the coating. A typical

experimental setup is shown in figure 6A. In this photograph, taken at the beginning of the test, the bars are coated with material No. 16. After 30 min of applica- tion of 2 V copious amounts of corrosion products were observed (fig. 6B).

The results of these voltage studies are presented in table 12. Altogether 31 coatings were investigated and

19 of these permitted the evolutoin of hydrogen gas

within 15 min. No holidays developed in three of the polyvinyl chloride coated specimens, Nos. 23, 24, and

30, nor in two of the epoxy coated specimens, Nos. 22

and 31, during a test period of over 90 h.

15
FIGURE 6. A. Applied voltage test at beginning of test. Anode and cathode coated with material No. 16. FIGURE 6.B. Results of application of 2 V for 30 min.

Table 12. Electrochemical studies of coated reinforcing bars

Code

number

Time to evolve H2 (g) a

at cathode

(hours)

Resistance (ohms) b Voltage (millivolts) b

ixatings

1 hour 1000 hours 1 hour 1000 hours

1 <Vi 537 200 -340 -570 3

2 <lA 250 190 -588 -576 3

3 <1A 400 180 -615 -604 3 4 <1/2 700 260 -470 -555 3

5 <lA 1.1 x 103 425 -513 -617 3

10 <1A 3

11 <lA 9.6 x 103 800 -497 -560 3 16 1 400 250 -516 -593 2

17 1.5 x 103 700 -430 -545 3

18 98 240 -516 -604 3

19 24 435 225 -503 -568 2 22 d <648 d25 x 105 d25 x 105 N. R.e N. R.e 1 23 d <120 d25 x 105 d25 x 105 N. R.e N. R.e 1 24 d <480 13 x 105 d25 x 105 N. R.e N. R.e 1 25 6 2x 105 d25 x 105 -613 -541 1 26 < XA 3 27 < lA 3 28 <Vt 250 240 -640 -606 3 29 <y4 475 300 -518 -565 2 30 d >1684 d25 x 105 d25 x 105 N. R.e N. R.e 1 31 d > 964 d25 x 105 1500 -532 -588 1 32 <Vi 800 540 e-617 -573 3 33 <Y* 550 400 -516 -565 3 38 B f <Y* 6360 h210 6-514 h-589 3 38 p

f < lA 6380 h220 g-481 b-606 3 39 B f <V4 6380 h240 e-557 h-610 2 39 p

f 3 6410 h230 6-557 h-643 2 40 B f <y4 6280 h200 6-513 ^608 3 40 p

f y2 6290 h240 s-481 h-606 2 41 y2 3.8 x 105 3.0 x 103 -451 -570 2

*42 <% 400 370 -526 -579 3 Uncoated immediate 200 370 -648 -634 4 bar

a Potential of 2 V was applied to coated bar. Bars partially immersed in 7 percent NaCl.

b Bars partially immersed in 3J/2 percent NaCl.

c Ratings sequence in order of decreasing corrosion protection: 1>2>3>4.

d Resistance values beyond capacity of measuring device.

e N. R. denotes no reading possible, i.e., no current flow because of holiday-free film.

f B represents sandblasted surfaces, only, while p indicates that the surfaces were phosphatized before applying the coatings.

6 Initial measurement taken after immersion time of 120 h. h Measured after 696 h. 'Same coating material as No. 41, however, applied to cold bars: coating applied to bars heated to 190 °C in the case of No. 4.
4.5.2. Electrical Potential and Electrical Resistance

Alternate means of assessing the protective qualities of barrier coatings are electrical potential measure- ments and the electrical resistance of the coating films. Such measurements were made on both coated rein- forcing bars partially immersed in 3.5 percent aqueous

solutions of NaCl and on coated bars embedded in

concrete specimens partially immersed in 3.r> percenl

NaCl solution. The electrode potentials were measured

using a Coleman Model 37A pH meter with a saturated calomel electrode (S.C.E.) as the reference electrode, as illustrated in figure 7. Measurements of electrical resistances were taken using a Yellow Springs Instru- ment Company Model 31 Conductivity Bridge along

with a platinum electrode, figure 8.

/POTENTIOMETER

SATURATED CALOMEL

ELECTRODE

COATED

'REBAR

3.5% AQUEOUS

'NaCl SOLUTION

PLATINUM ELECTRODE

CONDUCTIVITY BRIDGE

COATED

'REBAR

3.5% AQUEOUS

'NaCl SOLUTION

FIGURE 7. Measurement of electrical potentials of coated rein- forcing bars immersed in 3.5 percent solution of NaCl. FIGURE 8. Measurement of electrical resistance of coatings on

reinforcing bars immersed in 3.5 percent solution of NaCl.

4.5.2.1. Coated Reinforcing Bars in 3.5 Percent

Solution of Sodium Chloride The coated bars were partially immersed in aqueous

solutions of 3.5 percent NaCl in 3 liter polyethylene

buckets fitted with lids. Two holes were cut in each lid, one for the reinforcing bar, the other for the reference

electrode. The electrical potential and electrical resistance data

are presented in table 12. Low resistance values, below

500 fl, are indicative of coating films which either have

many holidays or are permeable to water and/or chlo- ride ions. The measured corrosion potential of un- coated steel reinforcing bars was —634 mV versus

S.C.E. after 1000 h. All of the specimens had electrical potentials below these values, even though numerous

corrosion sites were visually observed on all of the specimens which had resistances below 500 fl. The

electrical resistance values appear to be more reliable indicators of the corrosion state of the coated rein- forcing bars than the electrical potential values. The thicker films (above 15 mils), Nos. 22, 23, 24,

and 30, were free of holidays and had resistances above

24 x 105 fl, which are beyond the range of the measuring device. These films were in effect perfect insulators preventing the flow of current, therefore, the electrical potential of the protected bars could not be measured.

Potential and resistance data for three sets of rein- forcing bars, each set coated with a different epoxy

(Nos. 1, 25, and 31) are plotted versus test time in figures 9, 10 and 11. The wide variance in the initial millivolt and ohmic readings of duplicate and triplicate

specimens decreased rapidly during the first 200 h of

tesintg and after 1000 hours good agreements were

obtained for companion specimens. A rapid decrease

in the resistance of a coating probably can be attributed

to the emergence of holidays, while an increase in resistance is probably indicative of some type of healing

mechanism.

4.5.2.2. Coated Reinforcing Bars Embedded in Concrete The corrosion-test specimens, figure 12, consisting of reinforcing bars embedded in 2% x 4% x 15 in concrete blocks were partially immersed in an aqueous

solution of 3.5 percent NaCl. The solution was con- tained in a 105 gallon polyethylene-lined, fiberglass

reinforced, polyester tank, 4 x 2 x 2 ft. The bars were

in a vertical position with their lower ends, protected

by silicone sealant, fitted into 1 in diam holes drilled in 1 ft x 1 ft spacing racks of 34-in thick marie plywood. The racks rested on a sheet of marine plywood

laid on the floor of the tank, and spacing racks were

17
COX

CD

LdO

?

CO

CO

Ld

cr

EXPOSURE TIME (HOURS)

FIGURE 9. Electrical potential and resistance measurements of reinforcing bar coated with material No. 1 immersed in percent NaCl.

In the ordinate caption, M.V. versus S.C.E. denotes millivolt reading taken

using a saturated calomel electrode as the reference.

—• 25A10HMS) — 25BI0HMS) —0 25AIMV) — 258 (MV)

200 400 600 800 EXPOSURE TIME (HOURS)

4KI05

FIGURE 10. Electrical potential and resistance measurements

of reinforcing bar coated with material No. 25 immersed in i^/i percent NaCl.

In the ordinate caption, M.V. versus S.C.E. denotes millivolt reading taken

using a saturated calomel electrode as the reference.

UJo

CO

to>>

I—O

1

• 31 A (OHMS)

3IB (OHMS) O 3IA (MV)

3IB (MV)

^--1 -"f----4 +••—""'1

CO

LdO

CO

40xl03 CO

Ld

cr

3.0 »I0

3

EXPOSURE TIME (HOURS)

FIGURE 11. Electrical potential and resistance measurements

of reinforcing bar coated with material No. 31 immersed in S^/i percent NaCl.

In the ordinate caption, M.V. versus S.C.E. denotes millivolt reading taken

using a saturated calomel electrode as the reference. FIGURE 12. Corrosion-test specimen with coated reinforcing bar embedded in concrete block of dimensions 2% x 4

7/$ x 15 in.

18
placed on top of the specimens (fig. 13). The lower

13 in of each specimen was immersed in the NaCl solution, with the upper 2 in of the concrete being above

the level of the solution. The electrical potentials and electrical resistances of the corrosion-test specimens are listed in table 13. The

results are in general agreement with the protective

ratings given in table 12. No evidence of cracking in the concrete cover nor of rust stains were observed.

In section 4.5.2.1. it was noted that electrical potential measurements do not seem to accurately indicate the corrosion state of the coated reinforcing bars. The

uncoated bars have potentials of —180 and —207 mV

after 3480 h (table 13), which are considered to be in the passive region [34], while many of the coated bars

have much more active potentials.

Resistance measurements are probably more reliable indicators than potential measurements, since the resis- tance values are primarily dependent on the integrity of the coating films. The resistance of a film will sharplj

decrease if holidays develop or decrease more slowly

if the film is gradually overall deteriorating. The resis- tance of the protective layer of water-soaked concrete

is low [35], certainly much lower than the resistance of

a good protective coating on a bar. The corrosion-test specimens with the uncoated bars had the lowest resis- tance values measured, 220 and 230 ohms; while the specimens with bars protected with coating No. 30,

assigned a protective rating of 1, gave the highest resis- tance values of 2.1 x 105 and 1.6 x 10s CI. However, it is difficult to understand why many of the bars embedded in concrete had lower measured resistances than

the unembedded bars (sec. 4.5.2.1).

Table 13. Electrical potential and resistance measurements of corrosion- test specimens in aqueous solution of 3.5 percent NaCl

Coating Code No. a

Exposure time (hours)

Protective Rating c 24 3480

„. . rLlectncal potential ^ (MV)

Kesistance (ohms)

„. . rjlectrical potential ^ (MV)

Kesistance (ohms)

1 A -345.0 3.8 x 102 -283.0 3.9 x 102 3 B -408.8 7.0 x 102 -362.4 8.2 x 102 1-1 -337.0 2.5 x 102 -215.0 2.5 x 102 —

1-S -484.5 4.8 x 102 -371.5 4.2 x 102 3 A -285.6 3.1 x 102 -432.4 2.2 x 102 3 B -260.3 2.7 x 102 -365.5 2.4 x 102 4 A -339.2 2.4 x 104 -142.3 1.1 x 105 3 B -130.0 1.0 x 105 -115.5 1.4 x 104 18 -575.6 6.0 x 103 d-003.0 1.0 x 104 3

19 A -484.0 5.6 x 102 -399.5 5.4 x 102 2 B -438.0 6.1 x 102 -282.0 6.0 x 102 25 -542.7 4.1 x 102 d-271.4 5.1 x 102

1 27 A -654.6 1.3 x 104 d-167.0 7.2 x 104 3 B -571.5 6.8 x 103 -542.0 1.1 x 104 28 -461.5 5.2 x 102 d-262.8 5.4 x 102 3 29 A -376.3 6.4 x 102 4-163.0 7.8 x 102 2 B -403.4 6.6 x 102 -360.5 5.4 x 102 30 A -058.0 1.0 x 105 eS 2.1 x 105

1 B -448.2 1.5 x 105 d-127.4 1.6 x 105 31 A -359.8 1.5 x 103 d-038.5 9.8 x 104

1 B -092.2 9.8 x 103 -013.5 6.2 x 104 38 -392.7 3.2 x 102 -165.7 4.1 x 102 3 39-Phos A -513.0 4.9 x 102 -348.0 4.7 x 102 3 B -536.2 5.0 x 102 -402.0 4.8 x 102

• 40-Phos A -282.2 2.5 x 102 -256.6 2.2 x 102 2 40-Phos B -382.5 3.4 x 102 -325.5 2.7 x 102 40 A -431.8 2.9 x 102 -398.0 3.1 x 102 3 B -377.0 2.8 x 102 -316.9 2.3 x 102 41 A -540.5 6.0 x 103 -432.4 1.3 x 104 2 B -575.9 5.4 x 102 -324.4 2.5 x 104 Uncoated A -334.2 2.7 x 102 -206.6 2.3 x 102 4 B -264.0 2.6 x 102 -180.3 2.2 x 102

a A and B denotes duplicate specimens.

b Electrical potential versus S.C.E.

c Ratings from table 12. d Large shifts in electrical potential attributed to sealing small holes in the silicone seal.

e Not possible to measure.

10
FIGURE 13. Corrosion-test specimens immersed in 3.5 percent

solution of NaCl.

5. Bond Strength and

Creep Determinations

An important phase of the project was the determination of the bond between coated reinforcing bars and

concrete and of the creep characteristics of coated bars

in concrete. Probably, the main reason that little consideration was previously given to epoxy materials as protective coatings for reinforcing bars was the sup- position that the coated reinforcing bars would have

unacceptable bond strengths to concrete [22]. Few, if any, reports have been published of any type of struc- tural testing performed on epoxy coated bars embedded

in concrete. The bond with coated bars should not be

significantly less than that between uncoated bars and

concrete if coated bars are to be used in established bridge deck design. The structural characteristics of coated bars in concrete have been compared with the properties of uncoated bars by pullout tests and creep

tests.

5.1. Pullout Studies

The pullout tests are tests in which increasingly

higher loads are applied in equal increments to the rein- forcing bar until either the bar yields or the bond

strength between the reinforcing bar and concrete is greatly exceeded (estimated by measuring the slip of the reinforcing bar relative to the concrete prism)

.

Altogether 34 pullout specimens were tested consist- ing of 5 specimens with uncoated reinforcing bars, 23

specimens with epoxy-coated bars and 6 specimens with

polyvinyl chloride-coated bars.

5.1.1. Pullout Test Procedures

Pullout specimens were tested in a 200,000 lb capacity universal electromechanical testing machine 27 to 29 days after fabrication. A pullout specimen positioned on the testing machine is shown in figure 14. The pullout specimen shown in figure 15 is seated on

leather cushions on two segments of a 2 in base plate attached to a spherical bearing block. Free- and loaded- end slips of the reinforcing bar were measured with

1 x 10^ in micrometer dial gages and estimated to

1 x 10"5 in. At the loaded end of the specimen, two dial

FIGURE 14. Pullout specimen on electromechanical testing machine being prepared for testing.

FIGURE 15. Schematic of pullout specimen.

Size of concrete prism is 10 x 10 x 12 in.

20
gages were attached to a steel bar fastened to the face of the concrete by bolts secured into inserts cast in the concrete. The gages bore on a steel yoke fastened to the reinforcing bar about 1 in below the face of the concrete. The bar supporting the dial gages and the yoke was free to move in the recess in the base plate. The

average of the two gage measurements gave the dis- placement of the point on the reinforcing bar where

the yoke was attached, with reference to the face of the

concrete. Slip at the free end was measured with a gage

that bore on the exposed end of the reinforcing bar

(any coating material on the exposed end of the rein- forcing bar was removed prior to testing). The gage was mounted on a support attached to the top face of the concrete by bolts secured into inserts cast in the concrete. Loads were applied in increments of 2,000 pounds

to the reinforcing bars in the pullout tests until failure occurred either by yielding of the steel or excessive slip

between the bar and concrete was attained.

5.1.2. Results of Pullout Studies The relationships between applied load and the free- end and loaded-end slip are plotted in figure 16 for the 34 pullout specimens tested. Roman numerals denote

the concrete batch number while the Arabic numbers

next to the plots identify the coating materials (table

1). The loaded-end slip was larger than the free-end

slip for all specimens tested primarily because slipping

initiates at the loaded-end and extends toward the free- end as the load is increased. Bond failure in a reinforced concrete member is denned as excessive slip, or movement, of the free end

of a bar stressed in tension caused by only a slight increase in the applied load [28]. Therefore, the large

slips shown in figure 16, normally occurring at high

loads, are indicative of bond failures. The mode of failure, critical bond strengths, and

critical bond stresses are given in table 14. The critical bond strengths and critical bond stresses are defined as the values corresponding to either a loaded-end slip of 0.01 in or a free-end slip of 0.002 in whichever is lower [28]. The critical bond strengths corresponded to applied

loads ranging from 17,000 to 21,600 lb for uncoated

bars and for coated bars, except those coated with

materials Nos. 22, 23, 24, and 30. The average applied

loads corresponding to the critical bond strengths for bars coated with the latter materials were estimated to be 9,000, 1,100, 60 and 5,700 lb respectively. Note that

the mode of failure was yielding of the reinforcement

for all pullout specimens except those containg bars

with coatings Nos. 22, 23, 24, and 30. Bond stresses were compuetd from the formula [28]

fs As u = (2)

where fs is the stress in the reinforcing bar, As is the nominal cross sectional area of the bar, So is the nominal perimeter of the bar and L is the length of embedment of the reinforcing bar in the pullout specimen.

Values of As and So for each of the two tj pes of rebars

are given in table 2. The value of /« is given by

where P is the load or tensile force applied to the rein- forcing bar in pounds. Therefore, eq (2 J can In- reduced to

(4) SoL

which was used to calculate u from the pullout tests. Values of bond stress developed in the pullout speci- mens were compared with allowable values given in codes and specifications. The American Concrete Insti- tute Building Code 318—63 [36] allowed a working

bond stress design for deformed bars ( other than top

bars) conforming to ASTM A 305 [37] calculated from,

but not greater than, 500 psi

4.8 V fc D

(5)

where fc

' is the strength of the concrete and D is the nominal diameter of the bar in inches. Using the value

of fc as 6170 psi (average of the strength of the three batches of concrete used in the pullout studies) the bond stress, u, is 490 or about 500 psi.

The Standard Specification for Highway Bridges

Adopted by the American Association of State Highway

Officials [38] states that slabs (decks) designed for bending moment in accordance with the given provi- sions shall be considered satisfactory in bond and shear. In another section of this Standard Specification on

concrete design, the allowable bond stress for tension

bars conforming to AASHO M31 [38] and ASTM

A615-72 [25] is

4.8 V fc D

, 500 psi maximum (6)

and is the same as that given by the ACI 318—63 Code

[36]. The critical bond stresses and bond stresses corre- sponding to one half the maximum applied load, Um/2, were greater than 600 psi (table 14) for all pullout

specimens except those having bars coated with materials Nos. 22, 23, 24, and 30. An evaluation of the pullout tests results indicates

that epoxy-coated reinforcing bars have bond strengths

essentially equal to uncoated bars when the film thick- nesses are approximately 10 mils or less. Both liquid

and powder epoxies performed equally well, and the application method did not significantly affect the bond

strength of coated bars. The polyvinyl chloride coated

bars had bond strengths considerably less than that for uncoated bars and bars with these coatings are not recommended for structural use. The lower bond

strengths for polyvinyl coated bars are attributed in part to the thermoplastic nature of the polyvinyl chloride. The thickness of the polyvinyl chloride films was

greater than most of the epoxy films but thicker films are normal for thermoplastics [39].

21
I

n

40X103

1 1 1 1 1 ">UD >-UB LXJ^^

1 1 I 2SD-2 /

25D-I / —

T F 1 1 11 1 1 1 1

1

///(to !

22B-)/22BH /

II FREE END

II LOADED END

1 1 1 1 L

»B , 24T,//*8 "/

"/ ^240 ^ 1 1 1

j 1 1 /23B J/

1 r 1 1 1 1 1

L22B-2

1/22B-2

1 1 1 1

1000 ^

o

JOm

•&

500 E

K) 6 20 K> 15 20 0 5

SLIP (inches xlO"2

)

K) 15 20 10 15 20 25

40XI03 -

1000 0

(A

K) 15 20 5 20

SLIP (Inches xlO"')

20 10 15 20 25

FIGURE 16. Applied load to reinforcing bar in pullout specimens versus free-end and loaded-end slip. Roman numbers indicate concrete batch number, while Arabic numbers identify the coating materials (table 1).

22
Table 14. Pullout data

Piillonf No.

Load

corresponding

to critical bond strength Per (lb)

Maximum

slip observed at free end

(in)

Bond stress corresponding to: Urn Loaded-end

slip of 0.01

in ui (psi)

Free-end

slip of 0.002

in U2 (psi)

2

(psi) Mode of failure

U-B 20,300 0.006 723 978 712 Yielding of reinforcement; no cracks. U-B 18,000 .007 641 889 629 Yielding of reinforcement; small longi- tudinal crack extending one third length of one face. Small transverse crack at loaded end. U-B 20,000 .006 712 1157 729 Yielding of reinforcement. Small longi- tudinal crack extending one half length of specimen on one face. U-D 21,600 .006 764 1037 628 Yielding of reinforcement; no cracks. U-D 21,400 .002 755 ( a

) 664 Yielding of reinforcement; no cracks.

1-B 21,200 .003 751 1185 727 Yielding of reinforcement; no cracks.

1-D 18,000 .003 638 1060 645 Yielding of reinforcement. Small longi- tudinal crack extending one half length of specimen on two opposite

faces.

1-B-S 17,100 .01 609 925 727 Yielding of reinforcement; no cracks.

3-B 20,000 .006 712 1210 727 Yielding of reinforcement; no cracks. 3-D 21,000 .002 745 1199 646 Yielding of reinforcement. Small longi- tudinal crack extending one sixth of length of specimen on one face.

18-B 21,500 .002 766 1352 675 Yielding of reinforcement; no cracks.

18-D 18,800 .003 656 1197 673 Yielding of reinforcement; no cracks.

19-B 19,000 .004 677 1089 727 Yielding of reinforcement. Small longi- tudinal crack extending one sixth length of specimen on two faces.

19-D 21,400 .003 759 1277 726 Yielding of reinforcement; no cracks.

22-B-l 11,600 .01 AWOA 497 Bond failure. Small transverse crack extending one half length of loaded

end.

22-B-2 6,500 .007 363 231 Test stopped before concrete cracked.

23-B 700 ( b

) 107 25 447 Bond failure. Specimen badly cracked.

23-D 1,400 .03 167 50 395 Bond failure. Specimen badly cracked.

24-B 100 .05 18 5 133 Bond failure. Excessive free-end slip.

24-D 30 .06 18 1 165 Bond failure. Excessive free-end slip.

25-D-l 18,500 .003 656 1050 638 Yielding of reinforcement. Small longi- tudinal crack extending one half of length of specimen on two opposite

faces.

25-D-2 17,800 .005 631 922 628 Yielding of reinforcement. Small longi- tudinal crack extending one half of length of specimen on two opposite

faces.

29-B-l 17,000 .004 605 979 673 Yielding of reinforcement. Small longi- tudinal crack extending one third of length of specimen on two opposite

faces.

23
Table 14. Pullout data—Continued

Load

corresponding

to critical bond strength Per (lb)

Maximum

slip observed at free end

(in)

Bond stress corresponding to: Um

Pullout No. Loaded-end

slip of 0.01

in ui (psi)

Free-end

slip of 0.002

in U2 (psi)

2

(psi) Mode of failure

29-B-2 18,200 .004 648 1033 638 Yielding of reinforcement. Small longi- tudinal crack extending one third of length of specimen on two opposite

faces.

30-B 6,000 .03 410 214 605 Bond failure. Small longitudinal crack extending entire length of specimen

on two opposite faces.

30-D 5,400 .02 348 191 569 Bond failure. Numerous small longi- tudinal cracks on all faces.

31-D 19,500 .012 670 1056 675 Yielding of reinforcement. Small longi- tudinal cracks extending one third

of length of specimen on two opposite

faces.

31-B 18,700 .006 646 956 674 Yielding of reinforcement. Small longi- tudinal cracks extending one third of length of specimen on two opposite

faces.

38-B 19,700 .008 702 1129 766 Yielding of reinforcement; no cracks.

38-D-Ph 21,500 .003 762 1032 726 Yielding of reinforcement. Small longi- tudinal crack extending one third length of specimen on two opposite

faces.

39-D 20,000 .004 709 1177 638 Yielding of reinforcement. Small longi- tudinal crack extending one sixth of specimen on two opposite faces.

39-B 17,500 .004 623 1122 628 Yielding of reinforcement. Small longi- tudinal crack extending one sixth of specimen on two opposite faces.

41-D 18,500 .004 656 1046 675 Yielding of reinforcement. Small longi- tudinal crack extending entire length

of two opposite faces.

41-B 17,000 .004 605 1068 673 Yielding of reinforcement; no cracks.

a Unreliable data due to sticking gage.

b Not recorded, greater than 0.02 in.

5.2. Creep Studies

In contrast to the pullout tests, the creep tests were performed with two specific stress levels in the rein- forcing bars. Twenty-four specimens were studied

which consisted of 18 reinforcing bars coated in dupli- cate with 9 different epoxy materials; 2 reinforcing

bars coated with a polyvinyl chloride material; and 4

uncoated reinforcing bars. The two levels of tensile stresses were 15,000 and 30,000 psi (in the steel rein- forcing bars). These stress levels were selected because

the lower value represents the stress that rebars in bridge decks are normally subjected and the higher

value represents a stress which may be included in future bridge deck designs using high strength steel.

5.2.1. Creep Test Procedures

A creep specimen with the loading assembly attached

is illusrtated in figure 17. Tensile stresses of either 15,000 or 30,000 psi (in the steel reinforcing bar) were

attained by compressing the spring with a 30 ton hydraulic ram. The stress level in the reinforcing bar was

monitored with both the load cell and the strain gages

attached to the reinforcing bar. When the desired

tensile level was reached, the upper nut on the threaded

reinforcing bar was firmly tightened against the steel bearing plate holding the spring in a compressed position. Subsequently, the lower nut was released and the hydraulic ram, load cell and spacer assembly were

removed. Releasing the loading apparatus caused a

24
negligible decrease in the tensile stress in the reinforc- ing bar. Shown in figure 18 is a creep specimen under

test at a tensile stress of 30,000 psi.

The creep specimen in figure 18 was seated on leather cushions on two segments of the test frame (fig. 19).

The dial gages were of the same type and attached in the same way as described for the pullout specimens.

The free-end and loaded-end slip were also measured.

The dimensions of the steel spring used to exert the

tensile loads in the reinforcing bar were: height of 8 in

;

outside diameter of 51,4 in; and the steel coils had a

I , , Z2

LOAD CELL

Specimen Loading Assembly

FIGURE 17. Schematic of creep specimen.

Size of specimen is the same as the pullout specimen.

•J

1 1 I :. _ w

^1 i

llu . -

BBBSBIBBIH

FIGURE 18. Creep specimen loaded to a tensile stress level of 30,000 psi (in the steel reinforcing bar).

Test Frame

FIGURE 19. Schematic of creep test frame.

25
diameter of 1%6 hi. The springs were calibrated (load versus displacement) using the device shown in figure

20. The compressive displacement of the springs was

SPRING CALIBRATION APPARATUS

FIGURE 20. Apparatus for calibrating steel springs used to exert tensile stresses in the creep study.

measured with 1 x 10"4 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 14,000 lb (14 kips) and dial gage

readings of spring displacement 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 the two dial gages located dia- metrically opposite on the calibration device. The 24

springs had nearly the same displacement response to loading as indicated by the plot in figure 21, which

gives the range in displacement for corresponding load

application.

The strain gages, to monitor the tensile stresses, were

attached to the reinforcing bars approximately 3 in from the concrete prism with an epoxy adhesive. The

gages were covered with a protective coating of wax

followed by a coating of an epoxy material. Two strain gages, electrically connected in series, were attached

diametrically opposite on each bar. These gages when

attached as recommended by the manufacturer are claimed by the manufacturer to have ordy a small

intrinsic creep of 10 fie (microstrain units) /year. The

strain values were measured with a Vishay Instruments

Strain Indicator Model P 350 A. Strain measurements

were converted to stress values in psi using a calibraDISPLACEMENT, IMCHES FIGURE 21. Range of displacement response of 24 steel springs used in the creep study.

tion diagram obtained from tensile tests of reinforcing

bars instrumented the same as the bar in the creep specimens.

The tensile stresses in the reinforcing bar were also monitored periodically by comparing the heights of the compressed springs with the heights of the springs immediately after the application of load. These data were compared to the dial gage readings which indicate the

slip of the reinforcing bar relative to the concrete

prism. Based on the calibration of the displacement

response of springs to loading, any increase in the height of the compressed springs could be directely related to the amount of loss of tensile stress. After 45 days of testing, the average relaxation in tensile stress was 205 psi and 701 psi for specimens

having tensile stress of 15,000 psi and 30,000 psi,

respectively.

5.2.2. Results of Creep Studies The creep tests simulate more closely the long-term

structural rigors an acceptable coating must endure,

than do the pullout studies. In the creep test, tensile stresses were maintained whereas in the pullout test increasing increments of load were applied. Creep

properties of reinforcing bars embedded in concrete have not been well characterized. The performance of coated bars in the creep tests has been assessed, therefore, by comparing their slip-time relationships with

those of uncoated bars. It is the opinion of the authors

that the slip-time relationship for coated bars should

not vary significantly from the slip-time relationship

measured for uncoated bars for normally expected

steel stresses. Furthermore, there should be no signifi- cant increase in the magnitude of either free-end or loaded-end slip of the coated bar as compared to the uncoated bar. These criteria will be more quantitatively developed later in this section.

26
5.2.2.1. Slip-Time Relationships Both the free and loaded-end slip of coated and

uncoated bars, at tensile stresses of 15,000 and 30.000

in the bars, are plotted versus time in figure 22. Rates

of slip (analogous to creep) usually were highest dur- ing the first two days after loading the specimens, and

thereafter, the rates gradually decreased. However, even

after 45 days, measurable slip was still detected for all specimens. Similar to the behavior of the pullout speci- mens, the loaded-end slip-time relationships were significantly larger than the free-end slip-time relation- ships for all creep specimens, with the exception of the bars coated with material No. 30, primarily because

slipping initiates at the loaded-end and slip propagation towards the free-end is hindered by the deformations interlocking the bars in the concrete. The free-end

slip time curves, at tensile stresses of both 15,000 and

30,000 psi, with the bars coated with material No. 30

(a polyvinyl chloride coating) were essentially identical

to the respective loaded-end slip-time curves; therefore, these coated bars were not interlocking in the concrete and probably would not have acceptable reinforcing

properties if embedded in concrete. A comparison of the slip-time curves in figure 22

indicates that with the possible exceptions of materials Nos. 1 and 18, the epoxy coatings did not have a

detrimental effect on the magnitude of the slip-time

relationships developed with uncoated bars. In contrast, obviously the bars coated with the polyvinyl chloride

material, No. 30, developed unacceptable slip-time

relationships.

5.2.2.2. Slip Values at 45 Days Free- and loaded-end slip data, at 45 days, of coated

and uncoated bars are listed in table 15. The slip data obtained at the tensile stress level of 30,000 psi will be

emphasized. The respective slip values for both the coated and uncoated bars attained at the tensile stress of 15,000 psi were about 10 to 50 percent of the values obtained at 30,000 psi stress level. Furthermore, the same conclusions are derived by analyzing either set of data. Three creep specimens with uncoated bars were

tested at the 30,000 psi stress level and average loaded- end slip was 0.00164 in and the average free-end slip was 0.00077 in, at 45 days. The agreement between the

three loaded-end slip values and also the three free-end values was excellent for this type of experiment. The

range and percent coefficient of variation for the loaded- end data was 0.00022 inch and 4.0 percent, and 0.00013

in and 7.1 percent for the free-end slip data. Because

the variation in concrete strength was minor, no compensating adjustments were made in the slip values.

30,000 PSI 30,000 PSI 15.000 PSI 15.000 PSI

FREE END

- LOADED END

FREE END

LOADED END /

#1 #19 #31 #38 #39

UNCOATED A__.

/

1

1

1 —

!r

/

/

/

r . 10 20 30 DAYS

40 0 10 20 30 DAYS

40 0 10 20 30 DAYS

40 0 10 20DAYS30 40 0 10 20 30 40 DAYS0 10 20 30 40 DAYS

TIME

FIGURE 22. Free-end and loaded-end slips in creep specimens versus time. Roman numbers indicate concrete batch number, while Arabic numbers identify the coating materials (table 1).

27
Table 15. Creep of coated and uncoated bars embedded in concrete prisms at 45 days

Costing No. Compressive

strength of concrete

Steel

stress (psi)

Slip at loaded end

(in)

Slip at free end

(in)

Slip _ Coated bar

Ratio Uncoated bara

Loaded end Free end

ii OOOD l0,UUU A AAl A A A AAA"7A o.ooo /y 2.1 2.2

i oooo

OH AAA .UUZOU AAl r A .UOlDO 1.6 2.0

1 Q 1D,UUU AAA/C Q .UUUOo 1.8 lo qa aaa Ann aq ,UUl4-y OOl 1 Q .UUllo 0.90 1.5 10iy DOOD i r aaa nnnco .UUUOo AAAAQ .UUUOo 0.77 0.22

l oiy DOOD ou,uuu qa aaa ftm i a .UUX14< AAAA O .UUUOo 0.70 0.82 zo D4«y4) i c: aaa AAAQA .UUUoU AAAQl .UUUol 1.2 0.86 ZD o^y^ on AAA OU,UUU AAl CA .UUlDU AAAOC .U008D 0.91 1.1 zy

C A CIA 1 C AAA J.D,UUU nnmn AAAAT .00007 1.1 0.19 zy

on AAA oU,UUU (°) AAl AO .UOlOo 1.3 QAoU o^y^ 1 C AAA .UU4o4 .U0o84 6.3 10.7 oU Q/1 Q/1 OA AAA oU,UUU m oi k .UlZlo AT OOO .uizzy 7.4 16.0 ol OOOD 1D,UUU AAAC fl .uuuoy AAAAQ .UUUUo 0.86 0.22

Ql01 c;aac; OOOD on AAA Du,UUU OOl 3/1 .UUlo4 AAAOA .UUUzO 0.82 0.34 OO 0000 i z aaa .uuuoy AAA1 7 .UUU1 / 1.0 0.47

QQOO OOOD OA AAA .00168 AAAOA .UUU80 1.0 1.0 QOoy

r/z-r OOOD 15,000 AAAOA

.1)1)080 .00017 1.2 0.47 o9 OOOD OA AAA .00158 AAAA-7 .0009 / 0.96 0.99

A 1 41 o^y^ 1 C AAA AAl 1 A .00110 AAAAO .OOOOo 1.6 0.22 41 5494 30,000 .00212 .00100 1.3 1.3 U.C. 5494 15,000 .00069 .00036 1.0 1.0 U.C. 5494 30,000 .00176 .00071 1.1 0.02 U.C.-l 5665 30,000 .00163 .00084 0.99 1.1 U.C.-2 5665 30,000 .00154 .00076 0.95 0.99

a Slip for uncoated bars at tensile stress of 30,000 psi is average of 3 specimens, i.e., slip of 0.00164 in at loaded-end and 0.00077

in at free-end.

b Malfunction of dial gage.

The slip at the 30,000 stress level for the nine speci- ments with epoxy coated bars ranged from 0.00114

(No. 19) to 0.00260 (No. 1) for the loaded-end and

from 0.00026 (No. 31) to 0.00079 in (No. 1) for the

free-end. Excessive slips of 0.0122 in for the loadedend and 0.0123 for the free-end developed for the specimen with the polyvinyl chloride coated bar (material No. 30) . The slip of the coated bars are compared

with the average slip of the uncoated bars by computing

the following slip ratio

,. . slip of coated bar ._. slip ratio = —£ r t —j-r (7) average slip ot uncoated bar

for both loaded and free-end slip. These respective

ratios are listed under columns 6 and 7 in table 15. At the 30,000 psi stress level, the ratios for the loaded- end slip ranged from 0.70 to 2.1 for epoxy coated bars

and was 7.4 for the polyvinyl chloride coated bar. The

similar ratios for the free-end slip of epoxy coated bars

varied from 0.34 to 2.2, and was 16.0 for the polyvinyl

chloride coated bar. Unequivocal interpretation of the significance of the

ratios of slip of coated bar to average slip of uncoated

bar is difficult, because criteria for allowable creep of uncoated reinforcing bars, subjected to tensile stresses,

have not been established. Obviously, the high ratios of 7.4 and 16.0 for the polyvinyl chloride coated bar

(material No. 30) , should preclude its use as protective

coating for concrete reinforcement. Probably, all the bars coated with epoxy materials, with the possible

exceptions of Nos. 1 and 18, had acceptable slip ratios. Values of the slip ratios for the bar coated with No. 1 was about 2.0 for both the free and loaded-end slip. The slip ratio of 2.0 for the loaded-end is about twofold greater than the ratio with most other epoxy coated

bars, and the slip ratio for the free-end is about 2 to 6

times greater than the similar ratio for the epoxy

coated bars (except for No. 18). Therefore, its is felt that the bar coated with material No. 1 had undesirable creep characteristics. Similarly, analysis of the slip ratio for the bar with coating No. 18 indicates it had

acceptable loaded-end creep but possibly unacceptable

free-end creep (considering slip ratios at both 15,000

and 30,000 psi). It is felt that reasonable criteria re- quires bars coated with an approved coating material

should have both acceptable loaded-end and free-end creep characteristics, when subjected to tensile stresses near the level it would actually experience if used as the reinforcement in concrete. Further studies are necessary to determine the values

of acceptable slip ratios expressed by eq(7). Based on

28
the results of the current creep study, the following

values are proposed as being reasonable: maximum

slip ratio of 1.6 for the loaded-end; and maximum slip ratio of 1.3 for the free-end.

6. Discussion

Although, 47 coating materials (table 1) were evalu- ated and four coatings have been judged, on the basis of results in the testing program, to have overall ac- ceptable properties as potential coatings for the rein- forcing bars of concrete of bridge decks. These four

materials are Nos. 25, 31, 39, and 41, all powder epoxy

coatings. In the following section, the pertinent experimental results which lead to the selection of the four coating materials, will be briefly discussed.

6.1. Evaluation of Coating Materials

The evaluation of coating materials as protective

coating for steel reinforcing bars embedded in concrete of bridge decks was based on the following four

general test categories:

1. Chemical resistance of cured coatings.

2. Physical durabilities of coatings on reinforcing

bars.

3. Corrosion protection of reinforcing bars by coatings.

4. Structural characteristics of coated reinforcing

bars in concrete . Established tests were selected and when necessary new tests developed so that the probable performance

of coatings on bars embedded in concrete of bridge

decks could be evaluated. The implications of the results of these tests will be

discussed in this section. The major emphasis in the present study has been given to epoxy coatings be- cause of anticipated unacceptable structural characteristics of reinforcing bars coated with thermoplastics,

which has been subsequently experimentally confirmed

(sec. 6.1.4)

.

6.1.1. Chemical Resistance of Coating Materials Chemical resistance studies were implemented to make projected evaluations of the long-term durability

of coatings when in concrete. The resistance of coatings

to aqueous solutions of aggressive salts similar to those

in portland cement concrete was assessed by immersion

studies with specimens of both pure coatings (table 4)

and coating on bars (table 5). The weight changes of cured specimens of liquid epoxies (table 4) are in the range reported by other investigators [40]. It is felt that with the exception of the three solvents containing

epoxy systems, Nos. 7, 8, and 9, the liquid epoxy sys- tems performed satisfactorily and probably will not be

degraded by long-term embedment in concrete. The immersion of coated bars in aqueous solutions

of 3.5 percent (0.5M) NaCl was an excellent discrimi- natory test. Specimens in this test included bars coated

with both the powder epoxies and most of the liquid

epoxies, and with polyvinyl chloride materials. Seven

coatings consisting of 4 powder epoxy and three polyvinyl chloride materials, had ratings of 1 and 2 indi- cating they had sufficient chemical resistances to ade- quately protect the reinforcing bars from corrosion. The long-term durability of polyvinyl chlorides embedded in concrete, however, is still regarded by the authors to be of major concern, for if hydrolysis should

take place sufficient amounts of chloride ions could be

liberated to cause corrosion of the bars. The performance of a coating on bars in the immersion tests is not entirely governed by the chemical

resistance of the coating materials but is also dependent on the film integrity of the coating. Some coatings had

poor ratings (below 2) because of poor application

techniques by applicators, inadequate film thicknesses (below 5 mils) and uneven film coverage which left the top of the deformation either thinly coated or bare. Phosphatizing the surface of the metal substrates has

been considered advantageous to inhibiting corrosion

[36]. In the present study, however, the coated bars

with phosphatized steel surfaces, Nos. 38-Phosp, 39- Phosp and 40-Phosp, were, rusted when immersed in saturated Ca(OH) 2 and in 3.5 percent NaCl, to a greater extent than the companion coated bars with

blasted surfaces. Furthermore, the epoxy coatings over

the phosphatized surfaces softened while the coatings over the blasted surface were still hard after a year

of immersion.

6.1.2. Physical Durabilities of Coatings

Reinforcing bars are normally subjected to harsh

physical treatment while being shipped to the site of bridge construction and during the placement process. Furthermore, steel reinforcing bars are still being bent

to form hooks, in accordance with the specifications of some state highway departments. The ability of coatings on bars to withstand a reasonable amount of rough

treatment with minimum damage, therefore, is a neces- sary prerequisite.

The relative physical durabilities of coatings were

assessed by measuring the impact and abrasion resis- tances of coatings on steel plates (table 7), bending

coated reinforcing bars (table 9), impact tests on

coated bars (table 10), and hardness measurements of coatings (table 11), with the bending test probably

being the most important physical test. The performance of a coated bar in the bend test gives significant information concerning the flexibility of a coating; proper cure of the coating; surface prep- aration of the steel; and film thickness. Coatings with

little flexibility will crack when subjected to tensile forces caused by bending. Polyvinyl chlorides are inherently flexible materials and performed well, even

with film thicknesses up to 35 mils. Although epoxies

are intrinsically more brittle than polyvinyl chlorides, the relative performance of epoxy films ranged from

complete failure to excellent. Interestingly, the flexibili- ties do not appear to be directly related to the type of epoxy system, i.e., powder or liquid. Flexibilities of epoxy coatings will often be decreased by improper

cure caused by such factors as mixing incorrect ratios

29
of resin to hardener or by curing powder epoxies at improper temperatures. The flexibilities of epoxy coat- ings decrease inversely with their film thickness. Based

on the present study, it is recommended that the maximum allowable film thickness should be determined for each epoxy coating and consistent with good flexibili- ties and structural properties (sec. 6.1.4) should not exceed an average thickness of 10 mils.

6.1.3. Corrosion Protective Qualities of Coatings

The relative effectiveness of barrier-type organic

coatings in protecting steel reinforcing bars from ac- celerated corrosion attributed to chloride ions can be

associated with the following: physical and chemical

durabilities of the coatings (discussed in the previous

sections) ; intrinsic chloride ion permeabilities; film

integrity and film thickness; formulation of the coating,

including corrosion inhibitors [41]. The present study confirms the results of others [40] that epoxies absorb measurable amounts of water and,

therefore, thin epoxy films, about 2—10 mils, are not

entirely impervious to moisture. Chloride ion permeability rates, however, may be much lower than those of pure water. Little if any data on the rates of migration

of chloride ions through epoxy films have been previously reported. The results of the present study do

indicate that many thin epoxy films are essentially

impervious to chloride ions (at least during the test time of this study)

.

The film integrity of coatings on reinforcing bars is an important consideration because holidays are potential sites of corrosion. In general, the coatings on bars

with few or no holidays (table 8) had acceptable protective ratings of 1 or 2 (table 12). Holidays can be

produced by solvent evaporation, poor flow characteristics of coatings, mechanical damage, and inadequate

film coverage. Note in table 8 that films of all the solvent-containing systems had significant amounts of holidays (over 10 per 4 foot bar) regradless of the application method. Liquid epoxies have the tendency

to flow-off the higher portions of the deformations, be- fore hardening, thereby accumulating in the lower lying

regions and resulting in an inadequate thin film over

the deformations. In almost every corrosion study,

coating failures were first observed to occur on the deformations. The large number of holidays in some

powder epoxy films can possibly be attributed to either poor coating practices or to low film thicknesses. Holi- day-free films can be obtained by thick film buildups,

however, the maximum permissible film thickness must

be consistent with good structural and flexibility re- quirements.

Most of the powder epoxy coatings, when properly

applied to a film thickness of greater than 4 mils,

adequately protected reinforcing bars from corrosion

caused by chloride ions.

*6.1.4. Bond Strengths and Creep Characteristics of Coated Bars in Concrete An important aspect of this study was the determination that reinforcing bars coated with certain epoxy

materials had both adequate bond strengths and

satisfactory creep rates when embedded in concrete.

The bond strengths of coated bars embedded in concrete were measured by pullout tests and compared

to the values obtained with uncoated bars. The applied

load corresponding to the critical bond strength of pullout specimens with bars having epoxy coating

1 to 11 mils thick ranged from 17,000 to 21,500 lb with an average value of 19,100 lb, equivalent to an

average bond stress of 677 psi. Those average values

are about six percent less than the respective averages

of 20,300 lb and 720 psi for pullout specimens with

uncoated bars, and are believed to be in the acceptable

range. In contrast, bars coated with polyvinyl chloride

materials and epoxy coating with a film thickness

above 15 mils, were judged to have developed

unacceptable bond strengths.

The creep characteristics of coated bars were

evaluated by comparing their slip-time relationships

(figure 22) and free-end and loaded-end slip values

at 45 days (table 15) with those of uncoated bars. In general, the epoxy coated bars which had adequate

bond strength, also had acceptable creep properties

(sec. 5.2.). However, bars coated with epoxy materials Nos. 1 and 18 had unacceptable slip ratios, although

these bars performed well in the pullout test. Apparently, the creep test is more discriminating than the pullout test. The poor creep characteristics of the bar

coated with material No. 18 is easily rationalized: No. 18 is an epoxy-coal tar mixture and coal tar materials are susceptible to high creep rates, therefore, the epoxy-coal tar mixture should have larger creep

rates than the more pure epoxy coatings. The high

creep of the bars coated with material No. 1 is not

easily understood.

Based on the results of both the pullout test and

creep test, it is felt that the rebars coated with epoxy

materials Nos. 19, 25, 29, 31, 38, 39, and 41 can

be incorporated into existing bridge designs without

any compromise in the structural integrity of the bridge.

The polyvinyl chloride materials which were part

of this study should not be used to protect reinforcing

bars embedded in concrete because of unacceptable

bond strengths and creep characteristics.

6.2. Proposed Qualification Criteria for

Coating Materials

Probably, the determination that four epoxy materials had sufficient attributes to merit their selection as coatings for bars to be used in experimental construction was fortuitous, because none of the 47 coating

materials evaluated in this study were purposely

formulated to serve as protective coatings for steel reinforcing bars. It is anticipated, however, that if the experimental bridge decks constructed with epoxycoated reinforcement perform well, uniquely-formulated

coatings will become available. Based on the results of the evaluation program, proposed minimum per- formance levels are listed in table 16 which can serve

as a basis for the development of prequalification

specifications for organic coatings.

30
Table 16. Proposed criteria for qualifying coating materials

Test method

Test specimen

Section

describing

test

Test period a

test condition Acceptable performance level

Chemical resistance Coated Bar 4.1.2 45 days The coating must not blister, soften, dis- bond nor develop holidays .

Chloride

permeability

3 mil thick film 4.1.3 45 days Accumulative concentration of chloride ion permeating through film shall be less than 1 x 1(H.

Abrasion resistance Coated Steel plate 4.2 CS-10 wheels and

lOOOg load per wheel Weight loss shall not exceed 100 mg per 1000 cycles.

Bend test Coated No. 6 bar 4.4.1 Bars bent 120° over

3 in mandrel No visible crack in coating.

Impact test (falling weight method)

Coated No. 6 bar 4.4.2.2 Impact of 80 in-lb Area of damage should not exceed indented

area.

Hardness

Determination Coated bar 4.4.3.2 10 gram load Hardness shall equal or be greater than

16 KHN.

Applied voltage

test Coated bar 4.5.1 Maximum of 31 days No evolution of H2 at cathode or rusting

at anode within one hour. No undercutting during test.

Pullout test Coated and

uncoated No. 6 bar

5.1 Concrete age of 27-29 days Mean critical bond strengths for coated

bars should be no less than 80 percent of the strengths for uncoated bars.

Creep test Coated and

uncoated No. 6 bar

5.2 45 days at tensile stress

of 30,000 psi Average slip ratios for free-end creep should not exceed 1.3 and the ratio for loaded-end creep should not exceed 1.6.

a Exact test conditions are given in the section describing the test methods.

6.3. Implementation of Epoxy-Coated

Reinforcing Bars

Powder epoxy coatings have performed sufficiently well in this relatively short-term study, to warrant

their implementation in experimental bridge construction. The success of epoxy coatings in protecting the bars from corrosion will be governed by the application, fabrication, and installation processes. Crucial

aspects of the application process include: proper

substrate preparation prior to coating; correct powder

application, resulting in a cured film about 7 ± 2

mils thick and essentially free from holidays and

proper thermal treatment leading to well-cured, flexible epoxy films. In their fabrication, reinforcing bars

are bent to specific shapes and cut to prescribed

lengths. The present fabrication techniques for uncoated

bars will certainly cause some damage to the epoxy

coatings. The extent of such damage can probably

be reduced by using bearing rollers, and bending

wheels and anvils covered with pliable materials such

as nylon. An alternate, and preferred method, might

be to coat prefabricated reinforcing bars. Presently,

reinforcings are subjected to harsh treatment in their shipping and installation. Although epoxy coatings on

bars can withstand a moderate level of abuse, present

handling methods should need to be modified, such

as bundling coated bars together with nylon rope and

protecting them from rough treatment at the construction site. Extensively damaged areas should be repaired

with an approved material (such as a liquid epoxy)

after being placed in the forms just prior to casting

the concrete. The corrosion state of uncoated reinforcing bars

in concrete of existing bridge decks and buildings is currently determined by taking electrical potential

measurements [34]. As previously discussed in section

4.5.2, electrical potential measurements were not found

to be reliable indicators of the corrosion state of coated bars. Wolstenholme [42] has discussed the difficulties of interpretating electrical potential measurements and

concluded that in general electrochemical tests have

not been informative. Therefore, the use of epoxycoated reinforcing bars will probably necessitate the development of other electrochemical tests to monitor

the corrosion condition of the reinforcing steel. Suggested methods are electrical resistance measurements

[43] and electrical polarization measurements [43—45].

31
7. Conclusions and Recommendations

7.1. Conclusions and Recommendations

The following conclusions and recommendations

are based upon the results of the experimental investi- gation described in this report.

1. The powder epoxies, in general, have better overall properties as barrier coatings (considering

chemical resistance, chloride permeability and

corrosion protective qualities) than the liquid

epoxies within the liquid epoxy series the solvent

free materials performed better than the solvent containing systems.

2. Epoxy films on reinforcing bars can withstand

a moderate amount of abuse. However, modifications appear to be necessary in the current

fabrication, shipping, and installation practices

to prevent damage to the coatings.

3. For any epoxy coating to perform well, good

application techniques are important. Epoxy

coatings should be applied to blasted steel sur- faces as both phosphatized and mill scale surfaces are brittle and modest mechanical forces can

cause disbondment. The electrostatic spray gun

method is the most effective application method

in producing thin films free of defects. Proper

curing of the epoxy film is important as undercured materials are very brittle and susceptible

to mechanical damage.

4. Some epoxy coating materials have sufficient

flexibilities in cured film thicknesses below about

10 mils that coated bars can be bent to the normal shapes prescribed in most existing bridge

designs, with minimal damage to the coating.

5. All of the epoxy coated bars, with film thick- nesses not greater than 11 mils, tested in the pullout studies had acceptable bond to concrete. Nine epoxy coatings on bars were tested in the creep studies and seven were judged to have

acceptable creep charactersitics. Therefore, it is felt that selected epoxy coated bars can be used

in existing bridge and building designs without

compromising the structural integrity of the bridge. The polyvinyl chloride coated bars tested

in this study have unacceptable bond and creep

characteristics and, therefore, should not be used

in reinforced concreted.

6. Considering flexibility, bond strength and creep

characteristics, and minimum corrosion protective

requirements, the optimum film thickness of epoxy films on steel reinforcing bars is about

7 ± 2 mils.

7. Four powder epoxies, Nos. 25, 31, 39 and 40 are judged to have the best overall properties as potential coating materials for steel reinforcing

bars. It is recommended that these coatings be

further evaluated in experimental bridge decks

and buildings constructed using bars coated with

these materials.

7.2. Recommended Further Studies

The following studies are recommended to complete

certain aspects of this study:

1. Although the information on relative bond

strengths of coated and uncoated reinforcing

bars determined by means of pullout tests are

believed valid by the investigators, it is recom- mended that tests of flexural members (slabs)

be carried out to confirm these results.

2. Further creep studies of flexural members (slabs)

should be performed with coated and uncoated

bars to determine acceptable slip ratio for both

loaded-end and free-end creep. Different size of bars and concrete test specimens should be

included in further studies.

3. Electrical resistance and linear polarization measurements should be investigated as methods to monitor the condition of epoxy-coated reinforcing

bars in service in bridge decks. Electrical potential

measurements were not found to be reliable indicators of the corrosion state of coated bars

in the present study.

8. References

[1] Durability of Concrete Bridge Decks: A Cooperative Study,

State Highway Commission of Kansas, Bureau of Public Roads and Portland Cement Association. Report 1 (1965).

[2] Durability of Concrete Bridge Decks: A Cooperative Study,

Michigan State Highway Department, U. S. Department

of Commerce, Bureau of Public Roads and Portland Cement Association. Report 2 (1965).

[3] Durability of Concrete Bridge Decks: A Cooperative Study,

U. S. Department of Transportation, Bureau of Public Roads and Portland Cement Association. Report 3 (1967).

[4] Durability of Concrete Bridge Decks: A Cooperative Study, Missouri State Highway Commission, U. S. Department

of Transportation, Bureau of Public Roads and Portland Cement Association. Report 4 (1968).

[5] Durability of Concrete Bridge Decks: A Cooperative Study;

California, Illinois, Michigan, Minnesota, New Jersey, Ohio, Texas, and Virginia Highway Departments, U. S. Department of Transportation, Bureau of Public Roads

and Portland Cement Association. Report 5 (1969).

[6] Durability of Concrete Bridge Decks: A Cooperative Study;

California, Illinois, Kansas, Michigan, Minesota, Missouri, New Jersey, Ohio, Texas, and Virginia Highway

Departments, U. S. Department of Transportation, Bureau of Public Roads and Portland Cement Association. Final Report (1970).

[7] Larson, T. D., Cady, P. D., and Theisen, J. C, Durability

of Bridge Deck Concrete, Report No. 7, College of Engineering. The Pennsylvania State University, April (1969).

[8] Stratfull, R. F., The corrosion of steel in a reinforced concrete bridge, Corrosion 13, 173t (1957).

[9] Mozer, J. D., Bianchini, A. C, and Kelser, C. E., Corrosion

of reinforcing bars in concrete, J. Am. Concrete Inst. Proceedings 62, 909 ( 1965 )

[10] Environmental Degradation by De-Icing Chemicals and

Effective Countermeasurements, page 25, Highway Re- search Record Number 425 (1973).

[11] Mayne, J. E. O., Menter, J. W., and Pryor, M. J., The

Mechanism and Inhibitions of the Corrosion of Iron by

Sodium Chloride Solution, Part I, J. Chem. Soc. 3229

(1960).

32
[12] Speller, F. N., Corrosion—Causes and Prevention, 3rd ed. (McGraw-Hill Book Co., New York, N. Y., 1951).

[13] Timblin, L. 0., and Backstrom, T. E., A Study of Depassivation of Steel in Concrete, Report No. ChE-86, Bureau of Reclamation, Denver, Colorado (1969).

[14] Spellman, D. L., and Stratfull, R. F., Chlorides and Bridge

Deck Deterioration, Research Report No. M&R 635116-4,

Division of Highways, State of California (1969).

[15] Frazier, K. S., Value of galvanized reinforcing in concrete

structures, Materials Protection 4, 53 (1965).

[16] Cornet, I., and Bresler, B., Corrosion of steel and Galvanized

Steel in Concrete, Materials Protection 5, (1966).

[17] Griffin, D. F., Effectiveness of Zinc Coatings on Reinforc- ing Steel in Concrete Exposed to a Marine Environment,

Technical Note N-1032, U. S. Naval Civil Engineering

Laboratory, Port Hueneme, California, (1969).

[18] Pourbaix, M., Atlas of Electrochemical Equilibria in Aqueous Solutions (Pergamon Press, N. Y. 1966), pp. 409-410.

[19] Bird, C. E., and Strauss, F. J., Metallic coatings for rein- forcing steel, Materials Protection 6, 48, (1967).

[20] Tripler, A. B., White, E. L., Haynie, F. H., and Boyd, W.

K., Methods for Reducing Corrosion of Reinforcing Steel, NCHRP Report 23 (1966).

[21] Castleberry, J. R., Corrosion prevention for concrete and

metal reinforcing in the construction industry, Materials

Protection 7, 21 (1968).

[22] Robinson, R. C, Design of reinforced concrete structures

for corrosive environments, Materials Performance 11,

15 (1972).

[23] Steel Structures Painting Council Surface Preparation

Specification SSPC-SP5-63, amended 1971.

[24] Pascoe, W. R., Plastic Coatings for Metals, Modern Plastics Encyclopedia Issue, (McGraw Hill, Inc., New York,

N. Y., 1968).

[25] Standard Specifications for Deformed and Plain Billet-Steel Bars for Concrete Reinforcement, ASTM Designation

A615-72.

[26] Standard Method of Test for Compressive Strength of Molded Concrete Cylinders, ASTM Designation C39-66.

[27] ACI Standard, Recommended Practice for Evaluation of Compression Test Results of Field Concrete (ACI 214- 65), American Concrete Institute, 1965.

[28] Mathey, R, G., and Watstein, D., Investigation of 'bond in beam and pullout specimens with high-yield-strength deformed bars, ACI Journal 32, 1071 (1961).

[29] ACI Standard Code Requirement for Reinforced Concrete (ACI 318-71), February 1971.

[30] Hausman, D. A., Steel corrosion in concrete, Materials Protection 6, 19 (1967).

[31] Impact Resistance of Pipeline Coatings (Falling Weight

Method), ASTM Designation G14-69T.

[32] Standard Method of Test for Resistance of Transparent

Plastics to Surface Abrasion, ASTM Designation

D1044-56.

[33] Test for Indentation Hardness of Organic Coatings, ASTM

Designation D1474-68.

[34] Stratfull, R., Half Cell Potential and the Corrosion of Steel

in Concrete. Research Report Ca-Hy-MR-5116-7-72-42,

Division of Highways, State of California (1973).

[35] Rosa, E. B., McCoIlum, B., and Peters, O. S., Electrolysis

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

[36] ACI Standard Building Code Requirements for Reinforced

Concrete )ACI 318-63), June 1963.

[37] Standard Specifications for Minimum Requirements for the Deformations of Deformed Steel Bars for Concrete Reinforcement, ASTM Designation A305-65.

[38] Standard Specifications for Highway Bridges, Adopted by

the American Association of State Highway Officials, Eleventh Edition, 1973.

[39] Hamner, N. E., Coatings for Corrosion Protection, Chapter

14, in NACE Basic Corrosion Course, A. des. Brasunas and N. E. Hamner, Ed., National Association of Corrosion Engineers, Houston, Texas, 1970.

[40] Lee, H., and Neville, K., Handbook of Epoxy Resins (Mc- Graw Hill Book Co., New York, N. Y., 1967), pp. 6-45

to 6-52.

[41] Hackerman. N. and Snavely, E. S., Fundamentals of In- hibitors, Chapter 9, in NACE Basic Corrosion Course, A. des. Brasunas and N. E. Hamner, Ed., National Association of Corrosion Engineers, Houston, Texas, 1970.

[42] Wolstenholme, J.. Electrical methods of assessing the corro- sion of painted metals—Review, Corrosion Science 13,

521 (1973).

[43] Modern Electrical Methods for Determining Corrosion.

Rates, NACE Technical Unit Committee T-3D on In- struments for Measuring Corrosion, NACE Publication 3D170.

[44] Stern, M., A method for determining corrosion rates from

linear polarization data, Corrosion 14 440t (1958).

[45] Romanoff, M., Gerhold, W. F., Schwerdtfeger, M. J., Iver- son, W. P., Anderson, B. T., and Escalante, E., Proceedings of the 3rd International Congress on Marine

Corrosion and Fouling, 1972.

9. Appendix A

Firms Submitting Coating Materials

For Evaluation 6

Adhesive Engineering Company

Carboline

Celanese Coatings Company

CIBA-CEIGY Corporation

Resins Department

E. I. du Pont de Nemours Company, Inc. H. B. Fuller Company

General Mills Chemical, Inc. Hercules Incorporated

Michigan Chrome & Chemical Company

Minnesota Mining and Manufacturing Company

Mobil Chemical Company

NORDSON Corporation

Polymer Corporation H. C. Price

Products Research and Chemical Corporation

Republic Steel Corporation

Robroy Industries

Rowe Products, Inc. Royston Laboratories

SCM Corporation

Gates Engineering Division

Shell Chemical Company

SIKA Corporation

United States Steel Corporation

Whittaker Corporation

Narmco Materials Division

Wailes Bitumastic Ltd. Witco Chemical Corporation

"These firms submitted coatings materials which they handled for evaluation. They are not necessarily the manufacturers of the coating materials.

33
10. Appendix B

Conversion Factors of U. S. Units to SI Units

Inview of the accepted practice in the United States

at present, the units in this report are those commonly

used in the technological field for which the report is intended. In recognition of the position of the U.S.A.

as a signatory to the General Conference on Weights

and Measures and the action of the U.S. Congress,

readers interested in using the metric (SI) units may

use the conversions below, excerpted from Standard

Metric Practice Guide, E380-72 (a guide to the use

of SI—the international system of units), published

by the ASTM, 1916 Race Street, Philadelphia, Pa.

To concert from To Multiply by

degree Fahrenheit (°F) degree

celsius ( °C)

tF -32

tc 1.8 inch (in) metre (m) 2.540 000 x 10-2 *

gallon (gal) metre3 (m3

) 3.785 000 x 10-3 inch2 (in2

) metre2 (m2

) 6.451 600 x 10^*

kip (1000 lbf) newton (N) 4.448 222 x 103

kip /in2 (ksi) pascal (Pa) 6.894 757 x 106 pound-mass

(lb.m2 avordipois) kilogram (Kg) 4.535 924 x 10"1

pound-force/in2 (psi) pascal (Pa) 6.894 757 x 103

* Exact Conversion Factor

34
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. , BIBLIOGRAPHIC DATA , SHEET

1. PUBLICATION OR REPORT NO. NBS BSS - 65

2. Gov't Accession

No.

3. Recipient's Accession No.

A TITI R AMP) ^TIRTTTl P Nonmetallic Coatings for Concrete

Reinforcing Bars

5. Publication Date August 1975

6. Performing Organization Code

7. AUTHOR(S)

James R. Clifton, Hugh F. Beeghly, and Robert G. Mathey

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U.S. Department of Transportation

Federal Highway Administration

Offices of Research & Development

Washington, D.C. 20590

13. Type of Report & Period C ov 6 r c d Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number 75- 600058

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) This work was undertaken to ascertain the feasibility of using organic coatings,

especially epoxies, to protect the steel reinforcing bars embedded in concrete of

bridge decks from rapid corrosion. This corrosion is caused by the chloride ions from

the most commonly applied deicing salts, sodium chloride and calcium chloride.

Altogether, h-T different coating materials were evaluated to some extent, consisting of

21 liquid and 15 powder epoxies; 5 polyvinyl chlorides; 3 polyurethanes ; 1 polypropylene

1 phenolic nitrile; and one zinc rich coating. The chemical and physical durabilities,

chloride permeabilities, and protective qualities of coatings were assessed. The bonds

between coated and uncoated bars and concrete were measured by both pullout and creep

tests

.

The results indicate that both epoxy and polyvinyl chloride coatings, if properly

applied, should adequately protect steel reinforcing bars from corrosion. However,

only the epoxy coated bars had acceptable bond and creep characteristics when

embedded in concrete. The powder epoxy coatings overall performed better than

the liquid epoxies, and four powder epoxy coatings have been identified as promising

materials to be used on reinforcing bars embedded in concrete decks of experimental

bridges.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Bridge decks; chloride ions; concrete; corrosion; deicing salts; epoxy coatings;

organic coatings; polyvinyl chloride coatings; steel reinforcing bars.

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